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 18:12 (MDT) as the dusk sky fades, 63° above your southern horizon. It will then reach its highest point in the sky at 18:31, 63° above your southern horizon. It will continue to be observable until around 00:23, when it sinks below 7° above your western horizon.
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 February 1, the ecliptic is inclined at 66° 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 371,000 km. Its celestial coordinates will be as follows:
| Object | Right Ascension | Declination | Constellation | Angular Size |
| The Moon | 02h45m40s | +10°36' | Aries | 32'10" |
The coordinates above are given in J2000.0.
| The sky on 19 April 2021 | ||||||||||||||||||||||||||||||||||
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43% 7 days old |
All times shown in MDT.
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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
| 01 Feb 1963 | – Moon at First Quarter |
| 08 Feb 1963 | – Full Moon |
| 10 Feb 1963 | – The Moon at aphelion |
| 13 Feb 1963 | – The Moon at apogee |
Image credit
Simulated image courtesy of Tom Ruen.