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 Washington , it will become visible around 19:06 (MDT) as the dusk sky fades, 80° above your south-western horizon. It will then sink towards the horizon, setting at 02:26.

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.

Seasonal variation

Although the Moon passes first quarter every month, it is more favourably placed in the early evening sky at some times of year than others.

The first quarter moon appears high in the evening sky around the spring equinox, but much lower towards the horizon around the autumn equinox.

This is because it always lies close to a line across the sky called the ecliptic. This marks the flat plane in space in which all of the planets circle the Sun. It is the line through the zodiacal constellations that the Sun follows through the year.

The altitude at which the Moon appears above the horizon at sunset depends how steeply the line of the ecliptic is inclined to the horizon. If the plane of the ecliptic meet the horizon at a very shallow angle, the Moon will rise or set along a line which is almost parallel to the horizon, and a large separation from the Sun along this line would still only correspond to a very low altitude in the sky.

The inclination of the ecliptic plane to the horizon at Washington varies between 76° (sunset at the spring equinox) and 29° (sunset at the autumn equinox). On March 26, the ecliptic is inclined at 76° to the western sunset horizon, as shown by the yellow line in the planetarium view above, meaning that on this occasion the Moon is favourably placed for viewing from Washington.

The Moon's position

At the moment it reaches first quarter, the Moon's distance from the Earth will be 395,000 km. Its celestial coordinates will be as follows:

Object Right Ascension Declination Constellation Angular Size
The Moon 06h28m30s +28°34' Auriga 30'12"

The coordinates above are given in J2000.0.

The sky on 19 April 2021
Sunrise
06:52
Sunset
20:16
Twilight ends
21:48
Twilight begins
05:20

7-day old moon
Waxing Crescent

43%

7 days old

Planets
Rise Culm. Set
Mercury 06:55 13:31 20:07
Venus 07:16 13:57 20:39
Moon 12:03 19:41 02:32
Mars 10:05 17:30 00:56
Jupiter 04:16 09:37 14:59
Saturn 03:36 08:43 13:50
All times shown in MDT.

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

26 Mar 1950  –  Moon at First Quarter
02 Apr 1950  –  Full Moon
03 Apr 1950  –  The Moon at perigee
04 Apr 1950  –  The Moon at aphelion

Image credit

Simulated image courtesy of Tom Ruen.

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Washington

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Longitude:
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37.13°N
113.51°W
MDT

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