The Moon will pass last quarter phase, rising in the middle of the night and appearing prominent in the pre-dawn sky.
From Cambridge, it will be visible from soon after it rises, at 00:09, until soon before it sets at 11:21.
At this time in its monthly cycle of phases, it appears almost exactly half illuminated.
The Moon orbits the Earth once every four weeks, causing its phases to cycle through new moon, first quarter, full moon, last quarter, and back to new moon once every 29.5 days.
As it progresses through this cycle, it is visible at different times of day. At last quarter, it rises in the middle of the night and appears high in the sky by dawn. It sets at around lunchtime. More information about the Moon's phases is available here.
Observing the Moon at last quarter
Over coming days, the Moon will rise later each day, so that it is visible for less time before sunrise and rises less far above the eastern horizon before dawn. By the time it reaches new moon, it will rise at around dawn and set at around dusk, making it visible only during the daytime.
Its daily progress is charted below, with all times are given in Cambridge local time.
| Date | Sun rises at |
Moon rises at |
Altitude of Moon at sunrise |
Direction of Moon at sunrise |
| 14 Jan 2017 | 07:09 | 18:19 | 13° | west |
| 15 Jan 2017 | 07:09 | 19:26 | 20° | west |
| 16 Jan 2017 | 07:08 | 20:31 | 26° | west |
| 17 Jan 2017 | 07:08 | 21:33 | 31° | south-west |
| 18 Jan 2017 | 07:07 | 22:34 | 34° | south-west |
| 19 Jan 2017 | 07:07 | 23:33 | 35° | south-west |
| 20 Jan 2017 | 07:06 | 00:31 | 35° | south |
| 21 Jan 2017 | 07:05 | 01:28 | 34° | south |
| 22 Jan 2017 | 07:05 | 02:25 | 31° | south |
| 23 Jan 2017 | 07:04 | 03:20 | 27° | south |
| 24 Jan 2017 | 07:03 | 04:14 | 22° | south-east |
| 25 Jan 2017 | 07:02 | 05:06 | 16° | south-east |
The exact moment of last quarter
The exact moment of last quarter is defined as the time when the Moon's ecliptic longitude is exactly 90° away from the Sun's ecliptic longitude, as observed from the center of the Earth. However, the Moon does not appear in any way special at this instant in time, and a last quarter moon can be observed at any time in the pre-dawn sky.
At the moment it reaches last quarter, the Moon's distance from the Earth will be 402,000 km. Its celestial coordinates will be as follows:
| Object | Right Ascension | Declination | Constellation | Angular Size |
| The Moon | 13h57m00s | 7°21'S | Virgo | 29'41" |
The coordinates above are given in J2000.0.
The sky on 19 Jan 2017
| The sky on 19 January 2017 | ||||||||||||||||||||||||||||||||||
|
45% 21 days old |
All times shown in EST.
|
|||||||||||||||||||||||||||||||||
Source
The circumstances of this event were computed using the DE430 planetary ephemeris published by the Jet Propulsion Laboratory (JPL).
This event was automatically generated by searching the ephemeris for planetary alignments which are of interest to amateur astronomers, and the text above was generated based on an estimate of your location.
Related news
| 19 Jan 2017 | – Moon at Last Quarter |
| 27 Jan 2017 | – New Moon |
| 03 Feb 2017 | – Moon at First Quarter |
| 10 Feb 2017 | – Full Moon |
Image credit
Simulated image courtesy of Tom Ruen.