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 Cambridge , it will be visible from soon after it rises, at 11:21, until soon before it sets at 02:39.

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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 Cambridge local time.

Date Sun
sets at
Moon
sets at
Altitude of Moon
at sunset
Direction of Moon
at sunset
15 Apr 202119:2522:5836°west
16 Apr 202119:2723:5846°west
17 Apr 202119:2800:5455°west
18 Apr 202119:2901:4664°south-west
19 Apr 202119:3002:3169°south-west
20 Apr 202119:3103:1169°south
21 Apr 202119:3203:4563°south-east
22 Apr 202119:3304:1553°south-east
23 Apr 202119:3404:4342°south-east
24 Apr 202119:3605:0929°south-east
25 Apr 202119:3705:3616°east
26 Apr 202119:3806:06east

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 391,000 km. Its celestial coordinates will be as follows:

Object Right Ascension Declination Constellation Angular Size
The Moon 08h12m50s 23°56'N Cancer 30'31"

The coordinates above are given in J2000.0.

The sky on 20 Apr 2021

The sky on 20 April 2021
Sunrise
05:53
Sunset
19:31
Twilight ends
21:15
Twilight begins
04:09

8-day old moon
Waxing Gibbous

55%

8 days old

Planets
Rise Culm. Set
Mercury 06:01 12:49 19:37
Venus 06:15 13:07 20:00
Moon 11:55 19:37 03:11
Mars 08:55 16:38 00:22
Jupiter 03:31 08:44 13:58
Saturn 02:53 07:49 12:45
All times shown in EDT.

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

20 Apr 2021  –  Moon at First Quarter
26 Apr 2021  –  Full Moon
03 May 2021  –  Moon at Last Quarter
11 May 2021  –  New Moon

Image credit

Simulated image courtesy of Tom Ruen.

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42.38°N
71.11°W
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