Distorted corona

A distorted corona, caught by Star Cammy on a mid-afternoon in late February, over Hong Kong, China. The sun is bright and on the left. The green ball on the right is a camera artifact – an internal reflection from the camera – known as a lens flare.

On February 27, 2018, Star Cammy on Facebook posted this this photo and two more, taken within minutes of it. Immediately, her friends began buzzing about whether the photo showed random cloud iridescence or a fragment of a circular corona around the sun. In fact, the cloud iridescence and coronas are related, both caused by the diffraction of light by tiny water droplets (sometimes small ice crystals) in clouds.

Matthew Chin, a friend of Cammy’s in Hong Kong and also a friend of EarthSky’s, solved the mystery by writing to sky optics guru Les Cowley about Cammy’s photo. Les, who runs the amazing website Atmospheric Optics, called it a distorted corona around the sun, produced by a non-uniformity in the size of the water droplets that are creating the rainbow-like colors.

Les’ response is below. You can also check out Matthew’s blog about this photo (if you can read Chinese).

Bottom line: A photo of a distorted corona around the sun, captured over Hong Kong in February, 2018.

from EarthSky http://ift.tt/2Fl2PoH

A distorted corona, caught by Star Cammy on a mid-afternoon in late February, over Hong Kong, China. The sun is bright and on the left. The green ball on the right is a camera artifact – an internal reflection from the camera – known as a lens flare.

On February 27, 2018, Star Cammy on Facebook posted this this photo and two more, taken within minutes of it. Immediately, her friends began buzzing about whether the photo showed random cloud iridescence or a fragment of a circular corona around the sun. In fact, the cloud iridescence and coronas are related, both caused by the diffraction of light by tiny water droplets (sometimes small ice crystals) in clouds.

Matthew Chin, a friend of Cammy’s in Hong Kong and also a friend of EarthSky’s, solved the mystery by writing to sky optics guru Les Cowley about Cammy’s photo. Les, who runs the amazing website Atmospheric Optics, called it a distorted corona around the sun, produced by a non-uniformity in the size of the water droplets that are creating the rainbow-like colors.

Les’ response is below. You can also check out Matthew’s blog about this photo (if you can read Chinese).

Bottom line: A photo of a distorted corona around the sun, captured over Hong Kong in February, 2018.

from EarthSky http://ift.tt/2Fl2PoH

Moon sweeps past morning planets March 7 to 11

Before sunrise in the next several mornings – March 7 to 11, 2018 – let the waning moon be your guide the morning planets, Jupiter, Mars and Saturn.

Jupiter. That brilliant starlike object close to the moon on the mornings of March 7 and 8 is Jupiter, 5th planet outward from the sun. It’ll be hard to miss Jupiter, as it’s the second-brightest celestial object (after the moon) to light up the morning sky. Venus is a brighter planet than Jupiter, but Venus is now in the early evening sky and will remain an evening “star” until October 2018. Jupiter, meanwhile, comes up around midnight in early March 2018, and it shines high in the sky at dawn.

Jupiter is bright for a good reason. It’s the most massive planet in the solar system, with a very reflective cloud cover. With a mass of 318 Earths, the king planet Jupiter has more than twice the mass of all other solar system planets, dwarf planets, moons and minor planets (asteroids) combined. Jupiter has a volume of over 1,300 Earths. Yet Jupiter is only about 1/1000th the mass and size of the sun!

Jupiter as seen by the Juno spacecraft on October 24, 2017. Image via NASA/JPL-Caltech/MSSS/SwRI/Kevin M. Gill. See more recent images of Jupiter from Juno.

On March 9, 2018, Jupiter is stationary in front of the constellation Libra the Scales, signaling the beginning of its retrograde motion in front of the stars. Normally, planets move eastward in front of the backdrop stars, but, as Earth prepares to pass between an outer planet (like Jupiter) and the sun, we see the planets change direction and begin moving toward the west.

We’ll go between Jupiter and the sun on May 9, 2019. Then astronomers will say that Jupiter is in opposition to the sun. In May, Jupiter will be rising in the east as the sun is setting in the west. Opposition marks the middle of the best time of year to see a planet.

The beginning of Jupiter’s retrograde motion on March 9 marks the beginning of this special time!

Niko Powe in Kewanee, Illinois caught Jupiter and Spica (upper right) on the morning of January 22, 2017. The bright object in this photo is the moon.

Mars and Saturn. Although Mars and Saturn are nowhere as bright as Jupiter, they still shine as brilliantly as first-magnitude stars. You can notice them any morning before dawn now, but look for them particularly around March 9, 10 and 11, when the moon is sweeping past.

2018 will be a banner year for Mars. Most of the time, Jupiter ranks as he fourth-brightest celestial body to light up the heavens, after the sun, moon and Venus. But this year Mars will outshine Jupiter – claiming the title of the 4th-brightest celestial body – for roughly two months, from early July to early September 2018. Why? You guessed. Earth will be passing between Mars and the sun around then.

