See the marvels of the sky

Last year was a big year for astronomy fans - so big that it was formally designated the International Year of Astronomy, in recognition of the 400th anniversary of Galileo Galilei's groundbreaking telescope observations. But the week ahead is a big week as well, and not just because it's been designated Astronomy Week. Here's what you can look forward to, in the skies and on the Web:

Astronomy Day (and Week, and Month)

Astronomy Day comes two times a year, traditionally on a Saturday in the April-May time frame as well as in October, around the time of the first-quarter moon. Those tend to be times when the weather and the night-sky viewing conditions make stargazing easy.

This season's Astronomy Day is April 24, with the days leading up to the date observed as Astronomy Week. Astronomy clubs around the globe have scheduled special events to introduce newcomers to the marvels of the night sky. To find out what's going on in your neck of the woods, check out the activities listed by the Astronomical League and Astronomy.com.

This year, the whole month of April has been designated Global Astronomy Month, with extra emphasis on amateur observing. To find out what's going on with GAM, check out the Web site's event calendar/map, tune in to the @GAM_2010 Twitter account, or sign on to the project's Facebook page. Discovery News' Ian O'Neill offers more GAM goodies.

See the space shuttle streak by

If the space shuttle Discovery heads back to Earth on Monday morning as scheduled, skywatchers across a wide swath of North America could be in for a rare treat. "Viewers in the Pacific Northwest and northern Rockies will, weather permitting, be able to see the fireball in the pre-dawn sky of the fiery atmospheric re-entry," NBC News space analyst James Oberg writes in an e-mail.

Here's how Oberg figures the schedule will work: The shuttle should be visible over British Columbia around 4:30 a.m. PT Monday, as it passes above Queen Charlotte Sound, Kamloops and south of Lethbridge. From there, Discovery is due to sail just north of Great Falls, Mont., at 5:35 a.m. MT. It'll cross the southwest tip of North Dakota, go over parts of South Dakota and zip right over Omaha just as the sun is coming up.

Oberg says the shuttle would look like a "dazzling-bright golden spark," crossing from one horizon to the other in just three minutes. "Behind the spark would be a wide white ribbon, a trail of angry ions glowing in the spaceplane's wake for several minutes," he writes. "That trail broadens slowly and then fades out, usually after the fireball has already 'set' in the east."

Some folks say they hear a hiss or a whoosh as the shuttle passes overhead. Oberg says the effect is real. "It is caused by radio static generated in the twisted magnetic field lines in the plasma trail behind the shuttle (or behind any really big bolide fireball). The static is strong enough to 'couple' into some materials near some witnesses, causing the material to vibrate and thus generate sound," he writes.

There's another way to hear the shuttle's passing: Discovery's supersonic re-entry generates a rolling sonic boom that can resound minutes after its passage, depending on atmospheric conditions. The same shuttle followed a similar track for its descent back in 2007, and although the times are different, the sonic boom effect is well-described in this Space.com report from three years ago.

Discovery's flight marks the last space shuttle descent scheduled to take place over America's heartland. But if you miss Discovery's re-entry, there are still plenty of chances to see the International Space Station. NASA's real-time tracking database tells you where and when to look. 

Lots to see on the Web

Even if it turns out that the skies are cloudy all day and night over the coming week, you can stll get a good dose of out-of-this-world wonders over the World Wide Web. Take the eruption of Iceland's Eyjafjallajökull volcano, for example. The cloud of ash has caused a terrible air-traffic jam on both sides of the Atlantic, but from the perspective of NASA's orbiting satellites, it makes for an impressive show. The European Space Agency offers additional satellite imagery and an animation that fills out the picture.

April 22 is Earth Day, and in recognition of the date, NASA has put together a portal Web page that's chock-full of Earth imagery as well as information about the space agency's Earth Day activities. We have our own slideshows that feature Earth as seen from space, plus Earth imagery that's cool enough to hang in a modern art gallery.

The piece de resistance comes on April 24 - that's right, Astronomy Day - when NASA marks the 20th anniversary of the Hubble Space Telescope's launch. The Hubble team always releases something special to celebrate Hubble's birthday. The Big 2-0 will likely be an extra-special occasion, especially when you consider that the telescope was given its final scheduled upgrade less than a year ago. So stay tuned: The best is yet to come.

Update for 11:59 p.m. April 19: Discovery's landing was postponed on Monday, but there are still some good opportunities to see the space shuttle's descent (and hear its sonic boom) on Tuesday. Check out these maps of Discovery's potential routes for Tuesday's landing opportunities in Florida and California. 

To prepare yourself for next week's marvels, click through our "Hubble's Greatest Hits" slideshow - as well as Hubble's latest hits. Join the Cosmic Log corps by signing up as my Facebook friend or hooking up on Twitter. You can also check out my book, "The Case for Pluto." Next week, I'll be doing book-related events in the Boston area and New York.