Astronomers would do well to teach young children about Halloween, or not. And if it’s the holiday associated with death and murder, they’ll probably want to keep a furtive watch. Even with Halloween’s general Lovecraftian resonance, the term Hunter’s Moon as some labels it might not seem a suitable metaphor for it, and others recognize what’s really at play.
If I were in charge of teaching young people about the history of Halloween, I’d also want to make sure they knew that the moon’s silhouette on the horizon at around dusk is part of what identifies it as a hunting moon, literally a constellation.
The moon is also known as a perigee moon – it passes closest to the Earth. Historically, mythologically, it’s been celebrated in some cultures as a hunter’s moon, which sounds an awful lot like a jinx in their words. It’s true that in late August, the moon is at perigee, and some insects stage mass migrations in the anticipation. As it warms up, it doesn’t get so hot, which implies that trees and small creatures might be moving around rather more than they normally do at this time of year. Oh, and it seems to have just been so cold that trees and plants were up and dying, which was bad luck.
Without getting into too much big talk, it probably means something else. When the moon passes perigee it appears closer to the horizon, and so forms a deeper shadow. When the moon is farthest from the Earth, it becomes more impressive, and can be found on the far side of the planet. This leaves September, October and November at the end of the string, during which the lunar perigee is the most dramatic. Every so often, the perigee can become catastrophic.
The basics are quite simple.
Near a constellation, the limb of the moon looks like it’s in a dark shadow, or very prominent, as it passes into the constellation. If a constellation is close to the light from the moon, it gives a clear line. The sign with a star at the top (e.g. Taurus with a Sagittarius star at the bottom) shows the position when the moon passed into the constellation. If not, then the shadow would be much narrower, making the effect look as if the moon had “lit up”.
If an area is dead, it is a Hunter’s Moon. But not exclusively. It can also happen if the moon is near a constellation when it passes on its elliptical orbit, which is the case of this October’s perigee moon.