Read more: Mars brighter in 2018 than since 2003

View larger. | See the Curiosity Mars rover looking at its own camera? This recent selfie from Curiosity was acquired in January 2018. Image via NASA/JPL-Caltech/MSSS.

You can discern Saturn from Mars by color. Saturn appears golden while Mars glowers red. If you have difficulty distinguishing color with the eye alone, try looking at these colorful celestial gems with binoculars. Or, if you have a telescope, you can easily tell which is Saturn because of this planet’s majestic rings, which are quite visible in even a modest, backyard telescope.

Here’s another chart, focusing on Mars and Saturn around the time the moon goes past them:

As the moon moves past the planets before dawn, it’ll also be waning in phase. Last quarter moon is March 9.

For the fun of it, we show the dwarf planet Pluto on the sky chart above. You won’t see Pluto. This faint and distant world is more than 2,000 times dimmer than the faintest star visible to the unaided eye on a dark night. It’s some 300,000 times fainter than Saturn.

Saturn is the most distant world you can easily see with the unaided eye, at a distance of about 10 astronomical units (that is, 10 AU, or 10 times the Earth’s distance from the sun). Pluto lies over three times the distance of Saturn, at 34 AU.

Click to find Saturn’s and Pluto’s present distance from Earth and sun, in AU

Because Mars is closer to the sun and Earth than Saturn and Pluto are, Mars travels at a much faster clip through the constellations of the zodiac than either Saturn and Pluto. Traveling in an eastward direction – toward sunrise – Mars will catch up with Saturn on April 2, 2018, and then will catch up Pluto on April 25, 2018.

Earth will catch up to Saturn – bringing Saturn to its 2018 opposition in our sky – on June 27.

The tilt of Saturn’s rings has a great impact on its overall brightness. In years when Saturn’s rings are edge-on as seen from Earth (2009 and 2025), Saturn appears considerably dimmer than in years when Saturn’s rings a maximally titled toward Earth (2017 and 2032). Image via Wikimedia Commons.

Bottom line: Three bright, superior planets – that is, those orbiting the sun outward from Earth’s orbit – can be found between midnight and dawn now. The moon sweeps past Jupiter, then Mars, then Saturn on the mornings of March 7 to March 11, 2018.

from EarthSky http://ift.tt/2FXItmR

Before sunrise in the next several mornings – March 7 to 11, 2018 – let the waning moon be your guide the morning planets, Jupiter, Mars and Saturn.

Jupiter. That brilliant starlike object close to the moon on the mornings of March 7 and 8 is Jupiter, 5th planet outward from the sun. It’ll be hard to miss Jupiter, as it’s the second-brightest celestial object (after the moon) to light up the morning sky. Venus is a brighter planet than Jupiter, but Venus is now in the early evening sky and will remain an evening “star” until October 2018. Jupiter, meanwhile, comes up around midnight in early March 2018, and it shines high in the sky at dawn.

Jupiter is bright for a good reason. It’s the most massive planet in the solar system, with a very reflective cloud cover. With a mass of 318 Earths, the king planet Jupiter has more than twice the mass of all other solar system planets, dwarf planets, moons and minor planets (asteroids) combined. Jupiter has a volume of over 1,300 Earths. Yet Jupiter is only about 1/1000th the mass and size of the sun!

Jupiter as seen by the Juno spacecraft on October 24, 2017. Image via NASA/JPL-Caltech/MSSS/SwRI/Kevin M. Gill. See more recent images of Jupiter from Juno.

On March 9, 2018, Jupiter is stationary in front of the constellation Libra the Scales, signaling the beginning of its retrograde motion in front of the stars. Normally, planets move eastward in front of the backdrop stars, but, as Earth prepares to pass between an outer planet (like Jupiter) and the sun, we see the planets change direction and begin moving toward the west.

We’ll go between Jupiter and the sun on May 9, 2019. Then astronomers will say that Jupiter is in opposition to the sun. In May, Jupiter will be rising in the east as the sun is setting in the west. Opposition marks the middle of the best time of year to see a planet.

The beginning of Jupiter’s retrograde motion on March 9 marks the beginning of this special time!

Niko Powe in Kewanee, Illinois caught Jupiter and Spica (upper right) on the morning of January 22, 2017. The bright object in this photo is the moon.

Mars and Saturn. Although Mars and Saturn are nowhere as bright as Jupiter, they still shine as brilliantly as first-magnitude stars. You can notice them any morning before dawn now, but look for them particularly around March 9, 10 and 11, when the moon is sweeping past.

2018 will be a banner year for Mars. Most of the time, Jupiter ranks as he fourth-brightest celestial body to light up the heavens, after the sun, moon and Venus. But this year Mars will outshine Jupiter – claiming the title of the 4th-brightest celestial body – for roughly two months, from early July to early September 2018. Why? You guessed. Earth will be passing between Mars and the sun around then.

