Fun with Filters

Telescopes See in Black and White...

You know those really neat color photographs you see in Astronomy books? Would you believe that that one photograph is made of at least five different pictures all overlayed to make one color image? Well it's true!

Cool Links!

The Use of Astronomical Filters - How and why astronomers use filters to view stars and planets

Hubble: Behind the Pictures - The Meaning Of Color - The different filters used by the Hubble Space Telescope

How we Visualize the Light We Can't See - A very basic overview of how images are created that our eyes normally would not be able to process

As you probably know, white light is made up of all the colors of the rainbow. Red filters filter out all light EXCEPT red light and blue filters filter out all light EXCEPT blue light.

Seeing a pattern?

Telescopes can detect white light radiating from stars billions of miles away. Filters are used to pick up detail in stars, clusters, nebulae, and even planets. As you can imagine, each picture is just a bit different based on which filter is used with the telescope. When those pictures are combined using appropriate software and tools, color images can emerge. You must keep in mind, however, that these colors may not be the same ones you would see if you were to fly by the steller object in a spaceship. So why colorize them at all?

Firstly, it's pretty and visually interesting. That is probably the most obvious answer.

Secondly, overlaying the pictures to make a color image can assist scientists in identifying trends or other visual effects they may not see as clearly in black and white photos.

Another way to observe how filters work has nothing to do with using your eyes. Confused? Maybe this activity will help.