Earliest sunrises come before the summer solstice

Top of post: June sunrise in Sea Bright, New Jersey, via Steve Scanlon Photography.

For the Northern Hemisphere: June is a super month for an early morning walk. The dawn light is beautiful at this time of year. At mid-northern latitudes in the Northern Hemisphere, your earliest sunrises of the year happen around now. That’s despite the fact that the northern summer solstice – and year’s longest day for this hemisphere – are still about a week away.

For the Southern Hemisphere: If you relish the daylight, as many do, you’ll be glad to know your sunsets will soon be shifting later! The earliest sunsets of the year are taking place around now for those at mid-latitudes in the Southern Hemisphere. That’s even though the winter solstice – the south’s shortest day – isn’t for another week.

Moon and Mars in the southeast sky before dawn.

At mid-northern latitudes, you’ll have to get up mighty early to catch the moon and the red planet Mars before sunrise this week! Read more.

Pink clouds under glowing white sky reflected in calm water.

Early sunrise in Sweden via Per Ola Wiberg.

The exact date of earliest sunrise (and earliest sunset) varies with latitude. At 40 degrees north latitude – the latitude of, say, Philadelphia in Pennsylvania – the earliest sunrise of the year will happen on June 14. For that same latitude, the latest sunset of the year will fall on or near June 27. Meanwhile, the longest day of the year – the day containing the greatest amount of daylight, overall – comes on the solstice on June 20.

So it is for other Northern Hemisphere latitudes. The dates of earliest sunrise and latest sunset don’t coincide exactly with the solstice. Appreciably south of Philadelphia’s latitude, the earliest sunrise has already come and gone (in late May or early June) and the latest sunset occurs at a later date (sometimes as late as July). In Hawaii, for instance, the earliest sunrise precedes the June solstice by about two weeks, and the latest sunset comes about two weeks after. Farther north, the earliest sunrise and latest sunset happen closer to the June solstice. Check it out at your latitude, using links on our almanac page.

The earliest sunrises come before the summer solstice because the day is more than 24 hours long at this time of the year. In the Southern Hemisphere, the earliest sunsets of the year come before the winter solstice for the same reason.

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Orange-yellow sunrise under dark blue sky reflected in water.

View larger. | June sunrise over Currituck, North Carolina. Image via Greg Diesel Walck – Lunar/Landscape Photographer.

In June, the day (as measured by successive returns of the midday sun) is nearly 1/4 minute longer than 24 hours. Hence, the midday sun (solar noon) comes later by the clock on the June solstice than it does one week before. Therefore, the sunrise and sunset times also come later by the clock, as the tables below help to explain.

For Philadelphia (40 degrees north latitude)

Date Sunrise Midday (Solar Noon) Sunset Daylight Hours
June 13 5:31 a.m. 1:00 p.m. 8:30 p.m. 14h 59m 03s
June 20 5:32 a.m. 1:02 p.m. 8:32 p.m. 15h 00m 36s

For Valdivia, Chile (40 degrees south latitude)

Date Sunrise Midday (Solar Noon) Sunset Daylight Hours
June 13 8:12 a.m. 12:53 p.m. 5:34 p.m. 9h 22m 07s
June 20 8:14 a.m. 12:54 p.m. 5:35 p.m. 9h 20m 38s

Source: timeanddate.com.

The primary reason for the earliest sunrise preceding the summer solstice (and the earliest sunset preceding the winter solstice) is the inclination of the Earth’s rotational axis. The earliest sunrise or sunset would take place before the solstice even if the Earth went around the sun in a circular orbit.

However, the Earth’s elliptical orbit does affect the severity of the phenomenon. At the June solstice, Earth in its orbit is rather close to aphelion – its farthest point from the sun – which lessens the effect. At the December solstice, Earth is rather close to perihelion – its closest point to the sun – which accentuates it.

At middle latitudes, the earliest sunrise/sunset comes about one week before the June summer/winter solstice, and the latest sunset/sunrise about one week after the June solstice.

Yet, at the other end of the year, at middle latitudes, the earliest sunset/sunrise comes about two weeks before the December winter/summer solstice, and the latest sunrise/sunset about two weeks after the December solstice.

Foggy orange scene with trees below and sun seen through fog above.

Early sunrise by Flickr user Rafal Zieba.

Bottom line: Are you an early riser? If so – if you live in the Northern Hemisphere – you might know your earliest sunrises of the year are happening now. Southern Hemisphere? Your earliest sunsets are around now.

EarthSky astronomy kits are perfect for beginners. Order today from the EarthSky store

Donate: Your support means the world to us



from EarthSky https://ift.tt/2MPxzUl

Top of post: June sunrise in Sea Bright, New Jersey, via Steve Scanlon Photography.

For the Northern Hemisphere: June is a super month for an early morning walk. The dawn light is beautiful at this time of year. At mid-northern latitudes in the Northern Hemisphere, your earliest sunrises of the year happen around now. That’s despite the fact that the northern summer solstice – and year’s longest day for this hemisphere – are still about a week away.

For the Southern Hemisphere: If you relish the daylight, as many do, you’ll be glad to know your sunsets will soon be shifting later! The earliest sunsets of the year are taking place around now for those at mid-latitudes in the Southern Hemisphere. That’s even though the winter solstice – the south’s shortest day – isn’t for another week.

Moon and Mars in the southeast sky before dawn.

At mid-northern latitudes, you’ll have to get up mighty early to catch the moon and the red planet Mars before sunrise this week! Read more.

Pink clouds under glowing white sky reflected in calm water.

Early sunrise in Sweden via Per Ola Wiberg.

The exact date of earliest sunrise (and earliest sunset) varies with latitude. At 40 degrees north latitude – the latitude of, say, Philadelphia in Pennsylvania – the earliest sunrise of the year will happen on June 14. For that same latitude, the latest sunset of the year will fall on or near June 27. Meanwhile, the longest day of the year – the day containing the greatest amount of daylight, overall – comes on the solstice on June 20.

So it is for other Northern Hemisphere latitudes. The dates of earliest sunrise and latest sunset don’t coincide exactly with the solstice. Appreciably south of Philadelphia’s latitude, the earliest sunrise has already come and gone (in late May or early June) and the latest sunset occurs at a later date (sometimes as late as July). In Hawaii, for instance, the earliest sunrise precedes the June solstice by about two weeks, and the latest sunset comes about two weeks after. Farther north, the earliest sunrise and latest sunset happen closer to the June solstice. Check it out at your latitude, using links on our almanac page.

The earliest sunrises come before the summer solstice because the day is more than 24 hours long at this time of the year. In the Southern Hemisphere, the earliest sunsets of the year come before the winter solstice for the same reason.

Enjoying EarthSky so far? Sign up for our free daily newsletter today!

Orange-yellow sunrise under dark blue sky reflected in water.

View larger. | June sunrise over Currituck, North Carolina. Image via Greg Diesel Walck – Lunar/Landscape Photographer.

In June, the day (as measured by successive returns of the midday sun) is nearly 1/4 minute longer than 24 hours. Hence, the midday sun (solar noon) comes later by the clock on the June solstice than it does one week before. Therefore, the sunrise and sunset times also come later by the clock, as the tables below help to explain.

For Philadelphia (40 degrees north latitude)

Date Sunrise Midday (Solar Noon) Sunset Daylight Hours
June 13 5:31 a.m. 1:00 p.m. 8:30 p.m. 14h 59m 03s
June 20 5:32 a.m. 1:02 p.m. 8:32 p.m. 15h 00m 36s

For Valdivia, Chile (40 degrees south latitude)

Date Sunrise Midday (Solar Noon) Sunset Daylight Hours
June 13 8:12 a.m. 12:53 p.m. 5:34 p.m. 9h 22m 07s
June 20 8:14 a.m. 12:54 p.m. 5:35 p.m. 9h 20m 38s

Source: timeanddate.com.

The primary reason for the earliest sunrise preceding the summer solstice (and the earliest sunset preceding the winter solstice) is the inclination of the Earth’s rotational axis. The earliest sunrise or sunset would take place before the solstice even if the Earth went around the sun in a circular orbit.

However, the Earth’s elliptical orbit does affect the severity of the phenomenon. At the June solstice, Earth in its orbit is rather close to aphelion – its farthest point from the sun – which lessens the effect. At the December solstice, Earth is rather close to perihelion – its closest point to the sun – which accentuates it.

At middle latitudes, the earliest sunrise/sunset comes about one week before the June summer/winter solstice, and the latest sunset/sunrise about one week after the June solstice.

Yet, at the other end of the year, at middle latitudes, the earliest sunset/sunrise comes about two weeks before the December winter/summer solstice, and the latest sunrise/sunset about two weeks after the December solstice.

Foggy orange scene with trees below and sun seen through fog above.

Early sunrise by Flickr user Rafal Zieba.

