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[1] due to Earth's rotation.[2]

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[2] for observers outside 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.[3]

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.[4] A waning gibbous is best seen from late night to early morning.[5] The Moon rises 30 to 70 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.[6]

Moonrise/moonset for different moon phases
Lunar phase (illustration as seen from northern hemisphere) Moonrise[a] Culmination time (highest point) Moonset Best seen
New moon Sunrise Noon Sunset Not visible unless there is an eclipse
Waxing crescent Late morning Afternoon Late evening Late morning to early evening
First quarter Noon Sunset Midnight Early evening to late night
Waxing gibbous Afternoon Late evening Predawn Early evening[7] and most of night
Full moon Sunset Midnight Sunrise Sunset to sunrise (all night)
Waning gibbous Late evening Predawn Late morning Most of night and early morning[5]
Last quarter Midnight[4] Sunrise Noon[4] Predawn to post-sunrise
Waning crescent Predawn Late morning Afternoon 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.[8]

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.[9] This is also the reason the Moon appears red during a deep partial or total lunar eclipse.[10]

Notes

  1. ^ Varies slightly. (Same note for "Culmination time (highest point)" and "Moonset".)

References

  1. ^ "Does the Moon rise and set as the Sun rises in the east and..." Old Farmer's Almanac. Retrieved 2021-06-02.
  2. ^ a b "Why does the Sun rise in the east and set in the west?". starchild.gsfc.nasa.gov. Goddard Space Flight Center. Retrieved 2021-06-02.
  3. ^ "Does the Moon rise and set as the Sun rises in the east and..." Old Farmer's Almanac. Retrieved 2021-06-02.
  4. ^ a b c "What is a last quarter moon? | Moon Phases | EarthSky". earthsky.org. 2021-01-01. Retrieved 2021-06-02.
  5. ^ a b "What is a waning gibbous moon? | Moon Phases | EarthSky". earthsky.org. 2021-01-01. Retrieved 2021-06-02.
  6. ^ Scudder, Jillian. "Why Does The Moon Rise Later Each Day?". Forbes. Retrieved 2021-06-02.
  7. ^ "What is a waxing gibbous moon? | Moon Phases | EarthSky". earthsky.org. 2021-01-21. Retrieved 2021-06-03.
  8. ^ Preston Dyches, By. "The Moon Illusion: Why Does the Moon Look So Big Sometimes?". NASA Solar System Exploration. Retrieved 2021-06-03.
  9. ^ "What Is the Meaning of a Yellow Moon?". Reference.com. 4 August 2015. Retrieved 2021-06-03.
  10. ^ "What Is a Blood Moon?". www.timeanddate.com. Retrieved 2021-06-03.