Monday, December 1, 2008

Astronomy Tonight: Moon, Venus & Jupiter Trio

Look outside about half an hour to an hour after sunset. The crescent moon will be very low in the southwest. Just to its lower right, you'll see two bright planets, Venus and Jupiter. Venus is the brighter of the pair. The two are separated by only 2°. That's about the width of your index finger held at arm's length.

Tuesday, October 7, 2008

Astronomy Tonight: The Moon and Sagittarius

Astronomy start chart of the mmon and Sagittarius
Tonight the moon is to the left of Sagittarius. Look for the familiar teapot shape to the lower right of the moon. Jupiter is the brightest object to the right of the moon.

Monday, October 6, 2008

Astronomy Tonight: The Moon and Jupiter

Astronomy star chart of the moon, Jupiter & Sagittarius
Look for the moon in the early evening. The bright "star" to its upper right is the planet Jupiter.

Take a look at the stars surrounding the moon. They form a familiar teapot shape. This asterism is the easiest way to identify the constellation Sagittarius. The moon is in the teapot's handle.

Friday, September 19, 2008

The Moon & Pleiades

Astronomy start chart of the moon and Pleiades
If you're up late, say 11pm or midnight, look for the moon low in the east. Immediately to its upper right is a cluster of stars known as the Pleiades. If the glare of the moon interferes with your view of this bright cluster, use your hand to block off the moon.

The Pleiades, also known as the Seven Sisters, is one of the few clusters visible to the naked eye under city skies. At least 6 stars are visible even without binoculars.

Thursday, September 18, 2008

Constellation Lyra

Astronomy start chart of constellation Lyra
Vega, the brightest star in the Summer Triangle, belongs to the constellation Lyra. It's the brightest star in the constellation. At magnitude 0, it's also the fifth brightest star in the sky.

Hanging off Vega are two pairs of stars. Two of them, the brighter of the pairs, are named Sheliak and Sulafet. The four stars form a parallelogram, as shown in the chart above.

Note another star labeled the Double Double. If your eyes are sharp enough, this star appears as a double star. These stars are doubles themselves, making the Double Double a quadruple star system. A sharp telescope on a good night will show all four stars.


The 10 Brightest Stars
Constellation Lyra

Wednesday, September 17, 2008

Constellation Cygnus

Astronomy start chart of constellation Cygnus
The stars of the Northern Cross belong to the constellation Cygnus, the swan. Deneb, at magnitude 1.25, is the brightest of the stars. It's also among the top 20 brightest stars in the sky.

Deneb marks the tail of the swan. In fact, Deneb is Arabic for "tail." At the opposite end is the star Albireo marking the head of the swan. Albireo is a popular among amateur astronomers because it appears as a beautiful yellow and blue double star through a telescope.


List of Brightest Stars
Constellation Cygnus

Tuesday, September 16, 2008

The Northern Cross

Astronomy start chart of the Northern Cross
Take a closer look at Deneb, the northernmost and faintest star in the Summer Triangle. Off to the south, or the right, of Deneb are three stars. The middle star is labeled Sadr in the chart above. Farther to the south, or right, is the fainter star Albireo.

These stars make up what is known as the Northern Cross. Deneb marks the top of the cross. Sadr is at the intersection of the arms of the cross, and Albireo is at the bottom of the cross.

Deneb to Albireo spans 22°. If you hold your outstretched hand at arm's length against the sky, the width from your thumb to your little finger covers about 25°. The Northern Cross should fit within your outstretched hand.


Constellation Cygnus
Star Science in the Autumn Sky

Monday, September 15, 2008

The Summer Triangle

Astronomy start chart of the Summer Triangle
Go outside about half an hour after sunset. One by one, the brightest stars in the sky will start popping out. If you look directly overhead, the first three stars to appear form the asterism known as the Summer Triangle. Even though it's almost autumn, the Summer Triangle is still high overhead at nightfall.

Vega, the star farthest to the west, is the brightest among the three. Altair, towards the south, is the second brightest. Deneb, the one farthest north, is the faintest.

Unlike other asterisms that usually belong to a single constellation, the three stars of the Summer Triangle belong to three different constellations. Vega is the brightest star in the constellation Lyra. Altair is in the constellation Aquila. And Deneb belongs to the constellation Cygnus.


