Astronomy: The Original Science

• How did people in ancient times tell time?• The studied the movement of stars, planets and the moon. They

watched as the seasons changed.• Farmers learned the best time to plant and harvest crops by

watching the yearly cycles of time.• What was built due to the fact of ancient people watching the

movement of objects in the sky?• Observatories.• What did the study of the night sky eventually become known as?• The science of astronomy which is the study of the universe.• What do we call the scientists that study the universe?• astronomers

Mapping the StarsPatterns in the Sky

When people in ancient cultures connected stars in patterns they named sections of the sky based on

these patterns.What are these patterns called?

Constellations

ConstellationsWhat are constellations?They are sections of the sky that contain

recognizable star patterns.How did the following of the constellations help

ancient people?By understanding the location and movement of

the constellations it helped them to navigate and keep track of time.

Every star or galaxy is located within 1 of how many constellations?

88

Leo the Lion

Horizon and Light Year

• What is the horizon?• It is the line where the sky and the

Earth appear to meet.• What is a light year?• It is the distance light travels in

one year which is about 9.46 trillion kilometers (88,179,380,564,073,582,184,704,01-8.81 sextillion miles)

The Apparent Motion of Stars

• Why does the Earth appear to move across the sky?• It appears to move across the sky due to the Earth’s rotation.• Do the stars appear to move at night also?• Yes• All the stars we see at night appear to rotate around which star?• Polaris which is the North Star• Where is Polaris located?• Directly above the Earth’s North Pole.• Stars are actually moving in space, but since they are so distant ,

their movement is hard to see.• Over time, due to this movement, the shapes of star patterns such

as the Big Dipper and other groups, change.

The Life Cycle of Stars

• The Beginning and End of Stars

• How does a star enter its life cycle?• It enters the first stage as a ball of gas.• What pulls the gas and dust together into a sphere?• Gravity• What happens as the sphere becomes denser?• It gets hotter and the hydrogen changes to helium.• What is that process called?• Nuclear fusion.• What happens when a star dies?• Some of the material returns to space and combines with more gas

and dust to form new stars.

Different Types of Stars

How are stars classified?Size, mass, brightness, color,

temperature, spectrum, and age.

Main Sequence Stars

• After a star forms, it enters the second and longest stage of its life cycle known as what?

• Main sequence

• What happens during this stage?

• Energy is generated in the core of the star as hydrogen atoms fuse into helium atoms.

Giants and Supergiants• After the main sequence stage a star can enter the third

stage of its life cycle.• What can a star become in this stage?• Red giant- a star that expands and cools once it uses all

of its hydrogen.• What happens to the center of the star?• It shrinks due to the loss of hydrogen.• How big can red giants and supergiants become?• Red giants 10 or more times bigger than the sun and

supergiants at least 100 times bigger than the sun.

White Dwarfs

• In the final stages of a star’s life cycle, it has the same mass as the sun or smaller and is called a white dwarf.

• A white dwarf is a small hot star that is the leftover center of what?

• An older star.• Does a white dwarf have hydrogen left at this

stage?• No, therefore, it can no longer generate energy.• How long can white dwarfs shine?• Billions of years before they cool completely.

H-R Diagram

A Tool for Studying Stars• The combination of research done between Danish astronomer

(Hertzsprung) and American astronomer (Henry Norris Russell) on the brightness and temperature of stars resulted in a graph called what?

• H-R diagram• What does the diagram show?• It shows the relationship between a star’s surface temperature

and its absolute magnitude (brightness).• On the H- R diagram which color represents hot stars and

which color represents cool stars?• Blue-hot on the left and cool-red on the right.• Bright stars are at the ________ and dim stars are at the

_______• Top/bottom

• What is the main sequence on the diagram?

• It is the diagonal pattern where most stars lie.

• A star spends most of its lifetime in the __________ ____________.

• Main sequence

When Stars Get OldWhen Stars Get Old

SuperSuperSupernovasSupernovasMassive blue stars use their hydrogen much faster Massive blue stars use their hydrogen much faster

than stars like the sun do.than stars like the sun do.Blue stars do not have long lives.Blue stars do not have long lives.What happens at the end of a blue stars life?What happens at the end of a blue stars life?It may explode in a large, bright flash called a It may explode in a large, bright flash called a

supernova.supernova.What is a supernova?What is a supernova?It is a gigantic explosion in which a massive star It is a gigantic explosion in which a massive star

collapses.collapses.

