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 axis 2. Revolve around another star 3. Move away or toward the Earth.

Distance Light Year = 9.5x10 12 km; 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