Moon Glossary: I - O

moon, glossary


Intercalation - the term that describes bissextile year, or the addition of other periods of time that can differ from our calendar in order to make solar year and our year coincide. It is needed, because a solar year is 365 ¼ days, so every four years we need to compensate one full day to synchronize with the Sun's rhythm. Some time ago people used to add periods longer than one day for intercalation. Lunar calendar may also have some additional days or months.


Lacus - It is a name derived from Latin to describe former lakes on the lunar or planet's surface.
Last Quarter - It is the time between the Waning Gibbous and Waning Crescent, when the half of the Moon can be seen and then begins to shrink and disappears from the night sky.
Latitude - A system to identify the location of the object on the surface of the celestial body regarding to the equator of this body. There are 90° of latitude north and south of the equator.
Librations - The slight shaking motions of the Moon while it orbits the Earth. These movements allow us to see a little bit of the side of the Moon that is unseen from the earth (far side). Due to this motion we see 59% of the Moon in general.
Limb - The very border of any celestial body.
Longitude - The system of coordinates on any celestial body that provides an accurate location regarding to the certain point of meridians. Meridians are the vertical lines that pass through the northern peak on the horizon joining at the celestial pole. The meridians were not established by the same pattern, so the center meridian of each body is chosen conditionally. On the Moon, zero meridian with 90° of longitude is located from the west to the east.
Lunar Day - 1) The time needed for the Moon to rotate around on its axis regarding to the Sun. 2) The amount of time needed for the Moon to rotate around the Earth's orbit. Lunar orbit isn't stable, so the time of such Lunar Day may be different.
Lunar Eclipse - It happens when the Earth blocks the light from the Sun and the Moon traps into the shadow of the Earth, when the Earth is situated amongst the Sun and the Moon.
Lunar Interval - the time difference between the phase of the Moon or tide by Greenwich and by local meridian time. The interval is the track the Moon passes through this time.
Lunar Rays - The traces left on the celestial body created by the collapse of meteors into the surface. They can be found on the lunar and Martian crust.
Lunitidal Interval - It is a difference in time of the closest point to the Earth and the tide that follows this process.


Magnitude - Celestial body's level of illumination. The lower the magnitude - the brighter the celestial object.
Mare - It refers to so-called seas on the Moon's surface. They are former now inactive volcanoes and consist of basalt. They are called "seas" because of their huge territory that can only be compared to our seas.
Mascon - A place on the surface of the celestial body which is in many times thicker than usual body's crust. Such mascons opt to create gravitational abnormalities. Moon has some reservoirs with same characteristics.
Meridian - Meridians are the vertical lines that pass through the northern peak on the horizon joining at the celestial pole. The meridians were not established by the same pattern, so the center meridian of each body is chosen conditionally.
Meteoroid - Meteoroid is a celestial body that has a mass enough to be seen by the radars, but not enough to be called an asteroid, as it is way smaller. The precise size of the meteoroids that can be considered as asteroids is a very debatable topic in scientific circles, but nowadays all the objects, smaller than 50 m in diameter are classified as meteoroids.
Moon - Earth's only natural satellite. Moon is a name for any natural satellite around any planet.
Moon Rise - it has the same conception as a sunrise, it is the first time we see the Moon during a day. Mostly, it depends on the location of the observer.
Moon Set - An antonym for the Moon Rise. It describes the way Moon disappears from the sky and also it depends on the location of the observer.


Nadir - The point with a -90° placement according to the position of an observer. In another words, it is the point right below the feet of the observer.
Neap Tide - During the First Quarter or the Last Quarter of the Moon, its powers are slightly blocked by the Sun. This is a reason of a high tide that is lower than a usual one.
Near Side - This lunar side can be seen from our planet.
New Moon - When the Moon is located on the same side as the Sun (from the perspective of Earth), the face of the Moon that we see isn't lighted by the Sun, because the Sun illuminates the side of the Moon which is unseen for us. As the Sun doesn't illuminate the side we see it is unseen in the sky.
Nodes - Points where the paths of the Moon and the Sun are crossed. The second name for nodes is Lunar Nodes.
Nodical Month - A full circle of the lunar month. It consists of 27.212220 days, during which the Moon makes full circle and returns to its starting node.


Occultation - The process of one celestial body blocking the light of another one, so it is situated between the observer and the body in question. The most common types of occultation are lunar and solar eclipses.
Old Crescent Moon - Phase of the Moon that takes place right after the Last Quarter till the New Moon. During Old Crescent Moon only slim crescent is visible in the night sky.
Opposition - The term refers to the number of degrees when two celestial bodies are situated opposite to one another from the Earth's point of view. The typical example is a lunar eclipse when the Moon and the Sun are located opposite to each other with the Earth amidst.
Orbital Eccentricity - Usually the orbital path is close to the shape of circle. Cases, when the shape is far from circle or abnormal the amount of angular deviation is called Orbital Eccentricity.