Cold Moon to prelude Geminid peak

Above: Photo of the December 2018 full moon by Larry Marr

The last full moon of the year falls on December 11 or 12, 2019, depending upon your time zone. We in North America often call the December full moon the Cold Moon or Long Night Moon.

This year, the full moon comes only a few days before the expected peak night of the Geminid meteor shower. Yet, the Geminids tend to be bright, so we can expect some of these meteors to overcome the moonlit glare; moreover, the peak will come this weekend, making it easier to indulge in night owl activity.

Read more: Geminid meteors to peak this weekend

The full moon occurs on December 12, at 05:12 UTC (translate UTC to your time). At the Eastern Time Zone in the United states, that translates to 12:12 a.m. on December 12. Yet, for the rest of the country, the full moon actually takes place this evening, on December 11, 2019 – at 11:12 p.m. CST, 10:12 p.m. MST, 9:12 p.m. PST, 8:12 p.m. Alaskan Time and 7:12 p.m. Hawaiian Time.

Astronomers regard the moon as being full at the instant that it is 180 degrees opposite the sun in ecliptic longitude. However, tonight’s moon stays more or less opposite the sun all night long, so it’ll appear full all night long as well. At the vicinity of full moon, the moon pretty much rises in the east at sunset, climbs highest up for the night around midnight (midway between sunset and sunrise) and sets in the west around sunrise. In other words, around the world, expect the moon to light up the nighttime tonight from dusk till dawn.

At the instant of full moon, the elongation between the moon and sun equals 180 degrees. Visit Unitarium.com to know the present moon-sun elongation, remembering that a positive number means a waxing moon moon and a negative number a waning moon.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

Moonlight will wash out a number of Geminids in 2019. The bright moon passes in front of the constellation Gemini, the radiant point for the annual Geminid meteor shower, on December 11, 12 and 13, 2019.

Far-southern December sun means far-northern December full moon

In December, from around the world, the sun rises and sets farthest south of due east and west for the year. For the Northern Hemisphere, these far-southern sunrises and sunsets bring short days and long nights; and in the Southern Hemisphere, these far-southern sunrises and sunsets accompany long days and short nights.

North of the Arctic Circle, the sun neither rises or sets, because the far-southern sun stays below the horizon at these far northern latitudes. However, since the full moon lies opposite the sun, the December full moon mimics the position of the far-northern June sun. So, north of the Arctic Circle, this June full moon playacts as the June midnight sun.

South of the Antarctic Circle, the far-southern December sun neither rises nor sets, as well, except that the sun stays above the horizon for 24 hours around the clock. But, then, at these far-southern latitudes, the December full moon stays beneath the horizon, like the sun in June.

Yes, the full moon assumes the sun’s position for six months hence. This December full moon now shines in front of the constellation Taurus the Bull, or where you’ll find the sun six months from now. Despite the short days and long nights of December that must be endured at our northerly latitudes, the December full moon reminds us that the long days of June will prevail once again.

Visit Heavens-Above to see the moon’s present position on the zodiac

Bottom line: At our northerly latitudes, the Cold or Long Night Moon serves as our wonderful nocturnal sun, giving us a much appreciated reprieve in the dark season of short days and long nights.

from EarthSky https://ift.tt/2P9FuOp

Above: Photo of the December 2018 full moon by Larry Marr

The last full moon of the year falls on December 11 or 12, 2019, depending upon your time zone. We in North America often call the December full moon the Cold Moon or Long Night Moon.

This year, the full moon comes only a few days before the expected peak night of the Geminid meteor shower. Yet, the Geminids tend to be bright, so we can expect some of these meteors to overcome the moonlit glare; moreover, the peak will come this weekend, making it easier to indulge in night owl activity.

Read more: Geminid meteors to peak this weekend

The full moon occurs on December 12, at 05:12 UTC (translate UTC to your time). At the Eastern Time Zone in the United states, that translates to 12:12 a.m. on December 12. Yet, for the rest of the country, the full moon actually takes place this evening, on December 11, 2019 – at 11:12 p.m. CST, 10:12 p.m. MST, 9:12 p.m. PST, 8:12 p.m. Alaskan Time and 7:12 p.m. Hawaiian Time.

Astronomers regard the moon as being full at the instant that it is 180 degrees opposite the sun in ecliptic longitude. However, tonight’s moon stays more or less opposite the sun all night long, so it’ll appear full all night long as well. At the vicinity of full moon, the moon pretty much rises in the east at sunset, climbs highest up for the night around midnight (midway between sunset and sunrise) and sets in the west around sunrise. In other words, around the world, expect the moon to light up the nighttime tonight from dusk till dawn.

At the instant of full moon, the elongation between the moon and sun equals 180 degrees. Visit Unitarium.com to know the present moon-sun elongation, remembering that a positive number means a waxing moon moon and a negative number a waning moon.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

Moonlight will wash out a number of Geminids in 2019. The bright moon passes in front of the constellation Gemini, the radiant point for the annual Geminid meteor shower, on December 11, 12 and 13, 2019.

Far-southern December sun means far-northern December full moon

In December, from around the world, the sun rises and sets farthest south of due east and west for the year. For the Northern Hemisphere, these far-southern sunrises and sunsets bring short days and long nights; and in the Southern Hemisphere, these far-southern sunrises and sunsets accompany long days and short nights.

North of the Arctic Circle, the sun neither rises or sets, because the far-southern sun stays below the horizon at these far northern latitudes. However, since the full moon lies opposite the sun, the December full moon mimics the position of the far-northern June sun. So, north of the Arctic Circle, this June full moon playacts as the June midnight sun.

South of the Antarctic Circle, the far-southern December sun neither rises nor sets, as well, except that the sun stays above the horizon for 24 hours around the clock. But, then, at these far-southern latitudes, the December full moon stays beneath the horizon, like the sun in June.

Yes, the full moon assumes the sun’s position for six months hence. This December full moon now shines in front of the constellation Taurus the Bull, or where you’ll find the sun six months from now. Despite the short days and long nights of December that must be endured at our northerly latitudes, the December full moon reminds us that the long days of June will prevail once again.

Visit Heavens-Above to see the moon’s present position on the zodiac

Bottom line: At our northerly latitudes, the Cold or Long Night Moon serves as our wonderful nocturnal sun, giving us a much appreciated reprieve in the dark season of short days and long nights.

from EarthSky https://ift.tt/2P9FuOp

Researchers describe 71 new species in 2019

The newly described cat-eyed cardinalfish. Image © 2019 Mark Erdmann.

On December 5, 2019, researchers at the California Academy of Sciences announced the addition of 71 new plant and animal species to Earth’s tree of life. The new species for 2019 include 17 fish, 15 geckos, eight flowering plants, six sea slugs, five arachnids, four eels, three ants, three skinks, two skates, two wasps, two mosses, two corals, and two lizards.

