Sunday’s supermoon is closest of 2015


Most "super" supermoon of 2014 on August 10 Read more
Most "super" supermoon of 2014 on August 10 Read more

TONIGHT FORSEPTEMBER 26, 2015

Moon Phase
Moon Phase
Courtesy U.S. Naval Observatory

Above image contrasting largest and smallest full moons: Stefanao Sciarpetti
There are many superlatives to describe the September 27-28, 2015 full moon. It’s the biggest, closest and brightest supermoon of the year. In the Northern Hemisphere, this full moon enjoys the title of Harvest Moon. Last but hardly least, this supermoon will feature a total eclipse of the moon, visible on the night of September 27-28 from the Americas, the Atlantic, Greenland, Europe, Africa and the Middle East.
This post focuses on closest supermoon aspect of this fascinating, upcoming full moon. For eclipse info, look here.
The moon will reach the crest of its full phase on September 28, 2015 at 2:51 UTC. At North American’ time zones, the moon will turn full on September 27 at 11:51 p.m. ADT, 10:51 p.m. EDT, 9:51 p.m. CDT, 8:51 p.m. MDT, 7:51 p.m. PDT.
It’ll reach perigee – the moon’s closest point to Earth for this month – within an hour of that time. Thus it’s the closest full moon of the year, and appears largest (to extremely careful observers) and brightest in our sky. This happens to be the moon’s closest encounter with Earth for all of 2015, period. The moon won’t be so close to Earth again until the full moon of November 14, 2016.
We astronomers call this sort of close full moon a perigee full moon. The word perigeedescribes the moon’s closest point to Earth for any given month. Four years ago, when the closest and largest full moon fell on March 19, 2011, many used the term supermoon, which we’d never heard before. In the following years, we heard this term again to describe the year’s closest full moon on May 6, 2012, and again on June 23, 2013 and yet again on August 10, 2014.
Now the term supermoon is being used a lot. Last month’s full moon – on August 29, 2015 – was also a supermoon. But the September full moon is even more super! In other words, the time of full moon falls even closer to the time of the moon’s closest point to Earth.
What does supermoon mean exactly? And how special is the September 27-28, 2015 supermoon? Follow the links below to find out.
What is a supermoon?
How super is this supermoon?
How often is moon both full and closest to Earth?
Will the tides be higher than usual?
Does a supermoon have a super effect on us?
View larger. | Astronomers say you can't really tell the difference in size between a supermoon and any other full moon.  Check out this size comparison from our friend Alec Jones in the UK.
View larger. | Astronomers say you can't really tell the difference in size between a supermoon and any other full moon. Check out this size comparison from our friend Alec Jones in the UK.

View larger. | Astronomers say it’s tough to notice the difference in size between a supermoon and any other full moon. But photographs show it. Check out this size comparison from our friend Alec Jones in the UK.
The supermoon of March 19, 2011 (right), compared to an average moon of December 20, 2010 (left).  Note the size difference. Image Credit: Marco Langbroek, the Netherlands, via Wikimedia Commons.
The supermoon of March 19, 2011 (right), compared to an average moon of December 20, 2010 (left). Note the size difference. Image Credit: Marco Langbroek, the Netherlands, via Wikimedia Commons.

The supermoon of March 19, 2011 (right), compared to an average moon of December 20, 2010 (left). Note the size difference. Image via Marco Langbroek, the Netherlands, via Wikimedia Commons.

What is a supermoon? The word supermoon didn’t come from astronomy. Instead, it came from astrology. Astrologer Richard Nolle of the website astropro.com takes credit for coining the term supermoon. In 1979, he defined it as:
  • …a new or full moon which occurs with the moon at or near (within 90% of) its closest approach to Earth in a given orbit (perigee). In short, Earth, moon and sun are all in a line, with moon in its nearest approach to Earth.
By this definition, according to Nolle:
  • There are 4-6 supermoons a year on average.
That doesn’t sound very special, does it? In fact, the September 28 full moon lines up much more closely with perigee – the moon’s closest point to Earth – than Nolle’s original definition, which allows for a fairly wide latitude between full moon and perigee. The 2015 September full moon happens only about one hour after the moon reaches perigee, the moon’s closest point to Earth for this month and year. At perigee, the moon lies only 356,877 kilometers (221,753 miles) away. Two weeks before, on September 14, the moon swung out to apogee – its farthest point for the month and year – at 406,464 kilometers (252,565 miles) distant.
Day and night sides of Earth at instant of the September 28 full moon
Day and night sides of planet Earth at the instant of the September 2105 full moon (2015 September 28 at 2:51 Universal Time). You have to be on the nighttime side of Earth to see the moon at the instant that it turns full, at which time it'll be totally eclipsed by the Earth's dark shadow.
Day and night sides of planet Earth at the instant of the September 2105 full moon (2015 September 28 at 2:51 Universal Time). You have to be on the nighttime side of Earth to see the moon at the instant that it turns full, at which time it'll be totally eclipsed by the Earth's dark shadow.

