Pleiades star cluster, aka Seven Sisters

The Pleiades star cluster, by Ernie Rossi in Florida. Russ Drum submitted it and wrote: “The Pleiades (aka the Seven Sisters) is an open star cluster located in the constellation Taurus the Bull. It’s also known as the Halloween Cluster because it’s almost overhead in the sky at midnight on Halloween, October 31.”

The Pleiades star cluster – also known as the Seven Sisters or M45 – is visible from virtually every part of the globe. It can be seen from as far north as the North Pole, and farther south than the southernmost tip of South America. It looks like a tiny misty dipper of stars.

If you’re familiar with the famous constellation Orion, it can help you be sure you’ve found the Pleiades. See the three stars in a row in Orion? That’s Orion’s Belt. Draw a line through these stars to the V-shaped pattern of stars with a bright star in its midst. The V-shaped pattern is the Face of Taurus the Bull. The bright star in the V – called Aldebaran – depicts the Bull’s Eye. A bit past Aldebaran, you’ll see the Pleiades cluster, which marks the Bull’s Shoulder.

The 2019 lunar calendars are here! Order yours before they’re gone. Makes a great gift.

If you can find the prominent constellation Orion, you can find the Pleiades. Orion’s Belt points to the bright reddish star Aldebaran … then generally toward the Pleiades.

The Pleiades and Aldebaran. star name Aldebaran comes from an Arabic word for follower. It’s thought to be a reference to this star’s forever chasing the Pleiades across the heavens. As a general rule, the Pleiades cluster rises into the eastern sky before Aldebaran rises, and sets in the west before Aldebaran sets.

The only exception to this rule happens at far southern latitudes – for example, at South America’s Tierra del Fuego – where the Pleiades rise a short while after Aldebaran rises.

In our Northern Hemispheres skies, the Pleiades cluster is associated with the winter season. It’s easy to imagine this misty patch of icy-blue suns as hoarfrost clinging to the dome of night. Frosty November is often called the month of the Pleiades, because it’s at this time that the Pleiades shine from dusk until dawn. But you can see the Pleiades cluster in the evening sky well into April.

Tom Wildoner in Weatherly, Pennsylvania captured this image on October 31, 2016. He wrote: “It shows the Seven Sisters, Pleiades star cluster rising in the east behind some maple trees still sporting some late leaves.”

Legend of the Lost Pleiad. Most people see 6, not 7, Pleiades stars in a dark country sky.

However, the story about the lost 7th Pleiad harbors a universal theme. The astronomer Robert Burnham Jr. found the lost Pleaid myth prevalent in the star lore of European, African, Asian, Indonesian, Native American and Aboriginal Australian populations.

Moreover, Burnham suggested that the “lost Pleiad” may have basis in fact. After all, modern astronomy has found that the 7th brightest Pleiades star – Pleione – is a complicated and hard-to-understand “shell star” that goes through numerous permutations. These changes cause this star to vary in brightness.

Plus people with exceptional eyesight have been known to see many more stars in the Pleiades cluster. Claims go up as high as 20 stars. Agnes Clerke, an astronomer and writer in the late 1800s, reported that Michael Maestlin, the mentor of Johannes Kepler, mapped out 11 Pleiades stars before the invention of the telescope.

To see more than 6 or 7 Pleaides stars, you must have very good eyesight (or a pair of binoculars). And you must be willing to spend time under a dark, moonless sky. Stephen O’Meara, a dark-sky connoisseur, claims that eyes dark-adapted for 30 minutes are 6 times more sensitive to light than eyes dark-adapted for 15 minutes. The surest way to see additional Pleiades stars is to look at this cluster through binoculars or low power in a telescope.

The Lost Pleiad, a painting by French artist William-Adolphe Bouguereau (1825-1905). Image via Wikimedia Commons.

Pleiades as calendar, in history and in modern science. Historically, the Pleiades have served as a calendar for many civilizations. The Greek name “Pleiades” probably means “to sail.” In the ancient Mediterranean world, the day that the Pleaides cluster first appeared in the morning sky before sunrise announced the opening of the navigation season.

The modern-day festival of Halloween originates from an old Druid rite that coincided with the midnight culmination of the Pleiades cluster. It was believed that the veil dividing the living from the dead is at its thinnest when the Pleaides culminates – reaches its highest point in the sky – at midnight.

On a lighter note, the Zuni of New Mexico call the Pleiades the “Seed Stars,” because this cluster’s disappearance in the evening sky every spring signals the seed-planting season.

In both myth and science, the Pleiades are considered to be sibling stars. Modern astronomers say the Pleiades stars were born from the same cloud of gas and dust some 100 million years ago. This gravitationally bound cluster of several hundred stars looms some 430 light-years distant, and these sibling stars drift through space together at about 25 miles per second. Many of these Pleiades stars shine hundreds of times more brightly than our sun.

