Tonight’s moon – May 25, 2012 – is still in front of the constellation Gemini the Twins. Venus still shines brightly in the west, but it slipping ever-nearer the sunset as it prepares to transit the sun on June 5-6. The moon is waxing larger and appearing toward further east on the sky’s dome at each sunset, as it heads toward full moon and the partial lunar eclipse on June 4. As soon as darkness falls tonight, look westward to see the waxing crescent moon lining up – or nearly lining up – with Castor and Pollux, the two brightest stars in the constellation Gemini the Twins. The other bright star on the opposite side of the moon is Procyon, the brightest in the constellation Canis Minor the Little Dog.

The moon and bright planet Venus last night (May 24, 2012), as seen by EarthSky Facebook friend Jv Noriega in Manila, Philippines. Thank you, Jv! This photo faces west in very early evening. See how close Venus is to the horizon? Soon, it'll disappear in the sunset.

Click here to expand image above

The sky chart at the top of this post – showing tonight’s moon near the bright stars Castor, Pollux and Procyon – is designed for mid-northern North American latitudes. But the moon will be near these stars as seen from around the world.

At mid-northern latitudes in the world’s Eastern Hemisphere – Europe and Asia – the sky scene will look similar to our chart at nightfall, except that the moon won’t line up quite as well with Castor and Pollux. From Europe and Asia, you will see the moon lower down in the sky, more or less midway between Pollux and Procyon.

Procyon is the Little Dog Star

Pollux is the brighter of two Twin stars

Castor is really six stars

Earth is a planet, surrounded on all sides by stars. That's why the northern and southern hemispheres of the planet see the skies differently. From the northern half of Earth, your perspective on the surrounding stars is different from that of someone in the southern hemisphere. Image via HD Wallpapers

Click here to expand image above

From the southern hemisphere, tonight’s sky scene will be even more different – but, still, the moon tonight will be near Castor, Pollux and Procyon. The Gemini stars and Procyon are found on opposite sides of tonight’s moon in both the Northern and Southern Hemispheres. At northerly latitudes, we see the Gemini stars higher up in the sky than we see Procyon. At or near the equator, the Gemini stars and Procyon shine pretty much equally high above the horizon. At temperate latitudes in the Southern Hemisphere, Procyon beams higher up than the Gemini stars.

Why this difference? It’s simply because, as we stand on different parts of the globe of Earth, our perspective on the surrounding stars is different.

We are surrounded by stars. Because Earth orbits in a flat plane around the sun, we see the sun against the same stars again and again throughout the year. Those constellations, which have been special to people throughout the ages, are the constellations of the Zodiac. Image via Professor Marcia Rieke.

Bottom line: Every month, as the moon makes its monthly pilgrimage in front of the constellations of the Zodiac, the moon faithfully passes in between the Gemini stars and Procyon. From around the world on May 25, 2012, watch as the slender waxing crescent moon points out the stars Castor, Pollux and Procyon to you in the western sky at nightfall. The moon is waxing toward full now and the partial lunar eclipse on June 4 – morning from the Americas, evening from Asia. Venus is heading into the sunset, preparing for the last transit of Venus in our lifetimes on June 5-6.

Last transit of Venus in 21st century on June 5-6, 2012

Lunar eclipse: Americas before sunrise, Asia after sunset June 4

Gemini? Here’s your constellation

On the evening of May 24, 2012, the waxing crescent moon shines close to Castor and Pollux, the two brightest stars in the constellation Gemini the Twins. The moon is waxing toward a lunar eclipse on June 4. Finally, don’t forget to watch the bright planet Venus, as it drops into the sun’s glare.

Gemini? Here’s your constellation

People often refer to Castor and Pollux as “The Twins” but they aren’t really twins at all. At a distance of about 34 light-years, Pollux is the closest giant star to our solar system. It’s one of the very few giant stars in our galaxy known to have a planet.

Castor is farther away, at 52 light-years. It looks like a single star to the eye, but it’s actually six stars in one, all revolving around one another in an intricate dance.

Pollux on left. Castor on right. See the contrast in their colors? Pollux is golden, and Castor is white. (Warren Wilson College)

With binoculars, you might be able to discern Castor and Pollux’s contrasting colors. Pollux looks orange, while Castor appears white. An orange star has a relatively low surface temperature, indicating that Pollux is in the autumn of its years. On the other hand, a more youthful star – like Castor – displays a white color, a sure sign of this star’s higher surface temperature.

Meanwhile, tonight’s moon is in a waxing crescent phase. It’ll continue to wax larger until full moon in early June. Mark your calendar: this June 2012 full moon will feature a partial lunar eclipse. It’ll be visible throughout the Americas and Asia.

When you’re finished looking at the moon, Castor and Pollux, be sure to notice the planet Venus, still the brightest light besides the moon after sunset. Over the coming week, Venus will drop noticeably into the sun’s glare prior to the June 5-6 Venus transit – last one in this century! Venus is so bright that you can see it very near the sunset. And a lovely sight it is. You’ll need an unobstructed horizon, but if you have one it’ll be fun to watch until this wondrous planet, which has given us so much enjoyment in recent months, as it finally leaves the evening sky. The image below shows Venus near last night’s moon. It’s from our friend May Tama in Japan.