Read more: Mars brighter in 2018 than since 2003

View larger. | See the Curiosity Mars rover looking at its own camera? This recent selfie from Curiosity was acquired in January 2018. Image via NASA/JPL-Caltech/MSSS.

You can discern Saturn from Mars by color. Saturn appears golden while Mars glowers red. If you have difficulty distinguishing color with the eye alone, try looking at these colorful celestial gems with binoculars. Or, if you have a telescope, you can easily tell which is Saturn because of this planet’s majestic rings, which are quite visible in even a modest, backyard telescope.

Here’s another chart, focusing on Mars and Saturn around the time the moon goes past them:

As the moon moves past the planets before dawn, it’ll also be waning in phase. Last quarter moon is March 9.

For the fun of it, we show the dwarf planet Pluto on the sky chart above. You won’t see Pluto. This faint and distant world is more than 2,000 times dimmer than the faintest star visible to the unaided eye on a dark night. It’s some 300,000 times fainter than Saturn.

Saturn is the most distant world you can easily see with the unaided eye, at a distance of about 10 astronomical units (that is, 10 AU, or 10 times the Earth’s distance from the sun). Pluto lies over three times the distance of Saturn, at 34 AU.

Click to find Saturn’s and Pluto’s present distance from Earth and sun, in AU

Because Mars is closer to the sun and Earth than Saturn and Pluto are, Mars travels at a much faster clip through the constellations of the zodiac than either Saturn and Pluto. Traveling in an eastward direction – toward sunrise – Mars will catch up with Saturn on April 2, 2018, and then will catch up Pluto on April 25, 2018.

Earth will catch up to Saturn – bringing Saturn to its 2018 opposition in our sky – on June 27.

The tilt of Saturn’s rings has a great impact on its overall brightness. In years when Saturn’s rings are edge-on as seen from Earth (2009 and 2025), Saturn appears considerably dimmer than in years when Saturn’s rings a maximally titled toward Earth (2017 and 2032). Image via Wikimedia Commons.

Bottom line: Three bright, superior planets – that is, those orbiting the sun outward from Earth’s orbit – can be found between midnight and dawn now. The moon sweeps past Jupiter, then Mars, then Saturn on the mornings of March 7 to March 11, 2018.

from EarthSky http://ift.tt/2FXItmR

Lighting the Way: AFRL Partners with Entrepreneurs to Benefit the Warfighter

Have you ever used a glow stick? The Air Force is improving these fun toys into devices that are also useful in the battlefield.

from http://ift.tt/2H7Cqvc

Have you ever used a glow stick? The Air Force is improving these fun toys into devices that are also useful in the battlefield.

from http://ift.tt/2H7Cqvc

C60 Fullerene isomers

The Grimme group has examined all 1812 C₆₀ isomers, in part to benchmark some computational methods.¹ They computed all of these structures at PW6B95-D3/def2-QZVP//PBE-D3/def2-TZVP. The lowest energy structure is the expected fullerene 1 and the highest energy structure is the nanorod 2 (see Figure 1).

1

2

Figure 1. Optimized structures of the lowest (1) and highest (2) energy C₆₀ isomers.

About 70% of the isomers like in the range of 150-250 kcal mol^-1 above the fullerene 1, and the highest energy isomer 2 lies 549.1 kcal mol^-1 above 1. To benchmark some computational methods, they selected the five lowest energy isomers and five other isomers with higher energy to serve as a new database (C60ISO), with energies computed at DLPNO-CCSD(T)/CBS*. The mean absolute deviation of the PBE-D3/def2-TZVP relative energies with the DLPNO-CCSD(T)/CBS* energies is relative large 10.7 kcal mol^-1. However, the PW6B95-D3/def2-QZVP//PBE-D3/def2-TZVP method is considerably better, with a MAD of only 1.7 kcal mol^-1. This is clearly a reasonable compromise method for fullerene-like systems, balancing accuracy with computational time.

They also compared the relative energies of all 1812 isomers computed at PW6B95-D3/def2-QZVP//PBE-D3/def2-TZVP with a number of semi-empirical methods. The best results are with the DFTB-D3 method, with an MAD of 5.3 kcal mol^-1.

References

1) Sure, R.; Hansen, A.; Schwerdtfeger, P.; Grimme, S., "Comprehensive theoretical study of all 1812 C₆₀ isomers." Phys. Chem. Chem. Phys. 2017, 19, 14296-14305, DOI: 10.1039/C7CP00735C.

