Unit

Stars and the Universe

Stars• A star is a giant, hot ball

of gas. • Stars generate light and

heat through nuclear reactions.

• They are powered by the fusion of hydrogen into helium under conditions of enormous temperature, mass, and density.

Stars• a giant, hot ball of gas

composed mainly of H and He.

• generate light and heat through nuclear reactions.

• powered by fusion of H into He under conditions of enormous temperature, mass, and density.

Fusion and Fission

• Nuclear fusion forms larger nuclei from smaller ones.

• This is the opposite of nuclear fission, where nuclei of larger atoms are split to form smaller nuclei.

Stars• Astronomers classify stars according to their

physical characteristics. • The main characteristics used to classify

stars are temperature, size and brightness.

Temperature of an object determines its color

• The hotter an object is, the brighter and lighter the color.

– Example: a light blue flame is hotter than a red flame.

• The apparent brightness of an object depends on how far away it is and how much light it actually gives off (its absolute brightness).

• The mathematical relationship between these variables is known as the inverse square law and is used to determine the distance to stars and galaxies.

• The inverse square law shows how the apparent brightness of an object decreases as you move away from it.

• Parallax is the apparent change in position of an object when you look at it from different directions.

• To use parallax, astronomers determine the position of a star in the sky in relation to other stars that are too far away to show movement.

• Using geometry, they can determine the distance of the star from Earth.

Star Sizes• The sun, with a diameter of

1.4 million kilometers, is a medium-sized star.

• The largest stars, called supergiants, have a diameter that can exceed 1,000 times that of the sun.

• Giants, are about 250 times the diameter of the sun.

• Stars that are smaller than the sun come in two categories, white dwarfs and neutron stars.

H-R Diagram

• H-R diagrams are useful because they help astronomers categorize stars into distinct groups.

Stars that fall into the band that stretches diagonally from cool, dim stars to hot, bright stars are called main sequence stars.

Stars and Spectroscopy• Spectroscopy is a tool of astronomy in which

the electromagnetic radiation (including visible light) produced by a star or other object is analyzed.

Stars and Spectroscopy

• A spectrometer splits light into a spectrum of colors and displays lines of different colors along a scale.

• The scale measures the wavelength of each of the lines of color in nanometers (nm).

Galaxies and the Universe

• A galaxy is a huge group of stars, dust, gas, and other objects bound together by gravitational forces.

• The Milky Way is a typical

spiral galaxy. Our solar system is in one of the “arms” of the Milky Way.

Galaxies and the Universe• Astronomers classify galaxies

according to their shape. – Spiral galaxies like the Milky Way

consist of a central, dense area surrounded by spiraling arms.

– Elliptical galaxies look like the central portion of a spiral galaxy without the arms.

– Lenticular galaxies are lens-shaped with a smooth, even distribution of stars and no central, denser area.

– Irregular galaxies exhibit peculiar shapes and do not appear to rotate like those galaxies of other shapes.

The Big Bang Theory

• The universe is thought to be 10 to 15 billion years old.

• According to the Big Bang theory, all of the matter and energy in the universe started out compressed into a space no bigger than the nucleus of an atom.

• Immediately after the explosion, the universe began to expand and cool.

• The universe continued as a giant cloud of gas until about 300 million years after the Big Bang. Parts of the gas cloud began to collapse and ignite to form clusters of stars—the first galaxies.

Evidence for Big Bang

• In the early 1930s, Hubble had enough evidence to prove that galaxies were moving away from a single point in the universe. THE UNIVERSE IS EXPANDING.

• Later scientists discovered the cosmic microwave background radiation predicted by the Big Bang theory.

Redshift and Blueshift

• Redshift: If the light from a distant star is shifted to the red end of the spectrum, the star is moving away from the astronomer.

• Blueshift: If the light from a distant star is shifted to the violet end of the spectrum, the star is moving toward the astronomer.

Doppler Effect

• The Doppler effect explains the change in pitch of a siren as an ambulance passes by you.

• It’s also used in police radar to catch those troublesome teenage speeders!

1. What is the way in which stars generate energy?

Exp

losi

ons

Nucl

ear F

issi

o...

Nucl

ear f

usion

Rad

ioac

tive

de...

0% 0%

90%

10%

A. ExplosionsB. Nuclear FissionC. Nuclear fusionD. Radioactive decay

2. True or False: Astronomers use characteristics of stars such as temperature, size, and

brightness to classify them into categories.

Tru

e

Fal

se

0%

100%A. TrueB. False

3. The light and object seems to give off due to your location to the object:

Tota

l brig

htne.

..

Abso

lute

brig

h...

Appea

rance

Appar

ent b

righ...

0%

100%

0%0%

A. Total brightnessB. Absolute brightnessC. AppearanceD. Apparent brightness

4. What helpful device do astronomers use to help categorize stars into groups?

Par

alla

x

Spec

trom

eter

Inve

rse

Squar

e...

H-R

Dia

gram

4%

83%

0%

13%

A. ParallaxB. SpectrometerC. Inverse Square LawD. H-R Diagram

5. A giant hot ball of gas

sta

r

Duan

e’s

flatu

l...

Pla

net

neb

ula

100%

0%0%0%

A. starB. Duane’s flatulenceC. PlanetD. nebula

6. The specific stars that range from dim to hot diagonally on a chart are called:

Super

gia

nts

Whi

te d

war

fs

Med

ium

-size

d s...

Mai

n-seq

uence

...

