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Frequently asked Questions

What is SkyServer?

SkyServer is the education and outreach web site of the Sloan Digital Sky Survey (SDSS). SkyServer makes the entire survey available, free of charge, to the public. With SkyServer, you can study exactly the same stars and galaxies that professional astronomers are studying right now.

What is the Sloan Digital Sky Survey?

The SDSS is one of the most ambitious scientific projects of all time. Its goal is to make a high-quality three-dimensional map of the universe. The survey uses a specially-built 2.5-meter telescope in New Mexico, a CCD camera, and sophisticated data reduction and analysis software.

The SDSS began in June 1998. By the time it ends, the SDSS will have mapped 25% of the night sky, taking images of over 100 million objects. The survey has already completed a preliminary map of the universe: you can see the map in our First Discoveries section.

How do I get around the site?

Click one of the light or dark blue links on the main page, or click on a section of the menu bar at the top of any page.

What can I see on SkyServer?

SkyServer offers two types of data: images and spectra. Images are pictures of the night sky taken by our digital camera. Spectra are measurements of the amount of light a star or galaxy gives off at different wavelengths. SkyServer has images of more than 13 million stars and galaxies, and spectra for more than 50,000. For more on our data, see the Getting Started pages.

Where in the sky do these images come from?

Right now, SkyServer includes data in four long, narrow "stripes." Two stripes lie on the celestial equator (the Earth's equator projected in the sky) - one from ra = 145 to ra = 236, and one from ra = 351 to ra = 56. The other two stripes are diagonal stripes in the northern sky, near ra = 260, dec = 60. See the sky globe of the Navigation Tool to see where these four stripes are.

Over the next few years, we will add more data to SkyServer until we have about one-quarter of the sky covered.

How can I get all this information?

Use one of SkyServer's eight tools. Each tool is designed to access a single type of information - see the Getting Started pages for more details.

Here is a quick summary of what the most commonly used tools do. Famous Places is a gallery of beautiful SDSS images. The Navigation tool lets you point and click through the sky. The Object Explorer gives you access to complete data on a single star or galaxy. The Search tool lets you see data on all objects in a certain part of sky. Or, if you know SQL, you can use the search tool to return all objects that meet whatever criteria you can think of.

Did you get all that? The best place to start is with the Famous Places and Navigation tools. And don't worry, all the tools have Help pages.

What help is available?

SkyServer has an extensive Help section, including a Glossary and various How-To Tutorials. The Object Browser is essential for using the Search tool. SkyServer's About Astronomy and About SDSS sections also contain readings that help explain concepts from astronomy and the SDSS.

How can I use SkyServer to learn about astronomy?

SkyServer's Projects use SDSS data to interactively teach astronomy. With our Projects, you can learn about the evolution of stars, the types of galaxies, the history of the universe, and much more.

Teachers, we welcome you to use and adapt any of our projects in your classes, free of charge. For more information on what you can do with SkyServer in the classroom, see our Teacher FAQ.

Who is responsible for all this?!

See our Credits page.

Do you have other questions that aren't answered here? E-mail them to us!