Supermoon Nonsense Redux: November 2016

There seems to be a growing excitement about the “Supermoon” that is due to occur on 14 November 2016, when the Moon will be at its closest to Earth in this orbit, and closer than it has been at any time since 1948.

Sure the full moon will look big and bright this Sunday evening/Monday morning, but no more so than normal. It’ll be 14% larger and 30% brighter but your eyes and brain won’t see any difference from a normal full moon. It’s still worth a look – the moon is always a beautiful thing to see – but if you notice any difference in size or brightness, it’ll be your brain playing tricks on you. Maybe the power of suggestion or the Moon Illusion.

Read on to find out why it’s not any more super than normal…

The Moon orbits the Earth in an elliptical orbit, i.e. it is not perfectly circular, and so in each orbit there is a closest approach, called “perigee” and a furthest approach, called “apogee”.

At this month’s perigee the Moon will be 356,511km away from Earth. Closer than normal, sure but only 66km closer than the “Supermoon” that began all the hype back in 2011, so not that much closer.

Let’s start by comparing it to the Moon’s average distance from the Earth, which is ~385,000km. This perigee will be ~8% closer to the Earth than average. OK, that’s a bit closer, but not significantly so.

What about comparing it to the Moon’s average perigee distance, which is ~364,000km. So this “Supermoon” will be ~2% closer to the Earth than it is most months at perigee. Wow!

The brilliant XKCD sums up the Supermoon hype nicely

So what will this mean to you? Nothing at all. The Moon will be 14% bigger in the sky, but your eye won’t really be able to tell the difference. It will also be 30% percent brighter, but your eye will compensate for this too, so altogether this “Supermoon” will look exactly the same as it always does when it’s full.

As to all of those soothsayers claiming that there will be earthquakes and tidal waves. There very well might be, but they’ll be nothing at all to do with the Moon.

Post Script

Supermoons aren’t all that rare. In fact they occur once every 13.5 months.

Thanks to Steve Bell at the UK Hydrographic Office for providing the calculations below:

The Moon orbits the Earth once every 27.321 days (called the sidereal period), but as the Earth is orbiting the Sun at the same time, the Moon’s phases appear to repeat every 29.530 days (called the synodic period, which is the time we use to derive the month).

The Moon’s orbit is elliptical (a squashed circle) and so you would expect a perigee once every 27.321 days. However the elliptical path around which the Moon orbits the Earth precesses (that is it is not fixed with the perigee occurring at the same part of each orbit; the place where perigee occurs moves, or precesses) with a period of 8.8504 years, so that perigee doesn’t occur once every 27.321 days but rather once every 27.554 days (called the anomalistic period).

To calculate the frequency of perigee full moons (“Supermoons”) you need to use the equation:

1/P(perigee&full) = 1/P(perigee) – 1/P(full)

where P(perigee) is the anomalistic period = 27.554 days, and
where P(full) is the synodic period = 29.530 days

and when you put those figures in you find that a full moon will occur at perigee once every 411.776 days (i.e. P(perigee&full)=411.776), or just less than once per year.

Leonids Meteor Shower 2012

One of the year’s regular meteor showers, the Leonids, happens this weekend, peaking at around 0930 on 17 November 2012. It (usually*) isn’t one of the very active showers (such as the Perseids, Geminids or Quadrantids), with the maximum rate in a normal year between 10-20 meteors per hour in perfect conditions.

The peak of the Leonids is quite broad, lasting several days, so between now and early next week it’s worth looking up to see if you can catch a glimpse of any shooting stars. The best time to view the Leonids shower is in the pre-dawn hours, but any time after 11pm on Thursday through to Tuesday night should mean you’ll see at least a few meteors.

How to see the Leonids Meteor Shower

1. Find somewhere dark with as little light pollution as possible. The countryside is best, but if you’re stuck in a city try and get away from as many lights as possible.
2. Bring a reclining deck chair. Standing outside looking up for long stretches of time gets uncomfortable.
3. Bring a blanket. It gets VERY cold outside at night in November.
4. Position yourself under your blanket on your reclining deck chair so that you take in as much of the sky as possible. Although the meteors all appear to radiate out of the constellation of Leo in the SE there’s no need to specifically face this direction as the meteors will streak across any part of the sky.
5. Wait. The rate of this shower isn’t very high, so you might only see one every five or ten minutes, maybe less often than that, so patience is a virtue.

* every 33 years the Leonids meteor shower turns into a meteor storm, in which the rates dramatically increase by a factor or 50 or more, up to perhaps several thousand meteors per hour. This regularity is due to the nature of the origin of the dust that causes these meteors. It comes from the tail of a comet, Comet Temple-Tuttle, which orbits the Sun once every 33 years. This means that the dust trail left behind by the comet – and subsequently hoovered up by the Earth to make a meteor shower at the same time every year – is refreshed every 33 years, resulting in a spike of activity for a few years afterward each pass of the comet. The comet last renewed the trail in 1998, and so the years 1999, 2001 and 2002 were all spectacular years for the Leonids, with storm rates peaking at 3000 Leonids per hour. I was lucky enough to see all of these showers, the most memorable being 2002 where in the space of just two hours under half-cloudy skies on the outskirts of Glasgow I saw over 300 shooting stars.