Skywatchers Guide: Summer Triangle helps orientation, observation

Friday, September 12, 2008

Moon & Neptune

The moon will be less than 1° from Neptune tonight. One degree is the width of your little finger held at arm's length.

Neptune, at magnitude 7.8, is too faint to see naked-eye. But if you own a telescope, it will be easy to find using the moon as your guidepost.

You can also try finding Neptune with binoculars. The typical binocular has a 5° field of view, so Neptune and the moon, with only 1° separating the two, should both fit in the field of view . You may want to move most of the moon out of the field of view though. Otherwise its glare may keep you from seeing the surrounding stars and planet.

Use the chart below to find Neptune.

Astronomy start chart of the moon and Neptune

Thursday, September 11, 2008

Astronomy Tonight: Venus & Mars

If you have a clear view of the western horizon, you'll see Venus & Mars practically on top of each other. Look very low to the west 30 minutes after sunset. Venus will be only 1/3° north (upper right) of Mars. One-third degree is less than half the width of your little finger held at arm's length.

Astronomy start chart of Venus and Mars

Tuesday, September 9, 2008

Astronomy Tonight: The Moon to the Left of the Teapot

Again, look to the south for the moon. If you've learned how to recognize the teapot asterism in Sagittarius, you'll see that the moon is just to the left of the teapot's handle. The bright "star" to the upper right of the moon is the planet Jupiter.

Tuesday, September 9

Monday, September 8, 2008

Astronomy Tonight: The Moon in Sagittarius

The moon has now moved into Sagittarius. If you've learned how to recognize the teapot asterism in Sagittarius, you'll see that the moon is just above the teapot's spout. Note bright Jupiter to the upper left.

Monday, September 8

Sunday, September 7, 2008

Astronomy Tonight: The Moon Between Sagittarius and Scorpius

Look to the south for the moon. It has now moved between the constellations Sagittarius and Scorpius.

This is a perfect time to learn how to recognize the two constellations. Sagittarius to the left of the moon looks like a teapot, and Scorpius to the right looks like a giant letter J. Also note bright Jupiter to the left of Sagittarius.

Sunday, September 7

Saturday, September 6, 2008

Astronomy Tonight: The Moon and Antares

Look for the moon to the south. The bright star Antares will be just to the upper left of the moon. The two will be about 1° apart. One degree is approximately the width of your little finger held at arm's length.

Antares is the brightest star in the constellation Scorpius. If you haven't learned how to recognize Scorpius, now is a good time with the moon to guide you.

Saturday, September 6

Thursday, September 4, 2008

Astronomy Tonight: Mercury, Venus and Mars Triangle

Thursday, September 4

Mercury, Venus and Mars will form a small triangle tonight. You'll need a very low western horizon to see this. Look 30 minutes after sunset but not much later. If it's not dark enough, use binoculars.

Monday, September 1, 2008

Astronomy Tonight: Mercury, Venus, Mars and Moon

Tonight the moon will join Mercury, Venus and Mars. Again, you'll need a very low horizon. If you live along the west coast, this is a perfect time to head for the beach.

About half an hour after sunset, look just above the western horizon for the moon. Mercury, Venus and Mars will be just to its upper right. You'll need binoculars to see all three planets if it's not dark enough. And don't wait too late or the planets and the moon will sink below the horizon.

Monday, September 1

Sunday, August 31, 2008

Astronomy Tonight: Mercury, Venus and Mars

If you have a clear view of the western horizon, you'll be able to see three planets tonight. Mercury, Venus and Mars are headed closer and closer together each day.

Look to the west 30 minutes after sunset. The planets will be very low on the horizon. If it's not dark enough yet, you may need to use binoculars to see all three planets.

Sunday, August 31

Tuesday, August 19, 2008

Astronomy Tonight: Venus and Mercury

Tonight and for the next several nights, Venus and Mercury will be about 1° apart. One degree is approximately the width of your little finger held at arm's length.

Look very low in the west half an hour after sunset. Venus is the brighter of the two planets. You may need binoculars to see Mercury if it's not dark enough yet.

