The

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 ...

is the largest

natural satellite A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are often colloquially referred to as ''moons ...

of and the closest major

astronomical object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...

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 surf ...

. The Moon may be observed by using a variety of

optical instrument An optical instrument (or "optic" for short) is a device that processes light waves (or photons), either to enhance an image for viewing or to analyze and determine their characteristic properties. Common examples include periscopes, microscope ...

s, ranging from the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...

to large

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to obse ...

s. The Moon is the only celestial body upon which surface features can be discerned with the unaided eyes of most people.

Optimal viewing times

Contrary to popular belief, the Moon should ideally not be viewed at its full phase. During a full moon, rays of sunlight are hitting the visible portion of the Moon

perpendicular In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the ''perpendicular symbol'', ⟂. It can ...

to the surface. As a result, there is less surface detail visible during a full moon than during other phases (such as the quarter and crescent phases) when sunlight hits the Moon at a much shallower angle. The brightness of a full moon as compared to a phase where a smaller percentage of the surface is illuminated tends to wash out substantial amounts of detail and can actually leave an

afterimage AfterImage is a Filipino rock band formed in 1986, best known for their songs "Habang May Buhay", "Next in Line", and "Mangarap Ka". They disbanded in 1997 and became active again in 2008 after they reunited and released their fourth studio alb ...

on an observer's eye that can persist for several minutes. First quarter (six to nine days past

new moon In astronomy, the new moon is the first lunar phase, when the Moon and Sun have the same ecliptic longitude. At this phase, the lunar disk is not visible to the naked eye, except when it is silhouetted against the Sun during a solar eclip ...

) is generally considered the best time to observe the Moon for the average stargazer.

Shadow A shadow is a dark area where light from a light source is blocked by an opaque object. It occupies all of the three-dimensional volume behind an object with light in front of it. The cross section of a shadow is a two-dimensional silhouette ...

s and detail are most pronounced along the "

terminator Terminator may refer to: Science and technology Genetics * Terminator (genetics), the end of a gene for transcription * Terminator technology, proposed methods for restricting the use of genetically modified plants by causing second generation s ...

", the dividing line between the illuminated (day side) and dark (night side) of the Moon.

Suggested viewing tools

Naked eye

Generally, the Moon can be viewed even with the naked eye, however it may be more enjoyable with optical instruments. The primary lunar surface features detectable to the naked eye are the lunar maria or "seas", large

basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...

ic plains which form imaginary figures as the traditional "

Moon Rabbit The Moon rabbit or Moon hare is a mythical figure in East Asian and indigenous American folklore, based on pareidolia interpretations that identify the dark markings on the near side of the Moon as a rabbit or hare. In East Asia, the rabbit i ...

" or familiar "

Man in the Moon In many cultures, several pareidolic images of a human face, head or body are recognized in the disc of the full moon; they are generally known as the Man in the Moon. The images are based on the appearance of the dark areas (known as lunar m ...

". The maria cover about 35% of the surface. The contrast between the less reflective dark gray maria and the more reflective gray/white lunar highlands is easily visible without optical aid. Under good viewing conditions, those with keen eyesight may also be able to see some of the following features: #Bright region around

Copernicus Nicolaus Copernicus (; pl, Mikołaj Kopernik; gml, Niklas Koppernigk, german: Nikolaus Kopernikus; 19 February 1473 – 24 May 1543) was a Renaissance polymath, active as a mathematician, astronomer, and Catholic canon, who formula ...

Mare Nectaris Mare Nectaris (Latin ''nectaris'', the "Sea of Nectar") is a small lunar mare or sea (a volcanic lava plain noticeably darker than the rest of the Moon's surface) located south of Mare Tranquillitatis southwest of Mare Fecunditatis, on the ne ...

Mare Humorum Mare Humorum (Latin ''hūmōrum'', the "Sea of Moisture") is a lunar mare. The impact basin it is located in is 425 kilometers across. Geology It was not sampled by the Apollo program, so a precise age has not been determined. However, geologi ...

#Bright region around

Kepler Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws of ...

