A moon filter is especially useful for visual astronomers to reduce glare, irradiation, and any excess image brightness while observing the lunar surface. You will notice that it will also improve the overall contrast between lunar albedo features. This green moon filter can screw directly into the barrel of most 1.25" eyepieces. You may be asking -- why is this filter green? This green hue cuts the glare of the brightly-lit Moon, while improving contrast so it is easier for you to see faint details that may otherwise be washed out by the Moon's bright surface.