Tue, August 19

Wednesday, August 20

Thursday, August 21

Friday, August 22

Saturday, August 23

Saturday, August 16, 2008

Tonight: Lunar Eclipse

There is a partial lunar eclipse tonight. It will be visible almost everywhere except North America. The entire eclipse can be seen from most of Europe and Africa and the western part of Asia.

The eclipse begins at 19:36 UT. Mid-eclipse is at 21:10 UT when 81% of the moon will be covered by the earth's shadow. The eclipse ends at 22:45 UT. You'll have to convert UT to your local time.

Sky & Telescope has details, including a map.

The next partial lunar eclipse in North America will be on June 26, 2010. The next total lunar eclipse visible anywhere will be on December 21, 2010.



Thursday, August 14, 2008

Arc to Arcturus

Find the Big Dipper and follow the arc of the handle to the brightest star you see, Arcturus. At this time of the year, it's high in the west. Athough Arcturus is only the 4th brightest star, it's the brightest one in the summer sky at magnitude 0.

The name Arcturus is Greek for bear guard. It watches over Ursa Major and Ursa Minor.

Arcturus belongs to the constellation Boötes (pronounced boh-oh-teez). The brightest star in a constellation is called alpha, and since Arcturus is the brightest star in Boötes, it is also known as Alpha Boötis.


Arc to Arcturus
The 10 Brightest Stars

Wednesday, August 13, 2008

Tonight: Moon East of Teapot

The moon is just to the left (east) of Sagittarius tonight. Bright Jupiter is to the upper right (northwest) of the moon.

Tuesday, August 12, 2008

Tonight: Moon in Teapot

Tonight the moon will be in the lid of the teapot asterism in the constellation Sagittarius. The bright "star" to the upper left (northeast) of the moon is the planet Jupiter.

Monday, August 11, 2008

Tonight: Perseid Meteor Shower

Tonight is your best chance to catch the Perseid Meteor Shower. The best time to watch is after 2 AM when the moon sets. Find a dark location and enjoy the show.

If you look to the south earlier in the evening before the moon sets, you'll see the moon between Sagittarius and Scorpius.

Sunday, August 10, 2008

Tonight: Antares Near the Moon

Antares is easy to find tonight. It is just to the upper right (northwest) of the moon.

Saturday, August 9, 2008

Tonight: Moon Next To Scorpius

If you tried to look for Scorpius yesterday and couldn't figure out where the constellation is, take another look today. The moon will be just to the right (west) of the upper end of Scorpius.

Scorpius in Myth

In Greek Mythology, Scorpius was a giant scorpion sent by Gaia to kill Orion. Gaia, or Mother Earth, was angered when Orion, the hunter, threatened to kill all the beasts of the earth.

Scorpius & Orion are at opposite sides of the sky. The scorpion can never catch the hunter because one sets as the other rises. At the same time, the scorpion is being chased by the archer Sagittarius whose arrow is pointed straight at its heart. Scorpius dominates the southern summer sky while Orion dominates the winter sky.


Orion and Scorpius Constellations

Friday, August 8, 2008

How to Find Scorpius

If you can find Sagittarius, you can find Scorpius. Like Sagittarius, Scorpius is low in the southern sky and is just to the west (right) of Sagittarius. Its brightest stars look somewhat like a scorpion. Or perhaps you can think of it as a skewed letter J or a giant letter S or even a fish hook.

This is what it looks like next to the teapot asterism in Sagittarius.

This is close-up view of it.

Note the orange star near the upper end of Scorpius. It is the brightest star in the constellation and is therefore given the alpha designation, i.e., Alpha Scorpii. The star is better known, however, as Antares, meaning rival of Ares (Mars). Antares is the 16th brightest star in the sky.

Also note that the farther north you live, the less likely you are to see the bottom part of Scorpius.


Fishhook? Snake? Letter "J"? It's Scorpius the Scorpion!
The Brightest Stars

Thursday, August 7, 2008

The Archer: Sagittarius in Myth

The name Sagittarius comes from sagitta, Latin for arrow. In Greek mythology, Sagittarius represents a centaur holding a bow and arrow. A centaur is a creature with the body of a horse and the torso of a man. Sagittarius is sometimes identified with Chiron, a kind and gentle centaur who was taught archery by Apollo.