# Gassendi region # Plinius region #

Mare Vaporum Mare Vaporum (Latin ''vapōrum'', the "sea of vapors") is a lunar mare located between the southwest rim of Mare Serenitatis and the southeast rim of Mare Imbrium. It was named by Giovanni Battista Riccioli in 1651.''Autostar Suite Astronome ...

# Lubiniesky region #

Sinus Medii Sinus Medii (Latin ''sinus mediī'' "Middle Bay") is a small lunar mare. It takes its name from its location at the intersection of the Moon's equator and prime meridian; as seen from the Earth, this feature is located in the central part of the ...

#Faintly shaded area near Sacrobosco #Dark spot at foot of

Mons Huygens Mons Huygens is the Moon's tallest mountain (but not its highest point, which is Selenean Summit). It is about high and is located in the Montes Apenninus. Adjacent to the west is Mons Ampère. The Montes Apenninus were formed by the impact tha ...

Riphean Mountains In Greco-Roman geography, the Riphean Mountains (also Riphaean; , or ; '' grc, Ῥιπαῖα ὄρη''; Latin: ''Rhipaei'' or ''Riphaei montes'') were a supposed mountain range located in the far north of Eurasia. The name of the mountains is ...

Another interesting phenomenon visible with the naked eye is

Earthshine 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 ...

. Best visible shortly before or after new a moon (during the waning and waxing crescent phases respectively), Earthshine is the faint glow of the non-illuminated (night) side of the Moon caused by sunlight reflecting off the surface of Earth (which would appear nearly full to an observer situated on the Moon at this time) and onto the night side of the Moon. By the time the Moon reaches first its quarter however, the sunlight illuminated portion of the Moon becomes far too bright for Earthshine to be seen with the naked eye, however it can still be observed telescopically.

Binoculars and telephoto camera lenses

Binoculars are commonly used by those just beginning to observe the Moon, and many experienced

amateur astronomers Amateur astronomy is a hobby where participants enjoy observing or imaging celestial objects in the sky using the unaided eye, binoculars, or telescopes. Even though scientific research may not be their primary goal, some amateur astronomers ...

prefer the view through binoculars over that through higher-power telescopes due to the larger

field of view The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation. Humans a ...

. Their high level of portability makes them the simplest device used to see more detail on the lunar surface than what is visible to the naked eye. The primary disadvantage of binoculars is that they cannot be held as steadily unless one utilizes a commercial or homemade binocular tripod. The recent introduction of image-stabilized binoculars has changed this to some extent; however, cost is still an issue. A 10× pair of binoculars will magnify the Moon approximately as much as a 200mm camera lens can. The photos below were shot with a 200mm lens. The first photo was taken on 13 November 2016 at 6:20pm PST, observing the full Moon just hours before it would officially become the largest

supermoon A supermoon is a full moon or a new moon that nearly coincides with perigee—the closest that the Moon comes to the Earth in its elliptic orbit—resulting in a slightly larger-than-usual apparent size of the lunar disk as viewed from Earth. ...

since 1948. The second photo was shot 24 hours later, and the contrast was enhanced to bring out details such as mountainous terrain. The next supermoon will not occur this large until the year 2034. File:Pre-Super Moon 11-13-2016.jpg, Pre-supermoon on , at 6:20 pm PST, just a few hours before it would be officially called the "Supermoon of 2016" File:Super-Moon-3 11-14-2016.jpg,

Supermoon A supermoon is a full moon or a new moon that nearly coincides with perigee—the closest that the Moon comes to the Earth in its elliptic orbit—resulting in a slightly larger-than-usual apparent size of the lunar disk as viewed from Earth. ...

officially on , at 7:19 pm PST

Telescopes

To some it may be more desirable to utilize a telescope in which case far more options for observing the Moon exist. Even a small, well-made telescope will show the observer much greater detail than is visible with the naked eye or small binoculars. As the

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An ...

of the telescope mirror (in the case of a

reflecting telescope A reflecting telescope (also called a reflector) is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century by Isaac Newton as an alternati ...

) or lens (in the case of a

refracting telescope A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope). The refracting telescope design was originally used in spyglasses and ...