InChIs

1: InChI=1S/C60/c1-2-5-6-3(1)8-12-10-4(1)9-11-7(2)17-21-13(5)23-24-14(6)22-18(8)28-20(12)30-26-16(10)15(9)25-29-19(11)27(17)37-41-31(21)33(23)43-44-34(24)32(22)42-38(28)48-40(30)46-36(26)35(25)45-39(29)47(37)55-49(41)51(43)57-52(44)50(42)56(48)59-54(46)53(45)58(55)60(57)59
InChIKey=XMWRBQBLMFGWIX-UHFFFAOYSA-N

2: InChI=1S/C60/c1-11-12-2-21(1)31-41-32-22(1)3-13(11)15-5-24(3)34-43(32)53-55-47-36-26-6-16-17-7(26)28-9-19(17)20-10-29-8(18(16)20)27(6)37-46(36)54(51(41)55)52-42(31)33-23(2)4(14(12)15)25(5)35-44(33)58-56(52)48(37)39(29)50-40(30(9)10)49(38(28)47)57(53)59(45(34)35)60(50)58
InChIKey=AGZHNPDQKMDYHI-UHFFFAOYSA-N

from Computational Organic Chemistry http://ift.tt/2FW4p1t

The Grimme group has examined all 1812 C₆₀ isomers, in part to benchmark some computational methods.¹ They computed all of these structures at PW6B95-D3/def2-QZVP//PBE-D3/def2-TZVP. The lowest energy structure is the expected fullerene 1 and the highest energy structure is the nanorod 2 (see Figure 1).

1

2

Figure 1. Optimized structures of the lowest (1) and highest (2) energy C₆₀ isomers.

About 70% of the isomers like in the range of 150-250 kcal mol^-1 above the fullerene 1, and the highest energy isomer 2 lies 549.1 kcal mol^-1 above 1. To benchmark some computational methods, they selected the five lowest energy isomers and five other isomers with higher energy to serve as a new database (C60ISO), with energies computed at DLPNO-CCSD(T)/CBS*. The mean absolute deviation of the PBE-D3/def2-TZVP relative energies with the DLPNO-CCSD(T)/CBS* energies is relative large 10.7 kcal mol^-1. However, the PW6B95-D3/def2-QZVP//PBE-D3/def2-TZVP method is considerably better, with a MAD of only 1.7 kcal mol^-1. This is clearly a reasonable compromise method for fullerene-like systems, balancing accuracy with computational time.

They also compared the relative energies of all 1812 isomers computed at PW6B95-D3/def2-QZVP//PBE-D3/def2-TZVP with a number of semi-empirical methods. The best results are with the DFTB-D3 method, with an MAD of 5.3 kcal mol^-1.

References

1) Sure, R.; Hansen, A.; Schwerdtfeger, P.; Grimme, S., "Comprehensive theoretical study of all 1812 C₆₀ isomers." Phys. Chem. Chem. Phys. 2017, 19, 14296-14305, DOI: 10.1039/C7CP00735C.

InChIs

1: InChI=1S/C60/c1-2-5-6-3(1)8-12-10-4(1)9-11-7(2)17-21-13(5)23-24-14(6)22-18(8)28-20(12)30-26-16(10)15(9)25-29-19(11)27(17)37-41-31(21)33(23)43-44-34(24)32(22)42-38(28)48-40(30)46-36(26)35(25)45-39(29)47(37)55-49(41)51(43)57-52(44)50(42)56(48)59-54(46)53(45)58(55)60(57)59
InChIKey=XMWRBQBLMFGWIX-UHFFFAOYSA-N

2: InChI=1S/C60/c1-11-12-2-21(1)31-41-32-22(1)3-13(11)15-5-24(3)34-43(32)53-55-47-36-26-6-16-17-7(26)28-9-19(17)20-10-29-8(18(16)20)27(6)37-46(36)54(51(41)55)52-42(31)33-23(2)4(14(12)15)25(5)35-44(33)58-56(52)48(37)39(29)50-40(30(9)10)49(38(28)47)57(53)59(45(34)35)60(50)58
InChIKey=AGZHNPDQKMDYHI-UHFFFAOYSA-N

from Computational Organic Chemistry http://ift.tt/2FW4p1t

Wildfires will likely get worse in western North America

The Thomas Fire (above), which consumed 281,893 acres in California’s Santa Barbara and Ventura counties in December 2017, was the largest in the state’s history. The Nazko Complex Fire in British Columbia – which merged with other fires in August, 2017 – burned more than 1 million acres and ultimately became the largest ever recorded for the province. Image via U.S. Forest Service.

The massive wildfires that burned in California, Oregon, Montana, Idaho, British Columbia in 2017 exhibited a disturbing trend: a marked increase in the amount of area burned. While it may have been an exceptional year in some respects, new research predicts that years like 2017 are likely to become more common over time.

States in the interior western United States, in particular, may be faced with large increases in total wildfire area burned, potentially beyond anything that has been experienced in the past, according to the study, published in the journal PLOS ONE on December 15, 2017 as the 2017 fire season was ending.

The study projects where the greatest increases in area burned are likely to occur across the western U.S. and Canada in coming decades, suggesting that large fires years such as the recent ones in southern and northern California may become more common.

Projected change in annual area burned for the period 2010–2039, with red colors indicating areas with the greatest increase in area burned annually in wildfires, and dark blue the leas. Image via University of Arizona.

Environmental scientist Don Falk of the University of Arizona led this study. Falk said in a statement:

We used 34 years of climate data to calibrate area burned in 1,500 grid cells across western North America, so we could capture the different ways that seasonal climate regulates fire in different regions.

