The Moon Dictionary

Measured in days. For example, a Full Moon typically has an age of approximately 14.7 days.

The Moon has a surprisingly low albedo of about 0.12, meaning it reflects only 12% of the sunlight that hits it — similar to worn asphalt. It appears bright only because of the darkness of surrounding space. A Supermoon’s increased brightness is partly due to reduced distance, not any change in albedo.

This occurs when the moon is near apogee (farthest from Earth), making it appear too small to fully cover the sun’s disc.

Observers standing in the antumbra will see an Annular Eclipse (Ring of Fire). It is the cone-shaped extension of the umbra beyond the point where the Moon no longer fully blocks the Sun.

When a Full Moon coincides with apogee, it is sometimes called a “Micromoon” — it appears slightly smaller and dimmer than average. Together, apogee and perigee are called the apsides.

The line connecting them is called the “line of apsides.” Because the Moon’s orbit is not perfectly circular, these points shift slightly with each orbit.

Known in astrology as the “North Node” or “Dragon’s Head.” Eclipses can only occur when the Moon is near one of the two nodes.

Named because this was the time of year when beavers began to take shelter in their lodges for winter.

It can also refer to a February with no Full Moon. It is the invisible counterpart to a Blue Moon, and because New Moons are not visible, a Black Moon passes unnoticed by most people.

The red colour comes from Rayleigh scattering — sunlight filtering through Earth’s atmosphere bends around the planet and projects the colours of all the world’s sunrises and sunsets onto the lunar surface simultaneously.

The older “seasonal” definition refers to the third Full Moon in a season that has four. Neither definition causes the Moon to appear blue. The phrase “once in a blue moon” predates the astronomical usage.

Named because this is the time of year when male deer (bucks) begin to grow their new velvet antlers.

Named for the settling in of winter cold. Also sometimes called the Long Night Moon.

These names are not official astronomical designations. They arise when multiple independent phenomena coincide — e.g., a Supermoon + Total Lunar Eclipse + January Full Moon. While dramatic, each component is a normal event; their overlap is just a scheduling coincidence.

These are popular targets for astrophotographers. Technically, two objects are in conjunction when they share the same right ascension as viewed from Earth.

Known for its terraced inner walls and central peaks. It is often cited as the textbook example of a complex lunar impact crater.

Often used when the Harvest Moon falls in October instead, making the September moon the “Corn Moon.”

Because the Moon has no atmosphere, weather, or tectonic activity, craters are preserved for billions of years. Famous examples include Tycho (with its visible rays) and Copernicus.

Often used interchangeably with “New Moon,” though some traditions distinguish the Dark Moon as the one or two days before the New Moon, when the crescent has fully disappeared.

There is no permanent “dark side.” Every part of the Moon receives sunlight over the course of a lunar month. The term “dark” originally meant unknown or hidden, not unlit. The correct term is Far Side.

Known in astrology as the “South Node” or “Dragon’s Tail.”

Also called the “Da Vinci Glow.” It lets you see the outline of the full lunar disc even when only a crescent is directly lit by the Sun. Best visible a few days either side of New Moon.

There are usually two eclipse seasons per year, roughly six months apart.

The Moon’s orbit is tilted about 5° relative to the ecliptic. This tilt is why eclipses don’t occur every month — the Moon usually passes slightly above or below Earth’s shadow at Full Moon.

Used in the calculation of the date of Easter and other moveable feasts in the Christian calendar.

First photographed by the Soviet Luna 3 probe in 1959. It is more heavily cratered than the near side and has far fewer maria (dark volcanic plains). It is not permanently dark — see “Dark Side (misnomer).”

It rises around noon and sets around midnight. It is called “First Quarter” because the Moon has completed one quarter of its orbit since New Moon.

Named for the abundance of wildflowers blooming during this month in the Northern Hemisphere.

The Moon is approximately 180° opposite the Sun in the sky. It rises at sunset and sets at sunrise. Technically, a Full Moon is also the Moon at opposition.

From the Latin gibbosus, meaning humpbacked. It describes two phases in the lunar cycle: Waxing Gibbous (growing toward Full) and Waning Gibbous (shrinking after Full).

The Metonic Cycle is a 19-year period after which the lunar phases recur on the same calendar days. The Golden Number is used in ecclesiastical calculations.

Famous for rising shortly after sunset for several consecutive nights, giving farmers extra light to bring in the harvest. This effect is caused by the shallow angle of the Moon’s orbit relative to the horizon at this time of year.