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The Pleiades – aka the Seven Sisters – captured by Greg Hogan in Kathleen, Georgia on October 31, 2016.

Bottom line: November is often called the month of the Pleiades – or Seven Sisters – because it’s at this time that the Pleiades shine from dusk until dawn.

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

The Pleiades star cluster, by Ernie Rossi in Florida. Russ Drum submitted it and wrote: “The Pleiades (aka the Seven Sisters) is an open star cluster located in the constellation Taurus the Bull. It’s also known as the Halloween Cluster because it’s almost overhead in the sky at midnight on Halloween, October 31.”

The Pleiades star cluster – also known as the Seven Sisters or M45 – is visible from virtually every part of the globe. It can be seen from as far north as the North Pole, and farther south than the southernmost tip of South America. It looks like a tiny misty dipper of stars.

If you’re familiar with the famous constellation Orion, it can help you be sure you’ve found the Pleiades. See the three stars in a row in Orion? That’s Orion’s Belt. Draw a line through these stars to the V-shaped pattern of stars with a bright star in its midst. The V-shaped pattern is the Face of Taurus the Bull. The bright star in the V – called Aldebaran – depicts the Bull’s Eye. A bit past Aldebaran, you’ll see the Pleiades cluster, which marks the Bull’s Shoulder.

The 2019 lunar calendars are here! Order yours before they’re gone. Makes a great gift.

If you can find the prominent constellation Orion, you can find the Pleiades. Orion’s Belt points to the bright reddish star Aldebaran … then generally toward the Pleiades.

The Pleiades and Aldebaran. star name Aldebaran comes from an Arabic word for follower. It’s thought to be a reference to this star’s forever chasing the Pleiades across the heavens. As a general rule, the Pleiades cluster rises into the eastern sky before Aldebaran rises, and sets in the west before Aldebaran sets.

The only exception to this rule happens at far southern latitudes – for example, at South America’s Tierra del Fuego – where the Pleiades rise a short while after Aldebaran rises.

In our Northern Hemispheres skies, the Pleiades cluster is associated with the winter season. It’s easy to imagine this misty patch of icy-blue suns as hoarfrost clinging to the dome of night. Frosty November is often called the month of the Pleiades, because it’s at this time that the Pleiades shine from dusk until dawn. But you can see the Pleiades cluster in the evening sky well into April.

Tom Wildoner in Weatherly, Pennsylvania captured this image on October 31, 2016. He wrote: “It shows the Seven Sisters, Pleiades star cluster rising in the east behind some maple trees still sporting some late leaves.”

Legend of the Lost Pleiad. Most people see 6, not 7, Pleiades stars in a dark country sky.

However, the story about the lost 7th Pleiad harbors a universal theme. The astronomer Robert Burnham Jr. found the lost Pleaid myth prevalent in the star lore of European, African, Asian, Indonesian, Native American and Aboriginal Australian populations.

Moreover, Burnham suggested that the “lost Pleiad” may have basis in fact. After all, modern astronomy has found that the 7th brightest Pleiades star – Pleione – is a complicated and hard-to-understand “shell star” that goes through numerous permutations. These changes cause this star to vary in brightness.

Plus people with exceptional eyesight have been known to see many more stars in the Pleiades cluster. Claims go up as high as 20 stars. Agnes Clerke, an astronomer and writer in the late 1800s, reported that Michael Maestlin, the mentor of Johannes Kepler, mapped out 11 Pleiades stars before the invention of the telescope.

To see more than 6 or 7 Pleaides stars, you must have very good eyesight (or a pair of binoculars). And you must be willing to spend time under a dark, moonless sky. Stephen O’Meara, a dark-sky connoisseur, claims that eyes dark-adapted for 30 minutes are 6 times more sensitive to light than eyes dark-adapted for 15 minutes. The surest way to see additional Pleiades stars is to look at this cluster through binoculars or low power in a telescope.

The Lost Pleiad, a painting by French artist William-Adolphe Bouguereau (1825-1905). Image via Wikimedia Commons.

Pleiades as calendar, in history and in modern science. Historically, the Pleiades have served as a calendar for many civilizations. The Greek name “Pleiades” probably means “to sail.” In the ancient Mediterranean world, the day that the Pleaides cluster first appeared in the morning sky before sunrise announced the opening of the navigation season.

The modern-day festival of Halloween originates from an old Druid rite that coincided with the midnight culmination of the Pleiades cluster. It was believed that the veil dividing the living from the dead is at its thinnest when the Pleaides culminates – reaches its highest point in the sky – at midnight.

