The

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

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 colloquially referred to as moons, a deriv ...

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 within the observable universe. In astronomy, the terms ''object'' and ''body'' are of ...

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. The Moon may be observed by using a variety of

optical instrument An optical instrument 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, microscopes, telescopes, and camera ...

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 magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...

to large

telescope A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...

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 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 mathematica ...

. During a full moon, rays of sunlight are hitting the visible portion of the Moon

perpendicular In geometry, two geometric objects are perpendicular if they intersect at right angles, i.e. at an angle of 90 degrees or π/2 radians. The condition of perpendicularity may be represented graphically using the '' perpendicular symbol'', � ...

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 An afterimage, or after-image, is an image that continues to appear in the eyes after a period of exposure to the original image. An afterimage may be a normal phenomenon (physiological afterimage) or may be pathological (palinopsia). Illusory ...

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 eclipse. ...

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

Shadow A shadow is a dark area on a surface where light from a light source is blocked by an object. In contrast, shade occupies the three-dimensional volume behind an object with light in front of it. The cross-section of a shadow is a two-dimensio ...

s and detail are most pronounced along the " terminator", the dividing line between the illuminated (day side) and dark (night side) of the Moon. It is a common misconception that the moon is not visible during the

daytime Daytime or day as observed on Earth is the period of the day during which a given location experiences Daylight, natural illumination from direct sunlight. Daytime occurs when the Sun appears above the local horizon, that is, anywhere on the ...

, although if the moon is a thin crescent or close to the Sun, viewing can require using a telescope. A person must be very cautious if they use a telescope where the Sun is nearby if they do not have appropriate filtering on that telescope, for the Sun's light is strong enough to very quickly blind a person through a telescope that does not have sufficient filters.

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 aphanite, 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 planetary surface, surface of a terrestrial ...

ic plains which form imaginary figures as the traditional "

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

" 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 (19 February 1473 – 24 May 1543) was a Renaissance polymath who formulated a mathematical model, model of Celestial spheres#Renaissance, the universe that placed heliocentrism, the Sun rather than Earth at its cen ...

# Mare Nectaris # Mare Humorum #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 p ...

# 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 Astronomer ...

# 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 #

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

Another interesting phenomenon visible with the naked eye is Earthshine. Best visible shortly before or after a new 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 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 angle, angular extent of the observable world that is visual perception, 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 elec ...

. 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 Image-stabilized binoculars are binoculars that have a mechanism for decreasing the apparent motion of the view due to binocular movement. Such binoculars are designed to minimize image shaking in hand-held applications. Higher- power 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 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 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, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...

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 (optics), lens as its objective (optics), objective to form an image (also referred to a dioptrics, dioptric telescope). The refracting telescope d ...

) 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 photographic filter, 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 ...

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 f ...

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 separation (in units of angle) describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the ''visual an ...

) 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 generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets by the most restrictive definition of the te ...

due to its close proximity to the

ecliptic The ecliptic or ecliptic plane is the orbital plane of Earth's orbit, Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. Fr ...

. Four first

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

stars,

Regulus Regulus is the brightest object in the constellation Leo (constellation), Leo and one of the List of brightest stars, brightest stars in the night sky. It has the Bayer designation designated α Leonis, which is Latinisation of names, ...

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. Analys ...

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

, and

Aldebaran Aldebaran () is a 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. Aldebaran varies in brightness from an apparent vis ...

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

star cluster A star cluster is a group of stars held together by self-gravitation. Two main types of star clusters can be distinguished: globular clusters, tight groups of ten thousand to millions of old stars which are gravitationally bound; and open cluster ...

s visible to the naked eye, the

Beehive Cluster The Beehive Cluster (also known as Praesepe (Latin for "manger", "cot" 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 tha ...

and the

Pleiades The Pleiades (), also known as Seven Sisters and Messier 45 (M45), is an Asterism (astronomy), asterism of an open cluster, open star cluster containing young Stellar classification#Class B, B-type stars in the northwest of the constellation Tau ...

, 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 Astronomical object, celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, th ...

, and

binary star A binary star or binary star system 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 as separate stars us ...

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 (; ; ) is a high-ranking political advisor or Minister (government), minister in the Near East. The Abbasids, Abbasid caliphs gave the title ''wazir'' to a minister formerly called ''katib'' (secretary), who was at first merely a help ...

Transient Lunar Phenomena

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

(TLP) or "Lunar Transient Phenomena" (LTP), refers to short-lived lights, colors, or changes in appearance of the

lunar surface The geology of the Moon (sometimes called selenology, although the latter term can refer more generally to "lunar science") is the structure and composition of the Moon, which is quite different from that of Earth. The Moon lacks a true atmosphe ...

. 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 (: hypotheses) is a proposed explanation for a phenomenon. A scientific method, scientific hypothesis must be based on observations and make a testable and reproducible prediction about reality, in a process beginning with an educ ...

. 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 review ...

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 (whic ...

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 geochronolo ...

: 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) Agrippa is a lunar impact crater that is located at the southeast edge of the Mare Vaporum. It is located to the north of the crater Godin, the irregular Tempel lies just to the east. To the north and northeast, the rille designated Rima Ari ...

