Earthlight is the diffuse reflection of sunlight reflected from Earth's surface and clouds. Earthshine (an example of planetshine), also known as the Moon's ashen glow, is the dim illumination of the otherwise unilluminated portion of the Moon by this indirect sunlight. Earthlight on the Moon during the waxing crescent is called "the old Moon in the new Moon's arms", [1] while that during the waning crescent is called "the new Moon in the old Moon's arms". [2]
Earthlight has a calculated maximum apparent magnitude of −17.7 as viewed from the Moon. [3] When the Earth is at maximum phase, the total radiance at the lunar surface is approximately 0.15 W m−2 from Earthlight. This is only 0.01% of the radiance from direct Sunlight. [4] Earthshine has a calculated maximum apparent magnitude of −3.69 as viewed from Earth. [3]
This phenomenon is most visible from Earth at night (or astronomical twilight) a few days before or after the day of new moon, [5] when the lunar phase is a thin crescent. On these nights, the entire lunar disk is both directly and indirectly sunlit, and is thus unevenly bright enough to see. Earthshine is most clearly seen after dusk during the waxing crescent (in the western sky) and before dawn during the waning crescent (in the eastern sky).
The term earthlight would also be suitable for an observer on the Moon seeing Earth during the lunar night, or for an astronaut inside a spacecraft looking out the window. [6] Arthur C. Clarke uses it in this sense in his 1955 novel Earthlight .
High contrast photography is also able to reveal the night side of the moon illuminated by Earthlight during a solar eclipse. [7]
Radio frequency transmissions are also reflected by the moon; for example, see Earth–Moon–Earth communication.
The phenomenon was sketched [8] and remarked upon in the 16th century by Leonardo da Vinci, who thought that the illumination came from reflections from the Earth's oceans (we now know that clouds account for much more reflected intensity than the oceans). [9]
It is referenced in "The Ballad of Sir Patrick Spens" (Child Ballad No. 58), in the phrase "‘A saw the new muin late yestreen/ Wi the auld muin in her airm." [10]
Astronaut Dr Sian Proctor was moved by seeing and experiencing earthlight from orbit as mission pilot of Inspiration4 space mission and wrote the poem, "Earthlight". [11] In 2024, Proctor authored EarthLight: The Power of EarthLight and the Human Perspective on the concept and nature of earthlight.
The Moon is Earth's only natural satellite. It orbits at an average distance of 384,400 km (238,900 mi), about 30 times the diameter of Earth. Tidal forces between Earth and the Moon have over time synchronized the Moon's orbital period with its rotation period at 29.5 Earth days, causing the same side of the Moon to always face Earth. The Moon's gravitational pull – and to a lesser extent, the Sun's – are the main drivers of Earth's tides.
A lunar phase or Moon phase is the apparent shape of the Moon's directly sunlit portion as viewed from the Earth. In common usage, the four major phases are the new moon, the first quarter, the full moon and the last quarter; the four minor phases are waxing crescent, waxing gibbous, waning gibbous, and waning crescent. A lunar month is the time between successive recurrences of the same phase: due to the eccentricity of the Moon's orbit, this duration is not perfectly constant but averages about 29.5 days.
Moon landing conspiracy theories claim that some or all elements of the Apollo program and the associated Moon landings were hoaxes staged by NASA, possibly with the aid of other organizations. The most notable claim of these conspiracy theories is that the six crewed landings (1969–1972) were faked and that twelve Apollo astronauts did not actually land on the Moon. Various groups and individuals have made claims since the mid-1970s that NASA and others knowingly misled the public into believing the landings happened, by manufacturing, tampering with, or destroying evidence including photos, telemetry tapes, radio and TV transmissions, and Moon rock samples.
Planetshine is the dim illumination, by sunlight reflected from a planet, of all or part of the otherwise dark side of any moon orbiting the body. Planetlight is the diffuse reflection of sunlight from a planet, whose albedo can be measured.
In astronomy, an extraterrestrial sky is a view of outer space from the surface of an astronomical body other than Earth.
Karl Gordon Henize was an American astronomer, space scientist, NASA astronaut, and professor at Northwestern University. He was stationed at several observatories around the world, including McCormick Observatory, Lamont–Hussey Observatory, Mount Wilson Observatory, Smithsonian Astrophysical Observatory and Mount Stromlo Observatory (Australia). He was a member of the astronaut support crew for Apollo 15 and Skylab 2, 3, and 4. As a mission specialist on the Spacelab-2 mission (STS-51-F), he flew on Space Shuttle Challenger in July/August 1985. He was awarded the NASA Exceptional Scientific Achievement Medal in 1974.