On a lighter note, the Zuni of New Mexico call the Pleiades the “Seed Stars,” because this cluster’s disappearance in the evening sky every spring signals the seed-planting season.

In both myth and science, the Pleiades are considered to be sibling stars. Modern astronomers say the Pleiades stars were born from the same cloud of gas and dust some 100 million years ago. This gravitationally bound cluster of several hundred stars looms some 430 light-years distant, and these sibling stars drift through space together at about 25 miles per second. Many of these Pleiades stars shine hundreds of times more brightly than our sun.

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

The Pleiades – aka the Seven Sisters – captured by Greg Hogan in Kathleen, Georgia on October 31, 2016.

Bottom line: November is often called the month of the Pleiades – or Seven Sisters – because it’s at this time that the Pleiades shine from dusk until dawn.

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

Year’s farthest perigee on October 31

At top: Last quarter moon simulated image via U.S. Naval Observatory

The moon sweeps to perigee – its closest point to Earth in its orbit – for the second time this month on October 31, 2018. This perigee counts as the most distant of this year’s 14 perigees. So you might say today’s moon is the farthest close moon.

How far away is the moon today? It’s 230,034 miles (370,204 km) away. That’s in contrast to 2018’s closest perigee of 221,559 miles (356,565 km) on January 1.

Notice … this most distant perigee comes when the moon is at the last quarter phase. That is not an accident. If you’re game, we’ll share a secret with you about why a quarter moon at perigee is farther than the mean perigee of 225,804 miles or 363,396 km, and why a quarter moon at apogee is closer than the mean apogee distance of 251,969 miles or 405,504 km. We’ll also explain why a full moon or new moon at perigee is closer than the mean perigee, yet why a full moon or new moon at apogee is farther than the mean apogee. It all has to do with the varying eccentricity of the moon’s orbit.

The moon’s orbit around Earth isn’t a perfect circle. But it’s very nearly circular, as the above diagram shows. Diagram by Brian Koberlein.

The moon’s eccentric orbit

The moon’s orbit around Earth, like Earth’s orbit around the sun, isn’t a perfect circle. It’s a slightly oblong ellipse. That’s why, every month, the moon reaches a nearest point to Earth at perigee and a farthest point at apogee.

However, the moon’s orbit isn’t highly eccentric (oblong), but nearly circular, as shown on the illustration above.

What’s more, like everything else in nature, the moon’s orbit is always in flux. Its shape, and its orientation relative to the Earth and sun, change all the time.

So we have a moon at perigee – closest to Earth for the month – and also a moon at its last quarter phase on October 31, 2018.

Last quarter moon: October 31, 2018 at 16:40 UTC
Lunar perigee: October 31, 2018 at 20:05 UTC

Image credit: NASA. The moon’s orbit is closer to being a circle than the diagram suggests, but the exaggeration helps to clarify. The moon is closest to Earth in its orbit at perigee and farthest away at apogee.

The illustrations above label perigee (moon’s closest point to Earth) and apogee (moon’s farthest point from Earth). A line drawn from perigee to apogee defines the major axis, or the longest diameter, of the moon’s elliptical orbit. In the parlance of astronomers, the perigee-to-apogee line is called the line of apsides. The center of the line of apsides to either the perigee point or apogee point is called the semi-major axis.

Earth does not lie at the center of the line of apsides. Instead, the Earth is offset from the center of the major axis, or line of apsides, toward the lunar perigee point. To be more precise, the Earth resides at one of the two foci of the ellipse.

Keep in mind, also, that the moon’s major axis (longest diameter of an ellipse) always makes a right angle to the moon’s minor axis (shortest diameter of an ellipse).

Varying eccentricity of the moon’s orbit

When the moon’s major axis, or line of apsides, makes a right angle to the sun-Earth line (B in below diagram), the moon’s eccentricity decreases to a minimum. In other words, the moon’s orbit is closest to being circular when the moon’s minor axis points toward the sun. Although the moon still swings closest to Earth at perigee and farthest from Earth at apogee, the perigee distance increases and the apogee distance decreases whenever the moon’s eccentricity lessens, or more closely approaches a circle in shape.

In short, when the major axis makes a right angle with the sun-Earth line (B in below diagram), the quarter moons closely align with perigee and apogee.

Image via Bedford Astronomy Club.

Close and far moons in 2018

Some 103 days before and after the minor axis points sunward (B in above diagram), it’s then the moon’s major axis that points in the sun’s direction (A and C in above diagram). When the major axis, or line of apsides, aligns with the sun-Earth line, the eccentricity of the moon’s orbit increases to a maximum, and its orbit becomes maximally oblong. That causes the moon to swing extra-far from Earth at lunar apogee – yet extra-close to Earth at lunar perigee.

And that brings us to the full moon. It’s also no accident that 2018’s closest perigee closely aligned with the full moon.

