One area of study that has been neglected by many observers is the examination of the earthshine region of the Moon. This area of the Moon is a major source of lunar transient phenomena reports over the centuries. The most exceptional account took place on the crescent Moon on 26 November 1540. A woodcut of the crescent Moon done in Worms, Germany shows a star between the eyes of the man in the Moon. This event was observed by the naked eye, and extremely bright to be commemorated with the effort of a woodcutting. This is only one of dozens of such accounts of star like lights, glowing spots, and other unusual illuminations being witnessed in the earthshine region. Observers even in modern times have reported seeing the crater Aristarchus glowing in the earthshine without optical aid.

When making a study of the earthshine region one quickly finds that certain periods of the year are more favorable for observation than others. This is apparent when you see the crescent Moon high in the west at its most northerly inclination. If the Moon is in the southwest it is very difficult to get a good view of the earthshine due to atmospheric extinction. Obstructions also along the horizon can prevent a successful program. I have found that my western horizon has become overgrown with trees that make it very difficult to see the early crescent Moon. When conducting earthshine studies it may be necessary to make a road trip to the observing site that provides the best view. If this is the case for you as it is for me you may want to secure a portable and easily deployable telescope to make the observing session a convenient outing and not logistical nightmare.

When I began my study of the Moon's earthshine it became apparent to me that I could give a standard value to its intensity of brightness, similar to what is used during the total eclipse of the Moon. I decided to establish a scale range from 0 to 5, with the darkest earthshine being 0 and the brightest being 5. My description for different levels of brightness was established after several years of reviewing my observing journals.

0: Earthshine region is very opaque with no features visible on the disk, even at the limb of the Moon. Nothing can be seen using binoculars or telescope.

1: Earthshine region is very opaque with no features visible on the disk, except along the limb of the Moon. Features such as Grimaldi and Mare Crisium can be detected but very little else can be seen.

2: Earthshine region is dusky in appearance and many of the darker Maria is visible. No bright craters, features, or rays are visible. The Moon disk stands out in the night sky and can be detected with the naked eye.

3: Earthshine region is bright with Maria plainly visible. Limb brightening may be visible. Bright craters like Aristarchus, Copernicus, and Kepler are visible.

4: Earthshine region intense with all lunar formations easily visible. The Maria is dark and defined on the lunar disk. The brighter craters stand out with great clarity. The ray structure is very evident. Earthshine can be easily observed with entire disk of Moon in eyepiece field of view. Glare from illuminated portion of Moon has no effect on the intensity of the earthshine. The earthshine stands out with great clarity to the night sky using the naked eye only.

5: Earthshine region extremely bright with craters like Aristarchus, Copernicus, and Tycho visible to the naked eye. Many small craters appear as star like points in the telescopic view. Low albedo features stand out with great clarity. There is no effort to seeing small details. Earthshine is very intense to the naked eye and no optical device is needed to see all formations.

Image taken by David O. Darling