PHYS 118 - Intro Astronomy: Galaxies

These flashcards cover key terms, theories, and classifications related to galaxies as discussed in the astronomy course.

Great Debate

Contentious debate in the 1920s regarding the nature of spiral nebulae and the scale of the universe.

Island Universe Theory

Theory proposed by Heber Curtis that spiral nebulae are distant independent galaxies.

Single Galaxy Theory

Theory proposed by Harlow Shapley stating that the Milky Way is the only galaxy.

Hubble Sequence

Classification system developed by Edwin Hubble comprising four main types of galaxies: spiral, barred spiral, elliptical, and irregular.

Grand Design Spiral Galaxies

Spiral galaxies with well-defined spiral arms and active star formation.

Flocculent Spiral Galaxies

Spiral galaxies showing loose patches of spiral arms and less defined structure.

Barred Spiral Galaxies

Galaxies with spiral arms that extend from a central rectangular bar of stars.

Elliptical Galaxies

Galaxies that are elliptical in shape with a smooth distribution of stars and minimal structure.

Dwarf Galaxies

Small, low-mass galaxies that are rare among spiral galaxies but common in other types.

Irregular Galaxies

Galaxies with amorphous shapes that do not fit into the typical categories of spiral or elliptical.

Stellar Halo

A region of stars surrounding a galaxy that differs in structure between types of galaxies.

Supermassive Black Hole

A massive black hole typically found at the center of a galaxy.

Cepheid Variable Star

A type of star whose brightness changes periodically, helping to determine distances in astronomy.

Density Waves

Patterns of high-density areas within spirals that help explain spiral arm formation.

Tuning Fork Diagram

Hubble's graphical representation of galaxy classifications, resembling a fork, indicating possible evolutionary paths.

Gas Content

The presence and amount of interstellar gas in galaxies which influences star formation rates.

Star Formation Rate

The rate at which new stars are being formed within a galaxy.