Moon and Venus on May 23, 2012 from EarthSky Facebook friend May Tama in Okayama, Japan.

Click here to expand image above

Bottom line: On the evening of May 24, 2012, the waxing crescent moon shines close to Castor and Pollux, the two brightest stars in the constellation Gemini the Twins. Mark your calendar for the June 4 lunar eclipse. Watch the bright planet Venus drop into the sun’s glare as it leaves the evening sky.

Castor is the fainter of two Twin stars

Pollux: Brightest star of the Twins

Lunar eclipse: Americas before sunrise, Asia after sunset June 4

The moon still shines in the vicinity of the planet Venus after sunset this Wednesday evening, May 23, 2012, as shown on our chart above. But the moon and Venus were paired most closely for the month on May 22. The moon and Venus – the brightest and second-brightest orbs of nighttime, respectively – pop out low in the west almost immediately after sunset tonight as seen from around the globe.

Moon and Venus on May 22, 2012 as seen in Normany, France by EarthSky Facebook friend Mohamed Laaifat Photography. Thank you, Mohamed.

Click here to expand image above

As people watched from around the world last night, the moon moved higher in the sky, going from below Venus as seen from the Middle East and Europe to side by side with it as seen from the U.S. West Coast. Tonight’s moon will be above Venus. Why this difference? Because the moon is moving in its orbit around Earth. No matter where you are on Earth, be sure to catch these shining beauties shortly after the sun goes down tonight.

Moon and Venus on May 22, 2012 as seen shining over the YMCA in New Albany, Indiana. Photo via EarthSky Facebook friend Duke Marsh. Thank you, Duke.

Click here to expand image above

The moon and Venus will follow the sun below the horizon by nightfall or early evening tonight. As seen from mid-northern latitudes, Venus sets about 100 minutes after the sun tonight and 40 minutes after sundown by the month’s end. For middle latitudes in the Southern Hemisphere, Venus sets about an hour after the sun tonight and tapers down to less than one-half hour after sunset by the month’s end.

Moon and Venus on May 22, 2012 as seen from Los Angeles. See how the moon was below Venus as seen from France (photo at top), but higher as seen from Indiana (second photo from top), and side by side with Venus as seen in this photo from Los Angeles? What you're seeing is the moon's motion in orbit around Earth. Photo via friend Peter Rodney Breaux. Thank you, Peter.

Click here to expand image above

As you might guess from those diminishing setting times, Venus is about to disappear in the sun’s glare.

This is the moon. See how the darkened portion glows faintly? That glow is called earthshine. It's light reflected from Earth's day side. Photo credit: Robbo-Man

If you looked at Venus through a telescope tonight, you'd see it in a crescent phase - much like the crescent moon. EarthSky Facebook friend Alan Murta took this serene photo of a crescent Venus in mid-May 2012. Thank you, Alan.

Because Venus lies inside of the Earth’s orbit, this world exhibits the full range of phases – much like our moon. In fact, the rest of May 2012 presents an especially good time to observe the phases of Venus through the telescope. Like the moon, Venus shows a slender crescent phase tonight. You might even be able to tell with your binoculars that Venus is something other than perfectly round.

Tonight, Venus appears about six percent illuminated in sunshine as seen from Earth. But this world is now waning, or showing us less and less of its day side. Venus will shrink to one percent illumination as seen from Earth by the end of May 2012. Venus will pass between the Earth and sun on June 5-6, 2012. Right now, Venus is headed for that event – preparing to pass between the Earth and sun on June 5-6 – and thus the distance between our two worlds is getting smaller. As a result, as seen from Earth, the crescent of Venus will wane in phase – yet become lengthier – in the coming weeks.

Starting tonight, watch as the moon and Venus part company in the May 2012 evening sky. In other words, for the next two weeks, note the positions of the moon and Venus as they come out after sunset. Venus will be sinking westward (toward the sunset point on the horizon) while the moon will be moving eastward (toward the sunrise point on the horizon). Thus the distance between the moon and Venus on our sky’s dome will be increasing.

And remember … Venus is now waning toward new phase while the moon is waxing toward full. At full moon on June 4, 2012, there will be a partial eclipse of the moon. And as Venus goes between the Earth and sun on June 5-6, 2012, this world will move as a dark dot in front the sun in what astronomers call a transit of Venus. There are at least two lunar and two solar eclipses every year. But this will be the last transit of Venus in this century.

Partial lunar eclipse for the Americas before sunrise June 4

Transit of Venus for North America on afternoon of June 5

When can you see earthshine on crescent moon?

Bottom line: On the evening of May 23, 2012, you can still see the moon in the vicinity of Venus, although the moon isn’t as close to Venus as it was last night. Through a telescope, both the moon and Venus would show you a crescent phase this evening.