Its first sighting is crucial in the Islamic Calendar for determining the start of months such as Ramadan and Shawwal. In many Muslim communities, the month begins only when this crescent is physically observed.

Named because the bright moonlight historically allowed hunters to track game that was preparing for winter.

Due to libration, approximately 59% of the lunar surface is visible from Earth over the course of many months — not just the 50% you might expect from a tidally locked body.

Astronomers distinguish between the “bright limb” (the edge nearest the Sun, where sunlight meets shadow) and the “dark limb” (the edge in shadow). During occultations, stars disappear and reappear at the limb, allowing scientists to map its precise profile.

Can only happen during a Full Moon. There are three types: Total (full shadow, causes a Blood Moon), Partial (part of the Moon enters Earth’s umbra), and Penumbral (Moon passes through Earth’s lighter outer shadow, causing a subtle dimming).

This is the same as the Synodic Month and is the basis for most lunar calendars. It is longer than the Sidereal Month (27.3 days) because Earth itself is moving around the Sun during the Moon’s orbit.

While scientifically debunked, the “Lunar Effect” — the idea that the Full Moon influences human behaviour, ER admissions, or crime rates — remains a persistent cultural myth. Controlled studies have found no reliable correlation.

Also known as a Synodic Month, lasting approximately 29.53 days. Lunations are sequentially numbered; astronomers use this numbering system to identify specific lunar cycles.

Both terms are Latin — Mare means “sea” and Oceanus means “ocean.” Early astronomers mistook these dark plains for bodies of water. There is only one Oceanus: Oceanus Procellarum (Ocean of Storms). All other large dark plains are called Maria (e.g., Mare Tranquillitatis).

Discovered by the Greek astronomer Meton of Athens in 432 BC. It is the mathematical foundation of the Hebrew, Babylonian, and Greek lunisolar calendars, and is used to calculate the date of Easter.

It appears about 14% smaller and 30% dimmer than a Supermoon. Like “Supermoon,” this is an informal rather than official astronomical term.

The 22° angle is fixed by the geometry of hexagonal ice crystals. Folklore says a Moon halo predicts rain or snow, which is often true since cirrus clouds can precede weather fronts.

The Moon is actually the same angular size in both positions. The brain compares it to foreground objects (trees, buildings) near the horizon, causing it to be perceived as larger. This can be verified by measuring the Moon’s apparent size with a ruler at arm’s length.

Moonbows are much fainter than solar rainbows and often appear white to the naked eye. This is because in dim conditions, the eye switches from cone-dominated (colour-perceiving) to rod-dominated (monochromatic) vision — not because the colours aren’t there. Long-exposure photographs reveal their full spectrum. Best seen near waterfalls on bright Full Moon nights.

This is the best time for stargazing, as there is no moonlight to wash out faint objects. A solar eclipse can only occur at New Moon.

Occultations are used by astronomers to precisely refine the Moon’s orbital position and map the terrain of its limb. The sudden disappearance and reappearance of a star at the Moon’s edge is far more precise than direct measurement.

It is the only lunar “Oceanus” — all other dark plains are classified as “Maria” (Seas). It was the landing site of Apollo 12 and several Soviet Luna probes. See also: Mare / Mare vs. Oceanus.

A Full Moon is technically the Moon at opposition — it is 180° from the Sun. At opposition, the Moon rises at sunset and reaches its highest point at midnight. When opposition coincides with perigee, the result is a Supermoon (technically a “Perigee-Syzygy”).

A partial lunar eclipse looks as though a “bite” has been taken out of the Moon. A partial solar eclipse requires eclipse glasses to view safely.

In a Penumbral Lunar Eclipse, the Moon passes through Earth’s penumbra rather than its umbra. The Moon dims slightly and takes on a subtle shading, but does not turn red or disappear. Many penumbral eclipses are barely noticeable to the naked eye.

The result is a subtle darkening or shading of part of the lunar disc — easy to miss without prior knowledge. It does not produce the dramatic red colour of a Total Lunar Eclipse. Penumbral eclipses are the most common type of lunar eclipse.

A Full Moon at or near perigee is popularly called a “Supermoon.” Together with Apogee, it forms the pair known as the apsides.

It does not appear pink. Named after the pink phlox (Phlox subulata) wildflowers that bloom across North America in early spring.

These rays are composed of “ejecta” — pulverised rock thrown out during the impact. They appear bright because the material is freshly exposed and not yet darkened by space weathering. The rays of Crater Tycho are visible with the naked eye at Full Moon.