The academy scientists, along with many more international collaborators, discovered these new plants and animals across 5 continents and 3 oceans, from Croatian caves, extreme ocean depths and savanna forests. Shannon Bennett is Academy Chief of Science. She said in a statement:

Despite decades of tirelessly scouring some of the most familiar and remote places on Earth, biodiversity scientists estimate that more than 90% of nature’s species remain unknown. A rich diversity of plants and animals is what allows life on our planet to thrive: the interconnectedness of all living systems provides collective resilience in the face of our climate crisis. Each newly discovered species serves as an important reminder of the critical role we play in better understanding and preserving these precious ecosystems.

Below are a few highlights from the 71 new species described by the Academy in 2019.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

A stunning new-to-science sea slug. Image via Terry Gosliner © 2018 California Academy of Sciences.

New-to-science skate, Dipturus lamillai, from the Falkland Islands. Since the 1970s, the Falkland Island fisheries have been one of the largest distributors of skates – cartilaginous ray-like fish that live at depths down to almost 2,000 feet (600 meters). The fish are particularly popular in Korea, where they are fermented or filleted into steaks. Image © 2019 Francisco Concha.

This girdled lizard is found on the second highest mountain peak in Angola. Image © 2019 Ishan Agarwal.

A marvelous new flowering plant from Mexico. Image © 2019 Jonathan Amith.

This coral is found in the deep sea just off the coast of California. Image via Gary Williams © 2019 California Academy of Sciences.

Myrmecicultor chihuahuensis, The firsta – nd only – species in a new family of “ant-worshipping” spiders. These curious arachnids spend most of their time underground in ant mounds, although scientists aren’t sure why. It wasn’t until a recent expedition to Mexico’s Chihuahuan desert – the spider’s namesake – that scientists were first able to witness the species in the wild. But since they were found scattered around the surface of a collapsed ant nest, their underground behavior remains a mystery. Image © Durrell Ubick 2019 California Academy of Sciences.

Emeritus Curator of Botany Frank Almeda, described a rare white-blossomed plant Trembleya altoparaisensis this year based on several specimens collected over 100 years ago by the famous 19th-century botanist Auguste François Marie Glaziou. As rare now as it was then, the plant proved difficult to find in the wild. Luckily, Ricardo Pacifico, a Ph.D. student working with Almeda, was able to track down a living specimen on a recent expedition to the lush canyons of Chapada dos Veadeiros National Park in Brazil. Image © 2019 Ricardo Pacifico.

Bottom line: Researchers described 71 new species in 2019.

Via California Academy of Sciences

from EarthSky https://ift.tt/2RG6N4l

The newly described cat-eyed cardinalfish. Image © 2019 Mark Erdmann.

On December 5, 2019, researchers at the California Academy of Sciences announced the addition of 71 new plant and animal species to Earth’s tree of life. The new species for 2019 include 17 fish, 15 geckos, eight flowering plants, six sea slugs, five arachnids, four eels, three ants, three skinks, two skates, two wasps, two mosses, two corals, and two lizards.

The academy scientists, along with many more international collaborators, discovered these new plants and animals across 5 continents and 3 oceans, from Croatian caves, extreme ocean depths and savanna forests. Shannon Bennett is Academy Chief of Science. She said in a statement:

Despite decades of tirelessly scouring some of the most familiar and remote places on Earth, biodiversity scientists estimate that more than 90% of nature’s species remain unknown. A rich diversity of plants and animals is what allows life on our planet to thrive: the interconnectedness of all living systems provides collective resilience in the face of our climate crisis. Each newly discovered species serves as an important reminder of the critical role we play in better understanding and preserving these precious ecosystems.

Below are a few highlights from the 71 new species described by the Academy in 2019.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

A stunning new-to-science sea slug. Image via Terry Gosliner © 2018 California Academy of Sciences.

New-to-science skate, Dipturus lamillai, from the Falkland Islands. Since the 1970s, the Falkland Island fisheries have been one of the largest distributors of skates – cartilaginous ray-like fish that live at depths down to almost 2,000 feet (600 meters). The fish are particularly popular in Korea, where they are fermented or filleted into steaks. Image © 2019 Francisco Concha.

This girdled lizard is found on the second highest mountain peak in Angola. Image © 2019 Ishan Agarwal.

A marvelous new flowering plant from Mexico. Image © 2019 Jonathan Amith.

This coral is found in the deep sea just off the coast of California. Image via Gary Williams © 2019 California Academy of Sciences.

Myrmecicultor chihuahuensis, The firsta – nd only – species in a new family of “ant-worshipping” spiders. These curious arachnids spend most of their time underground in ant mounds, although scientists aren’t sure why. It wasn’t until a recent expedition to Mexico’s Chihuahuan desert – the spider’s namesake – that scientists were first able to witness the species in the wild. But since they were found scattered around the surface of a collapsed ant nest, their underground behavior remains a mystery. Image © Durrell Ubick 2019 California Academy of Sciences.

Emeritus Curator of Botany Frank Almeda, described a rare white-blossomed plant Trembleya altoparaisensis this year based on several specimens collected over 100 years ago by the famous 19th-century botanist Auguste François Marie Glaziou. As rare now as it was then, the plant proved difficult to find in the wild. Luckily, Ricardo Pacifico, a Ph.D. student working with Almeda, was able to track down a living specimen on a recent expedition to the lush canyons of Chapada dos Veadeiros National Park in Brazil. Image © 2019 Ricardo Pacifico.

Bottom line: Researchers described 71 new species in 2019.

Via California Academy of Sciences

from EarthSky https://ift.tt/2RG6N4l

Meet the microorganism that likes to eat meteorites

Meteorite dust fragments colonized and bioprocessed by the microbe M. sedula. Image via Tetyana Milojevic/ Universität Wien.

You’ve gotta eat to live. That’s a truism not just for humans but for other lifeforms, including microbes. Now an international team of scientists has announced a new study, showing that at least one type of earthly bacteria has a fondness for extraterrestrial food: meteorites, or rocks from space. These microbes even seem to prefer space rocks to their usual earthly fare of earthly rocks.

The intriguing peer-reviewed results were published in Scientific Reports (a publication of the journal Nature) on December 2, 2019.

Astrobiologist Tetyana Milojevic of the University of Vienna in Austria led the research, which demonstrated that an ancient single-celled bacteria known as Metallosphaera sedula (M. sedula) can not only process material in meteorites for food, but will even colonize meteorites faster than earthly rocks.

M. sedula belong to a family of bacteria known as lithotrophs; that is, they derive their energy from inorganic sources. The term “lithotroph” was created from the Greek terms ‘lithos’ (rock) and ‘troph’ (consumer), meaning “eaters of rock.”

For this study, the researchers ran tests on material from a meteorite labeled Northwest Africa 1172 (NWA 1172). They found that the microbes colonized the material much more quickly than they would terrestrial material.