Bottom line: Are you an early riser? If so – if you live in the Northern Hemisphere – you might know your earliest sunrises of the year are happening now. Southern Hemisphere? Your earliest sunsets are around now.

EarthSky astronomy kits are perfect for beginners. Order today from the EarthSky store

Donate: Your support means the world to us



from EarthSky https://ift.tt/2MPxzUl

What is the Big Bang?

A horn-shaped graphic depicting the various epochs of the universe with the origin at the narrow end.

Timeline of the universe, from Big Bang to present day. The far left depicts the earliest moment we can probe so far, when a period of cosmic inflation produced a burst of exponential growth in the universe. For the next several billion years, the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity. More recently, the expansion has begun to speed up again as the repulsive effects of dark energy have come to dominate the expansion of the universe. Read more about this image from NASA.

You’ve probably heard of the Big Bang as the event that gave rise to our universe. You might know most cosmologists believe it occurred some 13.8 billion years ago. It’s hard to fathom that, at the moment of the Big Bang, all of the energy in the universe – some of which would later become galaxies, stars, planets and human beings – was concentrated into a tiny point, smaller than the nucleus of an atom. And it’s not just matter that was born in the Big Bang. In the view of modern cosmologists, matter and space and time all began when that microscopic point suddenly expanded violently and exponentially.

The first atoms are thought to have formed when the universe was around 400,000 years old. Before that, the universe was simply too hot and too energetic to let atomic nuclei capture electrons. The first stars sparkled into life, cosmologists believe, about 250 million years after the Big Bang, and the first galaxies shortly after that.

A blue dot on a black background scattered with stars and distant galaxies. Inset showing dot enlarged.

The Hubble Space Telescope captured this image of an exceedingly distant galaxy called UDFj-39546284. This object has a redshift of z~10, meaning that it existed some 480 million years after the Big Bang. Image via NASA/ ESA/ Garth Illingworth/ Rychard Bouwens/ the HUDF09 Team/ Wikimedia Commons.

An irregular red blob in an inset box on a star field.

Here’s another exceedingly distant (and therefore old) object, captured by the Hubble Space Telescope in 2016. Galaxy GN-z11, shown in the inset, is seen as it was 13.4 billion years in the past, just 400 million years after the Big Bang, when the universe was only 3% of its current age. The galaxy is ablaze with bright, young, blue stars, but looks red in this image because its light has been stretched to longer spectral wavelengths by the expansion of the universe. Image via NASA/ ESA/ P. Oesch/ G. Brammer/ P. van Dokkum / G. Illingworth/ Hubblesite.

The Big Bang refers to a theory. How could it be otherwise? The current version of Big Bang theory – the one used most by modern cosmologists – is called the Lambda-CDM model. It postulates that our universe began at a specific instant, expanded to be flat (i.e. has zero curvature) and is made up of 5% baryons (i.e. the matter that makes up everything we see – galaxies, stars, planets, people), 27% cold dark matter (hence the “CDM” of the theory’s name) and 68% dark energy

The Lambda-CDM model further states that the universe is expanding at a rate referred to as Lambda (the Greek letter) and is governed by the principles of Einstein’s General Relativity. The Lambda-CDM model has been spectacularly successful at explaining what we observe in the universe. It makes predictions repeatedly confirmed by observation. But it is not without problems; as with all scientific theories, the Lambda-CDM model continues to evolve.

Now let’s pause a moment, so that we might draw a distinction between the appearance of all that energy in the Big Bang and its sudden expansion. In that sense, the Big Bang was not the event that caused our universe. Rather, it was the event that gave birth to the universe. Why is this distinction important? It’s important because, although science has been able to establish a history of the universe right back to when that tiny point suddenly created our entire cosmos, what preceded it, the reason for that tiny point of energy being there in the first place, is unknown, and may forever be unknowable.

The Big Bang is the theory we have constructed for how the universe we see around us came to be. It does not attempt to answer the most common question we humans ask about the origin of the cosmos: why? And this question likely cannot be answered, because, by definition, whatever caused the appearance of that tiny point of energy, containing the seeds of everything that would ever be, was not of this universe.

Therefore, whatever caused the universe left no evidence of its existence for us to study, no clue as to what it was. It is also likely that, being something completely outside the universe, we would, in any event, be unable to comprehend it. The laws of physics, of motion, of gravity, of electromagnetism, of thermodynamics, simply did not apply at the moment of the universe’s birth because they did not yet exist: they certainly cannot describe the presence and origin of that tiny seed.  

That has not stopped cosmologists, who study the history and large-scale structure of the universe, from trying to answer such questions, of course, because that’s the nature of science. Some people attribute the existence of that tiny seed of energy to a god, as humans have invented gods throughout the ages to explain things they could not understand, but there is absolutely no reason for believing that idea, other than perhaps wishful thinking. There is certainly nothing we observe in the history of the universe to suggest that its origin was anything other than a natural event, even if we cannot comprehend it. On the other hand, there’s nothing to suggest the origin of our universe was not caused by a god, either.

A cone shaped object with an actual arrow drawn below, with explosion on left end cosmic evolution proceeding rightward.

Artist’s representation of the history of the universe and the arrow of time. Big Bang theory implies that time moves in a single direction. However, scientists have discovered that, at the quantum level, in the realm of sub-atomic particles, many processes are what we call “time-reversible”: there is no distinction between past, present and future. Image via Forbes.

The Lambda-CDM model also states that time itself started at the Big Bang, on the basis that if there are no events, there is no time to measure. This raises an old philosophical question of whether time is a human construct or exists independently of us. This question has taxed some of the greatest philosophers and scientists but has never been answered satisfactorily. Still, if we define time as the period which elapses between events, it is fair to say that time started with the Big Bang.

Another common question is: what happened before the Big Bang? That question can have no meaning if we accept the Big Bang was the start of the universe’s clock: it’s like asking what’s north of the North Pole. This answer, while demonstrating the irrationality of asking about a “before”, is not, however, satisfactory to humans accustomed to cause and effect: we reason that if the Big Bang was an event which was the result of something, some change, some instability, there had to be a before. However, that is only in our experience, in the world we are familiar with, where an event always has a cause, and has absolutely no bearing on the universe coming into being because, again, the laws of physics, which in our world govern cause and effect, simply did not exist. And as if to underline how superficial, how biased, our perception of time, scientists have discovered that at the quantum level, in the realm of sub-atomic particles, many processes are what we call “time-reversible:” there is simply no distinction between past, present and future.

It’s also important to realize that, at the moment of the Big Bang, there was no space and there were no dimensions. Space itself, and the dimensions within that space, came into being at that moment, as the bubble of energy expanded. This means that, contrary to what most people believe, the Big Bang was not an explosion. Think of anything exploding, and it explodes into a space, an area, which was there already. But in the case of the Big Bang, there was no preexisting space for an explosion to occur in.

A related question which is often asked is: where did the Big Bang happen? Those who ask this believe you can point at a location in the sky and say, “it happened there.” But the answer to the question is that the Big Bang happened everywhere. It’s just that everywhere existed within that tiny bubble of infinitely-hot expanding energy, because there was literally nothing outside it – no space, no dimensions, nothing. Watch any documentary about the Big Bang and it will show it as a huge explosion, viewed from outside. But such a viewpoint is impossible – there was no “outside”. One cannot, of course, blame filmmakers for this: there is simply no way to portray the Big Bang visually in a way which is scientifically accurate. It’s doubtful we even have the vocabulary to describe it, let alone portray it.

On the left, a brilliant flash of light from which a 'universe' of stars and space expands rightward.

Space itself is believed to have been born in the Big Bang. Artist’s concept via Christine Daniloff/ MIT/ ESA/ Hubble/ NASA/ Phys.org.

If you find it difficult to get your head around the idea of the Big Bang happening everywhere, with no outside, at a particular moment when time started some 13.8 billion years ago, you are not alone. The human brain is not well equipped for dealing with such concepts. Even when Edwin Hubble, in the 1920s, demonstrated that the universe is expanding in all directions, and therefore, if you wind the clock back far enough, all of the universe must have occupied one tiny point, the idea that the universe had a definite beginning, and was therefore not infinitely old, was simply unacceptable to many. Among these who rejected the Big Bang were prominent scientists: Einstein himself denied the idea of an expanding universe. Another scientist who rejected the notion of a universe of finite age was famed British astronomer Sir Fred Hoyle, the man who, more than any other individual, unlocked the mystery of how stars work.

Hoyle gave a series of lectures on BBC radio in the late 1940s and early ’50s, and, on one of these – on the BBC’s Third Programme broadcast on March 28, 1949 – he poured derision on the idea of the universe beginning at a fixed point in time and referred to cosmologists’ description of the event as a “Big Bang.” Unfortunately for Hoyle, the name stuck, and we’ve called this event the Big Bang ever since.

An intelligent-looking man in old-fashioned glasses and a suit.

