Astronomical Dictionary on Letter #P

Pahoehoe

A basaltic lava with a smooth, undulating surface....

Parallax

The angular difference in apparent direction of an object seen from two different viewpoints. This o...

Parsec

The distance at which a star (or other object) would have a parallax of 1" (one second of arc)....

Penumbra

The partial shadow or darkness of an eclipse. Means, literally, "dim light". It most often refers ...

Periapsis

A genericterm. The point in an orbit closest to a body other than the Sun or the Earth. For bodies ...

Perigee

From the Greek "near the Earth." The point in its orbit where the Moon, or planet is closest to...

Perihelion

From the Greek "near the Sun." The point in its orbit when an object is closest to the Sun. Opposite...

Perturb

To cause a celestial body, to deviate from its predicted orbit, usually under the gravitational infl...

Photosphere

The visible surface of the Sun; ...

Plage

Bright regions in the Sun's chromosphere. ...

Planisphere

An aid to locatiing stars and constellations in the night sky. It consists of two discs. One with th...

Precession

Also called Precession of the Equinoxes. Circular motion about the axis of rotation of a body; fixed...

Prominence

A cloud, or plume, of hot, luminous gas in the Sun's corona. It appears bright when seen against the...

Phobos

In Greek mythology, a son of Ares (Mars) who, with brother Deimos, was a constant companion to his f...

Plateau

Any comparatively flat area of great extent or elevation....

Plume

A buoyant mass of hot, partially molten mantle material that rises to the base of the lithosphere....

Pluto

Planet ninth in order, and farthest, from the sun. In Greek mythology, god of the dead and the under...

Prometheus

A Greek mythological hero who gave humankind fire....