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 become visible around 20:34 (EDT) as the dusk sky fades, 28° above your south-western horizon. It will then sink towards the horizon, setting 3 hours and 35 minutes after the Sun at 23:49.

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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
20 Jul 202320:1822:1520°west
21 Jul 202320:1822:3624°west
22 Jul 202320:1822:5327°west
23 Jul 202320:1423:0930°south-west
24 Jul 202320:1423:2931°south-west
25 Jul 202320:1423:5130°south-west
26 Jul 202320:1300:1828°south
27 Jul 202320:1300:1725°south
28 Jul 202320:0900:4920°south
29 Jul 202320:0901:3014°south-east
30 Jul 202320:0902:25south-east
31 Jul 202320:0903:35south-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 391,000 km. Its celestial coordinates will be as follows:

Object Right Ascension Declination Constellation Angular Size
The Moon 14h00m20s 12°36'S Virgo 30'32"

The coordinates above are given in J2000.0.

The sky on 25 July 2023
Sunrise
05:30
Sunset
20:14
Twilight ends
22:14
Twilight begins
03:30

8-day old moon
Waxing Gibbous

55%

8 days old

Planets
Rise Culm. Set
Mercury 07:28 14:24 21:20
Venus 07:54 14:27 21:01
Moon 13:06 18:35 23:51
Mars 08:39 15:16 21:53
Jupiter 00:19 07:17 14:15
Saturn 21:44 03:06 08:28
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

25 Jul 2023  –  Moon at First Quarter
01 Aug 2023  –  Full Moon
08 Aug 2023  –  Moon at Last Quarter
16 Aug 2023  –  New Moon

Image credit

Simulated image courtesy of Tom Ruen.

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