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 2015 (GMT) New Moon First Quarter Full Moon Last Quarter ------------- ------------- ------------- ------------- Jan 5 04:53 Jan 13 09:47 Jan 20 13:14 Jan 27 04:48 Feb 3 23:09 Feb 12 03:50 Feb 18 23:47 Feb 25 17:14 Mar 5 18:06 Mar 13 17:48 Mar 20 09:36 T Mar 27 07:43 Apr 4 12:06 t Apr 12 03:44 Apr 18 18:57 Apr 25 23:55 May 4 03:42 May 11 10:36 May 18 04:13 May 25 17:19 Jun 2 16:19 Jun 9 15:42 Jun 16 14:05 Jun 24 11:03 Jul 2 02:20 Jul 8 20:24 Jul 16 01:24 Jul 24 04:04 Jul 31 10:43 Aug 7 02:03 Aug 14 14:54 Aug 22 19:31 Aug 29 18:35 Sep 5 09:54 Sep 13 06:41 P Sep 21 08:59 Sep 28 02:50 t Oct 4 21:06 Oct 13 00:06 Oct 20 20:31 Oct 27 12:05 Nov 3 12:24 Nov 11 17:47 Nov 19 06:27 Nov 25 22:44 Dec 3 07:40 Dec 11 10:29 Dec 18 15:14 Dec 25 11:11
The table above lists the date and time of the Moon’s phases throughout 2015. 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 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 2015. For instance, the fourth synodic month of 2014 (beginning Apr 18) is 3 hours 28 minutes shorter than the mean while the tenth month (beginning Oct 13) is 4 hours 57 minutes longer than the mean.
Synodic Months for 2015 Date/Time of Length of Dif. from New Moon (GMT) Synodic Month Mean Month ------------------ ------------- ----------- 2015 Jan 20 13:14 29d 10h 34m -02h 10m 2015 Feb 18 23:47 29d 09h 49m -02h 55m 2015 Mar 20 09:36 29d 09h 21m -03h 23m 2015 Apr 18 18:57 29d 09h 16m -03h 28m shortest 2015 May 18 04:13 29d 09h 52m -02h 52m 2015 Jun 16 14:05 29d 11h 19m -01h 25m 2015 Jul 16 01:24 29d 13h 29m +00h 45m 2015 Aug 14 14:53 29d 15h 48m +03h 04m 2015 Sep 13 06:41 29d 17h 24m +04h 40m 2015 Oct 13 00:06 29d 17h 41m +04h 57m longest 2015 Nov 11 17:47 29d 16h 42m +03h 58m 2015 Dec 11 10:29 29d 15h 01m +02h 17m
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 lies in the fact that the Moon’s orbit is elliptical. 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. You can also find the duration of every synodic month this century at Length of the Synodic Month: 2001 to 2100.
Because the Moon orbits Earth in ~29.5 days with respect to the Sun, its daily motion against the background stars and constellations is quite rapid. It averages about 12.2° per day. A table giving the Moon’s daily celestial coordinates throughout the year can be found at Moon Ephemeris for 2015. 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 Super Moon. The Full Moon then appears especially big and bright since it subtends its largest apparent diameter as seen from Earth. The table below lists the Super Moons occurring in 2015.
Super Moons for 2015 Full Moon Distance Diameter Relative (GMT) (km) (arc-min) Distance Jul 31 10:43 365112 32.73 0.930 Aug 29 18:35 358993 33.29 0.985 Sep 28 02:50 t 356878 m 33.48 1.000 Oct 27 12:05 359324 33.26 0.982 Nov 25 22:44 366149 32.64 0.921
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.
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 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 images from the Lunar Reconnaissance Orbiter (LRO) mission to create clever animations of the Moon’s ever changing phases and librations in 2015. The example below illustrates the Moon’s phase and libration at hourly intervals throughout 2015, as viewed from the northern hemisphere. Each frame represents one hour.
Besides presenting the Moon’s phase and apparent size, the video shows 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. The major cause of libration is due to our changing line of sight because of the Moon’s elliptical orbit. For more Moon animations from NASA/Goddard, see Moon Phase and Libration, 2015.
Finally, what discussion of the Moon would be complete without mentioning eclipses in 2015? There are two eclipses of the Moon and both of them are total. The first occurs on April 04 and the second, six months later on September 28. Both of them are visible from parts of North America. By coincidence, the September 28 eclipse also happens to be the closest Super Moon of 2015.
There are also two solar eclipses in 2015. The first is a total eclipse in the North Atlantic on March 20 (visible from the Faroe Islands and Spitzbergen). The second is a partial solar eclipse visible from most of southern Africa and Antarctica on September 13. For complete details on all these events, see Eclipses During 2015 (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) using Astronomical Algorithms (Jean Meeus).
- Reference Links
- Phases of the Moon: 2001 to 2100 (Greenwich Mean Time)
- Phases of the Moon: 2001 to 2100 (Eastern Standard Time)
- Phases of the Moon: 2001 to 2100 (Central Standard Time)
- Phases of the Moon: 2001 to 2100 (Mountain Standard Time)
- Phases of the Moon: 2001 to 2100 (Pacific Standard Time)
- Moon Ephemeris for 2015
- Length of the Synodic Month: 2001 to 2100
- Full Moon at Perigee (Super Moon): 2001 to 2100
- Perigee and Apogee: 2001 to 2100
- Ascending/Descending Nodes: 2001 to 2100
- Lunar Standstills: 2001 to 2100
- Moon Phases Photo Gallery
- Moon Phases Mosaics
- Eclipses During 2015 (EclipseWise.com) – detailed information, maps and tables
- Solar and Lunar Eclipses (EclipseWise.com) – a new web site containing predictions for thousands of solar and lunar eclipses
- Eclipses and the Moon’s Orbit (EclipseWise.com) – how the Moon’s orbital cycles are related to eclipses