Fred Hoyle. He coined the term “Big Bang” to describe the event in which our universe was born, while explaining a rival theory, the Steady State theory, in a radio talk in 1949 Image via Britannica.com.

A slide explaining that, in Steady State theory, matter has to be continually created.

Image via ExploringCosmos006.

Hoyle never accepted that the universe had a beginning, even until his death at the age at 86 in 2001. He became the leading proponent of Steady State Theory, which says that the universe has no beginning or end: it constantly regenerates itself, with new matter condensing out of nothing.

Hoyle’s blunt intransigence – he was from Yorkshire, an English county said to be famed for the plain-speaking and directness of its inhabitants – was not lessened by the subsequent success of Big Bang theory, not even after it successfully predicted the abundancies of light elements, such as hydrogen, helium and lithium, in the universe. Nor did he come to accept the Big Bang when Arno Penzias and Robert Wilson discovered the predicted Cosmic Microwave Background, the Big Bang’s dying echo, in 1964. Steady State Theory had predicted none of these things, nor did it have explanations for them.

Nor was Hoyle fazed when Alan Guth constructed the theory of Cosmological Inflation as a refinement to existing Big Bang theory in 1979. Inflation explains why the universe is the same temperature everywhere and is “flat”, amongst other features of the universe not hitherto explained, although it has yet to be observationally completely verified.

Even the year before he died, Hoyle published yet another scientific paper on Steady State theory, but by this time his ideas were completely rejected by most cosmologists. And, sadly for him, they were also rejected by the overwhelming observational evidence for the Big Bang. Steady State Theory just does not work, makes false predictions and is contradicted by what we actually see in the universe. As a hypothesis – lacking supporting observational evidence, it was that rather than a theory, although commonly referred to as such  – it essentially died with Hoyle.

Today, the Lambda-CDM Big Bang model is the only theory that makes any testable predictions and that is supported by observations.

Most cosmologists today believe we know the history of the universe back to 10-21 seconds after the Big Bang – that’s 0.0000000000000000000001 seconds. The painstaking piecing together of this history over the last 50 years, although lacking in fine detail as it undoubtedly is, represents humans’ greatest intellectual achievement, our species’ crowning glory. It has been achieved through an unparalleled synthesis of astronomy, astrophysics, cosmology, particle physics, chemistry and other sciences.

But science will not rest until we can push our theories back even further in time, to that exact moment when the universe came into being.

A colorful, mostly blue starburst pattern on a black background.

Artist’s concept of the Big Bang, the event now believed to have marked our universe’s birth. If we looked far enough back in time, could we witness the birth of the universe?

Bottom line: At the moment of the Big Bang, all of the energy in the universe – some of which would later become galaxies, stars, planets and human beings – was concentrated into a tiny point, smaller than the nucleus of an atom. And it’s not just matter that was born in the Big Bang. In the view of modern cosmologists, matter and space and time all began when that microscopic point suddenly expanded violently and exponentially.



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A horn-shaped graphic depicting the various epochs of the universe with the origin at the narrow end.

Timeline of the universe, from Big Bang to present day. The far left depicts the earliest moment we can probe so far, when a period of cosmic inflation produced a burst of exponential growth in the universe. For the next several billion years, the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity. More recently, the expansion has begun to speed up again as the repulsive effects of dark energy have come to dominate the expansion of the universe. Read more about this image from NASA.

You’ve probably heard of the Big Bang as the event that gave rise to our universe. You might know most cosmologists believe it occurred some 13.8 billion years ago. It’s hard to fathom that, at the moment of the Big Bang, all of the energy in the universe – some of which would later become galaxies, stars, planets and human beings – was concentrated into a tiny point, smaller than the nucleus of an atom. And it’s not just matter that was born in the Big Bang. In the view of modern cosmologists, matter and space and time all began when that microscopic point suddenly expanded violently and exponentially.

The first atoms are thought to have formed when the universe was around 400,000 years old. Before that, the universe was simply too hot and too energetic to let atomic nuclei capture electrons. The first stars sparkled into life, cosmologists believe, about 250 million years after the Big Bang, and the first galaxies shortly after that.

A blue dot on a black background scattered with stars and distant galaxies. Inset showing dot enlarged.

The Hubble Space Telescope captured this image of an exceedingly distant galaxy called UDFj-39546284. This object has a redshift of z~10, meaning that it existed some 480 million years after the Big Bang. Image via NASA/ ESA/ Garth Illingworth/ Rychard Bouwens/ the HUDF09 Team/ Wikimedia Commons.

An irregular red blob in an inset box on a star field.

Here’s another exceedingly distant (and therefore old) object, captured by the Hubble Space Telescope in 2016. Galaxy GN-z11, shown in the inset, is seen as it was 13.4 billion years in the past, just 400 million years after the Big Bang, when the universe was only 3% of its current age. The galaxy is ablaze with bright, young, blue stars, but looks red in this image because its light has been stretched to longer spectral wavelengths by the expansion of the universe. Image via NASA/ ESA/ P. Oesch/ G. Brammer/ P. van Dokkum / G. Illingworth/ Hubblesite.

The Big Bang refers to a theory. How could it be otherwise? The current version of Big Bang theory – the one used most by modern cosmologists – is called the Lambda-CDM model. It postulates that our universe began at a specific instant, expanded to be flat (i.e. has zero curvature) and is made up of 5% baryons (i.e. the matter that makes up everything we see – galaxies, stars, planets, people), 27% cold dark matter (hence the “CDM” of the theory’s name) and 68% dark energy

The Lambda-CDM model further states that the universe is expanding at a rate referred to as Lambda (the Greek letter) and is governed by the principles of Einstein’s General Relativity. The Lambda-CDM model has been spectacularly successful at explaining what we observe in the universe. It makes predictions repeatedly confirmed by observation. But it is not without problems; as with all scientific theories, the Lambda-CDM model continues to evolve.

Now let’s pause a moment, so that we might draw a distinction between the appearance of all that energy in the Big Bang and its sudden expansion. In that sense, the Big Bang was not the event that caused our universe. Rather, it was the event that gave birth to the universe. Why is this distinction important? It’s important because, although science has been able to establish a history of the universe right back to when that tiny point suddenly created our entire cosmos, what preceded it, the reason for that tiny point of energy being there in the first place, is unknown, and may forever be unknowable.

The Big Bang is the theory we have constructed for how the universe we see around us came to be. It does not attempt to answer the most common question we humans ask about the origin of the cosmos: why? And this question likely cannot be answered, because, by definition, whatever caused the appearance of that tiny point of energy, containing the seeds of everything that would ever be, was not of this universe.

Therefore, whatever caused the universe left no evidence of its existence for us to study, no clue as to what it was. It is also likely that, being something completely outside the universe, we would, in any event, be unable to comprehend it. The laws of physics, of motion, of gravity, of electromagnetism, of thermodynamics, simply did not apply at the moment of the universe’s birth because they did not yet exist: they certainly cannot describe the presence and origin of that tiny seed.  

That has not stopped cosmologists, who study the history and large-scale structure of the universe, from trying to answer such questions, of course, because that’s the nature of science. Some people attribute the existence of that tiny seed of energy to a god, as humans have invented gods throughout the ages to explain things they could not understand, but there is absolutely no reason for believing that idea, other than perhaps wishful thinking. There is certainly nothing we observe in the history of the universe to suggest that its origin was anything other than a natural event, even if we cannot comprehend it. On the other hand, there’s nothing to suggest the origin of our universe was not caused by a god, either.

A cone shaped object with an actual arrow drawn below, with explosion on left end cosmic evolution proceeding rightward.

Artist’s representation of the history of the universe and the arrow of time. Big Bang theory implies that time moves in a single direction. However, scientists have discovered that, at the quantum level, in the realm of sub-atomic particles, many processes are what we call “time-reversible”: there is no distinction between past, present and future. Image via Forbes.

The Lambda-CDM model also states that time itself started at the Big Bang, on the basis that if there are no events, there is no time to measure. This raises an old philosophical question of whether time is a human construct or exists independently of us. This question has taxed some of the greatest philosophers and scientists but has never been answered satisfactorily. Still, if we define time as the period which elapses between events, it is fair to say that time started with the Big Bang.

Another common question is: what happened before the Big Bang? That question can have no meaning if we accept the Big Bang was the start of the universe’s clock: it’s like asking what’s north of the North Pole. This answer, while demonstrating the irrationality of asking about a “before”, is not, however, satisfactory to humans accustomed to cause and effect: we reason that if the Big Bang was an event which was the result of something, some change, some instability, there had to be a before. However, that is only in our experience, in the world we are familiar with, where an event always has a cause, and has absolutely no bearing on the universe coming into being because, again, the laws of physics, which in our world govern cause and effect, simply did not exist. And as if to underline how superficial, how biased, our perception of time, scientists have discovered that at the quantum level, in the realm of sub-atomic particles, many processes are what we call “time-reversible:” there is simply no distinction between past, present and future.