Read more about what was measured for the study here.

Thousands of homes and buildings were destroyed in the Thomas Fire, which is estimated to have a total cost of more than $180 billion. Image via U.S. Forest Service.

The study’s findings for western and northern North America show that about half the states and provinces are projected to have a large increase — five or more times the current levels — in total wildfire area burned. Others may see smaller increases, say the researchers, indicating there is no “one-size-fits-all” model. Falk said:

Ultimately, this means that the large fire seasons of recent years, such as the one just ending, are likely to occur more frequently, affecting ecosystems, communities and public safety. These will be billion-dollar fire years. We’re just not ready for fire impacts of this kind, including post-fire effects from flooding after fire.

The total cost of the 2017 fires in California alone is projected to exceed $180 billion. This includes not only the immediate costs of firefighting, but also the much larger costs of landscape rehabilitation; medical and hospital costs; insurance losses and the costs of replacing thousands of homes and other buildings; lost economic productivity from the destruction of businesses; repair and replacement of key infrastructure such as roads, power lines and dams; and weeks of lost income by employees.

Seasonal climate variables in the winter and spring regulate snowpack, which forms from layers of snow that accumulate in geographic regions and high altitudes where the climate includes cold weather for extended periods during the year. Snowpacks can delay the onset of the fire season and are an important water resource that feed streams and rivers as they melt. Image via U.S. Geological Survey.

Falk said that seasonal climate changes are having the effect of making the fire season longer, so there is additional time for more acreage to burn. In years when seasonal climate drives lengthy fire seasons, fire management resources may be stretched to the limit. He said:

Wildfires act as a multiplier of other forces such as climate change, exposing more and more areas not only to the immediate effects of fire, but also to the resulting cascade of ecological, hydrological, economic and social consequences.

Environmental scientist Don Falk – who led this study – is chair of Global Ecology & Management in the University of Arizona’s School of Natural Resources and the Environment. His research areas include fire history, fire ecology, restoration ecology, landscape ecology, and impacts of land management and global change on ecosystems, including dynamics of abrupt change.

Bottom line: A recents study projects that wildfires in the western U.S. will likely get worse.

Source: Direct and indirect climate controls predict heterogeneous early-mid 21st century wildfire burned area across western and boreal North America

Read more from University of Arizona

from EarthSky http://ift.tt/2Fe4Lzy

The Thomas Fire (above), which consumed 281,893 acres in California’s Santa Barbara and Ventura counties in December 2017, was the largest in the state’s history. The Nazko Complex Fire in British Columbia – which merged with other fires in August, 2017 – burned more than 1 million acres and ultimately became the largest ever recorded for the province. Image via U.S. Forest Service.

The massive wildfires that burned in California, Oregon, Montana, Idaho, British Columbia in 2017 exhibited a disturbing trend: a marked increase in the amount of area burned. While it may have been an exceptional year in some respects, new research predicts that years like 2017 are likely to become more common over time.

States in the interior western United States, in particular, may be faced with large increases in total wildfire area burned, potentially beyond anything that has been experienced in the past, according to the study, published in the journal PLOS ONE on December 15, 2017 as the 2017 fire season was ending.

The study projects where the greatest increases in area burned are likely to occur across the western U.S. and Canada in coming decades, suggesting that large fires years such as the recent ones in southern and northern California may become more common.

Projected change in annual area burned for the period 2010–2039, with red colors indicating areas with the greatest increase in area burned annually in wildfires, and dark blue the leas. Image via University of Arizona.

Environmental scientist Don Falk of the University of Arizona led this study. Falk said in a statement:

We used 34 years of climate data to calibrate area burned in 1,500 grid cells across western North America, so we could capture the different ways that seasonal climate regulates fire in different regions.

Read more about what was measured for the study here.

Thousands of homes and buildings were destroyed in the Thomas Fire, which is estimated to have a total cost of more than $180 billion. Image via U.S. Forest Service.

The study’s findings for western and northern North America show that about half the states and provinces are projected to have a large increase — five or more times the current levels — in total wildfire area burned. Others may see smaller increases, say the researchers, indicating there is no “one-size-fits-all” model. Falk said:

Ultimately, this means that the large fire seasons of recent years, such as the one just ending, are likely to occur more frequently, affecting ecosystems, communities and public safety. These will be billion-dollar fire years. We’re just not ready for fire impacts of this kind, including post-fire effects from flooding after fire.

The total cost of the 2017 fires in California alone is projected to exceed $180 billion. This includes not only the immediate costs of firefighting, but also the much larger costs of landscape rehabilitation; medical and hospital costs; insurance losses and the costs of replacing thousands of homes and other buildings; lost economic productivity from the destruction of businesses; repair and replacement of key infrastructure such as roads, power lines and dams; and weeks of lost income by employees.

