DR2 Projects
     - Hubble Diagram
     - Color
     - Spectral Types
     - H-R Diagram
     - Galaxies
     - Sky Surveys
     - Quasars
     - Image Processing
 For Kids
 Games and Contests
 Links to Others
 Colors of SDSS stars
 Amounts of Light
 What is Color?
 SDSS Filters
 Light from Stars
 Radiation Curves
 Peak Wavelengths
 Color-color Diagrams
 Making a Diagram
 Diagram for SDSS
 Other Objects
 Color in Research
 Your Results

SDSS Filters


Wavelength (Angstroms)

Ultraviolet (u)


Green (g)


Red (r)


Near Infrared (i)


Infrared (z)


Knowing that the color of a star is related to the wavelength of light it gives off lets you understand the meaning of the SDSS's color filters. Each filter is designed to let in light around a specific wavelength. The filters work by blocking out light at all wavelengths except those around the wavelength they are designed to see. The table to the right shows the wavelengths at which SDSS's five filters work the best. The sensitivity of each filter falls off slowly at shorter and longer wavelengths.

If you know the wavelengths of the SDSS filters and the amount of light a star emits in each filter, you could make a crude plot of the amount of light a star emits at different wavelengths. But what if, instead of five filters between 3543 and 9134 Angstroms, you had a hundred filters? Or a thousand? You would get a clearer, more refined graph of amount of light and wavelength. Eventually, you would be able to see exactly how much light a star emitted at all the wavelengths of the electromagnetic spectrum.

Actually, astronomers do have a tool that lets them see how much light a star gives off as a function of wavelength. You'll learn about this tool, called an observed spectrum, later in this Project. But for now, think about how such a graph might look.

Question 1. If you made a graph of amount of light as a function of wavelength for some of the red stars you saw in Explore 1, what do you think the graph would look like? What about the blue stars?