Moon Glossary: P - Z

moon, glossary


Palus - It is a term that describes locations on the Moon that look like swamps or dark spots. The word has Latin origin.
Parallax - The process that we see from the point of the Earth, when we look at the sky while walking and the stars and the Moon seem to move with us. It happens only due to the movement of the observer.
Partial Eclipse - It happens when a celestial body is in the middle of two objects: an object of light, and another one. So it casts two shadows: full shadow - umbra and half-shadow - penumbra. Umbra blocks the source of the light fully and penumbra- partially. When the celestial body traps into penumbra it is called partial eclipse.
Penumbra - The term used to describe a slight shadow of a half-shadow cast by a celestial body that doesn't block the source of light fully.
Perigee - The nearest point to our planet in the lunar orbit.
Perigean Tide - The tide that takes place when the Moon is at its nearest point to our planet in terms of lunar orbit. Such tides are usually extremely high.
Perihelion - The point in the orbit of a particular heavenly body, when it is the nearest to the Sun.
Perilune - The point in the orbit of a particular heavenly body, when it is the nearest to the Moon.
Phases - Concerning the Moon, the phase describes the various level of lunar illumination by the Sun and consequentially it depicts different shapes of the Moon that are seen from the Earth.


Quadrature - When to celestial bodies are situated 90° apart from the Earth's perspective this phenomenon is called quadrature. For instance the Moon can be 90° to the Sun as it is seen from our planet.


Radius - It is a diameter of any sphere or circle that is divided in two.
Regression of nodes - when the Sun intercrosses lunar orbit on its way - the Moon's nodes make slight moves to the west, the process is called regression.
Revolution - A term to depict the motion of particular celestial body as it orbits another. The full revolution is a full orbit.
Rille - They are the “trenches” in the lunar surface which remind of channel or elongated gaps.
Rotation - The movement of a spherical body that revolves around its own axle. To understand rotation: imagine a terrestrial globe spinning.


Saber's Beads - the diffused points of light that can be seen through the limb of lunar crescents. This phenomenon was firstly admitted by an astronomer from USA - Stephen Saber.
Saros Cycle - it can predict the possibility of eclipses. For example once in the 18 years and 11.3 days the Sun, the Moon and the Earth stand in the position that leads to eclipse.
Satellite - Anybody that orbits another heavenly body.
Selenography - This study researches the peculiarities and geographical surface of the Moon.
Sidereal Month - It is the period of full Moon circle and then it starts a new one. The approximate duration is - 27.3 days.
Sinus - The word originated from Latin and used to describe the feature of the lunar surface that reminds embayment.
Solar Eclipse - It happens when the Moon is situated between the Sun and the Earth, shading the Sun.
Spring Tide - it happens when the Sun, the Earth and the Moon are in conjunction or opposition towards one another. During the Full Moon and the New Moon the Sun takes charge of the Moon's powers and causes tides that are way higher than usual.


Tektites - the glass created under the influence of meteorite's fire and Earth's sand. The Earth and the Moon has a lot of Tektites.
Terminator - The outer line that defines the edge of the shadow (night) and light (day) on a certain heavenly body. Typical example of a terminator is any lunar phase.
Tides - increasing and declining levels of ocean caused by the Moon's and Sun's gravitational pull on the Earth.
Transit - it is a pass of the heavenly body that crosses another. It depends on the point of the observer.
Tropical Month - It is approximately 27.3 days needed for the Moon to come back to a particular space longitude.


Umbra - The full shadow that completely blocks the light from the celestial body.


Waning Moon - The time between the Full Moon and a New Moon, while the Moon shrinks and disappears from the sky, regarding to the location of the observer on the Earth.
Waxing Moon - The time between the New Moon and the Full Moon, while the Moon grows and shines fully in the night sky, regarding to the location of the observer on the Earth.

X, Y, Z

Young Crescent Moon - It is a shape of the Moon right after the New Moon.
Zenith - The point in the sky right above the observer, or 90° above. Zenith is a direct opposition to Nadir.