Seasonal climate variables in the winter and spring regulate snowpack, which forms from layers of snow that accumulate in geographic regions and high altitudes where the climate includes cold weather for extended periods during the year. Snowpacks can delay the onset of the fire season and are an important water resource that feed streams and rivers as they melt. Image via U.S. Geological Survey.

Falk said that seasonal climate changes are having the effect of making the fire season longer, so there is additional time for more acreage to burn. In years when seasonal climate drives lengthy fire seasons, fire management resources may be stretched to the limit. He said:

Wildfires act as a multiplier of other forces such as climate change, exposing more and more areas not only to the immediate effects of fire, but also to the resulting cascade of ecological, hydrological, economic and social consequences.

Environmental scientist Don Falk – who led this study – is chair of Global Ecology & Management in the University of Arizona’s School of Natural Resources and the Environment. His research areas include fire history, fire ecology, restoration ecology, landscape ecology, and impacts of land management and global change on ecosystems, including dynamics of abrupt change.

Bottom line: A recents study projects that wildfires in the western U.S. will likely get worse.

Source: Direct and indirect climate controls predict heterogeneous early-mid 21st century wildfire burned area across western and boreal North America

Read more from University of Arizona

from EarthSky http://ift.tt/2Fe4Lzy

Why is Venus so bright?

These thin clouds were no match for the brightness of Venus, after sunset on February 27, 2018. Photo by Tanvi Javkar in Mississauga, Ontario, Canada. You’ll want a very clear sky all the way to the horizon in early March to see both Venus and Mercury.

Even though Jupiter is bright also (and up before dawn now, with the moon sweeping past it) and even though Mars will be exceedingly bright in 2018, brighter than since 2003, neither Jupiter nor Mars at its brightest can outshine Venus.

Our neighboring world – orbiting one step inward from Earth around the sun – is the third-brightest object in the sky, after the sun and moon. In early March 2018, Venus is low in the west after sunset, near another bright planet (although not as bright as Venus), Mercury.

Even though Venus is seen against a background of bright twilight now, after sunset, its brightness might surprise you.

Why is this world so bright?

Venus (l) is the brighter planet, but Mercury is there, too, in March 2018. Here they are, above the Olympics, as seen from Seattle, Washington, on March 3, 2018. Photo via Brett Joseph. See more Venus-Mercury photos.

As the planet next-inward from Earth in orbit around the sun, Venus is relatively nearby. But its nearness isn’t the only reason Venus is bright. Consider that Mars orbits one step outward from Earth. And Mars waxes and wanes in brightness in our sky. It’s only exceptionally bright around the time Earth passes between Mars and the sun, when the Red Planet is at its closest to us, which it will be this year, around late July.

With Venus, something else is going on. Astronomers use the term albedo to describe how bright a planet is in absolute terms. When sunlight strikes a planet, some of the light is absorbed by the planet’s surface or atmosphere – and some is reflected. Albedo is a comparison between how much light strikes an object – and how much is reflected.

As you might have guessed, Venus has the highest albedo of any major planet in our solar system.

Ken Christison wrote on March 3, 2018: “Venus and Mercury shone very nicely this evening after sunset from northeastern North Carolina.” See more Venus-Mercury photos.

The albedo of Venus is close to .7, meaning it reflects about 70 percent of the sunlight striking it. When the moon is close to full in Earth’s sky, it can look a lot brighter than Venus, but the moon reflects only about 10 percent of the light that hits it. The moon’s low albedo is due to the fact that our companion world is made of dark volcanic rock. It appears bright to us only because of its nearness to Earth. It’s only about a light-second away, in contrast for several light-minutes for Venus.

Venus is bright (it has a high albedo) because it’s blanketed by highly reflective clouds. The clouds in the atmosphere of Venus contain droplets of sulfuric acid, as well as acidic crystals suspended in a mixture of gases. Light bounces easily off the smooth surfaces of these spheres and crystals. Sunlight bouncing from these clouds is a big part of the reason that Venus is so bright.

By the way, Venus isn’t the most reflective body in our solar system. That honor goes to Enceladus, a moon of Saturn. Its icy surface reflects some 90% of the sunlight striking it.

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Andrew Kwon caught Venus and Mercury on March 2, 2018. He wrote: “Just happened to look out my living room window and notice I could see Mercury, just to the right of Venus.” See more Venus-Mercury photos.

We mentioned above that Mars is brightest when Earth passes between the Red Planet and the sun. At such times, Mars is closest to us, and so it appears brightest in our sky. A similar situation occurs for Venus: the planet is brightest in our sky around the time Venus passes between us and the sun, although not exactly at that time.

Because Venus orbits the sun inside Earth’s orbit, when it goes between us and the sun its lighted hemisphere, or day side, is facing away from us. At such times, it’s difficult or impossible to see Venus at all.

Because it’s an inner planet, as Venus approaches its time of passing between the Earth and sun, we see the planet exhibit phases, like a tiny moon. As Venus draws up behind Earth in orbit – and prepares to “lap” us in the race of the planets – observers on Earth can watch as the phase of Venus wanes. Meanwhile, as the crescent Venus in waning in phase, the overall size of the disk of Venus gets larger in Earth’s sky, as Venus draws closer to us and prepares to go between us and the sun.

