A few months ago, I was driving home along the waterfront in the San Francisco Bay Area, and looked up to see a huge moon glistening over the water. It was a stunning sight, a seemingly gigantic glowing orb reflected its soft white light into the deep blue, rippling waves.
The impressive sight happened to be a supermoon or a mega moon, which happens when a full moon is closest to Earth.
On November 14, 2016, we’ll have the chance to see another supermoon, except this time, the moon will be the closest it’s been to our planet since January 26, 1948.
What is a Supermoon?
The moon is the only natural satellite that orbits planet earth. The moon orbits the earth fully about once every 29 days.
That orbit is an oval or elliptical shape, so sometimes the moon comes closer to earth than at other times. That means that every two weeks, the moon is either at its furthest, or at its closest to the earth, depending on where it is in that orbit.
Because of the elliptical path the moon takes around the earth each month, the distance between the earth and moon varies between approximately 357,000 kilometers (222,000 mi) and 406,000 km (252,000 mi).
That difference of about 30 thousand miles makes the moon appear to vary in size and brightness. When the moon is closer to us, it looks bigger. At its closest point, the moon appears 14 per cent bigger, as well as 30% brighter than a normal moon, because more of the moon’s surface reflects light towards us.
When the moon is in a full moon stage, this phenomenon is known as a supermoon.
The scientific term for the closest point of the moon to the earth is perigee-syzygy, the furthest point is known as the apogee.
The term supermoon was first coined by astrologer Richard Nolle, who used the term to describe “… a new or full moon which occurs with the moon at or near (within 90 per cent of) its closest approach to Earth in a given orbit”, according to earthsky.org.
On Monday, November 14, 2016, the moon will be about 50,000 km (30,000 miles) closer to Earth than on October 31, 2016, its most recent apogee. It will also be a full moon that presents the closest supermoon since 1948, by about 30 miles.
Why this is a special Supermoon
Supermoons are fairly frequent, there are six supermoons in 2016. After the supermoon on November 14, the next supermoon will be on December 14, 2016.
This moon is particularly special because it will appear slightly larger than it has in decades because of the coincidence of the timing of the full moon and the perigree event. The moon will reach fullness just three hours after perigee on November 14. Because perigee and the full moon are so closely timed, this full moon will be the largest (relative to our perspective on Earth) since 1948.
According to NASA, the closeness of this particular astronomical event will not reoccur until November 25, 2034.
Robin Scagell, vice-president of the Society for Popular Astronomy, said: “It will be above rooftops and trees and chimneys and always appears bigger that way because you’re comparing it to foreground objects.
“I’m always pleased for people to get their binoculars out and look up at the craters and the seas.”
As well as being closer and brighter, the moon will also appear to be orange-red when it first rises. The earth’s atmosphere scatters light, which causes the orange-red hue of the lower moon. When the moon is closer to the horizon, moonlight passes through much more atmosphere than when the moon is above us or directly overhead. As the moon continues to rise in the sky, it returns to its normal whitish-yellow color.
— NASA (@NASA) November 13, 2016
The November 14th supermoon is expected to reach the peak of its full phase on the morning of Monday, Nov. 14, at 8:52 a.m. EST (13:52 GMT), but to the casual observer, it will still appear to be a full moon the day before and the day after the main event.
The Slooh Community Observatory will offer a live broadcast for November’s full moon on Nov. 13 at 8 p.m. EST (0100 GMT on Nov. 14). You can also watch the supermoon live on Space.com, courtesy of Slooh.
If you can’t wait, and want to see the Mega Moon this evening, November 13, you can watch it streaming live courtesy of slooh.com.
If you miss it, the next supermoon will be in December 2017.