Stars, Galaxies, and the Universe

Flashcards covering key vocabulary and concepts from Chapter 21 on stars, telescopes, and the evolution of the universe.

Electromagnetic radiation

Energy that travels through space in the form of waves.

Wavelength

The distance between the crest of one wave and the next crest.

Optical telescope

A telescope that collects and focuses visible light.

Star

A massive, luminous sphere of plasma—primarily hydrogen and helium—held together by its own gravity.

Light-year

A unit of distance that represents the distance light travels in one year, equal to $9.5 \times 10^6\,km$.

Parallax

The change in an object’s position you seem to see when you change your own position.

Hertzsprung-Russell diagram (H-R diagram)

A diagram used to classify stars that shows how the surface temperature of stars is related to their absolute brightness.

Nebula

A large cloud of gas and dust from which all stars begin.

Supernova

The explosion of a supergiant star that occurs after it runs out of fuel.

Galaxy

A huge group of stars that are held together by gravity.