Graphic showing the ingestion of inorganic material by the microbe M. sedula in the meteorite NWA 1172. Image via Tetyana Milojevic/ Universität Wien.

As Milojevic said in a statement:

Meteorite-fitness seems to be more beneficial for this ancient microorganism than a diet on terrestrial mineral sources. NWA 1172 is a multimetallic material, which may provide much more trace metals to facilitate metabolic activity and microbial growth. Moreover, the porosity of NWA 1172 might also reflect the superior growth rate of M. sedula.

This is certainly interesting, suggesting that M. sedula actually prefers the material coming from space over its local, home-grown, earthly food sources.

Scanning electron microscope image of meteorite NWA 1172, showing colonization of M. sedula microbes. Image via Tetyana Milojevic/ Universität Wien/ Daily Mail.

So how did the scientists make these findings?

They examined the meteorite-microbial interface at nanometer scale – one billionth of a meter – and traced how the material was consumed, investigating the iron redox behavior. Redox is is a type of chemical reaction in which the oxidation states of atoms are changed, and is common in biological processes. By combining several analytical spectroscopy techniques with transmission electron microscopy, they found a set of biogeochemical fingerprints left upon M. sedula growth on the meteorite. As Milojevic explained:

Our investigations validate the ability of M. sedula to perform the biotransformation of meteorite minerals, unravel microbial fingerprints left on meteorite material, and provide the next step towards an understanding of meteorite biogeochemistry.

Tetyana Milojevic at Universität Wien, who led the study. Image via Universität Wien.

It’s interesting that earthly microbes could use meteoric material for food and energy, so what about unearthly microbes? This study doesn’t address any evidence for alien biology in the meteorites, although claims of such discoveries have been made before, such as with the meteorite ALH84001 in 1996. It’s not hard to imagine, however, that extraterrestrial microscopic lifeforms could do the same thing, if any were present, either now or in the past.

The finding also has implications for the potential of extraterrestrial materials as a source of nutrients and energy for microorganisms on the early Earth billions of years ago. At that time, meteorite bombardment was a lot heavier than it is now. Could primitive microbes have used meteorites as a food source way back then? Did meteorites play a crucial role in the growth and evolution of life on Earth by providing sources of nutrients? It certainly seems plausible.

Bottom line: A new study shows that at least one type of microbe on Earth not only likes to eat material in meteorites, but even prefers it.

Source: Exploring the microbial biotransformation of extraterrestrial material on nanometer scale

Via Universität Wien

from EarthSky https://ift.tt/36iUoHI

Meteorite dust fragments colonized and bioprocessed by the microbe M. sedula. Image via Tetyana Milojevic/ Universität Wien.

You’ve gotta eat to live. That’s a truism not just for humans but for other lifeforms, including microbes. Now an international team of scientists has announced a new study, showing that at least one type of earthly bacteria has a fondness for extraterrestrial food: meteorites, or rocks from space. These microbes even seem to prefer space rocks to their usual earthly fare of earthly rocks.

The intriguing peer-reviewed results were published in Scientific Reports (a publication of the journal Nature) on December 2, 2019.

Astrobiologist Tetyana Milojevic of the University of Vienna in Austria led the research, which demonstrated that an ancient single-celled bacteria known as Metallosphaera sedula (M. sedula) can not only process material in meteorites for food, but will even colonize meteorites faster than earthly rocks.

M. sedula belong to a family of bacteria known as lithotrophs; that is, they derive their energy from inorganic sources. The term “lithotroph” was created from the Greek terms ‘lithos’ (rock) and ‘troph’ (consumer), meaning “eaters of rock.”

For this study, the researchers ran tests on material from a meteorite labeled Northwest Africa 1172 (NWA 1172). They found that the microbes colonized the material much more quickly than they would terrestrial material.

Graphic showing the ingestion of inorganic material by the microbe M. sedula in the meteorite NWA 1172. Image via Tetyana Milojevic/ Universität Wien.

As Milojevic said in a statement:

Meteorite-fitness seems to be more beneficial for this ancient microorganism than a diet on terrestrial mineral sources. NWA 1172 is a multimetallic material, which may provide much more trace metals to facilitate metabolic activity and microbial growth. Moreover, the porosity of NWA 1172 might also reflect the superior growth rate of M. sedula.

This is certainly interesting, suggesting that M. sedula actually prefers the material coming from space over its local, home-grown, earthly food sources.

Scanning electron microscope image of meteorite NWA 1172, showing colonization of M. sedula microbes. Image via Tetyana Milojevic/ Universität Wien/ Daily Mail.

So how did the scientists make these findings?

They examined the meteorite-microbial interface at nanometer scale – one billionth of a meter – and traced how the material was consumed, investigating the iron redox behavior. Redox is is a type of chemical reaction in which the oxidation states of atoms are changed, and is common in biological processes. By combining several analytical spectroscopy techniques with transmission electron microscopy, they found a set of biogeochemical fingerprints left upon M. sedula growth on the meteorite. As Milojevic explained:

Our investigations validate the ability of M. sedula to perform the biotransformation of meteorite minerals, unravel microbial fingerprints left on meteorite material, and provide the next step towards an understanding of meteorite biogeochemistry.

Tetyana Milojevic at Universität Wien, who led the study. Image via Universität Wien.

It’s interesting that earthly microbes could use meteoric material for food and energy, so what about unearthly microbes? This study doesn’t address any evidence for alien biology in the meteorites, although claims of such discoveries have been made before, such as with the meteorite ALH84001 in 1996. It’s not hard to imagine, however, that extraterrestrial microscopic lifeforms could do the same thing, if any were present, either now or in the past.

The finding also has implications for the potential of extraterrestrial materials as a source of nutrients and energy for microorganisms on the early Earth billions of years ago. At that time, meteorite bombardment was a lot heavier than it is now. Could primitive microbes have used meteorites as a food source way back then? Did meteorites play a crucial role in the growth and evolution of life on Earth by providing sources of nutrients? It certainly seems plausible.

Bottom line: A new study shows that at least one type of microbe on Earth not only likes to eat material in meteorites, but even prefers it.

Source: Exploring the microbial biotransformation of extraterrestrial material on nanometer scale

Via Universität Wien

from EarthSky https://ift.tt/36iUoHI

Why White Island erupted and why there was no warning

This footage was taken by Michael Schade, whose family got off Whakaari/White Island 20 minutes before it erupted.

By Shane Cronin, University of Auckland

Five people have been confirmed dead, 31 remain in hospital with injuries and eight are still missing after Monday’s (December 9, 2019) sudden volcanic eruptions on Whakaari/White Island off the east coast of New Zealand.

The island is a tourist destination and 47 people were on it when it erupted on Monday afternoon. Three of those rescued have now been discharged from hospital.

Volcanologists at GeoNet, which operates a geological hazard monitoring system, described the eruption as impulsive and short-lived, with an ash plume that rose to more than 2 miles (3 km) above the vent.

