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.