Author Ann Finkbeiner just released a new book on the Sloan Digital Sky Survey called a Grand and Bold Thing: An Extraordinary New Map of the Universe Ushering In a New Age of Discovery. The Sloan Digital Sky Survey (SDSS) is remarkable in many ways and I am really looking forward to reading this book. Universe Today posted an interview with the author today.The SDSS was a project to use a 2.5 meter telescope (not particularly large by modern standards) to make a map of about 1/4 of the night sky using a 125 megapixel CCD camera, the largest CCD camera constructed up to that point. The telescope's unique design let it look at a fairly large chunk of sky at one time. Even though, it would take over five years to complete the survey.
But that's not all. They also wanted to take spectra of one million galaxies and 100,000 quasars. Spectra allow let us see how far away an object is and learn about it temperature and physical makeup. It can take about an hour to collect enough light to take a spectra with a telescope of that size and one million hours is a long time. Therefore, they built this spectrograph with 640 fibers so they could take 640 spectra at once. After the took an image of a section of the sky, they would decide what objects to take spectra of and drill holes into a plate. Each hole represented a galaxy, star or quasar they wanted to observe.
The SDSS so revolutionized astronomy that one of these plates is on display at the Natio
nal Air and Space Museum. At the end of the survey, they gave away plates to people who worked on it (we had to pay shipping) so one of them is on display as a table at my place. I had a fellowship at Fermilab and worked on the SDSS in 2001-2002 and visited Apache Point Observatory as well.
Another unique aspect of the Sloan is that all the data is publicly available. You can look at it yourself on the Skyserver website. This data has been used widely in research and made the SDSS one of the most widely cited projects in astronomy research.
It wasn't all smooth sailing. The project had lots of growing pains early on (some of which I witnessed firsthand) but in the end, it exceeded expectations. There is hardly an area of astronomy that hasn't been touched by the SDSS.
Just last week, the National Research Council released its Decadal Survey. Their top priority for the next decade in ground based astronomy is the Large Synoptic Survey Telescope (LSST). The LSST will be an 8.4 meter telescope with a 3.2 gigapixel camera that can survey the entire visible sky every 3-4 nights. It is a successor to the SDSS and probably would not have been so highly rated if the SDSS had not shown us how valuable sky surveys can be in science. If you need any justification for spending the money, one of its goals is to find all asteroids that might impact Earth down to a size of 140 meters in addition to a plethora of astronomy and physics questions.
The SDSS had terabytes of data: the LSST will have petabytes of data. The SDSS did large data releases about every 18 months. The LSST will make all its data available as soon as possible...as soon as 60 seconds after the image is taken for alerts that indicate a moving object, supernova, or variable star(and there could easily be tens of thousands of alerts per night).
As we embark on the next chapter of large astronomical surveys, it is great to see someone document the previous large project.Reprinted with permission from the Half-Astrophysicist Blog.
So what are the plates made out of, glass, metal? Are the holes drilled to concentrate light to a certain area? I think it is cool you were able to get one for working on the project.
ReplyDeleteI am not 100% sure of the material of the plates, but it is metal (I have a plate of glass sitting on top of it for the table surface in the picture, but that is not part of the plate).
ReplyDeleteEach hole is drilled at a specific point where the star or galaxy of interest is located. A fiber optic cable is inserted into each little hole (by hand...it's a pain, trust me!) and the cable takes the light to the spectrograph.
Now here's a neat tidbit. You might recall from high school science that substances contract when cooled and expand when heated. Well, that plate does to so those holes can move closer together or farther apart based on the temperature at the time of observation. Astronomers are clever and they knew this would happen, so the telescope was designed with a bit of a zoom feature. The telescope could zoom in or out to get the locations of the stars and galaxies to match the location of the holes no matter what the temperature was at the time of observation.
I am the proud owner of plate #2973. As I said, all the data is online and you can find all the spectra taken by my plate here. Click on any of the 640 objects to see the spectra.