It’s also important to realize that, at the moment of the Big Bang, there was no space and there were no dimensions. Space itself, and the dimensions within that space, came into being at that moment, as the bubble of energy expanded. This means that, contrary to what most people believe, the Big Bang was not an explosion. Think of anything exploding, and it explodes into a space, an area, which was there already. But in the case of the Big Bang, there was no preexisting space for an explosion to occur in.

A related question which is often asked is: where did the Big Bang happen? Those who ask this believe you can point at a location in the sky and say, “it happened there.” But the answer to the question is that the Big Bang happened everywhere. It’s just that everywhere existed within that tiny bubble of infinitely-hot expanding energy, because there was literally nothing outside it – no space, no dimensions, nothing. Watch any documentary about the Big Bang and it will show it as a huge explosion, viewed from outside. But such a viewpoint is impossible – there was no “outside”. One cannot, of course, blame filmmakers for this: there is simply no way to portray the Big Bang visually in a way which is scientifically accurate. It’s doubtful we even have the vocabulary to describe it, let alone portray it.

On the left, a brilliant flash of light from which a 'universe' of stars and space expands rightward.

Space itself is believed to have been born in the Big Bang. Artist’s concept via Christine Daniloff/ MIT/ ESA/ Hubble/ NASA/ Phys.org.

If you find it difficult to get your head around the idea of the Big Bang happening everywhere, with no outside, at a particular moment when time started some 13.8 billion years ago, you are not alone. The human brain is not well equipped for dealing with such concepts. Even when Edwin Hubble, in the 1920s, demonstrated that the universe is expanding in all directions, and therefore, if you wind the clock back far enough, all of the universe must have occupied one tiny point, the idea that the universe had a definite beginning, and was therefore not infinitely old, was simply unacceptable to many. Among these who rejected the Big Bang were prominent scientists: Einstein himself denied the idea of an expanding universe. Another scientist who rejected the notion of a universe of finite age was famed British astronomer Sir Fred Hoyle, the man who, more than any other individual, unlocked the mystery of how stars work.

Hoyle gave a series of lectures on BBC radio in the late 1940s and early ’50s, and, on one of these – on the BBC’s Third Programme broadcast on March 28, 1949 – he poured derision on the idea of the universe beginning at a fixed point in time and referred to cosmologists’ description of the event as a “Big Bang.” Unfortunately for Hoyle, the name stuck, and we’ve called this event the Big Bang ever since.

An intelligent-looking man in old-fashioned glasses and a suit.

Fred Hoyle. He coined the term “Big Bang” to describe the event in which our universe was born, while explaining a rival theory, the Steady State theory, in a radio talk in 1949 Image via Britannica.com.

A slide explaining that, in Steady State theory, matter has to be continually created.

Image via ExploringCosmos006.

Hoyle never accepted that the universe had a beginning, even until his death at the age at 86 in 2001. He became the leading proponent of Steady State Theory, which says that the universe has no beginning or end: it constantly regenerates itself, with new matter condensing out of nothing.

Hoyle’s blunt intransigence – he was from Yorkshire, an English county said to be famed for the plain-speaking and directness of its inhabitants – was not lessened by the subsequent success of Big Bang theory, not even after it successfully predicted the abundancies of light elements, such as hydrogen, helium and lithium, in the universe. Nor did he come to accept the Big Bang when Arno Penzias and Robert Wilson discovered the predicted Cosmic Microwave Background, the Big Bang’s dying echo, in 1964. Steady State Theory had predicted none of these things, nor did it have explanations for them.

Nor was Hoyle fazed when Alan Guth constructed the theory of Cosmological Inflation as a refinement to existing Big Bang theory in 1979. Inflation explains why the universe is the same temperature everywhere and is “flat”, amongst other features of the universe not hitherto explained, although it has yet to be observationally completely verified.

Even the year before he died, Hoyle published yet another scientific paper on Steady State theory, but by this time his ideas were completely rejected by most cosmologists. And, sadly for him, they were also rejected by the overwhelming observational evidence for the Big Bang. Steady State Theory just does not work, makes false predictions and is contradicted by what we actually see in the universe. As a hypothesis – lacking supporting observational evidence, it was that rather than a theory, although commonly referred to as such  – it essentially died with Hoyle.

Today, the Lambda-CDM Big Bang model is the only theory that makes any testable predictions and that is supported by observations.

Most cosmologists today believe we know the history of the universe back to 10-21 seconds after the Big Bang – that’s 0.0000000000000000000001 seconds. The painstaking piecing together of this history over the last 50 years, although lacking in fine detail as it undoubtedly is, represents humans’ greatest intellectual achievement, our species’ crowning glory. It has been achieved through an unparalleled synthesis of astronomy, astrophysics, cosmology, particle physics, chemistry and other sciences.

But science will not rest until we can push our theories back even further in time, to that exact moment when the universe came into being.

A colorful, mostly blue starburst pattern on a black background.

Artist’s concept of the Big Bang, the event now believed to have marked our universe’s birth. If we looked far enough back in time, could we witness the birth of the universe?

Bottom line: At the moment of the Big Bang, all of the energy in the universe – some of which would later become galaxies, stars, planets and human beings – was concentrated into a tiny point, smaller than the nucleus of an atom. And it’s not just matter that was born in the Big Bang. In the view of modern cosmologists, matter and space and time all began when that microscopic point suddenly expanded violently and exponentially.



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Last quarter moon is June 13

One half the moon's face in sunlight, lighted portion facing downward, left side marked N for north.

View at EarthSky Community Photos. | Dr Ski in Valencia, Philippines, caught the last quarter moon shortly after it rose around midnight on the morning of September 22, 2019. This moon phase is perfect for helping you envision the location of the sun … below your feet. Thanks, Dr Ski!

A last quarter moon appears half-lit by sunshine and half-immersed in its own shadow. It rises in the middle of the night, appears at its highest in the sky around dawn, and sets around midday.

A last quarter moon provides a great opportunity to think of yourself on a three-dimensional world in space. Watch for this moon just after moonrise, shortly after midnight. Then the lighted portion points downward, to the sun below your feet. Think of the last quarter moon as a mirror to the world you’re standing on. Think of yourself standing in the midst of Earth’s nightside, on the midnight portion of Earth.

On a last quarter moon, the lunar terminator – the shadow line dividing day and night – shows you where it’s sunset on the moon.

Craters and other features, including a short straight white line on a dark flat mare floor.

View at EarthSky Community Photos. | September 22, 2019, photo by Dr Ski. He wrote: “The moon’s southern limb at last quarter. The Straight Wall is either black or white depending on the angle of the sun’s rays. At lunar sunset (now), it’s white. Around full moon, Tycho is one of the easiest craters to find due to the impact rays emanating from it. It’s like the hub of a spoked wheel! At last quarter, Tycho becomes unremarkable. Clavius, on the other hand, becomes remarkable at high magnification.”

Labeled craters and mountain ranges at the edge between dark and light.

View at EarthSky Community Photos. | September 22, 2019, photo by Dr Ski. He wrote: “The Sea of Rains at last quarter. The lunar Alps and Apennines are bisected by the moon’s meridian. You can get an idea of the height of these mountains by how far they extend into the dark side of the terminator. At an elevation of over 5,000 meters [16,000 feet], the Apennines are twice as tall as the Alps.”

Also, a last quarter moon can be used as a guidepost to Earth’s direction of motion in orbit around the sun.

In other words, when you look toward a last quarter moon high in the predawn sky, for example, you’re gazing out approximately along the path of Earth’s orbit, in a forward direction. The moon is moving in orbit around the sun with the Earth and never holds still. But, if we could somehow anchor the moon in space … tie it down, keep it still … Earth’s orbital speed of 18 miles per second would carry us across the space between us and the moon in only a few hours.

Want to read more about the last quarter moon as a guidepost for Earth’s motion? Astronomer Guy Ottewell talks about it here.

A great thing about using the moon as a guidepost to Earth’s motion is that you can do it anywhere … as, for example, in the photo below, from large cities.

Daytime sky. High small moon, left half visible, above conical-top water tower and tall tan brick chimney.

Ben Orlove wrote from New York City: “I was sitting in the roof garden of my building, and there was the moon, right in front of me. You were right, this is a perfect time to visualize … the Earth’s motion.”

As the moon orbits Earth, it changes phase in an orderly way. Read more: 4 keys to understanding moon phases

Bottom line: The moon reaches its last quarter phase on June 13, 2020, at 06:23 UTC. Translate UTC to your time. In the coming week, watch for the moon to rise in the east in the hours after midnight, waning thinner each morning.



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One half the moon's face in sunlight, lighted portion facing downward, left side marked N for north.

