Simulated image courtesy of Tom Ruen.

Moon at First Quarter

Dominic Ford, Editor
From the Moon feed

Objects: The Moon
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The sky at

The Moon will pass first quarter phase, appearing prominent in the evening sky and setting in the middle of the night.

From San Diego , it will become visible around 20:13 (PDT), 45° above your south-western horizon, as dusk fades to darkness. It will then sink towards the horizon, setting at 00:28.

Begin typing the name of a town near to you, and then select the town from the list of options which appear below.

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 first quarter, it appears high in the sky at sunset before sinking towards the horizon and setting in the middle of the night. More information about the Moon's phases is available here.

Observing the Moon at first quarter

Over coming days, the Moon will set later each day, becoming visible for more of the night. Within a few days, it will not make it very far above the eastern horizon before nightfall. By the time it reaches full phase, it will be visible for much of the night, rising at around dusk and setting at around dawn.

Its daily progress is charted below, with all times are given in San Diego local time.

Date Sun
sets at
sets at
Altitude of Moon
at sunset
Direction of Moon
at sunset
12 Jul 202119:5822:1627°west
13 Jul 202119:5822:5035°west
14 Jul 202119:5723:2241°west
15 Jul 202119:5723:5345°south-west
16 Jul 202119:5600:2447°south-west
17 Jul 202119:5600:5746°south
18 Jul 202119:5501:3541°south
19 Jul 202119:5502:1834°south
20 Jul 202119:5403:0826°south-east
21 Jul 202119:5404:0717°south-east
22 Jul 202119:5304:07south-east
23 Jul 202119:5305:12-2°south-east

The exact moment of first quarter

The exact moment of first 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 first quarter moon can be observed at any time in the evening sky.

At the moment it reaches first quarter, the Moon's distance from the Earth will be 372,000 km. Its celestial coordinates will be as follows:

Object Right Ascension Declination Constellation Angular Size
The Moon 13h37m00s 6°12'S Virgo 32'04"

The coordinates above are given in J2000.0.

The sky on 17 July 2021
Twilight ends
Twilight begins

7-day old moon
Waxing Gibbous


7 days old

Rise Culm. Set
Mercury 04:39 11:45 18:51
Venus 08:12 14:54 21:36
Moon 13:25 19:15 00:57
Mars 08:01 14:44 21:27
Jupiter 21:48 03:19 08:50
Saturn 20:47 02:01 07:15
All times shown in PDT.


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

17 Jul 2021  –  Moon at First Quarter
23 Jul 2021  –  Full Moon
31 Jul 2021  –  Moon at Last Quarter
08 Aug 2021  –  New Moon

Image credit

Simulated image courtesy of Tom Ruen.



San Diego



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