Telescope filters are a great way to better observe planets. Color filters allow backyard astronomers to see certain features easier because they exaggerate brightness differences (contrast). So, when you use a telescope filter, expect to see differences in brightness rather than color changes on the planet or in its clouds.

Manufacturers label color filters along their circumferences. To use one, screw it into the eyepiece’s barrel. All eyepiece filters have threads that match the threaded inside barrels of eyepieces.

All color filters work better with larger telescopes. It’s a simple rule of light throughput. For example, a #47 (violet) filter used with a 4-inch telescope to see cloud features on Venus just won’t work. The filter transmits only 3 percent of the light hitting it. However, the same filter used with a 12-inch scope easily reveals features.

Here is a simple guide on telescope color filters and the light they transmit:

• #8 Light yellow: 83%
• #11 Yellow-green: 78%
• #12 Yellow: 74%
• #15 Deep yellow: 67%
• #21 Orange: 46%
• #23A Light red: 25%
• #25A Red: 14%
• #38A Dark blue: 17%
• #47 Violet: 3%
• #56 Light green: 53%
• #58 Green: 24%
• #80A Blue: 30%
• #82A Light blue: 73%