On Tuesday morning, New Zealand Prime Minister Jacinda Ardern praised the courage of the first responders and pilots who conducted an aerial survey. She confirmed that the flyovers have shown no signs of life. Police are today assessing whether it is safe to return to the island for a recovery operation.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

The sudden eruption at White Island was short-lived but produced an ash plume that rose several kilometers above the vent. Image via GNZ Science.

Volcanic hazards

White Island is one of several volcanoes in New Zealand that can produce sudden explosive eruptions at any time. In this case, magma is shallow, and the heat and gases affect surface and ground water to form vigorous hydrothermal systems.

In these, water is trapped in pores of rocks in a super-heated state. Any external process, such as an earthquake, gas input from below, or even a change in the lake water level can tip this delicate balance and release the pressure on the hot and trapped water.

The resulting steam-driven eruption, also called a hydrothermal or phreatic eruption, can happen suddenly and with little to no warning. The expansion of water into steam is supersonic in speed and the liquid can expand to 1,700 times its original volume. This produces catastrophic impacts.

The expansion energy is enough to shatter solid rock, excavate craters and eject rock fragments and ash out to hundreds of meters away from the vent. We know of sites in New Zealand where material has been blasted out over 2 miles (3 km) from the vent by such eruptions.

The eruption on White Island sent sent huge amounts of steam and ash into the air in the blast. Image via GeoNet.

Potential for further eruptions

The hazards expected from steam-driven eruptions are violent ejections of hot blocks and ash, and the formation of “hurricane-like” currents of wet ash and coarse particles that radiate from the explosion vent. These can be deadly in terms of impact trauma, burns and respiratory injuries.

The eruptions are short-lived, but once one happens, there is a high chance for further, generally smaller ones as the system re-equilibrates. White Island is an acute location for such activity, but it is not the only location in New Zealand where this can happen.

Mount Ruapehu (crater lake), Mount Tongariro (Te Maari and Ketetahi) and geothermal areas of the central North Island all have the potential to cause such events. We know there have been more than 60 hydrothermal eruptions in the last 100 years in New Zealand. Some of these have caused loss of life.

Read more: Each volcano has unique warning signs that eruption is imminent

No warning

Monitoring and warning for hydrothermal eruptions is a huge challenge. We don’t normally see these eruptions coming, no matter how much we would like to. Many systems are already “primed” for such events, but the triggers are poorly understood.

The warning periods, once an event gets underway, are likely in the order of seconds to minutes. Our only hope for anticipating these events is to track potential vapor and liquid pressure in hydrothermal systems and to learn from their long-term behavior when they are at a super-critical state. Unfortunately there are no simple rules that can be followed and each hydrothermal system is different.

In this age of technology and instrumental monitoring, it seems irrational that there should be little or no warning for such eruptions. The eruption is not caused by magma, but by steam, and this is much harder to track in our current monitoring systems.

We have seen several other fatal hydrothermal catastrophes unfold in other parts of the world, such as the 2014 eruption of Mount Ontake in Japan. New Zealand has been luckier than many other parts of the world, until now.

Shane Cronin, Professor of Earth Sciences, University of Auckland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bottom line: A scientist explains why the December 9, 2019, eruption of the White Island volcano happened with no warning.

from EarthSky https://ift.tt/2LFI3pk

This footage was taken by Michael Schade, whose family got off Whakaari/White Island 20 minutes before it erupted.

By Shane Cronin, University of Auckland

Five people have been confirmed dead, 31 remain in hospital with injuries and eight are still missing after Monday’s (December 9, 2019) sudden volcanic eruptions on Whakaari/White Island off the east coast of New Zealand.

The island is a tourist destination and 47 people were on it when it erupted on Monday afternoon. Three of those rescued have now been discharged from hospital.

Volcanologists at GeoNet, which operates a geological hazard monitoring system, described the eruption as impulsive and short-lived, with an ash plume that rose to more than 2 miles (3 km) above the vent.

On Tuesday morning, New Zealand Prime Minister Jacinda Ardern praised the courage of the first responders and pilots who conducted an aerial survey. She confirmed that the flyovers have shown no signs of life. Police are today assessing whether it is safe to return to the island for a recovery operation.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

The sudden eruption at White Island was short-lived but produced an ash plume that rose several kilometers above the vent. Image via GNZ Science.

Volcanic hazards

White Island is one of several volcanoes in New Zealand that can produce sudden explosive eruptions at any time. In this case, magma is shallow, and the heat and gases affect surface and ground water to form vigorous hydrothermal systems.

In these, water is trapped in pores of rocks in a super-heated state. Any external process, such as an earthquake, gas input from below, or even a change in the lake water level can tip this delicate balance and release the pressure on the hot and trapped water.

The resulting steam-driven eruption, also called a hydrothermal or phreatic eruption, can happen suddenly and with little to no warning. The expansion of water into steam is supersonic in speed and the liquid can expand to 1,700 times its original volume. This produces catastrophic impacts.

The expansion energy is enough to shatter solid rock, excavate craters and eject rock fragments and ash out to hundreds of meters away from the vent. We know of sites in New Zealand where material has been blasted out over 2 miles (3 km) from the vent by such eruptions.

The eruption on White Island sent sent huge amounts of steam and ash into the air in the blast. Image via GeoNet.

Potential for further eruptions

The hazards expected from steam-driven eruptions are violent ejections of hot blocks and ash, and the formation of “hurricane-like” currents of wet ash and coarse particles that radiate from the explosion vent. These can be deadly in terms of impact trauma, burns and respiratory injuries.

The eruptions are short-lived, but once one happens, there is a high chance for further, generally smaller ones as the system re-equilibrates. White Island is an acute location for such activity, but it is not the only location in New Zealand where this can happen.

Mount Ruapehu (crater lake), Mount Tongariro (Te Maari and Ketetahi) and geothermal areas of the central North Island all have the potential to cause such events. We know there have been more than 60 hydrothermal eruptions in the last 100 years in New Zealand. Some of these have caused loss of life.

Read more: Each volcano has unique warning signs that eruption is imminent

No warning

Monitoring and warning for hydrothermal eruptions is a huge challenge. We don’t normally see these eruptions coming, no matter how much we would like to. Many systems are already “primed” for such events, but the triggers are poorly understood.

The warning periods, once an event gets underway, are likely in the order of seconds to minutes. Our only hope for anticipating these events is to track potential vapor and liquid pressure in hydrothermal systems and to learn from their long-term behavior when they are at a super-critical state. Unfortunately there are no simple rules that can be followed and each hydrothermal system is different.

In this age of technology and instrumental monitoring, it seems irrational that there should be little or no warning for such eruptions. The eruption is not caused by magma, but by steam, and this is much harder to track in our current monitoring systems.