Alphonsus (crater) Alphonsus is an ancient impact crater on the Moon that dates from the pre-Nectarian era. (Older sources state that it is Nectarian in age.) It is located on the lunar highlands on the eastern end of Mare Nubium, west of the Imbrian Highlands, ...

Archimedes (crater) Archimedes is a large lunar impact crater on the eastern edges of the Mare Imbrium. It was named by the IAU in 1935. Description The diameter of Archimedes is the largest of any crater on the Mare Imbrium. The rim has a significant outer ra ...

Aristarchus (crater) Aristarchus is a Lunar craters, 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. ...

Aristoteles (crater)
Atlas (crater)
Bullialdus (crater)

Calippus (crater) Calippus is a small Lunar craters, lunar impact crater that is located on the eastern edge of the rugged Montes Caucasus mountain range in the northern part of the Moon. It was named after Greek astronomer Callippus of Cyzicus. It lies to the so ...

Cassini (crater)

Censorinus (crater) Censorinus is a 3.8 km Lunar craters, lunar impact crater located on a rise to the southeast of the Mare Tranquillitatis. It is named after the ancient Rome, ancient Roman writer Censorinus. To the northwest is the crater Maskelyne (crate ...

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 ...

Cleomedes (crater) Cleomedes is a prominent lunar impact crater located in the northeast part of the visible Moon, to the north of Mare Crisium. It was named by the IAU in 1935 after Greek astronomer Cleomedes. It is surrounded by rough ground with multiple crate ...

Copernicus (crater)
Eratosthenes (crater)
Fracastorius (crater)
Gassendi (crater)
Grimaldi (crater)

Herodotus (crater) Herodotus is a Lunar craters, lunar impact crater located on a low shelf in the midst of the Oceanus Procellarum. To the east is the slightly larger crater Aristarchus (crater), Aristarchus. West across the Lunar mare, mare is Schiaparelli (lu ...

Sinus Iridum Sinus Iridum (Latin ''sinus īridum'' "Bay of Rainbows") 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 pr ...

Kepler (crater)

Lambert (lunar crater) Lambert is a lunar impact crater on the southern half of the Mare Imbrium basin. It was named after Swiss polymath Johann Heinrich Lambert. It lies to the east and somewhat south of the slightly larger crater Timocharis. To the south is the sm ...

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

Manilius (crater) Manilius is a Lunar craters, 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 ...

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. Mare Crisium is a basin of Nectarian age. It was formed by the flooding of basaltic lava that fill ...

Menelaus (crater)
Mons Piton

Mons Pico Mons Pico is a solitary Moon, lunar mountain that lies in the northern part of the Mare Imbrium basin, to the south of the dark-floored crater Plato (crater), Plato and on the southern rim of a Palimpsest (planetary astronomy), ghost crater. This ...

Picard (crater) Picard is a Lunar craters, 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 (cra ...

Plato (crater)

Posidonius (crater) Posidonius is a lunar impact crater that is located on the north-eastern edge of Mare Serenitatis, to the south of Lacus Somniorum. It was named after ancient Greek philosopher and geographer Posidonius of Apamea. The crater Chacornac is attac ...

Proclus (crater) Proclus is a young lunar impact crater located to the west of the Mare Crisium on the east shore of the Palus Somni. Its diameter is 27 km and it was named after 5th century Greek mathematician, astronomer and philosopher Proclus. It lie ...

Promontorium Laplace Promontorium Laplace is a raised mountainous cape situated at the end of Montes Jura in Mare Imbrium on the near side of the Moon. Its selenographic coordinates are 46.8° N, 25.5° W and it is 2600 meters high. It forms the northeast boundary o ...

Riccioli (crater)

Schickard (crater) Schickard is a Lunar craters, lunar impact crater of the form called a walled plain. It lies in the southwest sector of the Moon, near the lunar limb. As a result, the crater appears rectangle, oblong due to foreshortening. Attached to the northe ...

Taruntius (crater) Taruntius is a Lunar craters, lunar impact crater on the northwestern edge of Mare Fecunditatis. It was named after ancient Roman philosopher, mathematician and astrologer Lucius Tarutius Firmanus. To the northwest is the lava-flooded crater Lawr ...

Theophilus (crater)

Timocharis (crater) Timocharis is a prominent Lunar craters, lunar impact crater located on the Mare Imbrium. It was named after ancient Greek astronomer Timocharis. The closest crater of comparable dimensions is Lambert (lunar crater), Lambert to the west. The sm ...

Tycho (crater)
Vallis Schröteri
Zagut (crater)

Blinking devices

A number of observers employ different colored

filters Filtration is a physical process that separates solid matter and fluid from a mixture. Filter, filtering, filters or filtration may also refer to: Science and technology Computing * Filter (higher-order function), in functional programming * Fil ...

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 Plato (crater). 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.

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 a large space station that was Assembly of the International Space Station, assembled and is maintained in low Earth orbit by a collaboration of five space agencies and their contractors: NASA (United ...

) 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 Inc., Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, computer hardware, ...

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 was the university press of the University of Cambridge. Granted a letters patent by King Henry VIII in 1534, it was the oldest university press in the world. Cambridge University Press merged with Cambridge Assessme ...

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

Observation Observation in the natural sciences is an act or instance of noticing or perceiving and the acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also involve the percep ...