The solar eclipse was two days ago, but you can see a great image gallery of the eclipse here. This photo is from Dan Gauss in southern New Mexico

On May 22, 2012, for North America and most of the world, the moon swings closest to the planet Venus for this month. The moon will still be in the vicinity of Venus after sunset on May 23, but not as close as tonight. With Venus about to drop into the sun’s glare, tonight is the final curtain call for these two brightest nighttime objects – the last time you’ll see the moon and Venus appear so close in the evening sky for the rest of 2012. Enjoy!

Note the soft glow of earthshine on the dark side of the the waxing crescent moon tonight. Earthshine is light reflected from Earth’s day side, onto the moon’s night side.

Moon and Venus seen earlier today (May 22, 2012) by EarthSky Facebook friend Mohamed Laaifat Photography in Normandy, France.

Click here to expand image above

Look for earthshine - a soft glow on the moon's darkened portion - on tonight's crescent moon. Photo credit: Robbo-Man

When can you see earthshine on a crescent moon?

Venus now sets about two hours after the sun at mid-northern latitudes, and only about one hour after sundown at middle latitudes in the Southern Hemisphere. Use binoculars or dust off that telescope to more fully enjoy tonight’s evening tableau. Venus – the personification of beauty – will display her sleek and slender crescent as seen through a telescope tonight. Look as soon as you can after sunset, before Venus’ glare obtrudes on the crispness of the view. Venus appears as a crescent because she is about to pass between the Earth and sun, and so her lighted face is turned almost entirely away from our direction in space.

Transit of Venus on June 8, 2004. Image credit: Wikimedia Commons

Get ready for a transit of Venus! Venus will officially leave the evening sky some two weeks from today. This planet will transition from the evening to the morning sky, passing directly in between the sun and Earth for nearly seven hours on June 5/6, 2012. This much heralded event – called a transit of Venus – has been anticipated by astronomers for decades. As the transit takes place, Venus will appear as a dark dot in front of the sun from 22:09:38 (on June 5) till 4:49:35 (on June 6) Universal Time. This will be the last transit of Venus in this century. Venus will not cross the sun’s face again as seen from Earth until December 11, 2117. What will the world be like then?

Last transit of Venus in 21st century will happen in June 2012

Check out an observatory or astronomy club near you to see if it is hosting a public presentation of the event.

Strictly speaking, the transit times listed above (and in the diagram below) are for an imaginary observer at the center of the Earth – not on the Earth’s surface. However, if you are able to translate Universal Time to the clock time in your time zone, the times will be approximately right for your part of the globe. The error won’t be any greater than plus or minus seven minutes.

To make things simple, though, click here for the local times of the transit in your time zone. Keep in mind that the sun has to be above the horizon for you to see the transit of Venus. In EarthSky’s hometown of Austin, Texas, the transit starts at 17:05:21 (5:05:21 p.m.) and ends 23:48:57 (11:48:57 p.m.) on June 5 Central Daylight Time. However, the sunset is at 20:30 (8:30 p.m.) in Austin, meaning we can only see the first half of the transit in our sky.

Sunset time for your sky

Venus goes from east to west (left to right) across the solar disk

Image credit: Fred Espenak

By the way, proper eye protection is an absolute must for watching a transit of Venus.

Image credit: NASA Eclipse Web Site. Click here for a larger World Visibility Map

Bottom line: As soon as the sun goes down on the evening of May 22, 2012, look low in your west to northwest sky for the gorgeous pairing of the thin waxing crescent moon and Venus, the brightest star-like light in all the heavens. And get ready for the amazing transit of Venus coming up on June 5/6, 2012!

Today’s night sky chart presents the view toward the northeast in mid-evening in the month of May. As always, it’s the view from mid-northern latitudes. It’s by looking in this direction that you can get a good look at the bright star Deneb. This star is part of not one but two striking star patterns. And it’s one of the most distant stars we can see with the eye alone, well over 1,000 light-years away.

See a great image gallery from yesterday's partial and annular eclipse of the sun. This photo is from Dan Gauss in southern New Mexico

The famous summer triangle is up in the east in mid-evening by June. If you're looking in May, you might not see Altair ascend over the horizon until late evening. But you will be able to see Deneb to the lower left of the blue-white star Vega.

Looking for info on the May 20 or 21 solar eclipse? It’s over now, but still fun to read about. Click here.

Deneb is part of the Summer Triangle pattern. Deneb – along with the stars Vega and Altair – is part of the famous Summer Triangle asterism, which will be well up in the east in mid-evening next month. On these Northern Hemisphere late spring evenings, you might not be able to see the whole Summer Triangle until later at night. The star Altair will be the last of these three stars to rise. But you can see the bright star Deneb to the lower left of Vega, the Summer Triangle’s brightest star.