The archer's arrow is pointed at the heart of the adjacent constellation Scorpius, the scorpion.

Sagittarius in Myth
Sagittarius, the Archer
The Constellation Sagittarius

Wednesday, August 6, 2008

The Teapot: How to Find Sagittarius in 2008

Sagittarius is easy to find this summer because Jupiter is right next to it. So the first step in finding Sagittarius is to find Jupiter. Look to the southeast after sunset. Jupiter is the brightest object in the sky. It is so bright that it can be seen before it gets totally dark.

Once you find Jupiter, look just to the west (right) of it. The brightest stars in Sagittarius look like a teapot. The teapot is another famous asterism. It is about 13° wide, slightly wider than your fist held at arm's length.

This is what Sagittarius looks like with constellation lines drawn. Jupiter is just to the left of the teapot.

This is the same view without constellation lines.

And this is a wide view of the southern sky. Can you still find the teapot? Hint: Start with Jupiter and look just to the right of it.

Tuesday, August 5, 2008


In astronomy, an asterism is a distinctive pattern of stars that is not a constellation. It can be the most distinguishing feature of a single constellation, or it can be spread out over a few constellations. The Big Dipper is an asterism, not a constellation, and is the most famous asterism in the sky.

Here are some well-known asterisms:

Big Dipper in Ursa Major
Little Dipper in Ursa Minor
Summer Triangle
Northern Cross in Cygnus
Teapot in Sagittarius
Keystone in Hercules
W in Cassiopeia
Great Square in Pegasus
Sickle in Leo
Orion's Belt


List of Asterisms

Monday, August 4, 2008

Coming Up: The Perseid Meteor Shower

The Perseids are coming. Make plans for the morning of Tuesday, August 12 when the shower peaks. Stray meteors are already showing up now and will gradually increase till the shower peaks on August 12. The rate declines rapidly after that, but occasional meteors will be visible as late as August 22.

Catholics in some parts of England and Germany had long observed the Tears of St. Lawrence on the night of August 10 every year, when tears of fire fall from the sky. But it wasn't until 1837 that the Perseids were officially recognized as an annual event. The source of the shower is debris from Comet Swift-Tuttle.

The best time to view the shower is after 2am. The moon will have set by then, and Perseus, the constellation from which the shower seems to originate, will be higher in the sky. You can certainly view the shower much earlier in the evening (Monday night, August 11), but you will want to block the light from the moon using a tree or a building. While some meteors can be seen from the city, it would be best to get away from city lights.


The 2008 Perseid Meteor Shower
The Discovery of the Perseid Meteors
Meteor Showers Online
Major Meteor Showers in 2008

Friday, August 1, 2008

If You Missed The Eclipse

If you missed it, replays of the eclipse are available at the Exploratorium site. Scroll down and select either Program Replay or Telescope-Only Replay.

The next total solar eclipse will be on 22 July 2009, visible from India, China and other places. The maximum duration of totality is 6 minutes 39 seconds. In Shanghai, the eclipse will last over 5 minutes. Compare that to this year's eclipse at 2 minutes 27 seconds maximum duration. Tours are available now.

You'll have a long wait for North America where the next total solar eclipse isn't till 21 August 2017.

Thursday, July 31, 2008

Eclipse Webcasts for 1 August 2008

Image of 1999 eclipse courtesy of Luc Viatour

If you haven't made plans to travel to China or Russia for the total solar eclipse, you'll have to settle for watching a webcast.

These sites are planning live coverage of the 2008 eclipse in China and Russia:

University of North Dakota
Live! Eclipse

Check the program schedule for each site. Remember that if the times are given in UT (Universal Time), you can convert it to your local time using your UT offset.

Maximum totality is at approximately 10:21 UT. That's 6:21am EDT, 3:21am PDT, and 11:21am in most of Europe. Note that the eclipse begins about two hours prior to that and ends another two hours later.