Supernova explosion

Neutron Stars and PulsarsStars and Pulsars

• After a supernova occurs, the materials in the After a supernova occurs, the materials in the center of it are pushed together to form what?center of it are pushed together to form what?

• A new starA new star• What happens to the particles inside the star’s What happens to the particles inside the star’s

core at this time?core at this time?• They are forced together to form neutrons.They are forced together to form neutrons.• What is a neutron star?What is a neutron star?• It is a star that has collapsed under gravity to the It is a star that has collapsed under gravity to the

point at which all of its particles are neutrons.point at which all of its particles are neutrons.• What is a spinning neutron star called?What is a spinning neutron star called?• PulsarPulsar

Pulsar and Neutron Star

Black Holes

• What is a black hole?• It is an object that is so massive that even light

cannot escape its gravity.• They form sometimes from the leftovers of a

supernova that has collapsed.• How are black holes found by astronomers?• Sometimes gas or dust from a nearby star will

spiral into the black hole and give off X rays to help them detect their existence.

X-Rays From Black Holes

Galaxies• What are galaxies?• Large groups of stars, dust, and gas.• How many stars does the largest galaxy

contain?• More than a trillion.• Who began to classify galaxies by their shapes

in the 1920’s?• Edwin Hubble (astronomer that developed the

Hubble Space Telescope)• How did he classify the galaxies?• By their shapes.

Spiral GalaxiesWhat is a spiral galaxy?It is a galaxy with a bulge at the center

and spiral arms.What are the spiral arms composed of?Gas, dust and new stars.

The Milky WayThe Milky Way• Astronomers think we live in a spiral

galaxy for what reason?

• It is hard to see what type we live in but by observing other galaxies and making measurements inside our galaxy, astronomers are led to believe our solar system is a spiral galaxy and is called The Milky Way.

The Milky Way

Elliptical Galaxies

• Elliptical Galaxies are massive blobs of stars.• What percentage of all galaxies are massive blobs of stars?• About 1/3• Some look like _______ and others are stretched out.• Spheres• These galaxies usually have very _______centers.• Bright• They have very little ______ and ______.• Dust and gas• What age stars are elliptical galaxies composed of?• Old.• Why do few new stars form here?• There is so little free-flowing gas

Irregular Galaxies

• Hubble called the leftover galaxies that really did not have a shape irregular galaxies.

Contents of Galaxies

• What are galaxies composed of?What are galaxies composed of?

• Billions of stars and some planetary Billions of stars and some planetary systems.systems.

• What do some of these stars form?What do some of these stars form?

• Gas clouds and star clustersGas clouds and star clusters

Gas Clouds (Nebula)

• What is the Latin word for cloud?

• Nebula

• What is a nebula?

• It is a large cloud of gas and dust.

• Some nebulas glow, some absorb light and hide stars.

• Some reflect starlight and produce some amazing images.

• Eagle Nebula Crab Nebula

Star ClustersStar Clusters• What are globular clusters?What are globular clusters?• Groups of old stars that looks like a ball.Groups of old stars that looks like a ball.• How many stars can be in a globular How many stars can be in a globular

cluster?cluster?• Up to one millionUp to one million• Where are these clusters located?Where are these clusters located?• They are located in a spherical halo that They are located in a spherical halo that

surrounds spiral galaxies such as the surrounds spiral galaxies such as the Milky Way.Milky Way.

Globular cluster

• Open cluster-group of closely grouped stars (many blue stars)

QuasarsQuasars• What are quasars?What are quasars?• They are starlike sources of light that are They are starlike sources of light that are

extremely far away.extremely far away.• They are among the most powerful energy They are among the most powerful energy

sources in the universe.sources in the universe.• What do some scientists think may cause What do some scientists think may cause

quasars?quasars?• Massive black holes in the cores of some Massive black holes in the cores of some

galaxies.galaxies.