The Sloan Digital Sky Survey camera has five filters. Filters are pieces of glass that let in only certain colors of light. So the camera sees every sky object in five colors.
The first filter is u, or ultraviolet. Ultraviolet light is the invisible light that causes sunburns. The next two filters are green and red, called g and r. These are colors you see every day. The last two filters are “infrared light” filters called i and z. You can’t see infrared light, but you can feel it as heat from a stove or fireplace.
The brightness of a sky object is called its magnitude. The higher the magnitude, the fainter the object! That scale might seem backwards to you, but astronomers have used it for thousands of years.
You can use SkyServer’s Navigation tool to look up the magnitude for any of SkyServer’s hundreds of millions of objects. Click Next to find out how.