Day and night sides of planet Earth at the instant of the September 2105 full moon (2015 September 28 at 2:51 Universal Time). You have to be on the nighttime side of Earth to see the moon at the instant that it turns full, at which time it’ll be totally eclipsed by the Earth’s dark shadow.

How super is this supermoon? September 28 presents the moon’s closest encounter with Earth until November 14, 2016. The full moon on November 14, 2016, will will feature the closest full moon (356,509 kilometers) until November 25, 2034 (356,448 kilometers)! Maybe this helps you see that supermoons – while interesting – are fairly routine astronomical events.
Even the proximity of full moon with perigee isn’t all that rare. The extra-close moon in all of these years – 2011, 2012, 2013, 2014, 2015 and 2016 – finds the full moon taking place at or nearly the same hour as lunar perigee. More often than not, the closest perigee of the year (sometimes called proxigee) comes on the one day of the year that the full moon and perigee most closely coincide. (See table below.)
Moon closest to Earth

Year
Date
Distance
2011
March 19
356,575 km
2012
May 6
356,955 km
2013
June 23
356,991 km
2014
August 10
356,896 km
2015
September 28
356,877 km
2016
November 14
356,509 km
How often is moon both full and closest to Earth? Closest full moons recur in cycles of 14 lunar (synodic) months, because 14 lunar months almost exactly equal 15 returns to perigee (moon’s closest point to Earth). A lunar month refers to the time period between successive full moons, a mean period of 29.53059 days. An anomalistic month refers to successive returns to perigee, a period of 27.55455 days. Hence:
14 x 29.53059 days = 413.428 days

15 x 27.55455 days = 413.318 days
This time period is equal to about 1 year, 1 month, and 18 days. The full moon and perigee will realign again on November 14, 2016, because the 14th full moon after the 2015 September 28 full moon will fall on that date.
Looking further into the future, the perigee full moon will come closer than 356,500 kilometers for the first time in the 21st century (2001-2100) on November 25, 2034 (356,446 km). The closest full moon of the 21st century will fall on December 6, 2052 (356,425 km).
For the moon to come closer than 356,400 kilometers (221,457 miles) is quite a feat. In fact, this won’t happen at all in the 21st century (2001-2100) or the 22nd century (2101-2200). The last time the full moon perigee swung this close to Earth was on January 14, 1930 (356,397 km), and the next time won’t be till January 1, 2257 (356,371 km).
external image ocean_tide_430.jpg
Will the tides be higher than usual? Yes, all full moons bring larger-than-usual tides, and perigee full moons bring the highest (and lowest) tides of all. Each month, on the day of the full moon, the moon, Earth and sun are aligned, with Earth in between. This line up creates wide-ranging tides, known asspring tides. High spring tides climb up especially high, and on the same day low tides plunge especially low.
The extra-close full moon accentuates these monthly (full moon) spring tides all the more.
If you live along a coastline, watch for high tides caused by the September 28 perigee full moon – or supermoon – over the next several days. Will the high tides cause flooding? Probably not, unless a strong weather system moves into the coastline where you are. Still, keep an eye on the weather, because storms do have a large potential to accentuate high spring tides.
As a result, if you live near a coast, you’ll want to be on the lookout for higher-than-usual tides.
Because the moon – as always – shines pretty much opposite the sun at the vicinity of full moon, you’ll see the moon beaming all night tonight from dusk until dawn. This extra-close full moon is likely to usher in large tides along the ocean shorelines for the next several days, especially if these high tides are accompanied by strong onshore winds.
Bottom line: The full moon of September 28, 2015 is the closest and largest full moon of this year. By a new definition – one that has entered the world of astronomy from astrology – many will call it a supermoon. There are three full moons in 2015 that meet the definition of a supermoon – August, September and October. But this September 28 full moon is the mostsuper of the supermoons! A super-duper moon!
Looking for a tide almanac? EarthSky recommends . . .
Each full moon has its own name. Here’s a list.Supermoon informational texthttp://earthsky.org/tonight/most-super-supermoon-of-2015-on-september-28