Wednesday, July 30, 2008

Tips on Solar Safety

If you're lucky enough to experience a solar eclipse, take precautions when viewing the sun. Among the safe options:
  • Go to the nearest planetarium, science center, university or telescope store. They may have telescopes and binoculars set up with the proper solar filters.
  • Use pinhole projection. Make a pinhole through a piece of cardboard and hold it one meter away from another piece of cardboard or paper. See Quick & Easy at the Exploratorium eclipse site.
  • Use optical projection. Binoculars or a telescope can be used to project a magnified image of the sun onto a sheet of white paper. Make sure no one looks directly at the sun through the binoculars or telescope.
For direct viewing, these are safe:
  • Eclipse glasses with filters that are specifically designed for solar viewing, like this:
  • Shade #14 welder's glass
  • CDs with thick aluminum coatings. Light can't go through them, but the optical quality will be poor.
These are NOT safe:
  • CDs with thin aluminum coatings (light passes through them)
  • Most exposed film
  • Smoked glass
  • Sunglasses
Other tips on solar safety can be found at this NASA site. If in doubt, don't use it.

Tuesday, July 29, 2008

Partial Solar Eclipse on 1 August 2008

If you live in Europe, Asia or Canada, you may be able to experience a partial solar eclipse instead of a total solar eclipse. Here is a nice interactive map that gives you local times for the partial eclipse. Times are given in UT (Universal Time), so use your UT offset to calculate the local time.

These tables also list eclipse times:

United Kingdom & Canada
Asia Minor

Additional information on the eclipse is on the NASA site. Look under Local Circumstances to get eclipse times for other areas.

Monday, July 28, 2008

Total Solar Eclipse on 1 August 2008

A solar eclipse will occur on Friday, 1 August 2008. Northern Canada, northern Russia, western Mongolia and China will experience a total eclipse. Nearby areas such as northeastern North America, Europe and Asia will experience a partial eclipse.

This NASA map shows the areas the will experience a total or partial eclipse.

The total eclipse will be longest in northern Russia -- 2 minutes 27 seconds at 10:21:08 UT.



Friday, July 25, 2008

The Little Dipper

If you can find Polaris, you can find the Little Dipper in the constellation Ursa Minor. As shown in the chart below, Polaris marks the tip of the handle of the Little Dipper.

Finding the Little Dipper in the city can be a challenge. Most of its seven stars are rather faint. Here are the Little Dipper and Big Dipper with outlines drawn. The Little Dipper is on the right.

Here they are without the lines. Again, the Little Dipper is on the right.

This is what they look like from most big cities.

As you can see, only three of the Little Dipper's stars are visible -- Polaris and the two stars at the front of the bowl. The shape no longer looks familiar. Light pollution makes a big difference in what you can see in the sky.

Thursday, July 24, 2008

Finding North

I am constant as the northern star,
Of whose true-fix'd and resting quality
There is no fellow in the firmament.
- Julius Caesar (III, i, 60 – 62)

The stars at the front bowl of the Big Dipper, Merak and Dubhe, are called pointer stars. They point to Polaris, the North Star. Draw an imaginary line from Merak to Dubhe. Extend it five times the distance, and you'll end up at Polaris.

Contrary to Shakespeare, the North Star is neither constant nor fixed. Some facts about Polaris:
  • It resides in the constellation Ursa Minor.
  • It is the tip of the handle of the Little Dipper.
  • At magnitude 2, it is only the 48th brightest star in the night sky.
  • It is a variable star, its brightness varying over 4 days.
  • It is a binary star or double star. The second star is a faint magnitude 9.
  • It wasn't always the North Star. Thuban, in the constellation Draco, was the North Star around 3000 BC. In 3000 AD Gamma Cephei in the constellation Cepheus will become the North Star.

Wikipedia on the North Star
Wikipedia on Polaris
List of Brightest Stars
Constant as the North Star
Shakespeare Quote

Wednesday, July 23, 2008

How to Use a Planisphere

If you made your own planisphere but can't quite figure out how to use it, then this video is for you. The first four minutes of the video covers planispheres; the rest covers binoculars.

Tuesday, July 22, 2008

The Big Dipper

One of the most recognizable groups of stars in the sky is the Big Dipper in the constellation Ursa Major. Most people learn to find it as children. For those who missed that lesson, go outside after dark just as the stars are starting to come out and look to the northwest. The stars of the Big Dipper are fairly bright and should be one of the first ones to appear in the evening. See if you can recognize the shape from the chart above.