Lunar perigee: 2018 January 1 at 21:54 UTC
Full Moon: 2018 January 2 at 2:24 UTC

When the major axis points sunward (A and C in above diagram), it’s the new moon or full moon that closely aligns with perigee/apogee. In diagram A, it’s a new moon perigee and full moon apogee; and in diagram C, it’s a full moon perigee and new moon apogee.

Farthest perigees often recur in cycles of 14 lunar months (14 returns to the same lunar phase), a period of about 413 days (1 year, 1 month and 18 days). For instance, 14 lunar months ago (from October 31, 2018), the close coincidence of last quarter moon with perigee presented last year’s farthest perigee on September 13, 2017 (229,820 miles or 369,860 km). Moreover, 14 lunar months from today (October 31, 2018), the last quarter moon will again closely align with perigee, to stage next year’s farthest lunar perigee on December 18, 2019 (230,072 miles or 370,265 km).

Want to know more? Eclipses and the moon’s orbit

Resources:

Lunar perigee and apogee calculator

Moon at perigee and apogee: 2001 to 2100

Phases of the moon: 2001 to 2100

Bottom line: In 2018, the moon swings to its most distant perigee of the year on October 31, 2018.

from EarthSky https://ift.tt/2AB9VWm

At top: Last quarter moon simulated image via U.S. Naval Observatory

The moon sweeps to perigee – its closest point to Earth in its orbit – for the second time this month on October 31, 2018. This perigee counts as the most distant of this year’s 14 perigees. So you might say today’s moon is the farthest close moon.

How far away is the moon today? It’s 230,034 miles (370,204 km) away. That’s in contrast to 2018’s closest perigee of 221,559 miles (356,565 km) on January 1.

Notice … this most distant perigee comes when the moon is at the last quarter phase. That is not an accident. If you’re game, we’ll share a secret with you about why a quarter moon at perigee is farther than the mean perigee of 225,804 miles or 363,396 km, and why a quarter moon at apogee is closer than the mean apogee distance of 251,969 miles or 405,504 km. We’ll also explain why a full moon or new moon at perigee is closer than the mean perigee, yet why a full moon or new moon at apogee is farther than the mean apogee. It all has to do with the varying eccentricity of the moon’s orbit.

The moon’s orbit around Earth isn’t a perfect circle. But it’s very nearly circular, as the above diagram shows. Diagram by Brian Koberlein.

The moon’s eccentric orbit

The moon’s orbit around Earth, like Earth’s orbit around the sun, isn’t a perfect circle. It’s a slightly oblong ellipse. That’s why, every month, the moon reaches a nearest point to Earth at perigee and a farthest point at apogee.

However, the moon’s orbit isn’t highly eccentric (oblong), but nearly circular, as shown on the illustration above.

What’s more, like everything else in nature, the moon’s orbit is always in flux. Its shape, and its orientation relative to the Earth and sun, change all the time.

So we have a moon at perigee – closest to Earth for the month – and also a moon at its last quarter phase on October 31, 2018.

Last quarter moon: October 31, 2018 at 16:40 UTC
Lunar perigee: October 31, 2018 at 20:05 UTC

Image credit: NASA. The moon’s orbit is closer to being a circle than the diagram suggests, but the exaggeration helps to clarify. The moon is closest to Earth in its orbit at perigee and farthest away at apogee.

The illustrations above label perigee (moon’s closest point to Earth) and apogee (moon’s farthest point from Earth). A line drawn from perigee to apogee defines the major axis, or the longest diameter, of the moon’s elliptical orbit. In the parlance of astronomers, the perigee-to-apogee line is called the line of apsides. The center of the line of apsides to either the perigee point or apogee point is called the semi-major axis.

Earth does not lie at the center of the line of apsides. Instead, the Earth is offset from the center of the major axis, or line of apsides, toward the lunar perigee point. To be more precise, the Earth resides at one of the two foci of the ellipse.

Keep in mind, also, that the moon’s major axis (longest diameter of an ellipse) always makes a right angle to the moon’s minor axis (shortest diameter of an ellipse).

Varying eccentricity of the moon’s orbit

When the moon’s major axis, or line of apsides, makes a right angle to the sun-Earth line (B in below diagram), the moon’s eccentricity decreases to a minimum. In other words, the moon’s orbit is closest to being circular when the moon’s minor axis points toward the sun. Although the moon still swings closest to Earth at perigee and farthest from Earth at apogee, the perigee distance increases and the apogee distance decreases whenever the moon’s eccentricity lessens, or more closely approaches a circle in shape.

In short, when the major axis makes a right angle with the sun-Earth line (B in below diagram), the quarter moons closely align with perigee and apogee.

Image via Bedford Astronomy Club.

