Chapter 30.1: Characteristics of

Stars

At the center of the most violent starburst region in the local universe lies a cluster of brilliant, massive stars, known to astronomers as Hodge 301 (lower right hand corner of this photo)

Characteristics of Stars A star is a body of gases that gives off

energy in the form of light & heat. Size varies Color varies based on temperature Our sun is an average star

Composition Star composition observed through a spectrometer

Separates light into its individual colors Each color represents a different wavelength Three types of spectra

Emission or bright-line Absorption or dark-line Continuous

Since different elements absorb different wavelengths of light , elements can be determined.

Composition Continued Hydrogen is the most common element. Surface temperature of a star is indicated

by the color Red stars are the coolest and blue are the

hottest (Figure 2 on page 776).

Motion Two kinds of motion associated with

stars: Actual motion --- just like it sounds! Apparent motion --- This is motions visible

to the unaided eye in a dark sky; due to movement of Earth.

Motion Continued

Some stars create circular trails around a central star (Polaris aka the North Star)

Circumpolar: stars that never go below the horizon. (Circling stars).

Different stars become visible during different seasons.

Three actual motions:1. Rotate on an axis2. Revolve around another star3. Move away or toward the Earth.

Distance Distance

Light Year = 9.5x1012km; Distance that light travels in one year.

Astronomical Unit (AU) --A unit of length used to measure distances in solar system.

Stellar Magnitude

Magnitude: a way to measure the brightness of a body in the sky

Apparent magnitude = brightness of a star as it appears to us on Earth

Measure light from star using telescopes Measurement is then assigned a number

Brightest stars have lowest numbers Dimmest stars have highest numbers

Absolute: the true brightness of the object