View at EarthSky Community Photos. | Dr Ski in Valencia, Philippines, caught the last quarter moon shortly after it rose around midnight on the morning of September 22, 2019. This moon phase is perfect for helping you envision the location of the sun … below your feet. Thanks, Dr Ski!

A last quarter moon appears half-lit by sunshine and half-immersed in its own shadow. It rises in the middle of the night, appears at its highest in the sky around dawn, and sets around midday.

A last quarter moon provides a great opportunity to think of yourself on a three-dimensional world in space. Watch for this moon just after moonrise, shortly after midnight. Then the lighted portion points downward, to the sun below your feet. Think of the last quarter moon as a mirror to the world you’re standing on. Think of yourself standing in the midst of Earth’s nightside, on the midnight portion of Earth.

On a last quarter moon, the lunar terminator – the shadow line dividing day and night – shows you where it’s sunset on the moon.

Craters and other features, including a short straight white line on a dark flat mare floor.

View at EarthSky Community Photos. | September 22, 2019, photo by Dr Ski. He wrote: “The moon’s southern limb at last quarter. The Straight Wall is either black or white depending on the angle of the sun’s rays. At lunar sunset (now), it’s white. Around full moon, Tycho is one of the easiest craters to find due to the impact rays emanating from it. It’s like the hub of a spoked wheel! At last quarter, Tycho becomes unremarkable. Clavius, on the other hand, becomes remarkable at high magnification.”

Labeled craters and mountain ranges at the edge between dark and light.

View at EarthSky Community Photos. | September 22, 2019, photo by Dr Ski. He wrote: “The Sea of Rains at last quarter. The lunar Alps and Apennines are bisected by the moon’s meridian. You can get an idea of the height of these mountains by how far they extend into the dark side of the terminator. At an elevation of over 5,000 meters [16,000 feet], the Apennines are twice as tall as the Alps.”

Also, a last quarter moon can be used as a guidepost to Earth’s direction of motion in orbit around the sun.

In other words, when you look toward a last quarter moon high in the predawn sky, for example, you’re gazing out approximately along the path of Earth’s orbit, in a forward direction. The moon is moving in orbit around the sun with the Earth and never holds still. But, if we could somehow anchor the moon in space … tie it down, keep it still … Earth’s orbital speed of 18 miles per second would carry us across the space between us and the moon in only a few hours.

Want to read more about the last quarter moon as a guidepost for Earth’s motion? Astronomer Guy Ottewell talks about it here.

A great thing about using the moon as a guidepost to Earth’s motion is that you can do it anywhere … as, for example, in the photo below, from large cities.

Daytime sky. High small moon, left half visible, above conical-top water tower and tall tan brick chimney.

Ben Orlove wrote from New York City: “I was sitting in the roof garden of my building, and there was the moon, right in front of me. You were right, this is a perfect time to visualize … the Earth’s motion.”

As the moon orbits Earth, it changes phase in an orderly way. Read more: 4 keys to understanding moon phases

Bottom line: The moon reaches its last quarter phase on June 13, 2020, at 06:23 UTC. Translate UTC to your time. In the coming week, watch for the moon to rise in the east in the hours after midnight, waning thinner each morning.



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Biggest asteroid to pass close (and undetected) this year

We hear a lot about asteroids or comets passing close to Earth, but what does “close” mean? For a comet, it might mean millions of miles. For an asteroid, it might mean enormous distances as well, beyond the moon’s orbital distance of about a quarter-million miles. On the other hand, space rocks coming closer than our moon catch people’s attention, especially if the asteroids are good-sized! That was the case with asteroid 2020 LD, which swept closest to Earth on June 5, flying by at only about 80% of the moon’s distance (190,559 miles or 306,675 km). At around 400 feet (122 meters) in diameter, 2020 LD is the largest asteroid to have come within one lunar-distance this year … or last year … in fact, since 2011. And it also ranks as one of the biggest asteroids ever to fly this close to Earth without being previously detected. That’s right. 2020 LD passed undetected on June 5. No one noticed it until two days later, on June 7.

That’s when astronomers using the 0.5-meter ATLAS telescope at Mauna Loa, Hawaii, first noticed this Apollo type asteroid traveling at 60,826 miles per hour (97,890 km/h) relative to Earth.

It was only after analyzing the space rock’s orbit that scientists realized its closest approach to Earth had happened two days before, on June 5.

Asteroids fly between the moon’s orbit and Earth pretty frequently. You might be surprised at how frequently. The chart below – via The Watchers – shows the number of asteroids that have come that close from January 1 to June 9, 2020.

Bar graph showing number of asteroids per month that passed within the moon's distance so far in 2020.

Image via The Watchers.

But 2020 LD isn’t your typical close-passing asteroid. Again, it’s the biggest asteroid to have passed within the moon’s orbit since 2011.

Is a 400-foot asteroid large in an absolute sense? Not particularly. On the scale of asteroids in general – those orbiting mostly in the asteroid belt between Mars and Jupiter – we might say that 2020 LD falls somewhere between medium and small. The biggest asteroids are hundreds of miles in diameter.

That said, asteroid 2020 LD is big enough to cause considerable damage if it were to have hit us. As a comparison, the space rock that caused Meteor Crater near Flagstaff, Arizona – a crater around 0.75 miles wide (1.2-km wide) – was estimated to be about 150 feet (about 46 meters) in diameter. That asteroid struck some 50,000 years ago.

How about a more recent comparison? The asteroid that entered Earth’s atmosphere as an amazing meteor over Chelyabinsk, Russia, on February 15, 2013, didn’t cause a huge crater (although some fragments were eventually recovered). But it did cause a shockwave that broke windows in six Russian cities, causing some 1,500 people to seek medical attention, mostly for flying glass. That original asteroid was an estimated 66 feet (20 meters) in diameter.

Size isn’t the only factor when determining an asteroid’s potential to cause damage. The asteroid’s composition and its angle of entry into Earth’s atmosphere are also determining factors.

Did you know you can calculate the effects of any asteroid impact via this cool impact calculator created by Jay Melosh, an atmospheric scientist at Purdue Uniersity? You could take the numbers of the various asteroids mentioned in this article – and plug them into that calculator – and scare yourself handily! Visit the impact calculator.

In the meantime, as far as we know, space rock 2020 LD is nothing to worry about. At this writing, 50 years is the length for which its orbit has been well calculated. It won’t come so close to Earth again as it did this month for at least that many years … and likely much, much longer.

Bottom line: Asteroid 2020 LD passed within the moon’s distance on June 5, 2020, but wasn’t discovered until June 7. It’s the 45th known and the largest asteroid to sweep within a lunar-distance of Earth so far in 2020.



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We hear a lot about asteroids or comets passing close to Earth, but what does “close” mean? For a comet, it might mean millions of miles. For an asteroid, it might mean enormous distances as well, beyond the moon’s orbital distance of about a quarter-million miles. On the other hand, space rocks coming closer than our moon catch people’s attention, especially if the asteroids are good-sized! That was the case with asteroid 2020 LD, which swept closest to Earth on June 5, flying by at only about 80% of the moon’s distance (190,559 miles or 306,675 km). At around 400 feet (122 meters) in diameter, 2020 LD is the largest asteroid to have come within one lunar-distance this year … or last year … in fact, since 2011. And it also ranks as one of the biggest asteroids ever to fly this close to Earth without being previously detected. That’s right. 2020 LD passed undetected on June 5. No one noticed it until two days later, on June 7.

That’s when astronomers using the 0.5-meter ATLAS telescope at Mauna Loa, Hawaii, first noticed this Apollo type asteroid traveling at 60,826 miles per hour (97,890 km/h) relative to Earth.

It was only after analyzing the space rock’s orbit that scientists realized its closest approach to Earth had happened two days before, on June 5.

Asteroids fly between the moon’s orbit and Earth pretty frequently. You might be surprised at how frequently. The chart below – via The Watchers – shows the number of asteroids that have come that close from January 1 to June 9, 2020.

Bar graph showing number of asteroids per month that passed within the moon's distance so far in 2020.

Image via The Watchers.

But 2020 LD isn’t your typical close-passing asteroid. Again, it’s the biggest asteroid to have passed within the moon’s orbit since 2011.

Is a 400-foot asteroid large in an absolute sense? Not particularly. On the scale of asteroids in general – those orbiting mostly in the asteroid belt between Mars and Jupiter – we might say that 2020 LD falls somewhere between medium and small. The biggest asteroids are hundreds of miles in diameter.

That said, asteroid 2020 LD is big enough to cause considerable damage if it were to have hit us. As a comparison, the space rock that caused Meteor Crater near Flagstaff, Arizona – a crater around 0.75 miles wide (1.2-km wide) – was estimated to be about 150 feet (about 46 meters) in diameter. That asteroid struck some 50,000 years ago.

