Here comes the supermoon! But wait, doesn’t that only happen around full moon? Well, not always. Every month the moon swings around Earth in its elliptical (oval) orbit. On one side of the ellipse, it’s closest to Earth and on the opposite side, farthest. When it’s at its closest point, called perigee, at the time of full moon, we call it a supermoon.
During the closest supermoons, our satellite can appear up to 30% brighter and 14% larger. Whether anyone can actually see the difference is open to debate simply because there’s no normal-distance moon nearby with which to make a comparison.
No one pays attention to first quarter or crescent supermoons even though the moon can be closest to us at those phases, too. Thanks to incessant media coverage, only full supermoons get coverage. We like full moons for all sorts of reasons. When an extra close one’s in the offing, as happens on Sept. 27 this year, that’s just one more reason to like them.
Lest crescents and quarters get short shrift I’m here to hawk this month’s supermoon. Full disclosure. Since it occurs during new moon phase on Feb. 18 you won’t see it. No one sees a new moon except when it happens to be eclipsing the Sun. But northern hemisphere skywatchers can spot the moon two days before new and just one day after new this month, and it’ll be nearly as super as on the18th.
What’s more, if you have a good view of the southeast horizon, tomorrow morning’s skinny crescent will lie near the planet Mercury low in the southeastern sky 40 minutes before sunrise. Be sure to carry along a pair of binoculars as Mercury is near “last quarter” phase and not nearly as bright as it can be.
The moon’s average distance is 240,000 miles, but tomorrow morning at 6 a.m. (CST) it will lie just 226,549 miles from Earth. At 1 a.m. Feb. 18 – the time of the invisible supermoon – it will be 4,723 miles closer. The following day the moon slides out a bit to 222,092 miles en route to a striking double conjunction with Mars and Venus on Friday the 20th.
Even though we won’t see February’s supermoon, our planet will sense the difference. The additional gravitational force exerted by the close moon will make for unusually high tides. High tides occur when the Sun, moon and Earth are all in a line as they during both new moon phase and at full moon.
So tomorrow morning you can catch the moon near Mercury at dawn, and on Thursday the 19th you’ll have the chance to enjoy the delicate grin of a one-day-old crescent in the west at dusk. Finally, on Friday, don’t miss the close conjunction of the moon with Mars and Venus.
Our satellite has a busy schedule this week!