Venus is brightest when those two factors combine – waning crescent, plus largest overall size of Venus’ disk – so that the greatest amount of surface area of Venus shows in our sky. Astronomers call this greatest illuminated extent.

In 2018, Venus will reach greatest illuminated extent (in the evening sky) on September 21.

Venus is brightest at what’s called greatest illuminated extent, or greatest brilliancy. It happens when Venus is relatively near Earth, and when telescopes show it in a crescent phase, like a tiny crescent moon. Here’s a telescopic view of a crescent Venus (l) and the moon, in daytime, via NASA.

Bottom line: Venus is the third-brightest object in the sky, after the sun and moon. That’s partly because sunlight is easily reflected by acidic clouds in the atmosphere of Venus.

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These thin clouds were no match for the brightness of Venus, after sunset on February 27, 2018. Photo by Tanvi Javkar in Mississauga, Ontario, Canada. You’ll want a very clear sky all the way to the horizon in early March to see both Venus and Mercury.

Even though Jupiter is bright also (and up before dawn now, with the moon sweeping past it) and even though Mars will be exceedingly bright in 2018, brighter than since 2003, neither Jupiter nor Mars at its brightest can outshine Venus.

Our neighboring world – orbiting one step inward from Earth around the sun – is the third-brightest object in the sky, after the sun and moon. In early March 2018, Venus is low in the west after sunset, near another bright planet (although not as bright as Venus), Mercury.

Even though Venus is seen against a background of bright twilight now, after sunset, its brightness might surprise you.

Why is this world so bright?

Venus (l) is the brighter planet, but Mercury is there, too, in March 2018. Here they are, above the Olympics, as seen from Seattle, Washington, on March 3, 2018. Photo via Brett Joseph. See more Venus-Mercury photos.

As the planet next-inward from Earth in orbit around the sun, Venus is relatively nearby. But its nearness isn’t the only reason Venus is bright. Consider that Mars orbits one step outward from Earth. And Mars waxes and wanes in brightness in our sky. It’s only exceptionally bright around the time Earth passes between Mars and the sun, when the Red Planet is at its closest to us, which it will be this year, around late July.

With Venus, something else is going on. Astronomers use the term albedo to describe how bright a planet is in absolute terms. When sunlight strikes a planet, some of the light is absorbed by the planet’s surface or atmosphere – and some is reflected. Albedo is a comparison between how much light strikes an object – and how much is reflected.

As you might have guessed, Venus has the highest albedo of any major planet in our solar system.

Ken Christison wrote on March 3, 2018: “Venus and Mercury shone very nicely this evening after sunset from northeastern North Carolina.” See more Venus-Mercury photos.

The albedo of Venus is close to .7, meaning it reflects about 70 percent of the sunlight striking it. When the moon is close to full in Earth’s sky, it can look a lot brighter than Venus, but the moon reflects only about 10 percent of the light that hits it. The moon’s low albedo is due to the fact that our companion world is made of dark volcanic rock. It appears bright to us only because of its nearness to Earth. It’s only about a light-second away, in contrast for several light-minutes for Venus.

Venus is bright (it has a high albedo) because it’s blanketed by highly reflective clouds. The clouds in the atmosphere of Venus contain droplets of sulfuric acid, as well as acidic crystals suspended in a mixture of gases. Light bounces easily off the smooth surfaces of these spheres and crystals. Sunlight bouncing from these clouds is a big part of the reason that Venus is so bright.

By the way, Venus isn’t the most reflective body in our solar system. That honor goes to Enceladus, a moon of Saturn. Its icy surface reflects some 90% of the sunlight striking it.

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Andrew Kwon caught Venus and Mercury on March 2, 2018. He wrote: “Just happened to look out my living room window and notice I could see Mercury, just to the right of Venus.” See more Venus-Mercury photos.

We mentioned above that Mars is brightest when Earth passes between the Red Planet and the sun. At such times, Mars is closest to us, and so it appears brightest in our sky. A similar situation occurs for Venus: the planet is brightest in our sky around the time Venus passes between us and the sun, although not exactly at that time.

Because Venus orbits the sun inside Earth’s orbit, when it goes between us and the sun its lighted hemisphere, or day side, is facing away from us. At such times, it’s difficult or impossible to see Venus at all.

Because it’s an inner planet, as Venus approaches its time of passing between the Earth and sun, we see the planet exhibit phases, like a tiny moon. As Venus draws up behind Earth in orbit – and prepares to “lap” us in the race of the planets – observers on Earth can watch as the phase of Venus wanes. Meanwhile, as the crescent Venus in waning in phase, the overall size of the disk of Venus gets larger in Earth’s sky, as Venus draws closer to us and prepares to go between us and the sun.

