Why doesn SDSS have data for well-known visible stars (Sirius, Vega, etc.)?
The SDSS has a very sensitive camera. Stars that you can see with your unaided eyes are a little too bright for the SDSS’s camera, so they show up as washed out. The SDSS still gets an image of those stars (for example, here is Pollux – link opens in a new window), but their images are unreliable, and the SDSS gets no catalog data.