We have seen several other fatal hydrothermal catastrophes unfold in other parts of the world, such as the 2014 eruption of Mount Ontake in Japan. New Zealand has been luckier than many other parts of the world, until now.

Shane Cronin, Professor of Earth Sciences, University of Auckland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bottom line: A scientist explains why the December 9, 2019, eruption of the White Island volcano happened with no warning.

from EarthSky https://ift.tt/2LFI3pk

Christmas Bird Count starts December 14

Image via Audubon.

The Audubon Society’s cherished Christmas Bird Count is one of the longest-running citizen science projects in existence — it was started on Christmas Day in 1900 and is still going strong. During the event, people venture outdoors to designated areas and count the types and numbers of birds that they see and hear over the course of one day. The data are used to keep track of the health of bird populations in North America. This year’s count runs from December 14, 2019 – January 5, 2020.

Sign up to join the Christmas Bird Count here.

The counts are conducted within a 15-mile wide circle, and the counts for each circle are organized by a circle compiler. To participate in the count — it’s free — you need to sign up with a local circle compiler here. As of yesterday (Sunday, December 8), there were still several circles with open registrations available (the open ones are the circles shown below in yellow and green, and the red ones are full circles that are no longer accepting new participants). No worries if you are a beginning bird watcher because you will be matched up with a more experienced birder. Also, you can try checking with local nature centers in your area, as they may be hosting special Christmas Bird Count events.

Screenshot of circles for the Christmas Bird Count taken on December 8, 2019.

During last year’s 119th Christmas Bird Count, more than 2,600 species and 48 million birds were counted, and count efforts were at a record high level. Geoff LeBaron, director of the Christmas Bird Count program, said in a statement:

The Christmas Bird Count is a great tradition and opportunity for everyone to be a part of 120 years of ongoing community science. Adding your observations to twelve decades of data helps scientists and conservationists discover trends that make our work more impactful. Participating in the Christmas Bird Count is a fun and meaningful way to spend a winter for anyone and everyone.

Photograph of a pileated woodpecker taken by Jessica Nelson during the 118th Christmas Bird Count. Image via National Audubon Society.

During last year’s count, two very rare species were spotted—these species included a Little Stint in San Diego, California, and a Great Black Hawk in Portland, Maine. Ongoing declines in a native quail species, the Northern Bobwhite, were also noted across the eastern U.S.

This year’s 120th Christmas Bird Count is sure to yield additional interesting and important data that will help scientists better understand bird populations. You can share your bird count photographs and experiences on social media with the hashtag #ChristmasBirdCount. Of course, we here at EarthSky would love to have you send us your photographs too! Lastly, Audubon has developed a cool, new CBC Live tool for this year’s count where you can upload and share your photos. There are already a few pre-count photos on CBC Live—check them out here!

Bottom line: Audubon’s 120th Christmas Bird Count will take place from December 14, 2019 – January 5, 2020. This long-running citizen science project provides scientists with valuable information about the health of bird populations in North America.

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Image via Audubon.

The Audubon Society’s cherished Christmas Bird Count is one of the longest-running citizen science projects in existence — it was started on Christmas Day in 1900 and is still going strong. During the event, people venture outdoors to designated areas and count the types and numbers of birds that they see and hear over the course of one day. The data are used to keep track of the health of bird populations in North America. This year’s count runs from December 14, 2019 – January 5, 2020.

Sign up to join the Christmas Bird Count here.

The counts are conducted within a 15-mile wide circle, and the counts for each circle are organized by a circle compiler. To participate in the count — it’s free — you need to sign up with a local circle compiler here. As of yesterday (Sunday, December 8), there were still several circles with open registrations available (the open ones are the circles shown below in yellow and green, and the red ones are full circles that are no longer accepting new participants). No worries if you are a beginning bird watcher because you will be matched up with a more experienced birder. Also, you can try checking with local nature centers in your area, as they may be hosting special Christmas Bird Count events.

Screenshot of circles for the Christmas Bird Count taken on December 8, 2019.

During last year’s 119th Christmas Bird Count, more than 2,600 species and 48 million birds were counted, and count efforts were at a record high level. Geoff LeBaron, director of the Christmas Bird Count program, said in a statement:

The Christmas Bird Count is a great tradition and opportunity for everyone to be a part of 120 years of ongoing community science. Adding your observations to twelve decades of data helps scientists and conservationists discover trends that make our work more impactful. Participating in the Christmas Bird Count is a fun and meaningful way to spend a winter for anyone and everyone.

Photograph of a pileated woodpecker taken by Jessica Nelson during the 118th Christmas Bird Count. Image via National Audubon Society.

During last year’s count, two very rare species were spotted—these species included a Little Stint in San Diego, California, and a Great Black Hawk in Portland, Maine. Ongoing declines in a native quail species, the Northern Bobwhite, were also noted across the eastern U.S.

This year’s 120th Christmas Bird Count is sure to yield additional interesting and important data that will help scientists better understand bird populations. You can share your bird count photographs and experiences on social media with the hashtag #ChristmasBirdCount. Of course, we here at EarthSky would love to have you send us your photographs too! Lastly, Audubon has developed a cool, new CBC Live tool for this year’s count where you can upload and share your photos. There are already a few pre-count photos on CBC Live—check them out here!

Bottom line: Audubon’s 120th Christmas Bird Count will take place from December 14, 2019 – January 5, 2020. This long-running citizen science project provides scientists with valuable information about the health of bird populations in North America.

from EarthSky https://ift.tt/36gX2xv

Today’s volcano in New Zealand is on the Pacific Ring of Fire

Around 50 people – mostly tourists – were on White Island when the volcano erupted on Monday afternoon, December 9, 2019. Many remain unaccounted for at this writing. The eruption began at around 2:11 p.m., local time. Image via NewsHubNewZealand.

The volcano that erupted today (December 9, 2019) on White Island – which sits about 30 miles (50 km) offshore from mainland New Zealand – is one of a long chain of volcanos in what’s called the Ring of Fire. These volcanoes and other tectonically active structures surround the Pacific Ocean. The chain runs up along the western coast of South and North America, crosses over the Aleutian Islands in Alaska, runs down the eastern coast of Asia past New Zealand and into the northern coast of Antarctica. The Ring of Fire is one of the most geologically active areas on Earth, and is a site for frequent earthquakes and powerful volcanic eruptions.

Read more: 5 dead, many more missing in eruption of New Zealand volcano

Information about the volcano and its tragic aftermath is still coming out, but the tweet below – from volcanologist Jess Phoenix – has more about it.