Summer Triangle: Vega, Deneb, Altair

Deneb is also part of a smaller, cross-like pattern. Deneb is the brightest star in the constellation Cygnus the Swan. If you look at the cross-like pattern indicated on the chart at the top of this post, you might be able to imagine Deneb as the point marking the short tail of a long-necked swan flying toward the south. This is how early Arabian stargazers saw it. The name Deneb comes from the Arabic and means tail, and in skylore Deneb is often said to be the Tail of the Swan. The little star Albireo marks the Swan’s Head.

But there’s another way to see this pattern of stars that works equally well. In more modern skylore, this pattern is sometimes called the Northern Cross. It looks like a cross, right? If you prefer to see the Cross instead of the Swan, Deneb marks the head of the Cross. Cross or Swan … this is a lovely pattern to pick out on the sky’s dome.

Astronomers know that Deneb is one of the most distant stars we can see with the eye alone. The exact distance to Deneb can only be estimated, with estimates ranging from about 1,425 light-years to perhaps as much as 7,000 light-years. At any of these estimates distances, Deneb is one of the farthest stars the unaided human eye can see. It is so far, that the light that reaches the Earth today started on its journey well more than 1,000 years ago.

More about Deneb: Among most distant stars visible

Bottom line: The star Deneb is part of the Summer Triangle asterism. And it’s part of the constellation Cygnus the Swan, which can also be seen as a Cross. Look for the star Deneb tonight! At well over 1,000 light-years away, it’s one of the most distant stars we can see with the eye alone.

Upcoming lunar eclipse: Partial lunar eclipse for the Americas June 4

Check out these amazing photos of the annular eclipse: Gallery of partial and ring eclipse of May 20-21

If you’re at just the right place in the United States, you can watch an annular eclipse of the sun in the afternoon hours on Sunday, May 20, 2012. If you’re in Asia, you will see this same eclipse on the morning on Monday, May 21, 2012.

What’s the best way to view a solar eclipse safely?

Animation of the eclipse path. Red dot: annular eclipse

Find the time of the eclipse for you using this great online tool, the U.S. Naval Observatory’s eclipse computer. This solar eclipse computer gives times in Universal Time. In case the eclipse is cut off by sunset (in the Western Hemisphere), or by sunrise (in the Eastern Hemisphere), this solar eclipse computer gives the sunset or sunrise time. For instance, for one of the authors of this post (Bruce McClure in upstate New York) the eclipse starts 10 minutes before sunset. For the other author (Deborah Byrd in Austin), the eclipse starts 47 minutes before sunset. Unless you live in the northwestern part of the U.S. and North America, the eclipse will be happening as the sun sets on May 20, but Deborah will see more of the eclipse – a deeper eclipse of the sun by the moon – than Bruce.

Or find the time the eclipse for you with a different tool, an solar eclipse path map from NASA. As with the solar eclipse computer above, the eclipse path map gives times in Universal Time. It’s a nice tool, too, although it doesn’t give the times for sunset or sunrise, which you probably need for this eclipse. You can create a custom sunrise-sunset calendar here.

How do I translate Universal Time into my time?

Find astronomy clubs in your location

For U.S. observers: Annular or ring eclipse on Sunday May 20

This will be the first annular eclipse to take place in the mainland United States since May 10, 1994, and the next one won’t come until October 14, 2023. It’s the first solar eclipse of any kind in the mainland U.S. (not including Hawaii and Alaska) in the 21st century (2001-2100). Outside the path of the annular eclipse, sky watchers from much of North America will see a partial solar eclipse. For Asian viewers – who will se the eclipse on May 21, 2012 – the main eclipse path starts in China and passes through Japan, the most populous city in the world with 35 million inhabitants. It’s very cool to imagine them all getting to see this eclipse – assuming they are equipped with a safe way to view it. Outside the path of the annular eclipse, sky watchers in much of northern, central and southeastern Asia will see a partial solar eclipse.

Path of the annular eclipse across the United States on May 20

Image credit: Fred Espenak. Click here for a larger map and more information

Map of May 20-21 partial and annular solar eclipse

Partial solar eclipse can be seen as far north as the Arctic and as far south as Indonesia and Mexico

Image credit: Fred Espenak. Click here for a larger map

Map of annular eclipse path for the Eastern Hemisphere

The annular eclipse path passes through southeast China, northern Taiwan and southeast Japan in the morning hours on May 21

Map credit: Fred Espenak. Click here for a larger map and more information.

Total solar eclipse (A) on left and annular eclipse (B) on right

An annular eclipse happens whenever the new moon swings directly in front of the sun, blocking out all but the outer portion of the solar disk from view. This kind of eclipse presents an apparent ring of fire – really, the outer rim of the sun’s body – around the moon in the daytime sky at mid-eclipse.

Why doesn’t the moon block the sun completely, as in a total eclipse? It doesn’t because the moon is too far away in its monthly orbit around Earth to appear large enough in our sky to cover the sun completely.

An annular eclipse is essentially a partial eclipse in the sense that the moon never blots out the sun completely. At most, for the May 20-21 eclipse, the sun will be only 88% covered by the moon. The remaining 12% can cause permanent eye damage. Do not view the eclipse without eye protection.

