December 10, 2019

Spot the Lunar High- & Low-lands with the Naked Eye!

Did you happen to notice that the Moon was fat and nearly full Halloween night? The technical full Moon for November falls today, Monday the 2nd, at 2:14 PM EST (yes we’re back on standard time now; did you get to work an hour early this morning?) Of course, the full Moon, like all phases, only occurs at an instant in time. That instant is the time that the Moon is exactly 180 degrees, or 12 hours of right ascension opposite to the Sun.

This allows the lunar surface to be nearly 100% illuminated as seen from our Earthly perspective. Standing on the near side of the lunar surface, the Earth would be at “new!” The Moon never reaches that theoretical 100% however, as when its exactly opposite, it plunges into the Earth’s shadow in what is known as a lunar eclipse. Next month, it just nicks the Earth’s shadow on December 31. This is also the second Full Moon of December, which is also known as a Blue Moon. More on that next month. This month’s Full Moon is also referred as the Hunter’s Moon, a good source of extra illumination to track illusive game by. I also want to point your attention towards a simple but often overlooked observation that can be made with the naked eye during the Full Moon. Note that the silvery white surface is also mottled with relatively darker maria. The contrast is due to the dark flat lowlands of the Moon juxtaposed against the relatively brighter mountainous highlands. Keep in mind that even though the moon appears ivory white, it was actually a dark gray place to the astronauts that traveled there. At an average albedo of 12%, the Moon has a surface reflectivity of ash or coal! This illusion only occurs because we see the minuscule amount of reflected sunlight condensed into a tiny circle, smaller than your thumb held at arms length. I think its interesting that no maps exist of the nearside of the Moon from pre-telescopic times, since astronomers certainly had a go at sketching out the blurry surfaces of the other planets that appeared less distinct than the Moon does to the naked eye! In fact, some Greeks subscribed to a school of thought that the Moon was a large mirror of some kind that reflected the surface of the Earth! Of course, it would then be hard to explain why the image doesn’t change throughout the night…I know that many deep sky observers tend to pack it in on full Moon weeks, but do give our nearest natural neighbor a glance tonight!

Speaking of which, our astro-word of the week is Lilith. Did you know that it was once proposed that the Earth might have a second moon? The idea isn’t as preposterous as it sounds; at the turn of the 20th century, astronomer George Waltemath claimed to have even sighted a mysterious Earth orbiting object transiting the Sun! In 1918, Walter Gornold proposed the name Lilith, which comes from Mesopotamian mythology. Of course, no confirmed follow up sightings were ever made, and Lilith fell into the astronomical dust bin of spurious objects. More than once in the past decade, a brief amount of excitement has been generated as a new Earth trailing asteroid has been discovered, only to turn out to be an old Saturn V booster in solar orbit. The Moon does a good job at shepherding out any temporarily captured objects; with today’s modern sky surveys, its doubtful that there exists any rocks larger than 10 meters inside the Moon’s orbit. Of course, that doesn’t exclude a wider exterior orbit…could Lilith rise again?

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