Here's a little bit of info about the #WhiteIsland #volcano eruption. Please look to @geonet & @USGSVolcanoes for accurate information. The imagery on social media can be scary, but this is a relatively small (yet deadly) eruption. At least 5 people are now reported to have died. pic.twitter.com/uB7ORsMozK

— Jess Phoenix ? (@jessphoenix2018) December 9, 2019

For official information about the White Island eruption in New Zealand, follow @geonet & @gnsscience. Latest update here: https://t.co/4LlOOMpQpa https://t.co/0g53y12xzb

— USGS Volcanoes? (@USGSVolcanoes) December 9, 2019

The New Zealand volcano is one of more than 450 active and dormant volcanoes located within the Ring of Fire. Many of these volcanoes were created through the tectonic process of subduction whereby dense ocean plates collide with and slide under lighter continental plates.

The material from the ocean floor melts as it enters the Earth’s interior and then rises to the nearby surface as magma.

Other noteworthy volcanoes that dot the Ring of Fire include Mount St. Helens in the USA, Mount Fuji in Japan and Mount Pinatubo in the Philippines. Since 1850, approximately 90% of the 16 most powerful volcanic eruptions on Earth have occurred within the Pacific Ring of Fire.

Many volcanoes on Earth are located around the Pacific Ring of Fire. Image Credit: U.S. Geological Survey.

Image of an oceanic plate being subducted under a continental plate. Image Credit: U.S. Geological Survey.

My god, White Island volcano in New Zealand erupted today for first time since 2001. My family and I had gotten off it 20 minutes before, were waiting at our boat about to leave when we saw it. Boat ride home tending to people our boat rescued was indescribable. #whiteisland pic.twitter.com/QJwWi12Tvt

— Michael Schade (@sch) December 9, 2019

The majority of Earth’s earthquakes occur in the Ring of Fire, too. These earthquakes are caused by the sudden lateral or vertical movement of rock along plate margins. About 81% of the world’s largest earthquakes have occurred along the Ring of Fire. The largest earthquake ever recorded on Earth was a 9.5 magnitude earthquake that struck Chile on May 22, 1960. Other noteworthy earthquakes that have occurred along the Ring of Fire include a 9.2 magnitude earthquake that struck Prince William Sound, Alaska on March 28, 1964, a 9.1 magnitude earthquake that struck off the coast of Sumatra on December 26, 2004 and a 9.0 earthquake that struck near the coast of Honshu, Japan on March 11, 2011.

Deep ocean trenches are another common feature of the Ring of Fire. These trenches form along subduction zones where slabs of the ocean floor slide into the Earth. The deepest part of the ocean on Earth, the Mariana Trench, is located along the Ring of Fire in the western portion of the Pacific Ocean Basin.

Despite the high levels of volcanic and seismic activity, millions of people live among the breathtaking landscapes of the Ring of Fire. Scientists are currently working with government officials to help nations in the region improve their response to natural disasters and build their resiliency.

Video shows multiple people evacuating #WhiteIsland during the volcanic eruption. #NuevaZelanda pic.twitter.com/tpdlUegODC

— EL CÍRCULO ? (@CirculoGloBal_I) December 9, 2019

Bottom line: The White Island volcano in New Zealand on December 9, 2019 took place along the Pacific Ring of Fire. Approximately 90% of the most powerful volcanic eruptions and about 81% of the world’s largest earthquakes have occurred along the Ring of Fire.

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Around 50 people – mostly tourists – were on White Island when the volcano erupted on Monday afternoon, December 9, 2019. Many remain unaccounted for at this writing. The eruption began at around 2:11 p.m., local time. Image via NewsHubNewZealand.

The volcano that erupted today (December 9, 2019) on White Island – which sits about 30 miles (50 km) offshore from mainland New Zealand – is one of a long chain of volcanos in what’s called the Ring of Fire. These volcanoes and other tectonically active structures surround the Pacific Ocean. The chain runs up along the western coast of South and North America, crosses over the Aleutian Islands in Alaska, runs down the eastern coast of Asia past New Zealand and into the northern coast of Antarctica. The Ring of Fire is one of the most geologically active areas on Earth, and is a site for frequent earthquakes and powerful volcanic eruptions.

Read more: 5 dead, many more missing in eruption of New Zealand volcano

Information about the volcano and its tragic aftermath is still coming out, but the tweet below – from volcanologist Jess Phoenix – has more about it.

Here's a little bit of info about the #WhiteIsland #volcano eruption. Please look to @geonet & @USGSVolcanoes for accurate information. The imagery on social media can be scary, but this is a relatively small (yet deadly) eruption. At least 5 people are now reported to have died. pic.twitter.com/uB7ORsMozK

— Jess Phoenix ? (@jessphoenix2018) December 9, 2019

For official information about the White Island eruption in New Zealand, follow @geonet & @gnsscience. Latest update here: https://t.co/4LlOOMpQpa https://t.co/0g53y12xzb

— USGS Volcanoes? (@USGSVolcanoes) December 9, 2019

The New Zealand volcano is one of more than 450 active and dormant volcanoes located within the Ring of Fire. Many of these volcanoes were created through the tectonic process of subduction whereby dense ocean plates collide with and slide under lighter continental plates.

The material from the ocean floor melts as it enters the Earth’s interior and then rises to the nearby surface as magma.

Other noteworthy volcanoes that dot the Ring of Fire include Mount St. Helens in the USA, Mount Fuji in Japan and Mount Pinatubo in the Philippines. Since 1850, approximately 90% of the 16 most powerful volcanic eruptions on Earth have occurred within the Pacific Ring of Fire.

Many volcanoes on Earth are located around the Pacific Ring of Fire. Image Credit: U.S. Geological Survey.

Image of an oceanic plate being subducted under a continental plate. Image Credit: U.S. Geological Survey.

My god, White Island volcano in New Zealand erupted today for first time since 2001. My family and I had gotten off it 20 minutes before, were waiting at our boat about to leave when we saw it. Boat ride home tending to people our boat rescued was indescribable. #whiteisland pic.twitter.com/QJwWi12Tvt

— Michael Schade (@sch) December 9, 2019

The majority of Earth’s earthquakes occur in the Ring of Fire, too. These earthquakes are caused by the sudden lateral or vertical movement of rock along plate margins. About 81% of the world’s largest earthquakes have occurred along the Ring of Fire. The largest earthquake ever recorded on Earth was a 9.5 magnitude earthquake that struck Chile on May 22, 1960. Other noteworthy earthquakes that have occurred along the Ring of Fire include a 9.2 magnitude earthquake that struck Prince William Sound, Alaska on March 28, 1964, a 9.1 magnitude earthquake that struck off the coast of Sumatra on December 26, 2004 and a 9.0 earthquake that struck near the coast of Honshu, Japan on March 11, 2011.

Deep ocean trenches are another common feature of the Ring of Fire. These trenches form along subduction zones where slabs of the ocean floor slide into the Earth. The deepest part of the ocean on Earth, the Mariana Trench, is located along the Ring of Fire in the western portion of the Pacific Ocean Basin.

Despite the high levels of volcanic and seismic activity, millions of people live among the breathtaking landscapes of the Ring of Fire. Scientists are currently working with government officials to help nations in the region improve their response to natural disasters and build their resiliency.