) increases, smaller and smaller features will begin to appear. With large amateur telescopes, features as small as 0.6 miles (1 km) in diameter can be observed depending on atmospheric conditions. Most astronomers use different kinds of filters in order to bring out the contrast of certain surface features. Simple

neutral density filter In photography and optics, a neutral-density filter, or ND filter, is a filter that reduces or modifies the intensity of all wavelengths, or colors, of light equally, giving no changes in hue of color rendition. It can be a colorless (clear) o ...

s are also common as they can cut down the amount of light reaching the eye by 60–95%, something that is helpful especially when observing a full or gibbous moon so the surface does not appear as washed out.

Lunar occultations

occultation An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks ...

is an astronomical event where a celestial object appears completely hidden by another, closer body (with a greater

angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it i ...

) due to the passage of the closer object directly between the more distant object and the observer. Due to the large apparent size of the Moon, lunar occultations are quite common and when a bright celestial object is involved, the result is an event that can be easily observed using the naked eye. The Moon almost constantly occults faint stars as it orbits the Earth but because even a young Moon appears immensely brighter than these stars, these events are difficult to observe using amateur telescopes. However, the Moon does frequently occult brighter stars and even

planets A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young ...

due to its close proximity to the

ecliptic The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic agai ...

. Four first magnitude stars,

Regulus Regulus is the brightest object in the constellation Leo and one of the brightest stars in the night sky. It has the Bayer designation designated α Leonis, which is Latinized to Alpha Leonis, and abbreviated Alpha Leo or α Leo. Reg ...

Spica Spica is the brightest object in the constellation of Virgo and one of the 20 brightest stars in the night sky. It has the Bayer designation α Virginis, which is Latinised to Alpha Virginis and abbreviated Alpha Vir or α Vir. Anal ...

Antares Antares is the brightest star in the constellation of Scorpius. It has the Bayer designation α Scorpii, which is Latinised to Alpha Scorpii. Often referred to as "the heart of the scorpion", Antares is flanked by σ Scorpii and τ S ...

, and

Aldebaran Aldebaran (Arabic: “The Follower”, "الدبران") is the brightest star in the zodiac constellation of Taurus. It has the Bayer designation α Tauri, which is Latinized to Alpha Tauri and abbreviated Alpha Tau or α Tau. Aldeb ...

, are sufficiently close to the ecliptic that they may be occulted by the Moon. In addition, two

star cluster Star clusters are large groups of stars. Two main types of star clusters can be distinguished: globular clusters are tight groups of ten thousand to millions of old stars which are gravitationally bound, while open clusters are more loosely clus ...

s visible to the naked eye, the

Beehive Cluster The Beehive Cluster (also known as Praesepe (Latin for "manger" or "crib"), M44, NGC 2632, or Cr 189), is an open cluster in the constellation Cancer. One of the nearest open clusters to Earth, it contains a larger population of stars than other ...

and the

Pleiades The Pleiades (), also known as The Seven Sisters, Messier 45 and other names by different cultures, is an asterism and an open star cluster containing middle-aged, hot B-type stars in the north-west of the constellation Taurus. At a distance ...

, are often occulted. Depending on one's location on the Earth, there are usually several occultations involving naked eye objects every year and many more that can be observed using binoculars or a telescope. Accurate timings (accuracy at least +/-0.02 seconds) of lunar occultations are scientifically useful in fields such as lunar topography,

astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. Histor ...

, and

binary star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in ...

studies and are collected by the International Occultation Timing Association
IOTA
The archive of lunar occultations observations, (1623 to the present day) are maintained at

VizieR A vizier (; ar, وزير, wazīr; fa, وزیر, vazīr), or wazir, is a high-ranking political advisor or minister in the near east. The Abbasid caliphs gave the title ''wazir'' to a minister formerly called '' katib'' (secretary), who was ...

Transient Lunar Phenomena

transient lunar phenomenon A transient lunar phenomenon (TLP) or lunar transient phenomenon (LTP) is a short-lived light, color or change in appearance on the surface of the Moon. The term was created by Patrick Moore in his co-authorship of NASA Technical Report R-277 ''C ...

