Astronomy:Moonrise and moonset

Short description: Daily appearance and disappearance of the Moon at the Earth's horizon

"Moonrise" redirects here. For other uses, see Moonrise (disambiguation).

A full moon sinking behind San Gorgonio Mountain, California, on a midsummer morning

Moonrise and moonset are times when the upper limb of the Moon appears above the horizon and disappears below it, respectively. The exact times depend on the lunar phase and declination, as well as the observer's location. As viewed from outside the polar circles, the Moon, like all other celestial objects outside the circumpolar circle, rises from the eastern half of the horizon and sets into the western half due to Earth's rotation.

Direction and time

Direction

Since Earth rotates eastward, all celestial objects outside the circumpolar circle (including the Sun, Moon, and stars) rise in the east and set in the west for observers not in the polar circles. Seasonal variation means that they sometimes rise in the east-northeast or east-southeast, and sometimes set in the west-southwest or west-northwest. This north-south variation of the point along the horizon, for the moon, is bookended by two lunar standstills or turnarounds, the directions of which are sometimes depicted in archaeoastronomical constructions. It takes 18.6 years for the Moon to traverse this variation viewed from a vantage point on Earth.

Time

A waxing gibbous Moon, rising over mountains with coniferous trees

The Moon's position relative to Earth and the Sun determines the moonrise and moonset time. For example, a last quarter rises at midnight and sets at noon. A waning gibbous is best seen from late night to early morning. On average, the Moon rises 50 minutes later each day/night than the day/night before, due to the fact that the Moon moves 13 degrees every day. Hence, the Earth must move 13 degrees after completing one rotation for the Moon to be visible.

Note that this table shows moonrise and moonset times as if they were exactly 12 hours apart, rather than 12 hours and 25 minutes which the other references indicate, or some other seasonally varying time interval.

Moonrise/moonset for different moon phases

Lunar phase (illustration as seen from northern hemisphere)	Moonrise	Culmination time (highest point)	Moonset	Best seen
50x50px New moon	6:00 a.m.	60x60px Noon	6:00 p.m.	Not visible unless there is a solar eclipse
50x50px Waxing crescent	9:00 a.m.	60x60px Afternoon	9:00 p.m.	Late morning to early evening
50x50px First quarter	12:00 p.m.	60x60px Sunset	12:00 a.m.	Early evening to late night
50x50px Waxing gibbous	3:00 p.m.	60x60px Late evening	3:00 a.m.	Early evening and most of night
50x50px Full moon	6:00 p.m.	60x60px Midnight	6:00 a.m.	Sunset to sunrise (all night), a lunar eclipse is then possible
50x50px Waning gibbous	9:00 p.m.	60x60px Predawn	9:00 a.m.	Most of night and early morning
50x50px Last quarter	12:00 a.m.	60x60px Sunrise	12:00 p.m.	Predawn to post-sunrise
50x50px Waning crescent	3:00 a.m.	60x60px Late morning	3:00 p.m.	Predawn to afternoon

Visual appearance

Atmospheric distortion of the Moon's appearance at Earth's horizon.

The Moon appears to be larger at moonrise or moonset due to an illusion. This illusion, known as the Moon illusion, is caused by an effect of the brain. There is no definitive explanation for the Moon illusion. However, it is most likely because of how the brain perceives objects at different distances, and/or the distance we expect objects to be from us when they are near the horizon.

The Moon appears to be more yellowish near the horizon. This is for the same reason the Sun and/or sky appears to be orangey-red at sunrise/sunset. When the Moon appears near the horizon, the light coming from it has to pass through more layers of atmosphere. This scatters the blue away, and leaves yellow, orange, and red. This is also the reason the Moon appears red during a deep partial or total lunar eclipse.