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 18:15 (EDT) as the dusk sky fades, 21° above your southern horizon. It will then reach its highest point in the sky at 18:52, 21° above your southern horizon. It will continue to be observable until around 22:10, when it sinks below 8° above your south-western 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 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
17 Oct 202318:0418:51south-west
18 Oct 202318:0019:2211°south-west
19 Oct 202317:5920:0214°south-west
20 Oct 202317:5920:5217°south
21 Oct 202317:5521:5419°south
22 Oct 202317:5523:0420°south
23 Oct 202317:54--:--20°south-east
24 Oct 202317:5400:2319°south-east
25 Oct 202317:5001:4117°south-east
26 Oct 202317:5003:0014°east
27 Oct 202317:5004:1711°east
28 Oct 202317:4605:33east

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 20h05m40s 25°41'S Sagittarius 32'04"

The coordinates above are given in J2000.0.

The sky on 21 October 2023
Sunrise
07:03
Sunset
17:55
Twilight ends
19:31
Twilight begins
05:31

7-day old moon
Waxing Gibbous

55%

7 days old

Planets
Rise Culm. Set
Mercury 07:10 12:35 18:00
Venus 03:08 09:37 16:06
Moon 14:16 18:38 23:04
Mars 07:50 13:03 18:16
Jupiter 18:31 01:27 08:23
Saturn 15:42 20:57 02:11
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

21 Oct 2023  –  Moon at First Quarter
28 Oct 2023  –  Full Moon
05 Nov 2023  –  Moon at Last Quarter
13 Nov 2023  –  New Moon

Image credit

Simulated image courtesy of Tom Ruen.

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42.38°N
71.11°W
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