Astronomy Notes

ASTRONOMY

Formation of the Universe The Big Bang Theory: · most widely accepted theory · all matter and energy in the universe was in a very small space 13.7 bya which "exploded" outward

Astronomy Notes

· as time passed, and matter cooled, more diverse kinds of atoms began to form · eventually, they condensed into stars and galaxies – Other galaxies are STILL moving away from us, but at a MUCH slower rate

1 second after bang: protons & neutrons form 3 seconds after bang: Temp. dropped and protons & neutrons come together to form nuclei of basic elements Hydrogen, Helium, and Lithium 300 million years after bang: pockets of gas become more and more dense and stars ignite to form clusters of stars (galaxies)

Astronomy Notes

Theories about the end of the Universe: Dark Energy: the energy that continues to push galaxies apart faster and faster >

The Big Freeze: The universe continues to expand and cool to absolute zero. Stars run out of fuel to burn and everything grows dark.

>

The Big Rip: Dark Energy increases and tears galaxies apart and atoms are ripped apart.

Astronomy Notes

Galaxies Groups of billions of stars held together by their own gravity > