Simulated image courtesy of Tom Ruen.

Moon at Last Quarter

Dominic Ford, Editor
From the Moon feed

Objects: The Moon
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The Moon will pass last quarter phase, rising in the middle of the night and appearing prominent in the pre-dawn sky.

From Fairfield, it will be visible in the morning sky, becoming accessible around 23:57, when it reaches an altitude of 7° above your eastern horizon. It will then reach its highest point in the sky at 06:06, 63° above your southern horizon. It will be lost to dawn twilight around 06:34, 62° above your southern horizon.

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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 day-by-day progress is charted below, with all times are given in Fairfield local time.

Date Sun
rises at
Moon
rises at
Altitude of Moon
at sunrise
Direction of Moon
at sunrise
22 Nov 202106:4918:4430°west
23 Nov 202106:4919:3939°west
24 Nov 202106:5020:4047°west
25 Nov 202106:5421:4354°west
26 Nov 202106:5422:4959°south-west
27 Nov 202106:5423:5361°south-west
28 Nov 202106:55--:--58°south
29 Nov 202106:5501:0351°south
30 Nov 202106:5902:1342°south-east
01 Dec 202106:5903:2632°south-east
02 Dec 202107:0004:4220°south-east
03 Dec 202107:0006:03south-east

Seasonal variations

Although the Moon passes last quarter every month, it is more favourably placed in the pre-dawn sky at some times of year than others.

The last quarter moon appears high in the pre-dawn sky around the autumn equinox, but much lower towards the horizon around the spring equinox.

This is because it always lies close to a line across the sky called the ecliptic. This marks the flat plane in space in which all of the planets circle the Sun. It is the line through the zodiacal constellations that the Sun follows through the year.

The altitude at which the Moon appears above the horizon at sunrise depends how steeply the line of the ecliptic is inclined to the horizon. If the plane of the ecliptic meet the horizon at a very shallow angle, the Moon will rise or set along a line which is almost parallel to the horizon, and a large separation from the Sun along this line would still only correspond to a very low altitude in the sky.

The inclination of the ecliptic plane to the horizon at Fairfield varies between 72° (sunrise at the autumn equinox) and 25° (sunrise at the spring equinox). On November 27, the ecliptic is inclined at 55° to the eastern dawn horizon, as shown by the yellow line in the planetarium view above, meaning that on this occasion the Moon is favourably placed for viewing from Fairfield.

The Moon's position

At the moment it reaches last quarter, the Moon's distance from the Earth will be 388,000 km. Its celestial coordinates will be as follows:

Object Right Ascension Declination Constellation Angular Size
The Moon 10h36m00s +14°31' Leo 30'45"

The coordinates above are given in J2000.0.

The sky on 27 November 2021
Sunrise
06:54
Sunset
16:26
Twilight ends
18:06
Twilight begins
05:18

23-day old moon
Waning Gibbous

50%

23 days old

Planets
Rise Culm. Set
Mercury 06:51 11:35 16:18
Venus 10:22 14:48 19:13
Moon 23:53 06:01 13:02
Mars 05:29 10:30 15:31
Jupiter 12:04 17:16 22:27
Saturn 11:16 16:10 21:03
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

27 Nov 2021  –  Moon at Last Quarter
04 Dec 2021  –  New Moon
04 Dec 2021  –  The Moon at perigee
05 Dec 2021  –  The Moon at perihelion

Image credit

Simulated image courtesy of Tom Ruen.

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