Learning how to Observe Lunar Features


by Pat Browne

To learn how to observe the moon, you need a good guide, almost a companion, that can take you through the heights, depths, and breadth of lunar features which  sunlight and shadows throw into relief .Such a companion is Isabel Williamson’s guide The Williamson Lunar Observing Guide.  It is a compendium of both lunar science and educational tools for learning how to observe the lunar features.

Pick any one of the features in the guide from what you can see through the eyepiece. Most nights, the strip of lunar terrain just to the east of the sunrise terminator is your main hunting ground. For example, let’s say you are observing on April 29, 2017. First Quarter occurs on May 2 (Q-Day 0), so April 29 would be Q-Day –3. Accordingly, try to look for features in the Q-Day range –3 to –4: the Sea of Fertility (–4 E); the Rheita Valley (–4 S), the Taurus Mountains (–3 N), and the Pyrenees Mountains (–3 S); and the craters Newcomb (–4N), Macrobius (–4 N), Taruntius (–4 E), Atlas (–3 N), Hercules (–3 N), Cook (–4 E),Fractasorius (–3 S), and Piccolomini (–3 S). Note that some features may lie right on the terminator or even in shadow to the west, in which case you will want to observe these the following night. – above courtesy RASC Observe the Moon resources

… and find the corresponding  map Online version of Antonin Rukl’s Atlas of the Moon

Make sure you write down your observations. You can use the the Williamson forms provided. “R” means required observations and “C” means Challenging targets. You only need to do the “R” ones to get a lunar certificate from the program. As noted I did not see the smaller craterlets inside Cassini – which could be a function of lunar libration because the features were still in shadow.

For each feature you can fill in these  Williamson Forms

These drawings made by Galileo date from 1610 – 400+ years marking the beginning of lunar science based on telescopic observations.

The shadows at the terminator have long been used to estimate mountain heights…

To understand how these craters were formed check out: Evolution of the Moon – The Late Heavy Bombardment – courtesy Lunar Reconnaissance Orbiter Team (NASA)

For more information on Lunar Science check out our Millstone Night Sky – Lunar Science