How about a more recent comparison? The asteroid that entered Earth’s atmosphere as an amazing meteor over Chelyabinsk, Russia, on February 15, 2013, didn’t cause a huge crater (although some fragments were eventually recovered). But it did cause a shockwave that broke windows in six Russian cities, causing some 1,500 people to seek medical attention, mostly for flying glass. That original asteroid was an estimated 66 feet (20 meters) in diameter.

Size isn’t the only factor when determining an asteroid’s potential to cause damage. The asteroid’s composition and its angle of entry into Earth’s atmosphere are also determining factors.

Did you know you can calculate the effects of any asteroid impact via this cool impact calculator created by Jay Melosh, an atmospheric scientist at Purdue Uniersity? You could take the numbers of the various asteroids mentioned in this article – and plug them into that calculator – and scare yourself handily! Visit the impact calculator.

In the meantime, as far as we know, space rock 2020 LD is nothing to worry about. At this writing, 50 years is the length for which its orbit has been well calculated. It won’t come so close to Earth again as it did this month for at least that many years … and likely much, much longer.

Bottom line: Asteroid 2020 LD passed within the moon’s distance on June 5, 2020, but wasn’t discovered until June 7. It’s the 45th known and the largest asteroid to sweep within a lunar-distance of Earth so far in 2020.



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What is an opposition?

View from above solar system with Saturn to left, then Earth directly between it and the sun in the middle.

Artist’s concept of Saturn in opposition to the sun. Distances not to scale! Image via NASA.

There has been a lot of talk in this northern summer of 2020 about exciting times for observing Jupiter and Saturn. The two planets are very near each other now on the sky’s dome, heading for a great conjunction before this year’s end. And both reach opposition in July of 2020, Jupiter on July 14 and Saturn on July 20. Opposition marks the middle of the best time of year to view these planets. So … what is an opposition?

Imagine the solar system, with the planets running around in their orbits. Let’s keep things simple and just imagine the sun in the middle with the Earth a little way out, Jupiter about five times farther, and then Saturn about twice as far away from the sun as Jupiter. We’ll assume we’re watching from a spot high above Earth’s North Pole, which would mean that everything is moving counterclockwise.

Now, hit pause. Where are the planets? Maybe Earth is off to the left of the sun, and maybe Jupiter and Saturn are to the right. From this view, it doesn’t really matter what the line from the sun to Earth is like; after all, there’s always a straight line between any two objects in space. But what’s the Earth-sun line doing with respect to, say, Saturn? For most of every year, the Earth-sun line would need to jog off in a different direction to get to Saturn.

If we let our imaginary solar system run a little longer, though, the line will straighten. Nearly every year, there will be a point where it’s perfectly straight – sun, Earth, Saturn – as in the illustration below. Earth will be passing between Saturn and the sun in our planet’s yearly orbit.

Concentric circles with planet symbols on them.

An illustration of the solar system – as viewed from Earthly north – on the day of Jupiter’s opposition on July 14, 2020. Earth is passing between Jupiter and the sun on this date. It’ll pass between Saturn and the sun less than a week later, on July 20. In this illustration, the yellow ball in the center (with the central dot) is the sun. Jupiter is brown; Saturn is yellow; Earth is blue. Everything is moving counterclockwise. Image via Fourmilab.

What about the view in Earth’s sky? Since – at opposition – Earth is in the middle of a line between an outer planet and the sun, we see the sun at one end of our sky and the opposition planet in the opposite direction. It’s as if you’re standing directly between two friends as you chat in the supermarket, and you need to turn your head halfway around to see one, and then the other. At opposition, the sun is on the opposite side of the sky from the outer planet; when the sun sets in the west, the planet is rising in the east. As the planet drops below the horizon, the sun pops above it again: opposite.

To be technical, opposition for an outer planet happens when the sun and that planet are exactly 180 degrees apart in the sky. The word comes to English from a Latin root, meaning to set against.

Consider that Venus and Mercury can never be at opposition as seen from Earth. Their orbits are closer to the sun than Earth’s, so they can never appear opposite the sun in our sky. You will never see Venus in the east, for example, when the sun is setting in the west. These inner planets always stay near the sun, no more than 47 degrees from the sun for Venus, or 28 degrees for Mercury, in our sky.

Oppositions can only happen for objects that are farther from the sun than Earth is. We see oppositions for Jupiter, Saturn, Uranus and Neptune about every year. They happen as Earth, in its much-faster orbit, passes between these outer worlds and the sun. We see oppositions of the planet Mars, too, but Martian oppositions happen about every 27 months because Earth and Mars are so relatively close together in orbit around the sun; their orbits, and speeds in orbit, are more similar. We’ll have an opposition of Mars in 2020, too, on October 13. Between now and then, we’ll see Mars brighten dramatically in our sky, as Earth catches up to it, and passes it, on the inside track around the sun.

Since everything in space is always moving, oppositions of planets farther than us from the sun happen again and again. As far as the bright planets go, the next opposition is never too far away:

Mars was at opposition on July 27, 2018, and will be again on October 13, 2020, and December 8, 2022.

Jupiter was at opposition on June 10, 2019, and will be again on July 14, 2020, August 19, 2021, and September 26, 2022.

Saturn was at opposition on July 9, 2019, and will be again on July 20, 2020, August 2, 2021, and August 14, 2022.

Dark twilight sky with shining red dot above a long low hill.

View full-sized image. | Project Nightflight released this photo on September 2, 2018. It shows Mars in mid-August of that year, a couple of weeks after its last opposition. See how bright it is? Planets at opposition are bright partly because it’s around then that they are closest to us. Also, at opposition, an outer planet’s fully lighted face, or day side, faces us most directly. Photo via the Project Nightflight team. Read more about this image.

Looking along a country road, the Milky Way stretched above, two bright dots against the starry sky.

View at EarthSky Community Photos. | Eli Frisbie in Eagle Mountain, Utah, created this composite image from photos gathered on June 6, 2019, just a few days before Jupiter’s opposition. He wrote: “The Milky Way shines over a country road … The bright ‘star’ to the right of the Milky Way is the planet Jupiter. The slightly less-bright star to the upper left is the planet Saturn.” Thank you, Eli!

Why are planets at opposition so interesting to sky-watchers?

As mentioned, because they’re opposite the sun, planets at opposition rise when the sun sets and can be found somewhere in the sky throughout the night.

Secondly, planets at opposition tend to be near their closest point to Earth in orbit. Due to the non-circular shape of planetary orbits, the exact closest point might be different by a day or two, as is the case for Jupiter in 2020. Jupiter’s opposition is on July 14, and its exact closest point is on July 15. Still, for many weeks around opposition – between the time we pass between an outer planet and the sun – the outer planet is generally closest to Earth. At such a time, the planet is brightest, and more detail can be seen through telescopes.

And here’s another interesting aspect of opposition. Since the sun and outer planet are directly opposite each other in Earth’s sky, we see that far-off planet’s fully lighted daytime side. Fully-lit planets appear brighter to us than less-fully-lit planets. If you’re saying to yourself that this sounds a lot like the moon, you’re right! After all, what’s a full moon if not the moon at opposition? During the moon’s full phase, it’s directly opposite the sun in the sky, fully illuminated, and at its brightest for that orbit. As it moves through the rest of its orbit, the sun-Earth-moon line bends and gives us what we see from Earth as the moon’s phases.

Like so much in life, opposition is all about point of view. We’ve been talking about the view from Earth. What if we flip it around? When an outer planet – let’s say Jupiter – is at opposition for us, Earth is at inferior conjunction as seen from that planet. In other words, at the moment of opposition for us on Earth, observers on Jupiter would see Earth passing between their world and the sun. The Earth and the sun would be in the same side of Jupiter’s sky, Earth hidden in the sun’s glare except to skilled observers using special equipment. Consider also that the line from the sun to Jupiter passes through the Earth, which means Earth passes directly between the sun and Jupiter. Maybe one day, a visitor to Jupiter will see Earth transit the sun as seen from Jupiter. That is, they’ll see Earth’s darkened nighttime side, and all of humanity, cross the face of the sun from half a billion miles away.

A slightly fuzzy telescopic view of colorful, striped Saturn and its rings.

View at EarthSky Community Photos. | Patrick Prokop in Savannah, Georgia, caught this glorious image of golden Saturn on July 3, 2019, a few days before last year’s opposition. Thank you, Patrick!

Bottom line: Opposition marks the middle of the best time of year to see an outer planet. It’s when Earth is passing between an outer planet and the sun, placing the planet opposite the sun in our sky. A planet at opposition is closest to Earth, and it rises when the sun sets and can be viewed throughout the night.



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View from above solar system with Saturn to left, then Earth directly between it and the sun in the middle.

Artist’s concept of Saturn in opposition to the sun. Distances not to scale! Image via NASA.

There has been a lot of talk in this northern summer of 2020 about exciting times for observing Jupiter and Saturn. The two planets are very near each other now on the sky’s dome, heading for a great conjunction before this year’s end. And both reach opposition in July of 2020, Jupiter on July 14 and Saturn on July 20. Opposition marks the middle of the best time of year to view these planets. So … what is an opposition?