Close and far moons in 2018

Some 103 days before and after the minor axis points sunward (B in above diagram), it’s then the moon’s major axis that points in the sun’s direction (A and C in above diagram). When the major axis, or line of apsides, aligns with the sun-Earth line, the eccentricity of the moon’s orbit increases to a maximum, and its orbit becomes maximally oblong. That causes the moon to swing extra-far from Earth at lunar apogee – yet extra-close to Earth at lunar perigee.

And that brings us to the full moon. It’s also no accident that 2018’s closest perigee closely aligned with the full moon.

Lunar perigee: 2018 January 1 at 21:54 UTC
Full Moon: 2018 January 2 at 2:24 UTC

When the major axis points sunward (A and C in above diagram), it’s the new moon or full moon that closely aligns with perigee/apogee. In diagram A, it’s a new moon perigee and full moon apogee; and in diagram C, it’s a full moon perigee and new moon apogee.

Farthest perigees often recur in cycles of 14 lunar months (14 returns to the same lunar phase), a period of about 413 days (1 year, 1 month and 18 days). For instance, 14 lunar months ago (from October 31, 2018), the close coincidence of last quarter moon with perigee presented last year’s farthest perigee on September 13, 2017 (229,820 miles or 369,860 km). Moreover, 14 lunar months from today (October 31, 2018), the last quarter moon will again closely align with perigee, to stage next year’s farthest lunar perigee on December 18, 2019 (230,072 miles or 370,265 km).

Want to know more? Eclipses and the moon’s orbit

Resources:

Lunar perigee and apogee calculator

Moon at perigee and apogee: 2001 to 2100

Phases of the moon: 2001 to 2100

Bottom line: In 2018, the moon swings to its most distant perigee of the year on October 31, 2018.

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Last quarter moon is October 31

The moon was almost exactly at last quarter when Deirdre Horan in Dublin, Ireland, captured this photo. The terminator line, or line between light and dark on the moon, appears straight.

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. The moon reaches its exact half-illuminated phase, as viewed from Earth, on October 31, 2018 at 16:40 UTC; translate UTC to your time.

The October 31 last quarter moon is second of two for this month. The first one came on October 2, when the moon was shining in front of the constellation Gemini. The second last quarter moon on October 31 will appear in front of the constellation Cancer, one degree south of the Beehive star cluster.

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

A last quarter moon provides a great opportunity to think of yourself on a three-dimensional world in space. For example, it’s fun to see 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 middle of Earth’s nightside, on the midnight portion of Earth.

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 talked about it recently, too.

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.

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. Follow the links below to understand the phases of the moon.

New moon
Waxing crescent moon
First quarter moon
Waxing gibbous moon
Full moon
Waning gibbous moon
Last quarter moon
Waning crescent moon

Read more: 4 keys to understanding moon phases

Bottom line: Last quarter moon falls on October 31, 2018, at 16:40 UTC; translate UTC to your time.

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The moon was almost exactly at last quarter when Deirdre Horan in Dublin, Ireland, captured this photo. The terminator line, or line between light and dark on the moon, appears straight.

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. The moon reaches its exact half-illuminated phase, as viewed from Earth, on October 31, 2018 at 16:40 UTC; translate UTC to your time.

The October 31 last quarter moon is second of two for this month. The first one came on October 2, when the moon was shining in front of the constellation Gemini. The second last quarter moon on October 31 will appear in front of the constellation Cancer, one degree south of the Beehive star cluster.

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

A last quarter moon provides a great opportunity to think of yourself on a three-dimensional world in space. For example, it’s fun to see 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 middle of Earth’s nightside, on the midnight portion of Earth.

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 talked about it recently, too.

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.

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. Follow the links below to understand the phases of the moon.

New moon
Waxing crescent moon
First quarter moon
Waxing gibbous moon
Full moon
Waning gibbous moon
Last quarter moon
Waning crescent moon

Read more: 4 keys to understanding moon phases

Bottom line: Last quarter moon falls on October 31, 2018, at 16:40 UTC; translate UTC to your time.

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Parker solar probe becomes closest-yet spacecraft to sun

Parker Solar Probe, shown in this animation, became the closest-ever spacecraft to the sun on October 29, 2018. Image via NASA/JHUAPL.

The Parker Solar Probe now holds the record for closest approach to the sun by a human-made object. The spacecraft – which launched on August 12, 2018 – passed the current record of 26.55 million miles (43 million km) from the sun’s surface yesterday (October 29, 2018).

The previous record for closest solar approach was set by the German-American Helios 2 spacecraft in April 1976. As the Parker Solar Probe mission progresses, the spacecraft will repeatedly break its own records, with a final close approach of 3.83 million miles (6.2 million km) from the sun’s surface expected in 2024.

