Space Station Glossary P

P

Period-Luminosity Law:

A relationship, which describes how the luminosity or total brightness of a Cepheid variable star depends on the period of time over which that intensity varies.

Photometer:

An instrument that measures the brightness of light. Astronomers use photometers to gauge the brightness of celestial objects.

Planet:

An object, which orbits a star. Although lesser than stars, planets are comparatively large and shine only by reflect light. Planets are complete up mostly of rock or gas, with a small, solid core.

Pluto:

The outmost planet in our solar system. Pluto is, on standard, about 40 times the Earth’s distance from the Sun. Pluto orbit the Sun in 248 Earth years.

Proton:

An absolutely charged elementary particle that resides in the nucleus of every atom.