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Carolyn Collins Petersen
Guide since 2014


About.com Space / Astronomy

It's International Dark Sky Week!

Have you ever heard of light pollution? It's the overuse of light at night. Nearly everyone on Earth has experienced it. Cities are bathed in light, but lights also encroach on the wilderness and rural landscapes as well. This week is International Dark Sky Awareness week, seeking to share ways to reduce light pollution. The International Dark-Sky Association is a leading authority on light pollution, its causes, and ways to reduce it while preserving safety and security. Check out their Web site, and their video "Losing the Dark", available to watch on Youtube and Vimeo, and downloadable for educators, planetariums, and other outreach professionals.

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Observe the Beehive Cluster!
 An April Night Object to Check Out!

Celebrating Hubble Space Telescope

Horsehead Nebula

 This week astronomers and space enthusiasts celebrate the 24th anniversary of the launch of Hubble Space Telescope on April 24th. We'll look at a great Hubble image each day. Today's image is Hubble's view of the famous Horsehead Nebula in infrared light, which allows astronomers to look "into" this pillar of eroding gas and dust. The nebula is a small part of a huge starbirth region in the constellation Orion. In about 5 billion years, this lovely cloud of gas and dust will be gone, eaten away by radiation from hot young stars nearby.

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Space / Astronomy Spotlight10

Hubble Measures Distances in the Cosmos

Thursday April 24, 2014

How Far Away is that Star... or Galaxy... or Cluster of Galaxies?

One of Hubble Space Telescope's most fascinating discoveries isn't necessarily a pretty picture. It's something quite profound: refining distance measurements of the universe. Yes, it sounds rather boring, but knowing the dimensions of the universe is an important part of understanding the universe itself.

Hubble measures cosmic distances.

To get to Hubble's contribution to measuring the universe, let's look at how astronomers measure distances. One way to do it is to bounce a laser off of a nearby object. Measure the time it takes for the laser beam to go from Point A to Point B, and back to Point A again. You know that light goes 186,252 miles (299,000 km) per second, and so it's an easy calculation to figure out how far it went in the time it took for the light to make the round-trip. NASA has done this many times with the Moon. There are reflectors on the lunar surface, placed so that astronomers can bounce lasers off them. Using this method, the average time it takes is 1.28 seconds.  This puts the Moon at an average distance of 238,900 miles.

That method works well for very close objects that have hard surfaces. But, when you want to measure distances to stars or galaxies, different methods have to be used.  The most reliable one for making astronomical distance measurements to faraway objects is to use straightforward geometry. Astronomers use the 186-million-mile diameter of Earth's orbit to construct a baseline of a triangle, much as a land surveyor would use. If a target star is close enough, it will appear to zigzag on the sky during the year as Earth moves through its orbit.

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Look Deep Into the Universe

Thursday April 17, 2014

See Galaxies!

What do you see if you look out at the universe? From Earth's surface, you see stars, planets, and galaxies. Of all these objects, galaxies are the most fascinating and evocative, but also tougher to spot in the sky than the others. Yes, there are a few naked-eye galaxies: the Andromeda Galaxy, and the Large and Small Magellanic Clouds. If you want to be complete, of course the Milky Way Galaxy is extremely easy to spot, but only because we're IN it. Most other galaxies are outside ours and they require magnification (binoculars and telescopes) if you want to see more than fuzzy blob of light. Astronomers have always seen many more galaxies with their larger research observatories, but nowadays, with the advent of advanced telescopes, such as Hubble Space Telescope, they're seeing a LOT more galaxies than they used to!

Image of galaxies

This image shows a galaxy cluster set against a backdrop of more distant galaxies. This is a remarkable cross-section of the universe, showing objects at different distances and stages in cosmic history. They range from cosmic near neighbors to objects seen in the early years of the universe. (See the Hubble web page for this story to view a larger image.)

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Cosmos for the Next Generation

Thursday April 17, 2014

Are you watching Cosmos: A Spacetime Odyssey?  In the U.S., it airs on Sundays on Fox TV and on Mondays on National Geographic Channel. You can also see episodes online at CosmosOnTV.com. For space enthusiasts, astronomers, and others simply interested in learning more about our universe, this program is the one to see. It's the next generation of a series begun by Dr. Carl Sagan in 1980, a series that set a whole generation of astronomers and science writers on their career paths.

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Saturn May Have a New Moon

Tuesday April 15, 2014

Cassini Spots a New Object in Saturn's Rings

If you're out stargazing over the next few months, at some point, you will notice the planet Saturn. On these April nights, it's rising late in the evening (right now around 10 p.m. or thereabouts), so you have to stay up to find it. But, it's well worth the look. The rings alone give this planet an otherworldly and fascinating appearance.

Those of us who gaze at Saturn from our backyards aren't the only ones watching this planet. The Cassini spacecraft, which has been studying the Saturn system since 2004, has been our eyes, ears, and planetary science exploring, sending back incredible images and data.  It has sent the Huygens probe to the surface of Saturn's largest moon, Titan, returning amazing information about this weird world. Cassini has also found an ocean of salty water beneath the icy surface of the moon Enceladus, mapped the rings, and shown us the beauty of Saturn's ever-changing cloud tops. Recently, it documented the formation of a small icy object within one of the planet's outermost rings. It could be a new moon, forming from the chunks of ice that orbit Saturn and form its rings.

A possible new moon in Saturn's A ring.

A possible new moon of Saturn, discovered as part of a disturbance in Saturn's outermost A ring. Courtesy NASA/JPL-Caltech/Space Science Institute.

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