Venus is brightest when those two factors combine – waning crescent, plus largest overall size of Venus’ disk – so that the greatest amount of surface area of Venus shows in our sky. Astronomers call this greatest illuminated extent.

In 2018, Venus will reach greatest illuminated extent (in the evening sky) on September 21.

Venus is brightest at what’s called greatest illuminated extent, or greatest brilliancy. It happens when Venus is relatively near Earth, and when telescopes show it in a crescent phase, like a tiny crescent moon. Here’s a telescopic view of a crescent Venus (l) and the moon, in daytime, via NASA.

Bottom line: Venus is the third-brightest object in the sky, after the sun and moon. That’s partly because sunlight is easily reflected by acidic clouds in the atmosphere of Venus.

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Use Big Dipper to find North Star

People are always asking how to find Polaris, the North Star. It’s easy! Drawing a line through the two outer stars of the bowl of the Big Dipper faithfully points to Polaris.

At one time, sailors’ livelihoods and survival depended on their lucky stars – most especially, the pointer stars of the Big Dipper. Scouts also learn to use the Big Dipper and Polaris to find the direction north.

Polaris is not the brightest star in the sky, as is commonly believed. It is a moderately bright second-magnitude star, radiant enough to be fairly easily seen in a dark sky. Unlike the other stars – which either rise in the east and set in the west, or else wheel in a circle around Polaris – the North Star appears fixed in the northern sky.

Ken Christison captured these glorious star trails around Polaris, the North Star.

If you stand facing Polaris, then, you’re facing the direction north. If you place Polaris to your back, you’re facing south. You can use Polaris to find directions only in the Northern Hemisphere, however. South of the equator, Polaris drops below the northern horizon.

At this time of year, at nightfall and early evening, the seven stars of the Big Dipper will light up your northeastern sky. The Big Dipper is not a constellation, by the way. It’s an asterism, or noticeable pattern of stars. Unlike many constellations, this famous asterism looks like its namesake. It is one of several dipper patterns on the sky’s dome.

The two outer stars in the bowl of the Big Dipper always point to Polaris, the North Star. Image by EarthSky Facebook friend Abhijit Juvekar.

The Big Dipper is part of Ursa Major or the Big Bear constellation. Some sources say the Dipper makes up the Bear’s tail and hindquarters. Many people say they can’t see the Bear, but I’ve imagined I’ve seen a bear in these stars, on very dark night around this time of year. To me, the Big Dipper looks like it’s part of the stomach of the Bear. Still, what I’ve pictured in my mind – and what the early stargazers believed they saw – can be different. The sky is, after all, a huge Rorschach test, with its starry patterns open to a multitude of interpretations. What do you see in and around the Dipper’s stars?

Bottom line: One thing is certain. If you find the Big Dipper in the northeast on a March evening – and locate the two outermost stars in its bowl – those stars will point to Polaris! Give it a try.

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People are always asking how to find Polaris, the North Star. It’s easy! Drawing a line through the two outer stars of the bowl of the Big Dipper faithfully points to Polaris.

At one time, sailors’ livelihoods and survival depended on their lucky stars – most especially, the pointer stars of the Big Dipper. Scouts also learn to use the Big Dipper and Polaris to find the direction north.

Polaris is not the brightest star in the sky, as is commonly believed. It is a moderately bright second-magnitude star, radiant enough to be fairly easily seen in a dark sky. Unlike the other stars – which either rise in the east and set in the west, or else wheel in a circle around Polaris – the North Star appears fixed in the northern sky.

Ken Christison captured these glorious star trails around Polaris, the North Star.

If you stand facing Polaris, then, you’re facing the direction north. If you place Polaris to your back, you’re facing south. You can use Polaris to find directions only in the Northern Hemisphere, however. South of the equator, Polaris drops below the northern horizon.

At this time of year, at nightfall and early evening, the seven stars of the Big Dipper will light up your northeastern sky. The Big Dipper is not a constellation, by the way. It’s an asterism, or noticeable pattern of stars. Unlike many constellations, this famous asterism looks like its namesake. It is one of several dipper patterns on the sky’s dome.

The two outer stars in the bowl of the Big Dipper always point to Polaris, the North Star. Image by EarthSky Facebook friend Abhijit Juvekar.

The Big Dipper is part of Ursa Major or the Big Bear constellation. Some sources say the Dipper makes up the Bear’s tail and hindquarters. Many people say they can’t see the Bear, but I’ve imagined I’ve seen a bear in these stars, on very dark night around this time of year. To me, the Big Dipper looks like it’s part of the stomach of the Bear. Still, what I’ve pictured in my mind – and what the early stargazers believed they saw – can be different. The sky is, after all, a huge Rorschach test, with its starry patterns open to a multitude of interpretations. What do you see in and around the Dipper’s stars?

Bottom line: One thing is certain. If you find the Big Dipper in the northeast on a March evening – and locate the two outermost stars in its bowl – those stars will point to Polaris! Give it a try.

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

Donate: Your support means the world to us

from EarthSky http://ift.tt/1FiFv4z