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:

Wednesday, July 9, 2008

Mars and Saturn Conjunction

Tonight and for the next few nights, Mars and Saturn will appear very close to each other, i.e., they are in conjunction. Face west just as it's starting to get dark. The two planets will be the first two "stars" that appear. Saturn is the brighter of the two. If you notice a third bright star to the lower right, it's Regulus.

Tuesday, July 8, 2008

The Little King

If you attempted to see the lineup described in the previous post, you saw the star Regulus between Saturn and Mars. What made this lineup possible is that Regulus lies near the ecliptic, the path followed by the sun. The moon and the planets also closely follow this path.

Regulus is the brightest star in the constellation Leo. The brightest star in a constellation is usually designated alpha. Hence, Regulus is also known as Alpha Leonis. In ancient times, Regulus was known as Cor Leonis, which means "heart of the Lion." The more modern name Regulus was given by Copernicus. It is Latin for "little king."

Through a telescope, Regulus appears as two stars. Though difficult, it is possible to see both stars through binoculars. The dimmer of the two is actually a double star itself. You can see all three stars through a large telescope.

One unusual thing about Regulus is that it spins very rapidly. As a result, it is 32% wider at the equator than at the poles. Astronomers think that a previously unknown star is causing the rapid spinning. You can read more about Regulus's secret companion here.

Wikipedia on Regulus
S&T Regulus's Secret Companion

Saturday, July 5, 2008

Moon, Regulus, Mars, Saturn Aligned

Look for the crescent moon low in the west about an hour after sunset. Just to its upper left is the bright star Regulus in the constellation Leo. Approximately the same distance away is Saturn. And between Saturn and Regulus is faint Mars. The four objects are lined up nicely. Sky and Telescope's front page today has a nice chart. You can also make your own chart. Here's a screen shot from Starry Night Online:

If you missed the alignment tonight, try tomorrow night. The moon will have moved to form a triangle with Saturn and Regulus. But Regulus, Mars and Saturn will still be aligned.

Update: This is what it looked like from Santa Barbara.