If you're having trouble finding it, remember that the Big Dipper is huge, spanning 25°. Hold your hand at arm's length against the sky with your thumb and pinky finger extended. The width between those two fingers is approximately 25°. Don't forget to try your planisphere, if necessary.

Once you've located the Big Dipper, look for Mizar, the second star from the end of the handle of the Big Dipper. It is a double star, meaning it is actually two stars even though it appears a single star to the naked eye. Alcor is its companion star. Mizar and Alcor are easy to split in binoculars. If your eyes are very sharp, you might be able to see both stars without binoculars.

Monday, July 21, 2008

Callisto and Arcas

In Greek mythology, Callisto was a nymph of Artemis, the goddess of forests and hills. Zeus wanted her and took on the shape of Artemis in order to lure her and rape her. When Zeus's wife Hera found out that Callisto was pregnant, it enraged her, and she turned her into a bear.

Callisto bore a son named Arcas. Years later when Arcas was hunting, he came upon a bear. Not knowing that it was his mother, he was about to kill her when Zeus took pity on her. He placed Callisto in the sky as Ursa Major (Great Bear in Latin) and Arcas nearby as Ursa Minor (Little Bear).

Callisto is also the name of one of Jupiter's moons.


Wikipedia on Callisto
Ursa Major
Ursa Minor
Jupiter and Callisto engraving by Jacopo Amigoni

Sunday, July 20, 2008

How to Find the Planets

The easiest way to locate all the planets is to follow Sky & Telescope's directions. Go to This Week's Sky at a Glance, and scroll down to This Week's Planet Roundup.

Mercury, Venus, Mars, Jupiter and Saturn are bright and easy to spot even from the city. Uranus and Neptune require a telescope and a finder chart. Pluto is still listed for old times' sake and is a challenge to find. You'll need a big scope, dark sky, and detailed star chart.

Saturday, July 19, 2008

How to Identify Jupiter's Moons

If you have a telescope or binoculars that let you see Jupiter's moons, then the Jupiter's Moons JavaScript Utility from Sky & Telescope will help. It allows you to identify the four brightest moons at any given time. Adjust the time using your UT offset to determine the local time. The tool automatically retrieves the UT offset from your computer, but you may want to verify that it is correct.

You can confirm for yourself that the moons are constantly changing position. Click on one of the buttons repeatedly, e.g., "+1 hour," to simulate this.

Friday, July 18, 2008

How to Calculate Your Universal Time Offset

Universal Time, often abbreviated UT or UTC, is more or less the same as Greenwich Mean Time (GMT). Some astronomy tools require that you know the offset, or time difference, between UT and your time zone. The offset can also be used to convert UT to your local time.

You can look up your offset here:

Map-based lookup
Text-based lookup

If you're on Daylight Saving Time (DST), you may have to add one hour to the offset, depending on the tool. Note that if your offset is e.g., -8 hours, it becomes -7 hours with DST (not -9).

Thursday, July 17, 2008

Name That Moon

Photo courtesy of NASA and the NSSDC

Jupiter has 63 moons. The NASA web site has a list of the names.

The moons were named after the Roman god Jupiter's lovers, children and godchildren. Click on a name to see the lover or descendant's relationship to Jupiter, or go directly to the USGS Astrogeology site.

Notice that from the 50th moon on, the moons have catalog numbers. Those moons will eventually have proper names. Apparently Jupiter had no shortage of lovers.


Naming convention explained

Wednesday, July 16, 2008

Poor Simon Marius

Who was Simon Marius? He was a German astronomer who claimed to have discovered Jupiter's four moons a few days before Galileo did. But he didn't publish his findings till 1614. Galileo published his in 1610, the same year he discovered the moons.

So instead of being famous for discovering Jupiter's first four moons, Marius is merely a footnote in history as the man who gave the moons their names -- Io, Europa, Ganymede and Callisto, named after lovers of Jupiter.

This is a portrait of Simon Marius. He sure looks mad, doesn't he?


