This weekend, the media will proclaim a SuperMoon. You can’t blame them; NASA sent out a press release saying that the Full Moons of July, August and September are all SuperMoons. By that, they meant that the Moon’s monthly closest approach to Earth coincides with the Full Moon – and does so three months in a row.
By this reasoning, we are about to see a SuperMoon. On top of that, it’s the Harvest Moon as well: A harvest SuperMoon. Or a super Harvest Moon. Well, something’s coming up, so let’s see exactly what it is.
A month ago, on August 10, the closest Moon in 2 ½ years landed on the very same hour that the Moon was full. That was truly special, and many people enjoyed watching that enormous Moon rise just after sunset. This month, however, things are a little different. The Moon’s perigee, or monthly close approach, happens on Sunday night, September 7, at around midnight.
This time it’s not a particularly noteworthy perigee, but the fifth-closest approach of the Moon this year. Moreover, unlike last month, the Full Moon doesn’t happen the same hour or even the same night as the perigee. It’s a full day later, on Monday night. So many astronomy organizations are scratching their heads and wondered why NASA’s calling this a “SuperMoon.” Worse, NASA said (unless it has recently retracted it) that it would happen on Tuesday night, which is just plain wrong.
So, putting it all together, on Monday night we will see a Full Moon that is larger than usual, but not extraordinarily so. It will have reached its monthly close approach a night earlier.
But how could NASA in its press release have said that this Moon would be on Tuesday? It made this mistake because someone there apparently looked up when the Moon will be full using universal time or UTC, which is 1:38 a.m. Tuesday morning, and that planted the word “Tuesday” in someone’s mind. But it’s really a little after midnight on Monday night.
Using our own time zone, EDT, the Full Moon happens at 9:38 p.m. Monday night. By Tuesday night the party is long over. It will be interesting to see which major media sources proclaim Tuesday night as the SuperMoon.
The next issue is the Harvest Moon business. This is the most famous Full Moon of the year. It is defined as the Full Moon closest to the Autumnal Equinox. Now, it’s a close call this year – closer than we’ve had in a long time. The Equinox occurs on September 23 (my sister’s birthday: Happy birthday, Jane). Full Moons are 29 ½ days apart. If you do the math, the September 8 Full Moon is just about as close to the Autumnal Equinox as the next one, on October 8. (That’s using Eastern Time for both dates.) However, the one coming up this Monday night is slightly closer: It’s 14 versus 15 days. And there can only be one winner.
So this Monday night is the Harvest Moon – a harvest SuperMoon, if you like. Watch it rise due east, just after sunset.
Want to know more? To read Bob’s previous “Night Sky” columns, visit our Almanac Weekly website at HudsonValleyAlmanacWeekly.com.