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Moon at First Quarter

Dominic Ford, Editor
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The sky at

The Moon will be prominent in the evening sky, setting around midnight.

From Washington , it will become visible around 18:04 (MDT) as the dusk sky fades, 70° above your southern horizon. It will then reach its highest point in the sky at 18:18, 70° above your southern horizon. It will continue to be observable until around 00:34, when it sinks below 7° above your western horizon.

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.

Observing the Moon at first quarter

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 last quarter, it rises at around midnight, appears high in the sky by dawn, and sets at around midday. Click here for more information about the Moon's phases.

The period when the Moon shows half phase is ideal for observing the Moon with a pair of binoculars or a small telescope. The border between the light and dark portions of the Moon's disk is the best place to look for detail on its surface, because along this line, the Moon's surface is illuminated at a very shallow angle. As a result, mountains and crater rims cast long shadows which are very easy to see. An observer on the Moon would see the Sun on the horizon, casting long shadows just like the ones we see on Earth at sunrise and sunset.

At first quarter and last quarter, when the terminator line is down the middle of the Moon, it is best presented for view, without any foreshortening.

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.

It appears high up 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 January 23, the ecliptic is inclined at 63° to the western sunset horizon, as shown by the yellow line in the planetarium view above, meaning that on this occasion the Moon is very 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 374,000 km. Its exact position will be as follows:

Object Right Ascension Declination Constellation Angular Size
The Moon 01h56m20s +17°31' Aries 31'52"

The coordinates above are given in J2000.0.

The sky on 26 August 2019
Sunrise
06:58
Sunset
20:11
Twilight ends
21:43
Twilight begins
05:25

25-day old moon
Waning Crescent

22%

25 days old

Planets
Rise Culm. Set
Mercury 06:16 13:05 19:54
Venus 07:14 13:49 20:25
Moon 02:45 10:01 17:17
Mars 07:09 13:44 20:20
Jupiter 15:15 20:07 01:02
Saturn 17:24 22:14 03:08
All times shown in MDT.

Source

The circumstances of this event were computed using the DE405 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

23 Jan 1991  –  Moon at First Quarter
29 Jan 1991  –  Full Moon
06 Feb 1991  –  Moon at Last Quarter
14 Feb 1991  –  New Moon

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Washington

Latitude:
Longitude:
Timezone:

37.13°N
113.51°W
MDT

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