(TLP) or "Lunar Transient Phenomena" (LTP), refers to short-lived lights, colors, or changes in appearance of the lunar surface. Claims of these phenomena go back at least 1,000 years, with some having been observed independently by multiple witnesses or some in the scientific community. Nevertheless, the majority of transient lunar phenomena reports are irreproducible and do not possess adequate control experiments that could be used to distinguish among alternative

hypotheses A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obser ...

. Few reports concerning these phenomena are ever published in

peer reviewed Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work ( peers). It functions as a form of self-regulation by qualified members of a profession within the relevant field. Peer revie ...

scientific journals, and rightfully or wrongfully, the lunar scientific community rarely discusses these observations. Most lunar scientists will acknowledge that transient events such as

outgassing Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (which ...

and impact cratering do occur over

geologic time The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geoc ...

: the controversy lies in the frequency of such events. A number of astronomical societies around the world have implemented their own TLP watch programs and TLP alert networks.

Features with reported TLP Associations

Agrippa (crater)
Alphonsus (crater)

Archimedes (crater) Archimedes is a large lunar impact crater on the eastern edges of the Mare Imbrium. Its diameter is 81 km. Description The diameter of Archimedes is the largest of any crater on the Mare Imbrium. The rim has a significant outer rampart ...

Aristarchus (crater) Aristarchus is a lunar impact crater that lies in the northwest part of the Moon's near side. It is considered the brightest of the large formations on the lunar surface, with an albedo nearly double that of most lunar features. The feature i ...

Aristoteles (crater)
Atlas (crater)
Alphonsus (crater)

Bullialdus (crater) Bullialdus is a lunar impact crater located in the western part of the Mare Nubium. It was named after French astronomer Ismaël Boulliau. To the north by north-west is the broken-rimmed and lava-flooded crater Lubiniezky. South-west of Bulliald ...

Calippus (crater)
Cassini (crater)

Censorinus (crater) Censorinus is a tiny lunar impact crater located on a rise to the southeast of the Mare Tranquillitatis. It is named after the ancient Roman writer Censorinus. To the northeast is the crater Maskelyne. Censorinus is distinguished by an area ...

Clavius (crater) Clavius is one of the largest crater formations on the Moon and the second largest crater on the visible near side (very close in size to Deslandres). It is located in the rugged southern highlands of the Moon, to the south of the prominent r ...

Cleomedes (crater)
Copernicus (crater)
Eratosthenes (crater)
Fracastorius (crater)

Gassendi (crater) Gassendi is a large lunar impact crater feature located at the northern edge of Mare Humorum. It was named after French astronomer Pierre Gassendi. The formation has been inundated by lava during the formation of the mare, so only the rim ...

Grimaldi (crater) Grimaldi is a large basin located near the western limb of the Moon. It lies to the southwest of the Oceanus Procellarum, and southeast of the crater Riccioli. Between Oceanus Procellarum is Damoiseau, and to the north is Lohrmann. The inner wal ...

Herodotus (crater)
Sinus Iridum
Kepler (crater)
Lambert (lunar crater)

Linné (crater) Linné is a small lunar impact crater located in the western Mare Serenitatis. It was named after Swedish botanist Carl Linnaeus. The mare around this feature is virtually devoid of other features of interest. The nearest named crater is Banting t ...

Manilius (crater) Manilius is a lunar impact crater on the northeast edge of Mare Vaporum. Its diameter is 38 km. Description Manilius has a well-defined rim with a sloping inner surface that runs directly down to the ring-shaped mound of scree along the b ...

Mare Crisium Mare Crisium (Latin ''crisium'', the "Sea of Crises") is a lunar mare located in the Moon's Crisium basin, just northeast of Mare Tranquillitatis. The basin is of the Pre-Imbrian period, 4.55 to 3.85 billion years ago. Characteristics Mare C ...

Menelaus (crater) Menelaus () is a young lunar impact crater located on the southern shore of Mare Serenitatis near the eastern end of the Montes Hæmus mountain range. Its diameter is 27 km. To the southwest is the small crater Auwers, and to the west-sou ...

Mons Piton Mons Piton is an isolated Moon, lunar mountain that is located in the eastern part of the Mare Imbrium, to the north-northwest of the crater Aristillus (crater), Aristillus. Due east of Mons Piton is the flooded crater Cassini (lunar crater), C ...