Parker Solar Probe will begin its first solar encounter tomorrow (October 31), continuing to fly closer and closer to the sun’s surface until it reaches its first perihelion — the point closest to the sun on November 5. The spacecraft will face brutal heat and radiation conditions while providing humanity with unprecedentedly close-up observations of a star and helping us understand phenomena that have puzzled scientists for decades.

Project Manager Andy Driesman, from the Johns Hopkins Applied Physics Laboratory, said in a statement:

It’s been just 78 days since Parker Solar Probe launched, and we’ve now come closer to our star than any other spacecraft in history. It’s a proud moment for the team, though we remain focused on our first solar encounter, which begins on October 31.

Parker Solar Probe is also expected to break the record for fastest spacecraft traveling relative to the sun, also on October 29. The current record for heliocentric speed is 153,454 miles per hour, set by Helios 2 in April 1976.

According to a NASA statement:

The Parker Solar Probe team periodically measures the spacecraft’s precise speed and position using NASA’s Deep Space Network, or DSN. The DSN sends a signal to the spacecraft, which then retransmits it back to the DSN, allowing the team to determine the spacecraft’s speed and position based on the timing and characteristics of the signal. Parker Solar Probe’s speed and position were calculated using DSN measurements made on October 24, and the team used that information along with known orbital forces to calculate the spacecraft’s speed and position from that point on.

The 2019 lunar calendars are here! Order yours before they’re gone. Makes a great gift.

Bottom line: The Parker Solar Probe broke the record for closest approach to the sun by a human-made object on October 29, 2018.

Via NASA

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Parker Solar Probe, shown in this animation, became the closest-ever spacecraft to the sun on October 29, 2018. Image via NASA/JHUAPL.

The Parker Solar Probe now holds the record for closest approach to the sun by a human-made object. The spacecraft – which launched on August 12, 2018 – passed the current record of 26.55 million miles (43 million km) from the sun’s surface yesterday (October 29, 2018).

The previous record for closest solar approach was set by the German-American Helios 2 spacecraft in April 1976. As the Parker Solar Probe mission progresses, the spacecraft will repeatedly break its own records, with a final close approach of 3.83 million miles (6.2 million km) from the sun’s surface expected in 2024.

Parker Solar Probe will begin its first solar encounter tomorrow (October 31), continuing to fly closer and closer to the sun’s surface until it reaches its first perihelion — the point closest to the sun on November 5. The spacecraft will face brutal heat and radiation conditions while providing humanity with unprecedentedly close-up observations of a star and helping us understand phenomena that have puzzled scientists for decades.

Project Manager Andy Driesman, from the Johns Hopkins Applied Physics Laboratory, said in a statement:

It’s been just 78 days since Parker Solar Probe launched, and we’ve now come closer to our star than any other spacecraft in history. It’s a proud moment for the team, though we remain focused on our first solar encounter, which begins on October 31.

Parker Solar Probe is also expected to break the record for fastest spacecraft traveling relative to the sun, also on October 29. The current record for heliocentric speed is 153,454 miles per hour, set by Helios 2 in April 1976.

According to a NASA statement:

The Parker Solar Probe team periodically measures the spacecraft’s precise speed and position using NASA’s Deep Space Network, or DSN. The DSN sends a signal to the spacecraft, which then retransmits it back to the DSN, allowing the team to determine the spacecraft’s speed and position based on the timing and characteristics of the signal. Parker Solar Probe’s speed and position were calculated using DSN measurements made on October 24, and the team used that information along with known orbital forces to calculate the spacecraft’s speed and position from that point on.

The 2019 lunar calendars are here! Order yours before they’re gone. Makes a great gift.

Bottom line: The Parker Solar Probe broke the record for closest approach to the sun by a human-made object on October 29, 2018.

Via NASA

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Brightest comet in the night sky

Martin Mobberley posted a new image of comet 46P/Wirtanen taken remotely from Siding Spring in Australia on October 27, 2018. This image shows a large coma – or cloud around the comet – commonly seen when comets come near the sun. Image via Comets and Asteroids on Facebook.

Have you heard about comet 46P/Wirtanen? It’s approaching the inner solar system, due to pass closest to our sun and Earth in December, 2018. Comet Wirtanen is the brightest comet in the night sky now, although that doesn’t mean you can see it with the eye alone. In fact, it’s visible now only to astronomers with telescopes. But – in December 2018 – comet Wirtanen might be visible to the unaided eye, at least from dark skies. Closest approach to the sun will be December 12, 2018, and closest approach to Earth is just a few days later, on December 16.

According to astronomers at the University of Maryland, this passage of comet Wirtanen near the Earth (near by comet standards, that is) will be the 10th closest approach of a comet in modern times. At its closest to us, the comet will be about 30 times the moon’s distance (7.1 million miles, or 11.5 million km).