4%

83%

9%4%

A. Super giantsB. White dwarfsC. Medium-sized starsD. Main-sequence

stars

7. Our galaxy is classified as what type of galaxy?

Spira

l

Elli

ptical

Len

ticula

r

irre

gular

100%

0%0%0%

A. SpiralB. EllipticalC. LenticularD. irregular

8. What is it called when a star is moving away from an astronomer?

Blu

e sh

ift

Vio

let s

hift

Yel

low s

hift

Red

shift

4%

87%

4%4%

A. Blue shiftB. Violet shiftC. Yellow shiftD. Red shift

9. When a medium sized star dies it becomes a ________.

Super

nova

Neb

ula

Bro

wn dw

arf

Whi

te d

war

f

29%33%

0%

38%A. SupernovaB. NebulaC. Brown dwarfD. White dwarf

10. Stars are powered by the combining of a hydrogen atom and isotope to form helium in a process called:

Nucl

ear f

issi

o...

Nucl

ear f

usion

Exp

losi

ve re

ac...

Com

binin

g ato

m...

9%0%

13%

78%A. Nuclear fissionB. Nuclear fusionC. Explosive reactionsD. Combining atoms

11. What is the total light an object actually gives off?

Appar

ent b

righ...

Abso

lute

brig

h...

Tota

lity

Infin

ite b

righ...

13%

0%0%

87%A. Apparent

brightnessB. Absolute brightnessC. TotalityD. Infinite brightness

12. The first step when a solar system begins to form:

Fusi

on beg

ins

Pla

nets

form

Met

al a

nd ro

ck...

Neb

ula

colla

ps...

0%

100%

0%0%

A. Fusion beginsB. Planets formC. Metal and rock

combineD. Nebula collapses

13. The _____ not only allows us to catch speeders but also tells us that the Universe is expanding

Cosm

ic b

ackg

ro...

Doppl

er e

ffect

Rad

iatio

n effe

...

spec

trosc

opy

9%0%0%

91%A. Cosmic background

radiationB. Doppler effectC. Radiation effectD. spectroscopy

14. What is the tool astronomers use that uses electromagnetic radiation to determine a star’s

chemical composition?

Rad

ar g

un

Doppl

er e

ffect

Par

alla

x

Spec

trosc

opy

0%

91%

0%9%

A. Radar gunB. Doppler effectC. ParallaxD. Spectroscopy

15. Combining small nuclei into larger ones.

Fusi

on

Fis

sion

Gam

ma

Bet

a

48%

4%0%

48%A. FusionB. FissionC. GammaD. Beta

16. The sun is a _________ star.

Super

gia

nt

Med

ium

siz

ed

Whi

te d

war

f

gia

nt

0% 0%0%

100%A. Super giantB. Medium sizedC. White dwarfD. giant

17. What is the color of a star with the coolest temperature?

Red

Blu

e

Vio

let

yel

low

50%

23%

5%

23%

A. RedB. BlueC. VioletD. yellow

18. The apparent change of a position of a star when you look at it at different locations:

Inve

rse

Squar

e...

Spec

trosc

opy

Par

alla

x

Doppl

er E

ffect

0% 0%0%0%

A. Inverse Square LawB. SpectroscopyC. ParallaxD. Doppler Effect

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19. What determines the color of a star?

Siz

e

Brig

htnes

s

Tem

perat

ure

dis

tanc

e

0% 0%0%0%

A. SizeB. BrightnessC. TemperatureD. distance

30

20. During the Life Cycle of a star, what event is considered it’s birth?

Neb

ula

Super

nova

Bla

ck h

ole

pro

tost

ar

0% 0%0%0%

A. NebulaB. SupernovaC. Black holeD. protostar

30

21. According The Big Bang Theory the Universe started as:

Com

press

ed m

at...

An e

xplo

sion o

...

A c

hemic

al re

a...

Pote

ntial e

ner...

0% 0%0%0%

A. Compressed matter and energy

B. An explosion of particles

C. A chemical reactionD. Potential energy

30

22. What is the type of planet that forms closer to the Sun?

Gas

eous

Ter

rest

rial

Aquat

ic h

ot

0% 0%0%0%

A. GaseousB. TerrestrialC. AquaticD. hot

30

23. What is considered a huge group of stars, dust, and gas bound together by gravity?

Super

nova

Bla

ckhole

Gal

axy

vorte

x

0% 0%0%0%

A. SupernovaB. BlackholeC. GalaxyD. vortex

30

24. Who was the scientist that discovered the universe is expanding?

Gal

ileo

Hubbl

e

Her

schel

Kep

ler

0% 0%0%0%

A. GalileoB. HubbleC. HerschelD. Kepler

30

25. Which order best describes the life cycle of 25. Which order best describes the life cycle of a sun-life star?a sun-life star?

0% 0%0%0%

A.A. Nebula, protostar, red supergiant, supernova, Nebula, protostar, red supergiant, supernova, neutron starneutron star

B.B. Nebula, protostar, star, red giant, white dwarf, Nebula, protostar, star, red giant, white dwarf, black dwarfblack dwarf

C.C. Nebula, protostar, star, blue giant, neutron star, Nebula, protostar, star, blue giant, neutron star, black holeblack hole

D.D. Black hole, neutron star, protostar, red Black hole, neutron star, protostar, red supergiant, supernova, nebulasupergiant, supernova, nebula

45

26. What is the primary responsible for 26. What is the primary responsible for distributing elements throughout the universe?distributing elements throughout the universe?

0% 0%0%0%

A.A. Black holeBlack holeB.B. SupernovaSupernovaC.C. Neutron StarNeutron StarD.D. White DwarfWhite Dwarf

45