Galilean Moons
Simon Marius
Marius portrait

Tuesday, July 15, 2008

Jupiter Moon Dance

The year was 1610. Galileo, working from his home in Padua, Italy, pointed his homemade spyglass at Jupiter. Night after night, he noticed a line of four stars flanking Jupiter. These stars constantly changed position but never strayed far from the planet.

Galileo had discovered that Jupiter, like the Earth, had moons. The widespread belief that everything revolved around the Earth had just been proven wrong.

In this document, you can see the sketches Galileo drew of Jupiter and its moons as observed through his telescope.

Image courtesy of NASA

Today the four moons discovered by Galileo are known as the Galilean moons. In order of distance from Jupiter, they are Io, Europa, Ganymede and Callisto.

Here is a typical view of Jupiter and its moons, similar to what Galileo would have seen. At the time this photo was taken, Io was hiding behind the planet.

Photo courtesy of NASA/JPL/Malin Space Science Systems


Galileo document
The Discovery of the Galilean Satellites

Monday, July 14, 2008

Jupiter: The Gas Giant

If you look outside tonight, the brightest object you'll see in the southeast sky is Jupiter. If you live in the city, it may be the only thing visible in that area of the sky; you can't miss it. At magnitude -2.7, it's the third brightest object in the night sky next to the moon and Venus (Venus is not currently visible) and will be up for most of the night.

Jupiter is one of the gas giants, composed primarily of hydrogen. It takes less than 10 hours for it to rotate on its axis. The most prominent feature on the planet is the Great Red Spot (GRS), visible in telescopes. You'll see the GRS in the photo below.

Photo courtesy of NASA and the NSSDC

Related Posts:

Jupiter Moon Dance
How to Identify Jupiter's Moons
Name That Moon
Poor Simon Marius

Hubble Telescope photos

Sunday, July 13, 2008

Pack Your Bags: Upcoming Solar Eclipse

It's not too late to book a flight to China for the total solar eclipse on 2008 August 01. Read about it here.

Parts of Asia, Europe and North America will experience a partial solar eclipse. See Figure 2 under General Maps of the Eclipse Path for a map. Local times are listed under Local Circumstances.

If you can't make it to this eclipse, there will be another one next year on 2009 July 22, also visible from China.

More on next month's eclipse, including webcasts, as the date nears.

Saturday, July 12, 2008

Free Planisphere

A planisphere is a star chart that can be adjusted to show the sky for a specific time and date. It allows you to learn stars and constellations.

Sky & Telescope provides a planisphere that you can print for free. They call it a star wheel. Download it here.

Take the planisphere outside with you to compare the chart to what you see in the sky. You'll need a red flashlight to read it in the dark. If you don't have a red flashlight, cover a regular flashlight with red plastic or paper or tape. The flashlight should not be too bright, or it will ruin your night vision. Set the planisphere to the current date and time, and you're ready to go.

Update: Other versions can be found here and here.

Related post:
How to Use a Planisphere

Friday, July 11, 2008

The Nemean Lion

The constellation Leo is thought to have been named after the Nemean lion. Slaying the Nemean lion was the first of the twelve labors of Hercules (or Heracles) in Greek mythology.

A lion had been terrorizing the town of Nemea in Greece. Its hide was impenetrable by arrows. Hercules eventually cornered it in a cave and strangled it to death. To remove the hide as his trophy, he had to use the lion's own enormous claws to pierce its tough skin. With the hide being so impenetrable, he threw it over himself to use as an armor.

Zeus, the father of Hercules, put the slain Nemean lion into the sky as the constellation Leo.

Wikipedia on the Nemean Lion
Encyclopedia Mythica on the Nemean Lion

Thursday, July 10, 2008

The Sickle

Now that you know where Regulus is, you can identify the constellation Leo, the lion. The head of Leo looks like a backward question mark or a sickle. Regulus is at the bottom of the sickle. The lion's body follows to the southeast (upper left). This is what it looks like in the early evening:

At this time of year, Leo is getting ready to set, so look for Leo soon after dark. Leo is highest in the sky in the spring. If you familiarize yourself with Leo now, you'll be able recognize it in the early spring when it rises in the east looking like this: