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 Ashburn , it will be visible from soon after it rises, at 11:38, until soon before it sets at 00:37.

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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 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 Ashburn local time.

Date Sun
sets at
sets at
Altitude of Moon
at sunset
Direction of Moon
at sunset
15 Jan 202117:1119:5424°south-west
16 Jan 202117:1220:5833°south-west
17 Jan 202117:1321:5941°south
18 Jan 202117:1422:5948°south
19 Jan 202117:1523:5754°south
20 Jan 202117:1600:5557°south-east
21 Jan 202117:1801:5356°south-east
22 Jan 202117:1902:5353°south-east
23 Jan 202117:2003:5347°east
24 Jan 202117:2104:5240°east
25 Jan 202117:2205:5031°east
26 Jan 202117:2306:4322°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 404,000 km. Its celestial coordinates will be as follows:

Object Right Ascension Declination Constellation Angular Size
The Moon 01h59m50s 8°06'N Pisces 29'33"

The coordinates above are given in J2000.0.

The sky on 20 Jan 2021

The sky on 20 January 2021
Twilight ends
Twilight begins

7-day old moon
Waxing Gibbous


7 days old

Rise Culm. Set
Mercury 08:24 13:33 18:42
Venus 06:29 11:13 15:56
Moon 11:36 18:11 00:55
Mars 11:29 18:22 01:14
Jupiter 07:48 12:47 17:45
Saturn 07:37 12:32 17:28
All times shown in EST.


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

20 Jan 2021  –  Moon at First Quarter
28 Jan 2021  –  Full Moon
04 Feb 2021  –  Moon at Last Quarter
11 Feb 2021  –  New Moon

Image credit

Simulated image courtesy of Tom Ruen.





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