The Lowest Full Moon of the Year

Tonight (actually around 0130 tomorrow morning) the Full Moon will reach its highest point due south, just an hour and a half after the eclipse ends. Despite being at its highest in the sky, you’ll still struggle to see it, as it is very low down. In fact the Full Moon nearest the Summer Solstice is the lowest Full Moon of the Year.

Full Moon by Luc Viatour http://www.lucnix.be

First, let’s begin with the definition of “Full Moon”. A Full Moon occurs when the Moon is diametrically opposite the Sun, as seen from the Earth. In this configuration, the entire lit hemisphere of the Moon’s surface is visible from Earth, which is what makes it “Full”. There is an actual instant of the exactly Full Moon, that is the exact instant that the Moon is directly opposite the Sun. Therefore when you see timings listed for the Full Moon they will usually include the exact time (hh:mm) that the Moon is 180° round from the Sun (we call this point opposition).

Here’s a list of the times of all Full Moons between June 2011 and June 2012:

Month	Date of Full Moon	Time of Full Moon (UT)
June 2011	15 June	2014*
July 2011	15 July	0640*
August 2011	13 August	1857*
September 2011	12 September	0927*
October 2011	12 October	0206*
November 2011	10 November	2016
December 2011	10 December	1436
January 2012	09 January	0730
February 2012	07 February	2154
March 2012	08 March	0939
April 2012	06 April	1919*
May 2012	06 May	0335*
June 2012	04 June	1112*

* UK observers should add on one hour for BST

As you can see from this table, the instant of the Full Moon can occur at any time of day, even in the daytime when the Moon is below the horizon. So most often when we see a “Full Moon” in the sky it is not exactly full, it is a little bit less than full, being a few hours ahead or behind the instant of the Full Moon. I’ll refer to this with “” marks, to distinguish this from the instant of the Full Moon (they look virtually identical in the sky).

The Moon rises and sets, like the Sun does, rising towards the east and setting towards the west, reaching its highest point due south around midnight (although not exactly at midnight, just like the Sun does not usually reach its highest point exactly at noon). And like with the Sun the maximum distance above the horizon of the “Full Moon” varies over the year.

The Sun is at its highest due south around noon on the Summer Solstice (20 or 21 June) and at its lowest due south around noon on the Winter Solstice (21 or 22 Dec) (of course the Sun is often lower than this, as it rises and sets, but we’re talking here about the lowest high point at mid-day, i.e. the day of the year in which, when the Sun is at its highest point that day, that height is lowest…)

And because Full Moons occur when the Moon is directly opposite the Sun, you can imagine the Moon and Sun as sitting on either sides of a celestial see-saw: on the day when the Sun is highest in the middle of the day (in Summer), the Moon is at its lowest high point at midnight; and on the day when the Sun is at its lowest high point in the middle of the day (in Winter), the Moon is at its highest high point at midnight.

This means, in practical terms, that Summer “Full Moons” are always very low on the horizon, while Winter “Full Moons” can be very high overhead.

Here’s a table of the altitude of the “Full Moon” when due south. Remember the times in this table don’t match the exact time of the Full Moon, but instead have been chosen as the closest in time to that instant, and so have be labelled “Full Moon” (in quotes).

Month	Date of Full Moon	Time of Full Moon (UT)	Time/Date of “Full Moon” due S	Time from/since instant of Full Moon	Altitude due S (degrees)**
June 2011	15 June	2014*	0127BST 16 June 2011	+4h13m	10° 05′
July 2011	15 July	0640*	0012BST 15 July 2011	-7h28m	10° 24′
August 2011	13 August	1857*	0126BST 14 August 2011	+5h27m	19° 19′
September 2011	12 September	0927*	0049BST 12 September 2011	-9h38m	31° 49′
October 2011	12 October	0206*	0053BST 12 October 2011	-1h13m	44° 16′
November 2011	10 November	2016	0005GMT 11 November 2011	-3h49m	53° 24′
December 2011	10 December	1436	0030GMT 11 December 2011	+9h54m	56° 03′
January 2012	09 January	0730	0006GMT 09 January 2012	-7h24m	53° 36′
February 2012	07 February	2154	0031GMT 08 February 2012	+2h37m	43° 47′
March 2012	08 March	0939	0000GMT 08 March 2012	-9h39m	35° 37′
April 2012	06 April	1919*	0145BST 07 April 2012	+5h26m	21° 45′
May 2012	06 May	0335*	0102BST 06 May 2012	-3h33m	15° 20′
June 2012	04 June	1112*	0047BST 04 June 2012	-11h25m	11° 49′

* UK observers should add on one hour for BST
** The altitude here is based on my observing location in Glasgow, Scotland. You can find out how to work out how high these altitudes are here.

As you can see from this table, the highest “Full Moon” due S this year occurs at 0030 on 11 December 2011, when the Moon will be over 56° above the southern horizon (approximately the height of the midsummer mid-day Sun which culminates at 57°34′).

Compare this to the “Full Moon” this month, just after the eclipse, in the morning of 16 June, when the Moon barely grazes 10° above the horizon, and you can see just how low the midsummer Full Moon can be.

In fact the closeness of summer “Full Moons” to the horizon means that this is an ideal time of year to try and observe the Moon Illusion.

UPDATE: Here’s a very cool speeded up video of the Moon cycling through its phases, as see by the LRO spacecraft: