Moon

An explanation can be found here


Moon phases 2021

PhaseDate & time (UT1)Angle with sunPhaseDate & time (UT1)Angle with sunPhaseDate & time (UT1)Angle with sun
06 Jan 09:37 90° 00.0'11 May 19:21 1° 44.7'13 Sep 20:39 90° 00.0'
13 Jan 04:34 2° 52.2'19 May 19:12 90° 00.0'21 Sep 00:16175° 24.1'
20 Jan 21:01 90° 00.0'26 May 11:18179° 30.7'29 Sep 01:57 90° 00.0'
28 Jan 18:48176° 04.6'02 Jun 07:24 90° 00.0'06 Oct 11:31 3° 53.0'
04 Feb 17:37 90° 00.0'10 Jun 10:41 0° 49.5'13 Oct 03:25 90° 00.0'
11 Feb 18:44 4° 35.3'18 Jun 03:54 90° 00.0'20 Oct 15:27177° 03.4'
19 Feb 18:47 90° 00.0'24 Jun 18:20177° 58.2'28 Oct 20:05 90° 00.0'
27 Feb 08:10175° 02.0'01 Jul 21:10 90° 00.0'04 Nov 21:30 1° 43.1'
06 Mar 01:30 90° 00.0'10 Jul 00:45 3° 09.6'11 Nov 12:46 90° 00.0'
13 Mar 10:29 4° 56.6'17 Jul 10:10 90° 00.0'19 Nov 09:02179° 35.4'
21 Mar 14:40 90° 00.0'24 Jul 02:11175° 59.0'27 Nov 12:27 90° 00.0'
28 Mar 19:07175° 26.1'31 Jul 13:15 90° 00.0'04 Dec 07:33 0° 58.4'
04 Apr 10:02 90° 00.0'08 Aug 13:30 4° 40.1'11 Dec 01:35 90° 00.0'
12 Apr 03:02 3° 52.5'15 Aug 15:19 90° 00.0'19 Dec 04:08177° 43.4'
20 Apr 06:58 90° 00.0'22 Aug 11:55175° 01.9'27 Dec 02:23 90° 00.0'
27 Apr 03:55177° 05.9'30 Aug 07:13 90° 00.0'
03 May 19:50 90° 00.0'07 Sep 01:00 4° 56.8'

Explanation

On the website of the U.S. Naval Observatory (USNO) the following definition can be found for the phases of the moon: "Technically, the phases New Moon, First Quarter, Full Moon, and Last Quarter are defined to occur when the excess of the apparent ecliptic (celestial) longitude of the Moon over that of the Sun is 0, 90, 180, and 270 degrees, respectively. These definitions are used when the dates and times of the phases are computed for almanacs, calendars, etc. Because the difference between the ecliptic longitudes of the Moon and Sun is a monotonically and rapidly increasing quantity, the dates and times of the phases of the Moon computed this way are instantaneous and well defined."

However, it is more logical to define that full and new moon occur when the lunar distance of the sun reaches a maximum and a minimum value, respectively. For the time and date of the moon phases on this page this definition was used. As a consequence, for full and new moon the time on this page may differ from the official time by up to 30 minutes or slightly more. The reason for this difference is that the orbit of the moon is slightly inclined relative to the ecliptic plane.

If a solar or lunar eclipse occurs, the maximum of the eclipse occurs exactly at the moment when the lunar distance of the sun takes on its maximum (eclipse of the moon) or minimum (eclipse of the sun) value. Therefore, if an eclipse occurs, the time on this page is the time of the maximum of the eclipse.


Data was generated using Skyfield. From NASA's Navigation and Ancillary Information Facility (NAIF) the following ephemerides were used: de421.bsp, jup343.bsp, sat375.bsp.