If you need more than a full moon to get you outside with your eyes on the sky, this full moon is also a supermoon. Maybe. It’s kind of a controversy.
Astrologer Richard Nolle defined a supermoon, and the term has really taken off. Sometimes it seems as if every moon is a supermoon. (If everything is super, nothing is super.) Nolle said that a supermoon is a new or full moon that occurs when the moon is within 90 percent of its closest approach to Earth in a given orbit.
Long story short, Nolle has a list of all supermoons, and so does the former NASA astrophysicist Fred Espenak, but their lists disagree. Espenak’s list includes an extra supermoon in 2016 — this month’s harvest moon. EarthSky has a great explanation on why these lists differ. Strangely enough, Espenak’s list seems to meet Nolle’s original definition more than Nolle’s list does.
If you need even more of a reason to go sky-gazing, check out the bright Venus (-3.9 magnitude) early in the evening. Look to the west-south; the bright star Spica is under Venus, to the planet’s left. In the same neighborhood, the reddish Mars and the ringed Saturn in the south-southwestern sky. Both are bright, about 25 degrees up from the horizon, around 7:45 p.m.
Europe won’t need any more reason to look up at the Friday night sky than the penumbral lunar eclipse. For those in North America, you can still catch all of the shadowy eclipse action on slooh.com, with play-by-play and commentary Friday afternoon.
Officially, the eclipse starts at 12:54 p.m. Eastern time and ends at 4:54 p.m., notes Espenak. The deepest part of the eclipse will be at 2:54 p.m. Eastern Time (6:54 p.m. GMT). This is a deep penumbral eclipse, he said, as it has a strong penumbral eclipse magnitude of 0.9080. It will last about a half-minute shy of four hours.
What is a penumbral lunar eclipse? It occurs when the moon appears to scoot through the lightest portion of Earth’s shadow. Earthlings must remember that our own planet casts a shadow into space. The center of the shadow is the umbra, so when the moon passes through the umbra, we get partial and total lunar eclipses. In this case, the moon sashays through the penumbra; it’s a weaker, lighter shadow. Think archery target: umbra is the center, and the penumbra surrounds it.
As all eclipses belong to a family or series of eclipses, this event belongs to Saros 147 — a fairly young one that started in 1890 — and the series runs through 3134. Friday’s eclipse will be the eighth among 70 events. This is the last penumbral eclipse in the series for about 1,000 years. For the first totally awesome total lunar eclipse in this series, circle June 6, 2449, on your calendar.