Imagine the solar system, with the planets running around in their orbits. Let’s keep things simple and just imagine the sun in the middle with the Earth a little way out, Jupiter about five times farther, and then Saturn about twice as far away from the sun as Jupiter. We’ll assume we’re watching from a spot high above Earth’s North Pole, which would mean that everything is moving counterclockwise.

Now, hit pause. Where are the planets? Maybe Earth is off to the left of the sun, and maybe Jupiter and Saturn are to the right. From this view, it doesn’t really matter what the line from the sun to Earth is like; after all, there’s always a straight line between any two objects in space. But what’s the Earth-sun line doing with respect to, say, Saturn? For most of every year, the Earth-sun line would need to jog off in a different direction to get to Saturn.

If we let our imaginary solar system run a little longer, though, the line will straighten. Nearly every year, there will be a point where it’s perfectly straight – sun, Earth, Saturn – as in the illustration below. Earth will be passing between Saturn and the sun in our planet’s yearly orbit.

Concentric circles with planet symbols on them.

An illustration of the solar system – as viewed from Earthly north – on the day of Jupiter’s opposition on July 14, 2020. Earth is passing between Jupiter and the sun on this date. It’ll pass between Saturn and the sun less than a week later, on July 20. In this illustration, the yellow ball in the center (with the central dot) is the sun. Jupiter is brown; Saturn is yellow; Earth is blue. Everything is moving counterclockwise. Image via Fourmilab.

What about the view in Earth’s sky? Since – at opposition – Earth is in the middle of a line between an outer planet and the sun, we see the sun at one end of our sky and the opposition planet in the opposite direction. It’s as if you’re standing directly between two friends as you chat in the supermarket, and you need to turn your head halfway around to see one, and then the other. At opposition, the sun is on the opposite side of the sky from the outer planet; when the sun sets in the west, the planet is rising in the east. As the planet drops below the horizon, the sun pops above it again: opposite.

To be technical, opposition for an outer planet happens when the sun and that planet are exactly 180 degrees apart in the sky. The word comes to English from a Latin root, meaning to set against.

Consider that Venus and Mercury can never be at opposition as seen from Earth. Their orbits are closer to the sun than Earth’s, so they can never appear opposite the sun in our sky. You will never see Venus in the east, for example, when the sun is setting in the west. These inner planets always stay near the sun, no more than 47 degrees from the sun for Venus, or 28 degrees for Mercury, in our sky.

Oppositions can only happen for objects that are farther from the sun than Earth is. We see oppositions for Jupiter, Saturn, Uranus and Neptune about every year. They happen as Earth, in its much-faster orbit, passes between these outer worlds and the sun. We see oppositions of the planet Mars, too, but Martian oppositions happen about every 27 months because Earth and Mars are so relatively close together in orbit around the sun; their orbits, and speeds in orbit, are more similar. We’ll have an opposition of Mars in 2020, too, on October 13. Between now and then, we’ll see Mars brighten dramatically in our sky, as Earth catches up to it, and passes it, on the inside track around the sun.

Since everything in space is always moving, oppositions of planets farther than us from the sun happen again and again. As far as the bright planets go, the next opposition is never too far away:

Mars was at opposition on July 27, 2018, and will be again on October 13, 2020, and December 8, 2022.

Jupiter was at opposition on June 10, 2019, and will be again on July 14, 2020, August 19, 2021, and September 26, 2022.

Saturn was at opposition on July 9, 2019, and will be again on July 20, 2020, August 2, 2021, and August 14, 2022.

Dark twilight sky with shining red dot above a long low hill.

View full-sized image. | Project Nightflight released this photo on September 2, 2018. It shows Mars in mid-August of that year, a couple of weeks after its last opposition. See how bright it is? Planets at opposition are bright partly because it’s around then that they are closest to us. Also, at opposition, an outer planet’s fully lighted face, or day side, faces us most directly. Photo via the Project Nightflight team. Read more about this image.

Looking along a country road, the Milky Way stretched above, two bright dots against the starry sky.

View at EarthSky Community Photos. | Eli Frisbie in Eagle Mountain, Utah, created this composite image from photos gathered on June 6, 2019, just a few days before Jupiter’s opposition. He wrote: “The Milky Way shines over a country road … The bright ‘star’ to the right of the Milky Way is the planet Jupiter. The slightly less-bright star to the upper left is the planet Saturn.” Thank you, Eli!

Why are planets at opposition so interesting to sky-watchers?

As mentioned, because they’re opposite the sun, planets at opposition rise when the sun sets and can be found somewhere in the sky throughout the night.

Secondly, planets at opposition tend to be near their closest point to Earth in orbit. Due to the non-circular shape of planetary orbits, the exact closest point might be different by a day or two, as is the case for Jupiter in 2020. Jupiter’s opposition is on July 14, and its exact closest point is on July 15. Still, for many weeks around opposition – between the time we pass between an outer planet and the sun – the outer planet is generally closest to Earth. At such a time, the planet is brightest, and more detail can be seen through telescopes.

And here’s another interesting aspect of opposition. Since the sun and outer planet are directly opposite each other in Earth’s sky, we see that far-off planet’s fully lighted daytime side. Fully-lit planets appear brighter to us than less-fully-lit planets. If you’re saying to yourself that this sounds a lot like the moon, you’re right! After all, what’s a full moon if not the moon at opposition? During the moon’s full phase, it’s directly opposite the sun in the sky, fully illuminated, and at its brightest for that orbit. As it moves through the rest of its orbit, the sun-Earth-moon line bends and gives us what we see from Earth as the moon’s phases.

Like so much in life, opposition is all about point of view. We’ve been talking about the view from Earth. What if we flip it around? When an outer planet – let’s say Jupiter – is at opposition for us, Earth is at inferior conjunction as seen from that planet. In other words, at the moment of opposition for us on Earth, observers on Jupiter would see Earth passing between their world and the sun. The Earth and the sun would be in the same side of Jupiter’s sky, Earth hidden in the sun’s glare except to skilled observers using special equipment. Consider also that the line from the sun to Jupiter passes through the Earth, which means Earth passes directly between the sun and Jupiter. Maybe one day, a visitor to Jupiter will see Earth transit the sun as seen from Jupiter. That is, they’ll see Earth’s darkened nighttime side, and all of humanity, cross the face of the sun from half a billion miles away.

A slightly fuzzy telescopic view of colorful, striped Saturn and its rings.

View at EarthSky Community Photos. | Patrick Prokop in Savannah, Georgia, caught this glorious image of golden Saturn on July 3, 2019, a few days before last year’s opposition. Thank you, Patrick!

Bottom line: Opposition marks the middle of the best time of year to see an outer planet. It’s when Earth is passing between an outer planet and the sun, placing the planet opposite the sun in our sky. A planet at opposition is closest to Earth, and it rises when the sun sets and can be viewed throughout the night.



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Moon and Mars before dawn June 12 and 13

In the predawn sky these next few mornings – June 12 and 13, 2020 – use the waning crescent moon to find the red planet Mars. Look first for the moon. That nearby bright “star” will be Mars. Unlike a star, which shines by its own light, Mars shines by reflecting the light of the sun. You may note that Mars shines with a steadier light than the twinkling stars. And, if you’ve been watching, you’ll also notice how bright Mars is now! The planet is due to grow dramatically brighter by the time of its opposition – when Earth will fly between Mars and the sun – in October 2020.

At mid-northern latitudes, it’s now that beautiful time of year when we’re having our earliest sunrises. So northerners might be hard pressed to get up early enough to see the moon and Mars. If you’re a night owl, staying up past the midnight hour, you might try to catch the pair rising into your eastern sky before bedtime.

Live in the United States or Canada? Click on Old Farmer’s Almanac to find out the rising times of the moon and Mars.

To find out the rising times for the moon and Mars from virtually anyplace worldwide, check out TimeandDate.

On our chart at top, we also show the planet Neptune, the most distant (known) planet in our the solar system. You need an optical aid to see this distant world. Mars and Neptune will be in conjunction on June 12, 2020 (at about 12:00 UTC), with Mars passing 1.7 degrees to the south of Neptune. For reference, your index finger at arm’s length spans about 2 degrees of sky.

About half a day after the Mars-Neptune conjunction, the moon will pass 3 degrees to the south of Mars. Then about a quarter day after the moon meets up with Mars, the moon will reach its half-illuminated last quarter phase on June 13, 2020, at 6:24 UTC.

Earth is gaining on Mars in our faster, smaller orbit around the sun, and Mars, in turn, is growing ever brighter in Earth’s sky. Excluding our sun, only three stars are brighter than Mars at present: Sirius, Canopus and Alpha Centauri. Mars outshines Neptune by nearly 1,700 times, and the 1st-magnitude star Fomalhaut by nearly 3.5 times.