Commonly called “Moon dust.” Unlike Earth sand, lunar regolith particles are sharp and highly abrasive because there is no wind or water erosion to smooth them. This posed significant engineering challenges for Apollo missions.

Eclipses separated by a Saros cycle share nearly identical geometry. Known to ancient Babylonian astronomers, it was the basis for predicting eclipses long before orbital mechanics was understood.

It has a subtly bluish tint compared to other maria, owing to a high titanium content in its basaltic rock. Neil Armstrong and Buzz Aldrin landed here; Michael Collins orbited above.

The lunar equivalent of geography. Named for Selene, the Greek goddess of the Moon. Selenographers produced detailed maps long before any spacecraft reached the Moon.

This is shorter than the Synodic Month (29.53 days) because while the Moon orbits Earth, Earth itself moves along its orbit around the Sun — so the Moon needs extra time to “catch up” to the same phase.

Named for the heavy snowfalls typical in February across North America.

Can only happen during a New Moon. There are three types: Total (Moon fully covers the Sun), Partial (Moon covers only part of the Sun), and Annular (Moon appears too small to fully cover the Sun, leaving a Ring of Fire). Never look at a solar eclipse without certified eclipse glasses.

Named by Algonquin tribes for the short strawberry harvesting season in the northeastern United States and Canada.

Named because giant lake sturgeon were most readily caught in the Great Lakes during late summer.

There is no single agreed scientific definition. Astrologer Richard Nolle, who coined the term in 1979, defined it as a Full or New Moon within 90% of perigee. Other astronomers use stricter thresholds. The difference in apparent size between a Supermoon and a Micromoon is about 14%. The technical astronomical term is “Perigee-Syzygy.”

This is the basis for most lunar and lunisolar calendars throughout history. Also called a Lunar Month. It is longer than the Sidereal Month because Earth moves around the Sun during the Moon’s orbit.

Syzygy occurs at both New Moon (Sun–Moon–Earth) and Full Moon (Sun–Earth–Moon). It produces the strongest gravitational tidal forces, causing “Spring Tides” in the oceans.

The terminator is the best area to observe with a telescope. Craters, mountains, and ridges near the terminator cast long shadows, making surface features dramatically three-dimensional.

From the Latin for “lands.” The Terrae are older and far more heavily cratered than the dark Maria. They form the light-coloured regions visible to the naked eye.

Also called “Last Quarter.” It rises around midnight and sets around noon, making it visible in the morning sky.

This is why the Moon always shows the same face to Earth. It results from tidal friction over billions of years slowing the Moon’s original spin until it synchronised with its orbit.

Total Solar Eclipses briefly reveal the Sun’s outer atmosphere (the corona). Total Lunar Eclipses produce the Blood Moon effect. Both are considered among the most spectacular astronomical events visible from Earth.

Photographers plan ISS transits carefully, as the station crosses the lunar disc in under a second. The term also has a broader meaning in astronomy: the passage of the Moon across a specific meridian in the sky.

At Full Moon, Tycho’s rays stretch across much of the visible lunar face, making the crater appear as the Moon’s focal point. Named after the Danish astronomer Tycho Brahe.

To experience a Total Solar Eclipse, an observer must stand within the Moon’s umbra — a narrow corridor on Earth’s surface, typically only 100–200 km wide.

Illuminated on the left side as seen from the Northern Hemisphere. Rises in the early hours before dawn.

“Gibbous” means humpbacked — more than half lit. “Waning” means decreasing. This phase rises after sunset and is visible in the late night and morning sky.

Illuminated on the right side as seen from the Northern Hemisphere. The Hilal (Islamic crescent sighting) occurs during this phase.

“Gibbous” refers to the humpbacked appearance when more than half the disc is lit. “Waxing” means increasing. The Moon appears to grow larger each night during this phase.

Associated with the howling of hungry wolves outside villages during deep winter. One of the oldest recorded Full Moon names in North American tradition.

Named for the earthworms that begin to appear as the soil thaws, signalling the return of robins and the start of spring.

The Moon rarely passes through the exact zenith unless the observer is in the tropics (within about 28.5° of the equator, matching the Moon’s maximum declination). It is a key reference point when describing the Moon’s position in the sky.

Although not a lunar phenomenon, it is often confused with moonlight or lingering twilight. It is best seen during New Moon when skies are darkest — typically in the west after dusk or east before dawn, in spring and autumn respectively.