Video shows multiple people evacuating #WhiteIsland during the volcanic eruption. #NuevaZelanda pic.twitter.com/tpdlUegODC

— EL CÍRCULO ? (@CirculoGloBal_I) December 9, 2019

Bottom line: The White Island volcano in New Zealand on December 9, 2019 took place along the Pacific Ring of Fire. Approximately 90% of the most powerful volcanic eruptions and about 81% of the world’s largest earthquakes have occurred along the Ring of Fire.

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

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Why is Mars sometimes bright and sometimes faint?

Mars was very bright for several months around July 2018! And it was very red in color. Dennis Chabot of POSNE NightSky captured this photo of Mars on July 21, 2018.

Mars was brighter in 2018 than all the stars. It was even brighter than Jupiter. It was a blazing red dot of flame in our night sky for several months. This year, 2019, Mars was mostly faint. It was barely noticeable in our sky. Why? Why is Mars bright in some years, but faint in others? And what are the prospects for Mars in 2020?

Let’s talk about this week first. The week of December 9, 2019, is a good time to come to know Mars. That’s because – this week – Mars is near the star Zubenelgenubi in the east before sunup. Mars is faint now. But you can use the juxtaposition of Mars and this star to locate the planet on the sky’s dome. Read more.

So Mars can be faint, or it can be a bright planet. Keep reading to learn why the appearance of Mars varies so widely in our sky, making Mars one of the most interesting planets to watch!

Want to see Mars tonight or in the coming months? Bookmark EarthSky’s planet guide

Moon lovers! Order this year’s EarthSky lunar calendar here

A fun opportunity to see Mars comes around the morning of December 10, 2019. Look east before sunrise for the star Zubenelgenubi – Libra the Scales’ alpha star – above brighter Mars. Read more.

More than any other bright planet, the appearance of Mars in our night sky changes from year to year. Its dramatic swings in brightness are part of the reason the early stargazers named Mars for their god of war; sometimes, the war god rests and sometimes he grows fierce! Mars was faint throughout 2017, bright in 2018, and has been faint again for most of 2019. Mars is relatively faint now, a not-very-noticeable light in our eastern predawn sky.

Why? Why does Mars sometimes appear very bright, and sometimes very faint?

The first thing to realize is that Mars isn’t a very big world. It is only 4,219 miles (6,790 km) in diameter, making it only slightly more than half Earth’s size (7,922 miles or 12,750 km in diameter).

The small size of Mars is your first clue to its varying brightness. The small size means that, when Mars is bright, its brightness isn’t due to bigness, as is the case with the largest planet in our solar system, Jupiter.

Mars isn’t very big, so its brightness – when it is bright – isn’t due to its bigness, as is true of Jupiter. Mars’ brightness, or lack of brightness, is all about how close it is to us. Image via Lunar and Planetary Institute.

Matt Pollack captured Mars from Little Tupper Lake in the Adirondacks of upstate New York in July 2018. Read more about this photo.

Instead, the main reason for Mars’ extremes in brightness has to do with its nearness (or lack of nearness) to Earth.

Mars orbits the sun one step outward from Earth. The distances between Earth and Mars change as both worlds orbit around the sun. Sometimes Earth and Mars are on the same side of the solar system, and hence near one another. At other times, as it was for much of 2017 and was again for much of 2019, Mars was moving on the opposite side of the solar system from Earth.

Look at the diagrams below, which show Earth and Mars in their respective orbits around the sun in mid-2018 and this month, December 2019 …

Earth (blue) last passed between between the sun and Mars (red) on July 27, 2018. This was Mars’ opposition. It comes to opposition about every 2 years, and, at such times, Mars is always at its best for that 2-year period. There’s also a 15-year cycle of Mars, whereby the red planet is brighter and fainter at opposition. In July 2018, we were at the peak of the 2-year cycle – and the peak of the 15-year cycle – and Mars was very, very bright! Image via Fourmilab.

Mars passed most directly behind the sun from Earth in September 2019. This chart shows December 2019, when Mars (red) is still far across the solar system from Earth (blue). But, in 2020, Earth will catch up to Mars again! See the chart below. Image via Fourmilab.

This chart shows the relative positions of Earth (blue) and Mars (red) at the time of Mars’ coming opposition on October 13, 2020. Around that time, Mars will appear bright in our sky again – and in the sky all night long – but it won’t be as bright as it was in 2018. Image via Fourmilab.

Earth takes a year to orbit the sun once. Mars takes about two years to orbit once. Opposition for Mars – when Earth passes between Mars and the sun – happens every two years and 50 days.

So Mars’ brightness waxes and wanes in our sky about every two years. Last year, 2018, was a very, very special year for Mars, when the planet was brighter than it has been since 2003. Astronomers called it a perihelic opposition (or perihelic apparition) of Mars. In other words, in 2018, we went between Mars and the sun – bringing Mars to opposition in our sky – around the same time Mars came closest to the sun. The word perihelion refers Mars’ closest point to the sun in orbit.

Maybe you can see that – in years when we pass between Mars and the sun, when Mars is also closest to the sun – Earth and Mars are closest. That’s what happened in 2018.

2003 was the previous perihelic opposition for Mars. The red planet came within 34.6 million miles (55.7 million km) of Earth, closer than at any time in over nearly 60,000 years! That was really something.

Diagram by Roy L. Bishop. Copyright Royal Astronomical Society of Canada. Used with permission. Visit the RASC estore to purchase the Observer’s Handbook, a necessary tool for all skywatchers. Read more about this image.

And now? Earth will pass between Mars and the sun next on October 13, 2020. The red planet will appear brightest in our sky – very bright indeed and fiery red – around that time.

Mars is now in that part of its cycle with respect to Earth in which it’ll hover – faint and not at all noticeable – in our predawn sky for some months. Mars was in conjunction with the sun, that is, behind the sun as seen from Earth – on September 2, 2019. And now it remains far across the solar system from us, with Earth speeding around in its orbit, trying to catch Mars again. But it’ll be some months before we catch it.

And thus Mars alternates years in being bright in our sky, or faint. 2019 was a dull year, but 2020 will be an exciting one, for Mars! It’ll start slowly, though, with Mars sitting low in the east (much as it is now) as the year begins. January, February, March, April 2020 … you’ll still find Mars doing nothing much, low in the east before sunup. Earth will still be far across the solar system from Mars, but rushing along in our smaller, faster orbit, trying to catch up. As northern summer 2020 approaches, Mars will begin to change. It’ll begin to brighten more dramatically as, finally, Earth begins to catch up to Mars.

Watch for it!

Artist’s concept of Earth (3rd planet from the sun) passing between the sun and Mars (4th planet from the sun). Not to scale. This is Mars’ opposition, when it appears opposite the sun in our sky. Image via NASA.

