Apparent size in the context of Angular separation

In astronomy, a transit (or astronomical transit) is the passage of a celestial body directly between a larger body and the observer. As viewed from a particular vantage point, the transiting body appears to move across the face of the larger body, covering a small portion of it.

The word "transit" refers to cases where the nearer object appears smaller than the more distant object. Cases where the nearer object appears larger and completely hides the more distant object are known as occultations.

In lunar astronomy, libration is the cyclic variation in the apparent position of the Moon that is perceived by observers on the Earth and caused by changes between the orbital and rotational planes of the moon. It causes an observer to see slightly different hemispheres of the surface at different times. It is similar in both cause and effect to the changes in the Moon's apparent size because of changes in distance. It is caused by three mechanisms detailed below, two of which cause a relatively tiny physical libration via tidal forces exerted by the Earth. Such true librations are known as well for other moons with locked rotation.

The quite different phenomenon of a trojan asteroid's movement has been called Trojan libration, and Trojan libration point means Lagrangian point.

Pale Blue Dot is a photograph of Earth taken on February 14, 1990, by the Voyager 1 space probe from an unprecedented distance of over 6 billion kilometers (3.7 billion miles, 40.5 AU), as part of that day's Family Portrait series of images of the Solar System.

In the photograph, Earth's apparent size is less than a pixel; the planet appears as a tiny dot against the vastness of space, among bands of sunlight reflected by the camera. Commissioned by NASA and resulting from the advocacy of astronomer and author Carl Sagan, the photograph was interpreted in Sagan's 1994 book, Pale Blue Dot, as representing humanity's minuscule and ephemeral place amidst the cosmos.

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 orbit—resulting in a slightly larger-than-usual apparent size of the lunar disk as viewed from Earth.‍ The technical name is a perigee syzygy (of the Earth–Moon–Sun system) or a full (or new) Moon around perigee.‍ Because the term supermoon is astrological in origin, it has no precise astronomical definition.‍

The association of the Moon with both oceanic and crustal tides has led to claims that the supermoon phenomenon may be associated with increased risk of events like earthquakes and volcanic eruptions, but no such link has been found.‍