Yet, the great Mars show has barely begun. By the second half of August 2020, Mars will actually outshine Sirius, the brightest star of the nighttime sky. By October 2020, Mars will even outshine the king planet Jupiter. Jupiter is almost always the fourth-brightest celestial body, after the sun, moon and the queen planet Venus. But, Mars will displace Jupiter for one shining month, as Mars beams as the fourth-brightest celestial object, after the sun, moon and Venus, throughout October 2020.

Chart with moon, Mars, Saturn, Jupiter with an arrow pointing to Neptune's location.

Two other morning planets light up the June 2020 predawn/dawn sky. Look for the king planet Jupiter and the ringed planet Saturn to the west of the moon and Mars. Note: the moon appears much larger on our chart than it does in the real sky.

During these these few mornings – June 12 and 13, 2020 – the moon, Mars and Neptune appear close together on the sky’s dome, but they’re hardly close together in space. The moon lies about a quarter million miles (400,000 km) away from Earth. In contrast, Mars resides at better than 350 times the moon’s distance from Earth. Meanwhile, Neptune lodges way out there, at some 32 times Mars’ distance from Earth.

Bottom line: Enjoy the early morning sky on June 12 and 13, 2020, as the moon swings 3 degrees south of the red planet Mars, and Mars swings 1.7 degrees south of Neptune.



from EarthSky https://ift.tt/3ho2V2D

In the predawn sky these next few mornings – June 12 and 13, 2020 – use the waning crescent moon to find the red planet Mars. Look first for the moon. That nearby bright “star” will be Mars. Unlike a star, which shines by its own light, Mars shines by reflecting the light of the sun. You may note that Mars shines with a steadier light than the twinkling stars. And, if you’ve been watching, you’ll also notice how bright Mars is now! The planet is due to grow dramatically brighter by the time of its opposition – when Earth will fly between Mars and the sun – in October 2020.

At mid-northern latitudes, it’s now that beautiful time of year when we’re having our earliest sunrises. So northerners might be hard pressed to get up early enough to see the moon and Mars. If you’re a night owl, staying up past the midnight hour, you might try to catch the pair rising into your eastern sky before bedtime.

Live in the United States or Canada? Click on Old Farmer’s Almanac to find out the rising times of the moon and Mars.

To find out the rising times for the moon and Mars from virtually anyplace worldwide, check out TimeandDate.

On our chart at top, we also show the planet Neptune, the most distant (known) planet in our the solar system. You need an optical aid to see this distant world. Mars and Neptune will be in conjunction on June 12, 2020 (at about 12:00 UTC), with Mars passing 1.7 degrees to the south of Neptune. For reference, your index finger at arm’s length spans about 2 degrees of sky.

About half a day after the Mars-Neptune conjunction, the moon will pass 3 degrees to the south of Mars. Then about a quarter day after the moon meets up with Mars, the moon will reach its half-illuminated last quarter phase on June 13, 2020, at 6:24 UTC.

Earth is gaining on Mars in our faster, smaller orbit around the sun, and Mars, in turn, is growing ever brighter in Earth’s sky. Excluding our sun, only three stars are brighter than Mars at present: Sirius, Canopus and Alpha Centauri. Mars outshines Neptune by nearly 1,700 times, and the 1st-magnitude star Fomalhaut by nearly 3.5 times.

Yet, the great Mars show has barely begun. By the second half of August 2020, Mars will actually outshine Sirius, the brightest star of the nighttime sky. By October 2020, Mars will even outshine the king planet Jupiter. Jupiter is almost always the fourth-brightest celestial body, after the sun, moon and the queen planet Venus. But, Mars will displace Jupiter for one shining month, as Mars beams as the fourth-brightest celestial object, after the sun, moon and Venus, throughout October 2020.

Chart with moon, Mars, Saturn, Jupiter with an arrow pointing to Neptune's location.

Two other morning planets light up the June 2020 predawn/dawn sky. Look for the king planet Jupiter and the ringed planet Saturn to the west of the moon and Mars. Note: the moon appears much larger on our chart than it does in the real sky.

During these these few mornings – June 12 and 13, 2020 – the moon, Mars and Neptune appear close together on the sky’s dome, but they’re hardly close together in space. The moon lies about a quarter million miles (400,000 km) away from Earth. In contrast, Mars resides at better than 350 times the moon’s distance from Earth. Meanwhile, Neptune lodges way out there, at some 32 times Mars’ distance from Earth.

Bottom line: Enjoy the early morning sky on June 12 and 13, 2020, as the moon swings 3 degrees south of the red planet Mars, and Mars swings 1.7 degrees south of Neptune.



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Scientists to strike on June 10 #ShutDownSTEM #Strike4BlackLives

Poster-style artist's concept of people marching in a Black Lives Matter protest.

Image via ScienceMag.org, a publication of the American Association for the Advancement of Science, which has also endorsed the strike.

Thousands of physicists, astronomers, and other academics have pledged to pause their work – forgoing research, classes, meetings, and other normal business – on Wednesday, June 10, 2020, in order to pursue a day of action dedicated to protecting the lives of Black people. The strike is taking place due to the efforts of multiple organizers operating under banners including the Strike For Black Lives, #ShutDownSTEM, #ShutDownAcademia and #Strike4BlackLives. A group of 15 physicist organizers wrote on the website Particles for Justice that the Strike for Black Lives is needed to:

… hit pause, to give Black academics a break and to give others an opportunity to reflect on their own complicity in anti-Black racism in academia and their local and global communities.

Chanda Prescod-Weinstein, a particle cosmology theorist and feminist theorist at the University of New Hampshire, said:

I want non-Black people to respond as if lives depend on it because they do.

The organizers of #ShutDownSTEM state on its website:

In the wake of the most recent murders of Black people in the U.S., it is clear that white and other non-Black people have to step up and do the work to eradicate anti-Black racism. As members of the global academic and STEM [science, technology, engineering, and math] communities, we have an enormous ethical obligation to stop doing ‘business as usual.’

More information:

https://www.particlesforjustice.org

https://www.shutdownstem.com

https://www.aip.org/fyi/2020/scientists-strike-black-lives-shutdownstem-june-10

https://aas.org/posts/news/2020/06/aas-endorses-shutdownstem-shutdownacademia-strike4blacklives

Resources for #ShutDownSTEM, #ShutDownAcademia & #Strike4BlackLives:
https://aas.org/strike4blacklives

Bottom line: University laboratories, scientific societies, technical journals, and others have pledged to strike on June 10, 2020. The focus is on issues of racial equality and inclusiveness. The strike is taking place under multiple banners including the Strike For Black Lives, #ShutDownSTEM, #ShutDownAcademia, and #Strike4BlackLives. EarthSky is joining the strike.



from EarthSky https://ift.tt/2MOSYNe
Poster-style artist's concept of people marching in a Black Lives Matter protest.

Image via ScienceMag.org, a publication of the American Association for the Advancement of Science, which has also endorsed the strike.

Thousands of physicists, astronomers, and other academics have pledged to pause their work – forgoing research, classes, meetings, and other normal business – on Wednesday, June 10, 2020, in order to pursue a day of action dedicated to protecting the lives of Black people. The strike is taking place due to the efforts of multiple organizers operating under banners including the Strike For Black Lives, #ShutDownSTEM, #ShutDownAcademia and #Strike4BlackLives. A group of 15 physicist organizers wrote on the website Particles for Justice that the Strike for Black Lives is needed to:

… hit pause, to give Black academics a break and to give others an opportunity to reflect on their own complicity in anti-Black racism in academia and their local and global communities.

Chanda Prescod-Weinstein, a particle cosmology theorist and feminist theorist at the University of New Hampshire, said:

I want non-Black people to respond as if lives depend on it because they do.

The organizers of #ShutDownSTEM state on its website:

In the wake of the most recent murders of Black people in the U.S., it is clear that white and other non-Black people have to step up and do the work to eradicate anti-Black racism. As members of the global academic and STEM [science, technology, engineering, and math] communities, we have an enormous ethical obligation to stop doing ‘business as usual.’

More information:

https://www.particlesforjustice.org

https://www.shutdownstem.com

https://www.aip.org/fyi/2020/scientists-strike-black-lives-shutdownstem-june-10

https://aas.org/posts/news/2020/06/aas-endorses-shutdownstem-shutdownacademia-strike4blacklives

Resources for #ShutDownSTEM, #ShutDownAcademia & #Strike4BlackLives:
https://aas.org/strike4blacklives

Bottom line: University laboratories, scientific societies, technical journals, and others have pledged to strike on June 10, 2020. The focus is on issues of racial equality and inclusiveness. The strike is taking place under multiple banners including the Strike For Black Lives, #ShutDownSTEM, #ShutDownAcademia, and #Strike4BlackLives. EarthSky is joining the strike.



from EarthSky https://ift.tt/2MOSYNe