Contrast that number to another comet that swept relatively near us recently – 21P/Giacobini-Zinner, which caused a brief outburst in this year’s Draconid meteor shower – and which swept closest to Earth on September 9-10, 2018 at 36 million miles (58 million km). That was the closest Giacobini-Zinner had come in 72 years!

And you can see – from the paragraphs above – that Wirtanen is coming much closer, although still many times the moon’s distance.

This is what’s called a lightcurve. It’s a measurement of comet 46P/Wirtanen’s brightness, over time. The comet is getting brighter! It might become bright enough in December to be viewed with the eye alone, from a dark location. Image via University of Maryland’s comet 46P/Wirtanen: current status page.

Estimates indicate Wirtanen might reach a visual magnitude of 3.5 to 6. That would place the comet clearly in the realm of visibility with the unaided eye (although diffuse objects like comets are tougher to see than the pinpoints of stars at comparable magnitudes).

And, of course, comets have been shown to be unpredictable. We will keep you updated.

Want to stay up-to-date on Wirtanen’s brightness? This webpage from the University of Maryland is providing updates.

The December 16, 2018, close approach to Earth of comet Wirtanen will happen less than 4 days after the comet’s perihelion, or closest point to the sun. Because comets are increasingly active as they draw nearer the sun that binds them in orbit, this comet can be expected to be near its brightest around then. It might be visible to the eye from a dark location. Image via University of Maryland.

Bottom line: Comet Wirtanen will come closest to Earth in December. At that point, it might be visible to the eye alone.

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

Martin Mobberley posted a new image of comet 46P/Wirtanen taken remotely from Siding Spring in Australia on October 27, 2018. This image shows a large coma – or cloud around the comet – commonly seen when comets come near the sun. Image via Comets and Asteroids on Facebook.

Have you heard about comet 46P/Wirtanen? It’s approaching the inner solar system, due to pass closest to our sun and Earth in December, 2018. Comet Wirtanen is the brightest comet in the night sky now, although that doesn’t mean you can see it with the eye alone. In fact, it’s visible now only to astronomers with telescopes. But – in December 2018 – comet Wirtanen might be visible to the unaided eye, at least from dark skies. Closest approach to the sun will be December 12, 2018, and closest approach to Earth is just a few days later, on December 16.

According to astronomers at the University of Maryland, this passage of comet Wirtanen near the Earth (near by comet standards, that is) will be the 10th closest approach of a comet in modern times. At its closest to us, the comet will be about 30 times the moon’s distance (7.1 million miles, or 11.5 million km).

Contrast that number to another comet that swept relatively near us recently – 21P/Giacobini-Zinner, which caused a brief outburst in this year’s Draconid meteor shower – and which swept closest to Earth on September 9-10, 2018 at 36 million miles (58 million km). That was the closest Giacobini-Zinner had come in 72 years!

And you can see – from the paragraphs above – that Wirtanen is coming much closer, although still many times the moon’s distance.

This is what’s called a lightcurve. It’s a measurement of comet 46P/Wirtanen’s brightness, over time. The comet is getting brighter! It might become bright enough in December to be viewed with the eye alone, from a dark location. Image via University of Maryland’s comet 46P/Wirtanen: current status page.

Estimates indicate Wirtanen might reach a visual magnitude of 3.5 to 6. That would place the comet clearly in the realm of visibility with the unaided eye (although diffuse objects like comets are tougher to see than the pinpoints of stars at comparable magnitudes).

And, of course, comets have been shown to be unpredictable. We will keep you updated.

Want to stay up-to-date on Wirtanen’s brightness? This webpage from the University of Maryland is providing updates.

The December 16, 2018, close approach to Earth of comet Wirtanen will happen less than 4 days after the comet’s perihelion, or closest point to the sun. Because comets are increasingly active as they draw nearer the sun that binds them in orbit, this comet can be expected to be near its brightest around then. It might be visible to the eye from a dark location. Image via University of Maryland.

Bottom line: Comet Wirtanen will come closest to Earth in December. At that point, it might be visible to the eye alone.

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

Sun halo over Zimbabwe

Sun halo – October, 2018 – by Ryan Vanderlinde of Zambezi Boy Photography in Zimbabwe.

Footprints Zimbabwe posted this photo to EarthSky Facebook this week and wrote:

Ryan Vanderlinde (Zambezi Boy Photography) captured the recent sun halo seen across many places in Zimbabwe. African mythology claims it is a sign of great change, while other older beliefs say it is a promise of a good rainy season.

It’s easy to see how – in Africa, where these halo are seen less frequently than at latitudes closer to either pole – they’d be associated with change. And it’s also possible to understand the part of the African belief related to rain. In western skylore, we say the same thing, this way:

Ring around the moon (or sun) means rain soon.

