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A lunar day is the period of time for
Lunar days and other lunar data for many different cities
Lunarium.co.uk.
Lunar Standard Time (LST)
lunarclock.org. Day Day, lunar
A lunar day is the period of time for Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
's Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
to complete one rotation
Rotation, or spin, is the circular movement of an object around a '' central axis''. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. A three-dimensional ...
on its axis
An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to:
Mathematics
* Axis of rotation: see rotation around a fixed axis
* Axis (mathematics), a designator for a Cartesian-coordinat ...
with respect to the Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
. Due to tidal locking
Tidal locking between a pair of co-orbiting astronomical bodies occurs when one of the objects reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit. In the case where a tidally locked b ...
, it is the time the Moon takes to complete one orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...
around Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
(Earth rise
''Earthrise'' is a photograph of Earth and some of the Moon's surface that was taken from lunar orbit by astronaut William Anders on December 24, 1968, during the Apollo 8 mission. Nature photographer Galen Rowell described it as "the most infl ...
to Earth set) plus about 2.2 more Earth days to return to the same Moon phase
Phase or phases may refer to:
Science
*State of matter, or phase, one of the distinct forms in which matter can exist
*Phase (matter), a region of space throughout which all physical properties are essentially uniform
* Phase space, a mathematic ...
(due to the Moon's orbit around the Sun). The lunar day is roughly 29 Earth days, the length of a lunar month
In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month.
Variations
In Shona, Middle Eastern, and Europ ...
, and the time of which includes a full day-night cycle.
Main definition
Relative to thefixed stars
In astronomy, fixed stars ( la, stellae fixae) is a term to name the full set of glowing points, astronomical objects actually and mainly stars, that appear not to move relative to one another against the darkness of the night sky in the backgro ...
on the celestial sphere
In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, ...
, the Moon takes 27 Earth days, 7 hours, 43 minutes, 12 seconds to complete one orbit; however, since the Earth–Moon system advances around the Sun at the same time, the Moon must travel farther to return to the same phase. On average, this synodic period
The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets, ...
lasts 29 days, 12 hours, 44 minutes, 3 seconds, the length of a lunar month
In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month.
Variations
In Shona, Middle Eastern, and Europ ...
on Earth. The exact length varies over time because the speed of the Earth–Moon system around the Sun varies slightly during a year due to the eccentricity
Eccentricity or eccentric may refer to:
* Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal"
Mathematics, science and technology Mathematics
* Off-center, in geometry
* Eccentricity (graph theory) of a v ...
of its elliptical orbit, variances in orbital velocity, and a number of other periodic and evolving variations about its observed, relative, mean values, which are influenced by the gravitational perturbations of the Sun and other bodies in the Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
.
As a result, daylight at a given point on the Moon would last approximately two weeks from beginning to end, followed by approximately two weeks of ''lunar night''.
Alternate usage
* The term ''lunar day'' may also refer to the period between moonrises orhigh moon
''High Moon'' is a horror Western webcomic series featuring werewolves. It was developed in 2004 with a debut in 2007 as a part of Zuda, DC Comics' webcomic imprint. The first season concluded on July 8, 2008. Season two ran from August 16 to N ...
in a particular location on Earth. This period is typically about 50 minutes longer than a 24-hour Earth day, as the Moon orbits the Earth in the same direction
"Same Direction" is the third single from Hoobastank's second major studio album '' The Reason''. It was released as a single in 2004, a couple of months after the release of " The Reason" as a single. "Same Direction" reached No. 20 on the '' Bi ...
as the Earth's axial rotation.
* The term ''lunar day'' is also used in the context of night and day, i.e., opposite to the lunar night. This is common in discussions of the huge difference in temperatures, such as discussion about lunar rovers
A lunar rover or Moon rover is a space exploration vehicle designed to move across the surface of the Moon. The Apollo Program's Lunar Roving Vehicle was driven on the Moon by members of three American crews, Apollo 15, 16, and 17. Other rov ...
. For example, "the Soviet Union's Luna missions ..were designed to survive one lunar day (two Earth weeks).", or, China's
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
Yutu-2
''Yutu-2'' is the robotic lunar rover component of CNSA's Chang'e 4 mission to the Moon, launched on 7 December 2018 18:23 UTC, it entered lunar orbit on 12 December 2018 before making the first soft landing on the far side of the Moon on 3 J ...
rover, which landed in January 2019, was designed to survive lunar nights by shutting down.
Lunar calendars
In somelunar calendar
A lunar calendar is a calendar based on the monthly cycles of the Moon's phases (synodic months, lunations), in contrast to solar calendars, whose annual cycles are based only directly on the solar year. The most commonly used calendar, the Gre ...
s, such as the Vikram Samvat
Vikram Samvat (IAST: ''Vikrama Samvat''; abbreviated VS) or Bikram Sambat B.S. and also known as the Vikrami calendar, is a Hindu calendar historically used in the Indian subcontinent. Vikram Samvat is generally 57 years ahead of Gregorian Calend ...
, a lunar day, or ''tithi
In Vedic timekeeping, a ''tithi'' is a uration of two faces of moon that is observed from earth known as ''milа̄lyа̄'' (𑐩𑐶𑐮𑐵𑐮𑑂𑐫𑐵𑑅, मिलाल्याः) in Nepal Bhasa, or the time it takes for the longit ...
'', is defined as 1/30 of a lunar month
In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month.
Variations
In Shona, Middle Eastern, and Europ ...
, or the time it takes for the longitudinal
Longitudinal is a geometric term of location which may refer to:
* Longitude
** Line of longitude, also called a meridian
* Longitudinal engine, an internal combustion engine in which the crankshaft is oriented along the long axis of the vehicle, ...
angle between the Moon and the Sun to increase by 12 degrees. By this definition, lunar days generally vary in duration.
See also
*Lunisolar calendar
A lunisolar calendar is a calendar in many cultures, combining lunar calendars and solar calendars. The date of Lunisolar calendars therefore indicates both the Moon phase and the time of the solar year, that is the position of the Sun in the Ea ...
* Sol, the name for a Martian solar day
References
{{ReflistExternal links
Lunar days and other lunar data for many different cities
Lunarium.co.uk.
Lunar Standard Time (LST)
lunarclock.org. Day Day, lunar