Chapter 17 - Analyzing Starlight

Luminosity

The total energy emitted per second by a star.

Apparent Brightness

How bright a star looks from the perspective of Earth.

Magnitude

A system used to express the apparent brightness of stars based on human vision interpreting relative light intensity.

Color Index

The difference in the magnitudes measured at any two wavelengths, used by astronomers to measure the temperature of stars.

Spectral Classes

Categories that describe the spectra of stars in order of decreasing temperature: O, B, A, F, G, K, M, L, T, and Y.

Brown Dwarfs

Star-like objects that are cooler than M9 and fall under the L, T, and Y spectral classes.

Doppler Effect

A phenomenon used to determine the radial velocity of a star by measuring line shifts in its spectrum.

Proper Motion

The component of a star’s space velocity across the line of sight.

Giant

a star of exaggerated size with a large, extended photosphere

Radial velocity

motion toward or away from the observer; the component of relative velocity that lies in the line of sight

space velocity

the total (three-dimensional) speed and direction with which an object is moving through space relative to the Sun

spectral class

(or spectral type) the classification of stars according to their temperatures using the characteristics of their spectra; the types are O, B, A, F, G, K, and M with L, T, and Y added recently for cooler star-like objects that recent survey have revealed