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.
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).
Full Moon (UT)
“Full Moon” due S
instant of Full Moon
|Altitude due S
|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: