30.1 Characteristics of Stars

Characteristics of StarsSection 30.1

Stars· star = ball of gas that emits light· fueled by nuclear fusion· vary in color

Analyzing Starlight· spectrographs - device that separates light into different wavelengths (colors)· each star produces a unique spectrum (series of colors and lines)· a star's spectrum tells us

elements present (composition)surface temperaturehow fast the star is moving toward or away from Earth

Solar spectrum

Star Characteristics· composition

most common element - hydrogensecond most common - helium

· temperatureblue = hottestyellow (ex. sun)red = coolest

· size and massdwarf, medium,

and giant

1 How do scientists determine the composition and temperature of stars?

A by taking samples from the star's surface

B by analyzing the vibrations that the star emits

C through magnetic testing

Dby analyzing the spectra of the light that a star emits

2 What color are the warmest stars?

A yellow

B blue

C white

D red

30.1 Characteristics of Stars

Stellar Motion· apparent

motion visible to the unaided eyecaused by Earth's rotationappear to move counter-clockwise around Polaris

(the North Star)different stars appear in different seasonscircumpolar stars - always visible in the night sky

· actualrotate on an axisrevolve around another starmove away from or toward our solar system

· Doppler effectshifting wavelengths of light emitted by a light source

moving toward or away from an observerblue shift = moving toward Earthred shift = moving away from Earth

Red Shift = star moving away

Blue shift = star moving toward

Distances to Stars· light-year = distance light travels in one year

9.46 trillion km/yearsun = 8 light minutes awayProxima Centauri = 4.2 light-years awayPolaris = 700 light-years away

· parallax = apparent shift in a star's position when viewed from different locations

accurate up to 1000 light-years

Stellar Brightness· visibility of a star depends on brightness (magnitude) and distance from Earth

1 = brightness stars6 = faintest stars

· apparent magnitude = brightness of a star from Earth· absolute magnitude = how bright a star would be if it were 32.6light-years from Earth

aka true brightnesscompared against a standard

3 Why do stars appear to move in the sky?

A the sky is rotating

B the universe is expanding

C Earth is moving

D galaxies are forming

4 Scientists use parallax to determine

A a star's distance

B if the star is moving toward or away from Earth

C the brightness of a star

D a star's actual motion