Lunar Phases

Waxing, waning, first quarter, gibbous Moon, half Moon, full Moon, third quarter, waning Moon – the vocabulary for the different phases of the Moon can be and is daunting and confusing. Since sighting and observing the Apollo landing sites is dependent on the phase of the Moon for best views, it is best to review and clarify the various terms.

1. The Crescent Moon can be seen in the first 5 days after the New Moon. The line that differentiates the sunlit Moon and the dark shadowed Moon is known as the terminator (the reader can insert their own sci fi movie joke here). The crescent moon also represents the waxing phase of the Moon, with waxing describing the gradual illumination towards the full Moon. During the waxing phase of the Moon, the terminator begins on the eastern edge of the Moon and on subsequent days proceeds westward. The crescent Moon is a very attractive phase of the Moon, with deep shadows from the mountains and within craters. Look for the peaks of lunar mountains being illuminated while the lower elevations are still enshrouded in darkness. However, this early phase is of little interest to the observer seeking to discover the Apollo landing sites, since none are illuminated by sunlight at this time.

2. The next 3 days, days 6, 7, and 8, are the half Moon phase. This term is clearly named as half of the Moon being illuminated by sunlight. Confusingly, this phase can also be referred to as the first quarter. The lunar cycle proceeds from new Moon, first quarter, full Moon, last Quarter, and back to new Moon. The Moon is still waxing towards full. This is when the first opportunity is provided to view the Apollo landing sites. The earliest Apollo site to be clearly visible is the Apollo 17 on day 6, although sometimes Day 5 provides a glimpse. By Day 8, all Apollo landing sites with the exception of Apollo 12 can be seen during this half Moon phase.

3. Days 9 through 11 represents the gibbous Moon, which for all intents and pur­poses means more than half but less than full. The Moon is still waxing towards a full Moon. By now all the Apollo sites are visible to the earthbound observer. For amateur astronomers, the lead up to the full Moon is the best observing period since the terminator (the line separating sunlight lit and dark) provides shadows that can provide a 3D effect in lunar observations.

4. The Full Moon on days 12-16 are obviously days for locating the Apollo sites, although the full Moon can appear very bright. The brightness of the Moon will not damage the viewer’s eyesight (never look at the Sun unless properly equipped.), although some personal comfort benefits can be gained from using neutral density filters or polarizing filters to calm down the brightness of the moonlight. Because of the lack of shadows, the Moon tends to look a little flat from the direct reflection of sunlight and the lack of shadows.

5. The last 2 weeks of the lunar phases represent the Waning Moon, as the Moon passes through from Full, to waning gibbous, to half or Last Quarter Moon, to waning crescent. After the Full Moon, the terminator moves towards the western limb of the Moon. Like the waxing Moon, the waning Moon can afford very pleasing views cause of increasing amounts of dark shadows from the mountains and in the craters. Although the Apollo landing sites are observable during the waning Moon, but disappear in reverse order of their appearance during the wax­ing phase. The waning phases appear between midnight, gradually towards dawn, when most of us are asleep. Those readers with insomnia are invited to enjoy the still and quiet of these early a. m. hours and enjoy lunar observing.