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 Fairfield , it will become visible around 19:09 (EDT), 27° above your southern horizon, as dusk fades to darkness. It will then sink towards the horizon, setting at 23:32.

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 Fairfield local time.

Date Sun
sets at
sets at
Altitude of Moon
at sunset
Direction of Moon
at sunset
17 Sep 201219:0119:37west
18 Sep 201219:0020:1612°south-west
19 Sep 201218:5521:0018°south-west
20 Sep 201218:5421:5023°south-west
21 Sep 201218:5422:4826°south
22 Sep 201218:5323:5028°south
23 Sep 201218:5200:5328°south
24 Sep 201218:4702:0027°south-east
25 Sep 201218:4603:0924°south-east
26 Sep 201218:4504:1120°south-east
27 Sep 201218:4505:1816°east
28 Sep 201218:4006:1711°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 371,000 km. Its celestial coordinates will be as follows:

Object Right Ascension Declination Constellation Angular Size
The Moon 18h00m00s 20°41'S Sagittarius 32'07"

The coordinates above are given in J2000.0.

The sky on 22 September 2012
Twilight ends
Twilight begins

6-day old moon
Waxing Gibbous


6 days old

Rise Culm. Set
Mercury 07:31 13:22 19:14
Venus 03:07 10:05 17:03
Moon 13:59 18:52 23:50
Mars 10:58 15:54 20:50
Jupiter 22:23 05:48 13:14
Saturn 09:02 14:35 20:07
All times shown in EDT.


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

22 Sep 2012  –  Moon at First Quarter
29 Sep 2012  –  Full Moon
08 Oct 2012  –  Moon at Last Quarter
15 Oct 2012  –  New Moon

Image credit

Simulated image courtesy of Tom Ruen.






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