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 20:13 (EDT) as the dusk sky fades, 27° above your south-western horizon. It will then sink towards the horizon, setting 3 hours and 46 minutes after the Sun at 23:39.
At this time in its monthly cycle of phases, it appears almost exactly half illuminated.
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 day-by-day progress is charted below, with all times are given in Fairfield local time.
|Altitude of Moon
|Direction of Moon
|10 Aug 2021||20:02||21:33||16°||west|
|11 Aug 2021||19:58||22:00||22°||west|
|12 Aug 2021||19:58||22:27||25°||south-west|
|13 Aug 2021||19:57||22:53||28°||south-west|
|14 Aug 2021||19:53||23:21||29°||south-west|
|15 Aug 2021||19:53||23:54||28°||south|
|16 Aug 2021||19:53||00:36||26°||south|
|17 Aug 2021||19:52||00:35||22°||south|
|18 Aug 2021||19:48||01:26||17°||south-east|
|19 Aug 2021||19:48||02:25||11°||south-east|
|20 Aug 2021||19:48||03:36||5°||south-east|
|21 Aug 2021||19:43||04:46||0°||south-east|
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 Fairfield varies between 72° (sunset at the spring equinox) and 25° (sunset at the autumn equinox). On August 15, the ecliptic is inclined at 28° to the western sunset horizon, as shown by the yellow line in the planetarium view above, meaning that on this occasion the Moon is poorly placed for viewing from Fairfield.
The Moon's position
At the moment it reaches first quarter, the Moon's distance from the Earth will be 370,000 km. Its celestial coordinates will be as follows:
|Object||Right Ascension||Declination||Constellation||Angular Size|
The coordinates above are given in J2000.0.
|The sky on 15 August 2021|
7 days old
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.
|15 Aug 2021||– Moon at First Quarter|
|17 Aug 2021||– The Moon at perigee|
|20 Aug 2021||– The Moon at aphelion|
|22 Aug 2021||– Full Moon|
Simulated image courtesy of Tom Ruen.