Mons Pico Mons Pico is a solitary lunar mountain that lies in the northern part of the Mare Imbrium basin, to the south of the dark-floored crater Plato and on the southern rim of a ghost crater. This peak forms part of the surviving inner ring of the Im ...

Picard (crater) Picard is a lunar impact crater that lies in Mare Crisium. The crater is named for 17th century French astronomer and geodesist Jean Picard. It is the biggest non-flooded crater of this mare, being slightly larger than Peirce to the north-north ...

Plato (crater) 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 m ...

Posidonius (crater)
Proclus (crater)
Promontorium Laplace

Riccioli (crater) Riccioli is a lunar impact crater located near the western limb of the Moon. It lies just to the northwest of a larger crater, Grimaldi. To the southwest are the craters Hartwig and Schlüter that lie on the northeastern edge of Montes Cord ...

Schickard (crater)
Taruntius (crater)

Theophilus (crater) Theophilus is a prominent lunar impact crater that lies between Sinus Asperitatis in the north and Mare Nectaris to the southeast. It partially intrudes into the comparably sized crater Cyrillus to the southwest. To the east is the smaller ...

Timocharis (crater) Timocharis is a prominent lunar impact crater located on the Mare Imbrium. It was named after ancient Greek astronomer Timocharis. The closest crater of comparable dimensions is Lambert to the west. The smaller craters Feuillée and Beer lie ...

Tycho (crater) Tycho () is a prominent lunar impact crater located in the southern lunar highlands, named after the Danish astronomer Tycho Brahe (1546–1601)., accessed 19 February 2019 It is estimated to be 108 million years old. To the south of Tycho is ...

Vallis Schröteri Schroter's Valley, frequently known by the Latinized name Vallis Schröteri, is a sinuous valley or rille on the surface of the near side of the Moon. It is located on a rise of continental ground, sometimes called the Aristarchus plateau, that ...

Zagut (crater)

Blinking devices

A number of observers employ different colored

filters Filter, filtering or filters may refer to: Science and technology Computing * Filter (higher-order function), in functional programming * Filter (software), a computer program to process a data stream * Filter (video), a software component th ...

to determine colored transient events on the Moon. By quickly alternating filters of opposing colors in the telescopic light path, faintly colored areas on the Moon can stand out more by appearing to flicker on and off. A red area will appear brighter when viewed through a red filter and darker when seen through a blue filter. It is possible to alternate the filters manually however, this requires a certain dexterity of the hand and good coordination. A purpose built filter wheel is much more viable alternative, and this can be motorized, so the observer can devote all of their concentration to what is going on through the eyepiece. There are, however a number of features on the Moon that will appear to blink naturally, among them being the southwestern part of Fracastorius (crater), and a section of the western wall of

. A special filter wheel called a "crater extinction device" is capable of measuring the brightness of an individual lunar feature to be measured according to the point where it ceases to be visible.

Crescent Moon

During the first two weeks, the Moon is called 'crescent' (when the illuminated portion increases) while it is 'falling' for the next two weeks. For two weeks, the crescent Moon wanes before and waxes after

, or "change of Moon". The Moon when other than crescent or dark, is called a gibbous, waxing before and waning after

full moon The full moon is the lunar phase when the Moon appears fully illuminated from Earth's perspective. This occurs when Earth is located between the Sun and the Moon (when the ecliptic longitudes of the Sun and Moon differ by 180°). This mean ...

Other items of interest

Because the Moon is so bright, it is especially interesting to see objects "superimposed" on it. One particular point of interest is an ISS (

International Space Station The International Space Station (ISS) is the largest Modular design, modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos ( ...

) transit.

References

Observing the Moon: The Modern Astronomer's Guide
–

PDF Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems. ...

format * *Grego, Peter (2005), The Moon and how to Observe it, Springer, *Levy, David (2001), David Levy's Gude to the Night Sky,

Cambridge University Press Cambridge University Press is the university press of the University of Cambridge. Granted letters patent by Henry VIII of England, King Henry VIII in 1534, it is the oldest university press in the world. It is also the King's Printer. Cambr ...

,
The simple geometry of Sun, Moon, and star paths
{{DEFAULTSORT:Observing The Moon Observational astronomy Moon