CHAPTER 7

CONDUCTING A MOON BLINK

The following are the steps to take when conducting a Moon Blink for the detection of color events on lunar features.

The technique requires the use of a device using two filters. The Wratten #25 red and the Wratten #38a blue filter. You want the filters placed so that you can alternate rapidly between them for comparisons of lunar features under the prospective colors. This technique allows for faintly colored glows to appear as flickering spots, bright in its own color and dark in its complementary color. This technique requires practice and good eye and hand control. I have developed the technique of holding both filters in my right hand between the middle and index finger and moving these back and forth in front of the telescope eyepiece. I have found this to be as effective as some of the mechanical devices that others have built.


The thing that is important about a Moon Blink is the ability to determine if the color event being observed is spurious or is taking place on the Moon. If it is spurious it is being caused by local atmospheric conditions and is not a true lunar phenomena. Also color events caused by atmospheric conditions will also be covering a wide area on the Moon. If the color is positive and not spurious origin, a reaction as a blink should take place and the feature will exhibit a lightening or a darkening when seen through one filter. If you experiment with your two filters on objects around your home you will find that articles that are red will appear pale in the red filter and darker in the blue. So if a true red event is taking place the phenomena will appear as a dark patch in the blue filter. "As a red filter will tend to suppress a red event and a blue filter will not, the well-known persistence of vision effect come into play, and a faint red patch on the Moon may show up as a 'blinking spot' hence the name." Patrick Moore New Guide to the Moon.

I remember during one observing session I had using this technique I saw five dark spots around the crater Aristarchus while viewing with the blue filter. These spots would disappear when the red filter was placed in front of eyepiece. I have not had this same reaction in that region since that time and continue to monitor the area around Aristarchus.

According to Peter Foley of the British Astronomical Society there are several areas on the Moon that create a blink reaction naturally. These regions are the southwest quadrant of Fracastorius and part of the west wall of the crater Plato.

The most important thing that you can do to become proficient with this technique is to practice using the filters during each observing session. Conducting practice blinks on a formation known for this kind of reaction will also help you become more proficient.

The use of the Moon blink can be an effective way to help detect L.T.P. taking place on the Moon, it can be as sophisticated as placing a rotating wheel in the light path of your eyepiece to as simple as holding two filters in your finger and moving them back and forth. Whatever way you do it, the key is to do it during every observing session, and to become familiar with the filter reaction your target crater goes through.