30.3 and 30.4 Star Groups and The Big Bang Theory

Star Groups & The Big Bang Theory

Sections 30.3 & 30.4

Constellations· a group of stars organized in a recognizable pattern· helpful in locating a specific star· appear to be moving because Earth is moving· sky is divided into 88 constellations

given Latin namesusually animals, characters from mythology, or

familiar objectsex. Ursa Major = "the Great Bear"

Galaxies· large group of stars, gas and dust held together by gravity· typical galaxy

diameter of 100,000 light yearscontain about 200 billion stars

· Cepheid variables help astronomers locate galaxiesgiant stars that brighten and fade in regular cyclescompare their absolute and apparent magnitudes

to determine distance to galaxy

Types of Galaxies· elliptical

spherical to stretched-out footballvery few young starslittle dust and gas

· spiralmost commonnucleus of bright stars and flattened

arms that spiral around the nucleusarms contain young stars, gas,

and dust· irregular

no particular shapelost of dust and gas

The Milky Way· spiral galaxy· contains about 200 billion stars

our sun is on the outer edge· closest neighbors are about 170,000 light-years away

1 What type of galaxy is the Milky Way?

A elliptical

B spiral

C irregular

D spherical

30.3 and 30.4 Star Groups and The Big Bang Theory

2 Which of the following statements does NOT describe the typical galaxy?A It is loosely shaped and carries few stars.

B It contains billions of stars.

C It has a diameter of 100,000 light-years.

D It is one of billions of galaxies.

Expanding Universe· Edwin Hubble (1920s)

created spectra for distant galaxiesdiscovered that they had a red-shiftdetermined the speed at which

distant galaxies are moving away from Earth

the farther away, the faster they are moving

· proved the universe is expanding

Big Bang Theory· all matter and energy in the universe was concentrated into an extremely small volume (very dense)· about 14 billion years ago an enormous explosion ("big bang") sent matter and energy outward in all directions· some expanding matter gathered in clumps and formed galaxies· evidence for the Big Bang

red-shift of galactic spectracosmic background radiation

low levels of energy uniformly detected from every direction in space

believed to have been created by the big bang explosion

3 Red shift in the spectra of galaxies told Hubble that

A the universe is contracting

B the universe in expanding

Cmatter and energy are being absorbed by black holes

Dthe universe is composed primarily of red light

4 Evidence for the big-bang theory is provided by

A apparent parallax shifts

B differences in stellar luminosity

C cosmic background radiation

D star patterns called constellations