Eratosthenes crater is a relatively deep lunar impact crater that lies on the boundary between the Mare Imbrium and Sinus Aestuum mare regions. It forms the western terminus of the Montes Apenninus mountain range. It is named after ancient Greek astronomer Eratosthenes of Cyrene, who estimated the circumference of the Earth, and the distance from the Earth to the Sun.
Moonlight consists of mostly sunlight reflected from the parts of the Moon's surface where the Sun's light strikes.
Plato is a lava-filled lunar impact crater on the Moon. Its diameter is 101 km. It was named after ancient Greek philosopher Plato. It is located on the northeastern shore of the Mare Imbrium, at the western extremity of the Montes Alpes mountain range. In the mare to the south are several rises collectively named the Montes Teneriffe. To the north lies the wide stretch of the Mare Frigoris. East of the crater, among the Montes Alpes, are several rilles collectively named the Rimae Plato.
Messier 106 is an intermediate spiral galaxy in the constellation Canes Venatici. It was discovered by Pierre Méchain in 1781. M106 is at a distance of about 22 to 25 million light-years away from Earth. M106 contains an active nucleus classified as a Type 2 Seyfert, and the presence of a central supermassive black hole has been demonstrated from radio-wavelength observations of the rotation of a disk of molecular gas orbiting within the inner light-year around the black hole. NGC 4217 is a possible companion galaxy of Messier 106.
The Cone Nebula is an H II region in the constellation of Monoceros. It was discovered by William Herschel on December 26, 1785, at which time he designated it H V.27. The nebula is located about 830 parsecs or 2,700 light-years from Earth. The Cone Nebula forms part of the nebulosity surrounding the Christmas Tree Cluster. The designation of NGC 2264 in the New General Catalogue refers to both objects and not the nebula alone.
The far side of the Moon is the lunar hemisphere that always faces away from Earth, opposite to the near side, because of synchronous rotation in the Moon's orbit. Compared to the near side, the far side's terrain is rugged, with a multitude of impact craters and relatively few flat and dark lunar maria ("seas"), giving it an appearance closer to other barren places in the Solar System such as Mercury and Callisto. It has one of the largest craters in the Solar System, the South Pole–Aitken basin. The hemisphere has sometimes been called the "Dark side of the Moon", where "dark" means "unknown" instead of "lacking sunlight" – each location on the Moon experiences two weeks of sunlight while the opposite location experiences night.
Sinus Iridum is a plain of basaltic lava that forms a northwestern extension to the Mare Imbrium on Earth's moon. It is surrounded from the northeast to the southwest by the Montes Jura range. The protruding part of the range at the southwest end is named Promontorium Heraclides, while that at the northeast end is called Promontorium Laplace. This bay and the surrounding mountains is considered one of the most beautiful features on the Moon, and is a favorite among lunar observers.
The near side of the Moon is the lunar hemisphere that always faces towards Earth, opposite to the far side. Only one side of the Moon is visible from Earth because the Moon rotates on its axis at the same rate that the Moon orbits the Earth—a situation known as tidal locking.
Earthrise is a photograph of Earth and part 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 influential environmental photograph ever taken".
The Moon is the largest natural satellite of and the closest major astronomical object to Earth. The Moon may be observed by using a variety of optical instruments, ranging from the naked eye to large telescopes. The Moon is the only celestial body upon which surface features can be discerned with the unaided eyes of most people.
In astronomy, a phase curve describes the brightness of a reflecting body as a function of its phase angle. The brightness usually refers the object's absolute magnitude, which, in turn, is its apparent magnitude at a distance of one astronomical unit from the Earth and Sun.
Ralf Vandebergh is a Dutch astronomer, professional photographer and veteran satellite spotter from Nijswiller. He is known for photographing the Sun, Moon, planets, satellites, NASA Space Shuttles, and the International Space Station from Earth using a telescope-mounted camera.
Sian Hayley "Leo" Proctor is an American commercial astronaut, geology professor, artist, author, and science communicator. She became the first female commercial spaceship pilot on the all-civilian Inspiration4 orbital spaceflight, 15 September 2021. As pilot of the Inspiration4's SpaceX Crew Dragon space capsule, Proctor became the first African-American woman to pilot a spacecraft. She was also the education outreach officer for the first Hawaii Space Exploration Analog and Simulation (HI-SEAS) Mission.
The Earth phase, Terra phase, terrestrial phase, or phase of Earth, is the shape of the directly sunlit portion of Earth as viewed from the Moon. From the Moon, the Earth phases gradually and cyclically change over the period of a synodic month, as the orbital positions of the Moon around Earth and of Earth around the Sun shift.
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