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The Featured Collection for this issue of D-Lib Magazine is Astronomy Picture of the Day (APOD), a web site created in 1995 and edited by Robert Nemiroff, Michigan Technological University, and Jerry Bonnell, NASA/Goddard and Universities Space Research Association. The site is mirrored by fourteen other sites throughout the world, which is evidence of the wide appeal of the APOD collection of astronomy pictures.
The old cliche about "a picture being worth a thousand words" may not be true in all cases, but it is safe to say that APOD's collection of astronomy images is priceless. It was difficult to decide which ones to use to illustrate this feature because there are countless stunning images in the APOD archive from which to chooseeven when eliminating those that have copyright restrictions for further use.
Each "Picture of the Day" is annotated with an explanation of the image, and these annotations provide hyperlinks to additional fascinating information. For example, the annotation for sunspot image shown above reads:
It was a quiet day on the Sun. The above image shows, however, that even during off days the Sun's surface is a busy place. Shown in ultraviolet light, the relatively cool dark regions have temperatures of thousands of degrees Celsius. Large sunspot group AR 9169 is visible as the bright area near the horizon. The bright glowing gas flowing around the sunspots has a temperature of over one million degrees Celsius. The reason for the high temperatures is unknown but thought to be related to the rapidly changing magnetic field loops that channel solar plasma. Sunspot group AR 9169 moved across the Sun during 2000 September and decayed in a few weeks.
Be sure to follow the links in the annotation at least once to get a flavor of the wealth of information provided by APOD's editorsnot just to other information on the APOD site but to external sites as well.
Other features of the APOD site include a topical index, a search page for finding specific items of interest in the archive, a calendar where you can select a particular month from June 1995 to date and see thumbnails of every picture published that month, a glossary, and an annotated list of links to astronomy education resources. It is easy to see why APOD has received numerous accolades, including a 2001 Scientific American SciTech award. No matter how much knowledge you may have about astronomy, you're sure to enjoy visiting Astronomy Picture of the Day.
The URL for the Astronomy Picture of the Day web site is <http://apod.nasa.gov/>.
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