In fact, sun or moon halos may mean rain soon. High cirrus clouds containing ice crystals are what cause these halos, and these sorts of clouds often come before a storm.

Read more: What makes a halo around the sun or moon?

Bottom line: A 22-degree halo seen over Zimbabwe in October, 2018.

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

Sun halo – October, 2018 – by Ryan Vanderlinde of Zambezi Boy Photography in Zimbabwe.

Footprints Zimbabwe posted this photo to EarthSky Facebook this week and wrote:

Ryan Vanderlinde (Zambezi Boy Photography) captured the recent sun halo seen across many places in Zimbabwe. African mythology claims it is a sign of great change, while other older beliefs say it is a promise of a good rainy season.

It’s easy to see how – in Africa, where these halo are seen less frequently than at latitudes closer to either pole – they’d be associated with change. And it’s also possible to understand the part of the African belief related to rain. In western skylore, we say the same thing, this way:

Ring around the moon (or sun) means rain soon.

In fact, sun or moon halos may mean rain soon. High cirrus clouds containing ice crystals are what cause these halos, and these sorts of clouds often come before a storm.

Read more: What makes a halo around the sun or moon?

Bottom line: A 22-degree halo seen over Zimbabwe in October, 2018.

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

How 600,000 pounds of dead salmon nourished Alaskan trees

The 2019 lunar calendars are here! Order yours before they’re gone. Makes a great gift.

In this video, University of Washington professor Tom Quinn tells the story of an unusual 20-year study in which dead salmon, counted for a different study, were tossed to the side of a shallow creek in Alaska, but only to one side of the creek (so they wouldn’t be counted twice).

After 20 years, Quinn decided to end the study and measure trees to see if they grew differently during this time. It turns out that two decades of carcasses — nearly 600,000 pounds of fish — tossed to the left side of Hansen Creek did have a noticeable effect: White spruce trees on that side of the stream grew faster than their counterparts on the other side that received no salmon.

What’s more, nitrogen derived from salmon was found in high concentration in the needles of the spruce trees on the side of the tossed carcasses.

Essentially, said Quinn, the sockeye carcasses were fertilizing the trees. Quinn, a professor in University of Washington’s School of Aquatic and Fishery Sciences, is lead author of the study, published October 23, 2018 in the peer-reviewed journal Ecology. Quinn said in a statement:

Tossing the carcasses to the left side started out just as a convenience to keep from counting the same fish twice. I thought at some point in the future, it would be kind of cool to see it if had an effect.

An undergraduate student uses a hooked pole to throw a dead sockeye salmon onto the bank of Hansen Creek. Image via Dan DiNicola/U. Washington.

Source: A multidecade experiment shows that fertilization by salmon carcasses enhanced tree growth in the riparian zone

Bottom line: Video tells the story of how dead salmon thrown on one side of a shallow creek by researchers over 20 years had an unexpected benefit: healthier, faster-growing trees.

Via University of Washington

from EarthSky https://ift.tt/2Svj1L5

The 2019 lunar calendars are here! Order yours before they’re gone. Makes a great gift.

In this video, University of Washington professor Tom Quinn tells the story of an unusual 20-year study in which dead salmon, counted for a different study, were tossed to the side of a shallow creek in Alaska, but only to one side of the creek (so they wouldn’t be counted twice).

After 20 years, Quinn decided to end the study and measure trees to see if they grew differently during this time. It turns out that two decades of carcasses — nearly 600,000 pounds of fish — tossed to the left side of Hansen Creek did have a noticeable effect: White spruce trees on that side of the stream grew faster than their counterparts on the other side that received no salmon.

What’s more, nitrogen derived from salmon was found in high concentration in the needles of the spruce trees on the side of the tossed carcasses.

Essentially, said Quinn, the sockeye carcasses were fertilizing the trees. Quinn, a professor in University of Washington’s School of Aquatic and Fishery Sciences, is lead author of the study, published October 23, 2018 in the peer-reviewed journal Ecology. Quinn said in a statement:

Tossing the carcasses to the left side started out just as a convenience to keep from counting the same fish twice. I thought at some point in the future, it would be kind of cool to see it if had an effect.

An undergraduate student uses a hooked pole to throw a dead sockeye salmon onto the bank of Hansen Creek. Image via Dan DiNicola/U. Washington.

Source: A multidecade experiment shows that fertilization by salmon carcasses enhanced tree growth in the riparian zone

Bottom line: Video tells the story of how dead salmon thrown on one side of a shallow creek by researchers over 20 years had an unexpected benefit: healthier, faster-growing trees.

Via University of Washington

from EarthSky https://ift.tt/2Svj1L5