As the Moon orbits Earth, its changing geometry with respect to the Sun produces the characteristic phases. This composite image is a mosaic made from 25 individual photos of the Moon and illustrates its phases over one synodic month. For complete details about this image, see Moon Phases Mosaic. The individual images included in this composite can be found in the Moon Phases Gallery. For more composites, see Moon Phases Mosaics. Photo copyright 2012 by Fred Espenak.
We tend to take the Moon for granted but it shares a unique history with Earth. Shortly after its formation 4.5 billion years ago, “proto-Earth” collided with a Mars-sized object called Theia. Much of “proto-Earth” and Theia merged to become our Earth, but the impact also ejected a large amount of material into space. Some of it coalesced to become the Moon (see: Giant Impact Hypothesis).
The Moon’s orbit stabilizes the axial tilt of Earth, preventing it from undergoing chaotic variations that would lead to catastrophic changes in climate. And the daily rise and fall of the Moon-induced tides has left an indelible imprint on Earth. Some scientists even argue whether life on Earth would be possible without the influence of the Moon (see: Without the Moon, Would There Be Life on Earth?).
With this big picture in mind, we gain a new appreciation for the Moon as we watch its phases, cycles, and motions during 2016.
As the Moon orbits Earth, its changing geometry with respect to the Sun produces the Moon’s characteristic phases (New Moon, First Quarter, Full Moon and Last Quarter). One orbit of the Moon relative to the Sun (the synodic month) has a mean duration of 29.53 days.
Moon Phases for 2016 (GMT)
New Moon First Quarter Full Moon Last Quarter
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Jan 2 05:30
Jan 10 01:31 Jan 16 23:26 Jan 24 01:46 Feb 1 03:28
Feb 8 14:39 Feb 15 07:46 Feb 22 18:20 Mar 1 23:11
Mar 9 01:54T Mar 15 17:03 Mar 23 12:01n Mar 31 15:17
Apr 7 11:24 Apr 14 03:59 Apr 22 05:24 Apr 30 03:29
May 6 19:30 May 13 17:02 May 21 21:15 May 29 12:12
Jun 5 03:00 Jun 12 08:10 Jun 20 11:02 Jun 27 18:19
Jul 4 11:01 Jul 12 00:52 Jul 19 22:57 Jul 26 23:00
Aug 2 20:45 Aug 10 18:21 Aug 18 09:27 Aug 25 03:41
Sep 1 09:03A Sep 9 11:49 Sep 16 19:05n Sep 23 09:56
Oct 1 00:12 Oct 9 04:33 Oct 16 04:23 Oct 22 19:14
Oct 30 17:38 Nov 7 19:51 Nov 14 13:52 Nov 21 08:33
Nov 29 12:18 Dec 7 09:03 Dec 14 00:06 Dec 21 01:56
Dec 29 06:53
The table above lists the date and time of the Moon’s phases throughout 2016. The time of each phase is given in Greenwich Mean Time or GMT (a.k.a. Universal Time or UT). I’ve generated a table of the Moon’s phases covering 100 years on AstroPixels.com at Moon’s Phases – 21st Century (GMT). Similar 100-year tables for other time zones include Eastern Standard Time (EST), Central Standard Time (CST), Mountain Standard Time (MST), and Pacific Standard Time (PST). To convert GMT to other time zones, visit Time Zones.
What surprises many people is that the length of the synodic month can vary by over 6 hours from its mean value of 29.5306 days (29 days 12 hours 44 minutes). The table below gives the date of New Moon, the length of the synodic month, and the difference from the synodic month’s mean value for every synodic month in 2016. For instance, the fifth synodic month of 2016 (beginning May 06) is 5 hours 14 minutes shorter than the mean while the tenth month (beginning Oct 30) is 5 hours 56 minutes longer than the mean.
Synodic Months for 2016
Date/Time of Length of Dif. from
New Moon (GMT) Synodic Month Mean Month
------------------ ------------- -----------
2016 Jan 10 01:31 29d 13h 08m +00h 24m
2016 Feb 08 14:39 29d 11h 16m -01h 28m
2016 Mar 09 01:54 29d 09h 29m -03h 15m
2016 Apr 07 11:24 29d 08h 06m -04h 38m
2016 May 06 19:29 29d 07h 30m -05h 14m shortest
2016 Jun 05 03:00 29d 08h 01m -04h 43m
2016 Jul 04 11:01 29d 09h 44m -03h 01m
2016 Aug 02 20:45 29d 12h 19m -00h 25m
2016 Sep 01 09:03 29d 15h 08m +02h 24m
2016 Oct 01 00:11 29d 17h 27m +04h 43m
2016 Oct 30 17:38 29d 18h 40m +05h 56m longest
2016 Nov 29 12:18 29d 18h 35m +05h 51m
2016 Dec 29 06:53 29d 17h 14m +04h 30m
The year 2008 had even greater extremes in the synodic month – from 5 hours 48 minutes shorter, to 6 hours 49 minutes longer than the mean value. So what causes these variations? The explanation involves the Moon’s elliptical orbit and its orientation with respect to the Sun during any given month. If New Moon occurs when the Moon is nearest to Earth (perigee), then the synodic month is shorter than normal. On the other hand, if New Moon occurs when the Moon is farthest from Earth (apogee), then the synodic month is longer than normal. Furthermore, the orientation of the Moon’s ellipse-shaped orbit slowly rotates in space with a period of about 18 years. A more detailed discussion on this topic can be found at Moon’s Orbit and the Synodic Month (EclipseWise.com). You can also find the duration of every synodic month this century at Length of the Synodic Month: 2001 to 2100 (AstroPixels.com).
Because the Moon orbits Earth in about 29.5 days with respect to the Sun, its daily motion against the background stars and constellations is quite rapid. It averages 12.2° per day. A table giving the Moon’s daily celestial coordinates throughout the year can be found at Moon Ephemeris for 2016 (AstroPixels.com). This table lists a lot of other details about the Moon including its daily distance, apparent size, libration, phase age (days since New Moon) and the phase illumination fraction.
When a Full Moon occurs within 90% of the Moon’s closest approach to Earth in a given orbit, it is called a perigee-syzygy or more commonly a Super Moon. The Full Moon then appears especially big and bright because it subtends its largest apparent diameter as seen from Earth. The table below lists the Super Moons occurring in 2016.
Super Moons for 2016
Full Moon Distance Diameter Relative
(GMT) (km) (arc-min) Distance
Sep 16 19:05 n 364754 32.76 0.934
Oct 16 04:23 358475 33.33 0.987
Nov 14 13:52 356523 m 33.52 1.000
Dec 14 00:06 359450 33.24 0.979
The Relative Distance listed in the Super Moon table expresses the Moon’s distance as a fraction between apogee (0.0) and perigee (1.0). For more information on Super Moons and a complete list of them for this century, see Full Moon at Perigee (Super Moon): 2001 to 2100 (AstroPixels.com).
Besides its obvious phases, the Moon also undergoes some additional extremes in its orbit including: Perigee and Apogee, Ascending/Descending Nodes, and Lunar Standstills. Each of these AstroPixels links covers lunar phenomena for the entire 21st Century.
One of the first projects I tackled upon completing Bifrost Observatory in 2010 was to photograph the Moon’s phases every day for a complete month. Of course, the weather doesn’t always cooperate (even from sunny Arizona) so it actually took several months to complete the project. You can see the results at the Moon Phases Gallery. Clicking on any of the thumbnails pictures will give you an enlarged image with complete technical details. You can also visit Moon Phases Mosaics to see composites showing the Moon’s phases over a complete synodic month.
The NASA/Goddard Scientific Visualization Studio has used image data from the Lunar Reconnaissance Orbiter (LRO) mission to create clever animations of the Moon’s ever changing phases and librations in 2016. The example below illustrates the Moon’s phase and libration at hourly intervals throughout 2016, as viewed from the northern hemisphere. Each frame represents one hour.
And not to be accused of northern hemisphere chauvinism, here is a version as seen from the southern hemisphere.
Besides presenting the Moon’s phase and apparent size, these videos show the Moon’s orbit position, sub-Earth and subsolar points, distance from the Earth at true scale, and labels of craters near the terminator. As the Moon orbits Earth, it appears to wobble and tip on its axis. This motion is called libration and it allows us to see about 59% of the Moon’s surface (see Libration (EarthSky)). The major cause of libration is due to our changing line of sight because of the Moon’s elliptical orbit.
Ernie Wright of the NASA Scientific Visualization Studio has also used LRO data to create a web tool called Dial-A-Moon. Enter the month, day and hour and Dial-A-Moon will generate a visualization of the Moon showing the correct phase and libration for that instant during 2016 (see Moon Phase and Libration, 2016).
The last eclipse of the Moon visible from the USA occurred on the night of Sept. 27/28, 2015. It was a total eclipse as the Moon passed completely inside Earth’s dark umbral shadow. ©2015 by Fred Espenak.
Finally, what discussion of the Moon would be complete without mentioning eclipses in 2016? There are two eclipses of the Moon and both of them are penumbral. The first occurs on March 23 and is visible from the western hemisphere. The second happens six months later on September 16 and is visible from the eastern hemisphere. Penumbral eclipses are very subtle events and often transpire without any notice (see: Visual Appearance of Penumbral Lunar Eclipses). But the 2016 eclipses are both deep penumbral eclipses so a pale shading should be visible around the time of mid-eclipse. By coincidence, the September 16 eclipse also happens to occur during a Super Moon.
Some sources identify a third penumbral eclipse on August 18. But this prediction depends on different assumptions about the size of Earth’s penumbral shadow. Even if you accept these assumptions, the eclipse barely occurs at all because only a scant 1.7% of the Moon’s diameter enters the penumbral shadow. For those who want to dig deeper into this subject, see: Enlargement of Earth’s Shadows. If such a small eclipse were to occur, it would be completely undetectable with even the largest telescopes on Earth.
There are also two solar eclipses in 2016. The first is a total eclipse on March 16 visible from Indonesia and parts of the Pacific Ocean. The second is an annular solar eclipse on September 01 visible from southern Africa and Madagascar. For complete details on all these events, see Eclipses During 2016 (EclipseWise.com).
Watching the Moon’s phases wax and wane as well as the occasional lunar eclipse can best be enjoyed with the naked eye and binoculars. And you don’t even need a dark sky since the Moon is easily visible from the heart of brightly lit cities.
The Moon phases and lunar phenomena discussed here were all generated with computer programs I’ve written (THINK Pascal and FORTRAN 90 running on a Macintosh G4 and MacBook Pro) using Astronomical Algorithms (Jean Meeus).
– Fred Espenak