What’s the best way to view a solar eclipse safely?

Where to watch the annular eclipse in the U.S.

The maps above show the path of the annular eclipse across the United States and China on May 20 and May 21. The blue line outlines the northern and southern limits of the annular eclipse, while the red line marks the center.

Annular or ring eclipse seen in Bangui, Central African Republic on January 15, 2010. Image via Tino Kreutzer and Wikimedia Commons.

Here in the U.S., the annular eclipse will start in the relatively late afternoon on the west coast (6:23 p.m. Pacific Daylight Time) and will end at sunset over northwestern Texas (8:39 p.m. Central Daylight Time). People residing along the nearly 200-mile wide annular eclipse path stretching from the U.S. West Coast (California-Oregon border) to northwestern Texas get to watch the annular solar eclipse – the ring of fire encircling the moon.

The duration of annularity is rather short and sweet, even for observers on the red line. Any one place on the eclipse path in North America will see the annular eclipse for a maximum of about four and one-half minutes.

As the annular eclipse moves eastward across the southwestern United States, it swings through popular vacation spots such as Reno, Nevada, Utah’s Bryce Canyon, Arizona’s Grand Canyon and Albuquerque, New Mexico.

A partial eclipse of the sun precedes the annular eclipse by at least an hour, and follows it by roughly the same amount of time. Outside the path of the annular eclipse, the partial eclipse may be seen for two hours or more in the western parts of North America. Keep in mind, though, that for the most of the U.S. and North America, the sun will set in the west before the end of the eclipse.

Elsewhere in the United States and North America, a partial eclipse of the sun can be seen from as far north as Alaska and northernmost Canada, and as far south as Hawaii and Mexico. The only regions in North America to completely miss out on the May 20 partial eclipse are the U.S. East Coast and far southern Mexico.

Local eclipse times for U.S. time zones on May 20, 2012

Pacific Daylight Time (PDT)

Medford, Oregon:
Partial solar eclipse begins: 5:08 p.m. PDT
Annular solar eclipse begins: 6:24:35 p.m
Annular solar eclipse ends: 6:27:09 p.m.
Partial solar eclipse ends: 7:34 p.m.

Redding, California
Partial solar eclipse begins: 5:12 p.m. PDT
Annular solar eclipse begins: 6:26:22 p.m.
Annular solar eclipse ends: 6:30:55 p.m.
Partial solar eclipse ends: 7:36 p.m.

Reno, Nevada
Partial solar eclipse begins: 5:15 p.m. PDT
Annular solar eclipse begins: 6:28:31 p.m.
Annular solar eclipse ends: 6:32:54 p.m.
Partial solar eclipse ends: 7:37 p.m.

Carson City, Nevada
Partial solar eclipse begins: 5:16 p.m. PDT
Annular solar eclipse begins: 6:29:21 p.m.
Annular solar eclipse ends: 6:33:09 p.m.
Partial solar eclipse ends: 7:38 p.m.

Mountain Standard Time (MST)

Grand Canyon, Arizona
Partial solar eclipse begins: 5:25 p.m. MST
Annular solar eclipse begins: 6:33:59 p.m.
Annular solar eclipse ends: 6:37:12 p.m.
Partial solar eclipse ends after sunset

Mountain Daylight Time (MDT)

Bryce Canyon, Utah
Partial solar eclipse begins: 6:23 p.m. MDT
Annular solar eclipse begins: 7:31:28 p.m.
Annular solar eclipse ends: 7:35:46 p.m.
Partial solar eclipse ends: 8:37 p.m.

Albuquerque, New Mexico
Partial solar eclipse begins: 6:28 p.m. MDT
Annular solar eclipse begins: 7:33:36 p.m.
Annular solar eclipse ends: 7:38:00 p.m.
Partial solar eclipse ends after sunset

Central Daylight Time (CDT)

Lubbock, Texas
Partial solar eclipse begins: 7:31 p.m. CDT
Annular solar eclipse begins: 8:33:58 p.m.
Annular solar eclipse ends: 8:38:08 p.m.
Partial solar eclipse ends after sunset

Local eclipse times for Eastern Hemisphere (China, Taiwan, Japan) on May 21, 2012

China

Guangzhou
partial solar eclipse begins before sunrise
annular solar eclipse begins: 6:07:42 a.m.
annular solar eclipse ends: 6:12:04 a.m.
partial solar eclipse ends: 7:18 a.m.

Hong Kong
Partial solar eclipse begins before sunrise
Annular solar eclipse begins: 6:06:46 a.m.
Annular solar eclipse ends: 6:10:13 a.m.
Partial solar eclipse ends: 7:16 a.m.

Taiwan

Taipei
Partial solar eclipse begins: 5:07 a.m.
Annular solar eclipse begins: 6:10:17 a.m.
Annular solar eclipse ends: 6:11:29 a.m.
Partial solar eclipse ends: 7:24 a.m.

Japan

Osaka
Partial solar eclipse begins: 6:17 a.m.
Annular solar eclipse begins: 7:28:23 a.m.
Annular solar eclipse ends: 7:31:16 a.m.
Partial solar eclipse ends: 8:54 a.m.

Tokyo
Partial solar eclipse begins: 6:19 a.m.
Annular solar eclipse begins: 7:32:05 a.m.
Annular solar eclipse ends: 7:37:09 a.m.
Partial solar eclipse ends: 9:03 a.m.

Bottom line: A lucky few from China to Texas will be in just the right spot on Earth’s globe to see something special – an annular or ring eclipse of the sun. It will take place May 21, 2012 in China – and May 20, 2012 in the U.S. Yay International Date Line! The annular eclipse path crosses it, moving eastward, and that’s why the dates are so different.

Featured annular eclipse photo: sancho_panza

When is the next total solar eclipse in the U.S.?

The most amazing ring eclipse photo ever

From NASA: Eye safety during solar eclipses

Partial solar eclipse photo: UK

A wondrous annular or ring eclipse of the sun takes place on May 20, 2012 as seen from the southwestern U.S. – on May 21 according to calendars in Asia and Indonesia. For a comprehensive post about the annular eclipse, look here. This post will focus on the partial eclipse, which much of the world will be able to see. Given clear skies, all but the eastern part of North America can watch a partial eclipse of the sun in the afternoon hours on May 20. Much of eastern Asia and Indonesia will see the partial eclipse on the morning of May 21. Looking for eclipse times? Jump to the bottom of this post.

Map of May 20-21 partial and annular solar eclipse

Partial solar eclipse can be seen as far north as the Arctic and as far south as Indonesia and Mexico

Image credit: Fred Espenak. Click here for a larger map

Annular eclipse of the sun – China to Texas – on May 20 or May 21

Eye safety during solar eclipses

First, what happens on May 20/21? As seen on the map above, a partial solar eclipse can be viewed today (May 20 or 21 if you’re west of the International Dateline) from almost all over the North Pacific Ocean, much of North America, Greenland, eastern Asia and parts of Indonesia. The partial eclipse can be seen from a wide area that goes as far north as the Arctic and as far south as Indonesia and Mexico. Meanwhile, only a small sliver of the globe will be in a position to see the annular eclipse (the narrow red band extending from southeast China to the southwestern United States).

What is an annular eclipse? In an annular – or ring – eclipse, the moon crosses directly in front of the sun, much as it does during a total solar eclipse. But, at an annular eclipse, the moon is too far away in its monthly orbit around Earth to appear large enough in our sky to cover the sun completely. So, at mid-eclipse – instead of the moon covering the sun completely, as in a total eclipse, turning the sky dark and blotting the sun from view – in an annular eclipse a ring surrounds the moon silhouette. This dazzling ring is the outer edge of the sun. An annular eclipse is a partial eclipse in the sense that the moon never blots out the sun completely. At no time can you gaze at an annular eclipse without protective solar filters to prevent damage to your eyes.

What is a partial eclipse? In a partial eclipse of the sun, the moon’s distance from Earth isn’t so important. A partial eclipse differs from an annular eclipse only in that the moon doesn’t line up with the sun quite so directly, as seen from your vantage point. In a partial solar eclipse, the moon appears to take a bite out the solar disk. How big a bite? On May 20 (or 21 for those in Earth’s eastern hemisphere), that will depend on how close you are to the path of the annular eclipse on Earth’s surface – shown in the images above as that red central line (the one with circles inside it, indicating it’s the track of the moon’s shadow across Earth). The closer you are to that shadow track, the greater the partial eclipse you’ll see.

The eclipse starts at sunrise on May 21, 2012 in Asia, travels eastward across the North Pacific Ocean and ends at sunset on May 20, 2012 in North America – nearly six hours later. Strange that the date goes backwards? Yes, as the shadow path moves along over Earth’s surface, it crosses the International Date line, going east. In fact, midway between Asia and North America, the greatest eclipse happens at local noon, very close to the International Date Line.

We wish to remind you of the utmost importance of using proper eye protection when watching a partial or an annular solar eclipse.

Find astronomy clubs in your location

Annular eclipse of the sun – China to Texas – on May 20 or May 21

Watching the partial eclipse in North America

Because the eclipse happens in the late afternoon in North America, it’ll be to your advantage to find an unobstructed western horizon. The farther west you are in North America on the afternoon of May 20, the more of the eclipse that you will see. The U.S. East Coast will miss out entirely because the sun sets before the eclipse even begins.

Photo of a partial eclipse of the sun by Tim Ebbs

Image credit: Tim Ebbs

Remember, it’s of the utmost importance to use proper eye protection whenever watching a partial or an annular solar eclipse. Click here to find out if an astronomical organization near you is hosting a public presentation of the event.

Eye safety during solar eclipses

When is the partial eclipse visible from my part of the world?

Annular eclipse animation Locutus Borg

To know whether a partial or an annular eclipse is visible from your part of the world, and at what times, we provide links to two great resources. Click on this worldwide map, courtesy of the NASA eclipse web site, and scroll to your part of the world. Click at where you reside on the map to obtain eclipse times. Or go to this solar eclipse computer, courtesy of the U.S. Naval Observatory.

Keep in mind that both references give the times in Universal Time, so you need to convert from Universal Time into your time. For U.S. time zones, subtract 7 hours for Pacific Daylight Time, 6 hours for Mountain Daylight Time, 5 hours for Central Daylight time and 4 hours for Eastern Daylight Time.

How do I translate Universal Time into my time?

Animation of eclipse path. large gray shadow: partial eclipse; small red dot: annular eclipse

Find the time of the eclipse for you with the U.S. Naval Observatory’s eclipse computer. This solar eclipse computer gives times in Universal Time. In case the eclipse is cut off by sunset (in the Western Hemisphere), or by sunrise (in the Eastern Hemisphere), this solar eclipse computer gives the sunset or sunrise time.

Or find the time the eclipse for you with a different tool, an solar eclipse path map from NASA. As with the solar eclipse computer above, the eclipse path map gives times in Universal Time. It’s a nice tool, too, although it doesn’t give the times for sunset or sunrise, which you probably need for this eclipse. You can create a custom sunrise-sunset calendar here.

How do I translate Universal Time into my time?

Bottom line: North America, the North Pacific Ocean, Greenland, eastern Asia and parts of Indonesia will be able to watch the partial solar eclipse. The annular (ring of fire) eclipse will take place over a slice of the American Southwest, southeast China, far northern Taiwan and southeast Japan. If you live on the North American side of the Pacific, the eclipse will occur in the late afternoon hours before sunset on May 20, 2012. And if you live on the Asian side of the Pacific, the eclipse will be in the morning hours after sunrise on May 21, 2012.

Click here for more on the annular eclipse of the sun – China to Texas – on May 20 or May 21. Image Credit: Sancho Panza on Flickr

The star Deneb – visible by mid-evening every May – is one of the most distant of the bright stars. When you gaze at this star, you are gazing across a great distance of space. The exact distance to Deneb is not known for certain, with estimates ranging from about 1,425 light-years to perhaps as much as 7,000 light-years. EarthSky veteran sky blogger Larry Sessions said in his post about Deneb:

The best estimates likely are those obtained by the Hipparcos Space Astrometry Mission in the 1990s. A simple calculation from initial Hipparcos data gives the figure of 3,230 light-years, whereas the refined data yield just over 1,400 light-years. At any of these estimates distances, Deneb is one of the farthest stars the unaided human eye can see. It is so far, that the light that reaches the Earth today started on its journey well more than 1,000 years ago.

Why don’t astronomers know the distance to Deneb exactly, and why are there different estimates for the star’s distance? The answer is that science is not a body of facts. It’s a process. Different astronomers or teams of astronomers try to improve on published distance estimates to the stars, and their various estimates are then published and passed along.

Deneb is too far away for its distance to be measured by the only direct method – stellar parallax. The distance to stars within a few hundred light-years of the solar system can be determined fairly accurately by parallax. The basic principle of parallax you can demonstrate to yourself by holding a finger in front of your nose and gazing at it with one eye closed, then the other eye closed. When you do this, you see your finger appear to jump from side to side with respect to background objects. If you hold your finger farther from your nose, it’ll appear to jump a smaller distance.

As Earth orbits the sun, astronomers can measure the parallax of the nearer stars against the more distant starry background, first from one side of Earth’s orbit and then – six months later – from the opposite side. Measuring stellar distances directly by parallax (trigonometry) only works for the nearer stars, however. For more, read Wikipedia’s parallax page.

Delta Cephei, prototype of Cepheid variable stars

Indirect means – which may be subject to errors – must be employed to estimate the distances to the more distant stars, like Deneb. Deneb’s given distance represents an educational guess, not a certainty. But there is little doubt that Deneb is one of the most distant stars that you can easily see with the unaided eye.

Deneb is one the three brilliant stars in the famous Summer Triangle asterism, which you’ll see over the east-northeast horizon by mid to late evening tonight. An asterism is a recognizable group of stars that isn’t a constellation. At our mid-northern latitudes, Deneb will light up the evening sky from now till the end of the year.

Deneb: Among most distant stars visible

Summer Triangle: Vega, Deneb, Altair

How far is a light-year?

Where is the starlit band of the Milky Way on these May evenings? That luminous band of stars crossing the dome of sky is nowhere to be seen during the evening hours in May. Why?

Starlit band of the Milky Way. Photo by Larry Landolfi via NASA

Click here to expand image

The disk of our Milky Way galaxy is shaped like a pancake. On May evenings, the plane of the pancake-shaped galactic disk coincides with the plane of the horizon. Because the Milky Way rims the horizon in every direction in the evening in May, we can’t see this roadway of stars until later at night right now.

Three planets at nightfall!

The galactic disk most closely aligns with the horizon at about 30 degrees North latitude – the latitude of St. Augustine, Florida. Appreciably north of this latitude, the galactic disk tilts a bit upward of the northern horizon. Appreciably south of 30 degrees north latitude, the galactic disk tilts a bit above the southern horizon. Even so, the Milky Way is pretty much out of sight in our Northern Hemisphere sky during the evening hours in May.

Like the sun, the stars rise in the east and set in the west. If you stay up until late night – near midnight – you’ll begin to see the the stars of the Summer Triangle – Deneb, Vega, and Altair – rising above your eastern horizon. In a dark country sky, the Milky Way’s band of stars becomes visible as well, for the Milky Way passes right through the Summer Triangle.

An all-sky plot of the 25,000 brightest, whitest stars shows how these stars are concentrated along the Milky Way. This map shows our limited, inside view of the Milky Way galaxy. The large, dark patch near the middle of the picture is due to nearby dark nebulae, or clouds of gas and dust, which obscure the stars. Via altasoftheuniverse.com.

Click here to expand image above

Bottom line: The Milky Way’s softly-glowing band of luminescence hides behind the horizon at nightfall and early evening in the month of May. But if you stay up until around midnight, you’ll begin to see the starlit band of the Milky Way rising in the eastern sky.

We’ve had so many questions about the faint star near the bright planet Venus! That little star is Elnath, second-brightest star in the constellation Taurus the Bull. Look for Venus and Elnath in the west as darkness falls. Although Elnath is a respectably bright second-magnitude star, it pales next to Venus – the most brilliant celestial body to light up tonight’s evening sky.

Elnath marks direction to galactic anticenter

As a matter of fact, Venus outshines Elnath by about 250 times. Still, if your sky is dark enough – in other words, if it’s long enough after sunset – you should be able see Elnath pop into view with the unaided eye. If you can’t see a star next to Venus, try binoculars.

The star Elnath marks the Northern Horn of the Bull in the constellation Taurus. It also marks the direction opposite the center of our Milky Way galaxy. Read more about Elnath here.

Elnath has been near Venus throughout May 2012. By mid-month, Venus and Elnath shine about two degrees apart – that’s the width of your little finger. Hold your finger at arm’s length when making this measurement.

Brilliant Venus and the star Elnath in the west after sunset now. Photo taken on May 10, 2012 by EarthSky Facebook friend VegaStar Carpentier in Paris. Thank you.

Stacked image of Venus and Elnath, taken on May 13, 2012 by EarthSky Facebook friend Lee Phillips. Isn't it cool?

Click here to expand image above

On May 15, 2012, Venus was stationary according to astronomical almanacs. Stationary does not mean that this planet – like Polaris, the North Star – stays in the same spot in the sky all night long. In fact, you can count on Venus to follow the sun below the horizon a short while after nightfall tonight and every night.

Instead, stationary means that Venus has now reversed its course in front of the backdrop stars. It’s an indication that Venus will soon drop into the sunset glare. Venus is lingering near the star Elnath for many days in a row around now, as Venus stops going eastward through the constellation Taurus the Bull. On May 15, Venus paused briefly in front of the stars before heading back westward again.

Taurus? Here’s your constellation

Westward is in the direction of the setting sun. As Venus first pops out after sunset in the weeks ahead, it’ll fall closer and closer to the sunset point on the horizon. On June 5-6, 2012, Venus will transit, or cross right in front of the solar disk. This will be the last transit of Venus in most of our lifetimes – the last transit of Venus in the 21st century. After June 2012, the next transit of Venus won’t happen until December 11, 2117.

Read more: Last transit of Venus in 21st century will happen in June 2012

What is this heavenly image? A crescent moon? No. It's Venus, as you would find it through a telescope if you looked tonight. Like the moon, Venus shows phases. It's now in a waning crescent phase as it moves into position to pass between the Earth and sun on June 5-6. Photo by EarthSky Facebook friend Alan Murta. Gorgeous and tranquil image, Alan. Thank you!

Venus transit June 8, 2004. Click here for more about the last transit of Venus in the 21st century, on June 5-6 Image Credit: Wikimedia Commons

During a transit of Venus across the face of the sun, Venus appears as a small dark dot moving in front of the solar disk. Of course, proper eye protection is an absolute must when watching a transit of Venus.

The whole transit, from start to finish, will last for nearly seven hours. From the mainland United States, however, we will only see the first few to several hours of the transit during afternoon hours on June 5. From Austin, Texas, for example, the transit will take place from 17:05:18 (5:05:18 p.m.) Central Daylight Time until sunset. Click here to find out the local transit times in your sky.

Bottom line: In May 2012, Venus still shines brightly in the west after sunset. You can see it near a little star – actually the second-brightest star in the constellation Taurus – called Elnath. After mid-May 2012, watch as the planet Venus falls sunward and heads for its inevitable conjunction with the sun. How many days will pass before you can tell that Venus is no longer stationary in front of Taurus, but is actually dropping below the star Elnath in the western evening sky?

Venus goes from east to west (left to right) across the sun's disk.

Image credit: Fred Espenak. Click here for a larger diagram.