Bottom line: Mars alternates years in appearing bright and faint in our night sky. In 2018, we had a grand view of Mars … best since 2003! In 2019, we were in one of Mars’ faint years. But 2020 will – once again – be a bright year for Mars.

Photos of bright Mars in 2018, from the EarthSky community

from EarthSky https://ift.tt/2Puo0em

Mars was very bright for several months around July 2018! And it was very red in color. Dennis Chabot of POSNE NightSky captured this photo of Mars on July 21, 2018.

Mars was brighter in 2018 than all the stars. It was even brighter than Jupiter. It was a blazing red dot of flame in our night sky for several months. This year, 2019, Mars was mostly faint. It was barely noticeable in our sky. Why? Why is Mars bright in some years, but faint in others? And what are the prospects for Mars in 2020?

Let’s talk about this week first. The week of December 9, 2019, is a good time to come to know Mars. That’s because – this week – Mars is near the star Zubenelgenubi in the east before sunup. Mars is faint now. But you can use the juxtaposition of Mars and this star to locate the planet on the sky’s dome. Read more.

So Mars can be faint, or it can be a bright planet. Keep reading to learn why the appearance of Mars varies so widely in our sky, making Mars one of the most interesting planets to watch!

Want to see Mars tonight or in the coming months? Bookmark EarthSky’s planet guide

Moon lovers! Order this year’s EarthSky lunar calendar here

A fun opportunity to see Mars comes around the morning of December 10, 2019. Look east before sunrise for the star Zubenelgenubi – Libra the Scales’ alpha star – above brighter Mars. Read more.

More than any other bright planet, the appearance of Mars in our night sky changes from year to year. Its dramatic swings in brightness are part of the reason the early stargazers named Mars for their god of war; sometimes, the war god rests and sometimes he grows fierce! Mars was faint throughout 2017, bright in 2018, and has been faint again for most of 2019. Mars is relatively faint now, a not-very-noticeable light in our eastern predawn sky.

Why? Why does Mars sometimes appear very bright, and sometimes very faint?

The first thing to realize is that Mars isn’t a very big world. It is only 4,219 miles (6,790 km) in diameter, making it only slightly more than half Earth’s size (7,922 miles or 12,750 km in diameter).

The small size of Mars is your first clue to its varying brightness. The small size means that, when Mars is bright, its brightness isn’t due to bigness, as is the case with the largest planet in our solar system, Jupiter.

Mars isn’t very big, so its brightness – when it is bright – isn’t due to its bigness, as is true of Jupiter. Mars’ brightness, or lack of brightness, is all about how close it is to us. Image via Lunar and Planetary Institute.

Matt Pollack captured Mars from Little Tupper Lake in the Adirondacks of upstate New York in July 2018. Read more about this photo.

Instead, the main reason for Mars’ extremes in brightness has to do with its nearness (or lack of nearness) to Earth.

Mars orbits the sun one step outward from Earth. The distances between Earth and Mars change as both worlds orbit around the sun. Sometimes Earth and Mars are on the same side of the solar system, and hence near one another. At other times, as it was for much of 2017 and was again for much of 2019, Mars was moving on the opposite side of the solar system from Earth.

Look at the diagrams below, which show Earth and Mars in their respective orbits around the sun in mid-2018 and this month, December 2019 …

Earth (blue) last passed between between the sun and Mars (red) on July 27, 2018. This was Mars’ opposition. It comes to opposition about every 2 years, and, at such times, Mars is always at its best for that 2-year period. There’s also a 15-year cycle of Mars, whereby the red planet is brighter and fainter at opposition. In July 2018, we were at the peak of the 2-year cycle – and the peak of the 15-year cycle – and Mars was very, very bright! Image via Fourmilab.

Mars passed most directly behind the sun from Earth in September 2019. This chart shows December 2019, when Mars (red) is still far across the solar system from Earth (blue). But, in 2020, Earth will catch up to Mars again! See the chart below. Image via Fourmilab.

This chart shows the relative positions of Earth (blue) and Mars (red) at the time of Mars’ coming opposition on October 13, 2020. Around that time, Mars will appear bright in our sky again – and in the sky all night long – but it won’t be as bright as it was in 2018. Image via Fourmilab.

Earth takes a year to orbit the sun once. Mars takes about two years to orbit once. Opposition for Mars – when Earth passes between Mars and the sun – happens every two years and 50 days.

So Mars’ brightness waxes and wanes in our sky about every two years. Last year, 2018, was a very, very special year for Mars, when the planet was brighter than it has been since 2003. Astronomers called it a perihelic opposition (or perihelic apparition) of Mars. In other words, in 2018, we went between Mars and the sun – bringing Mars to opposition in our sky – around the same time Mars came closest to the sun. The word perihelion refers Mars’ closest point to the sun in orbit.

Maybe you can see that – in years when we pass between Mars and the sun, when Mars is also closest to the sun – Earth and Mars are closest. That’s what happened in 2018.

2003 was the previous perihelic opposition for Mars. The red planet came within 34.6 million miles (55.7 million km) of Earth, closer than at any time in over nearly 60,000 years! That was really something.

Diagram by Roy L. Bishop. Copyright Royal Astronomical Society of Canada. Used with permission. Visit the RASC estore to purchase the Observer’s Handbook, a necessary tool for all skywatchers. Read more about this image.

And now? Earth will pass between Mars and the sun next on October 13, 2020. The red planet will appear brightest in our sky – very bright indeed and fiery red – around that time.

Mars is now in that part of its cycle with respect to Earth in which it’ll hover – faint and not at all noticeable – in our predawn sky for some months. Mars was in conjunction with the sun, that is, behind the sun as seen from Earth – on September 2, 2019. And now it remains far across the solar system from us, with Earth speeding around in its orbit, trying to catch Mars again. But it’ll be some months before we catch it.

And thus Mars alternates years in being bright in our sky, or faint. 2019 was a dull year, but 2020 will be an exciting one, for Mars! It’ll start slowly, though, with Mars sitting low in the east (much as it is now) as the year begins. January, February, March, April 2020 … you’ll still find Mars doing nothing much, low in the east before sunup. Earth will still be far across the solar system from Mars, but rushing along in our smaller, faster orbit, trying to catch up. As northern summer 2020 approaches, Mars will begin to change. It’ll begin to brighten more dramatically as, finally, Earth begins to catch up to Mars.

Watch for it!

Artist’s concept of Earth (3rd planet from the sun) passing between the sun and Mars (4th planet from the sun). Not to scale. This is Mars’ opposition, when it appears opposite the sun in our sky. Image via NASA.

Bottom line: Mars alternates years in appearing bright and faint in our night sky. In 2018, we had a grand view of Mars … best since 2003! In 2019, we were in one of Mars’ faint years. But 2020 will – once again – be a bright year for Mars.

Photos of bright Mars in 2018, from the EarthSky community

from EarthSky https://ift.tt/2Puo0em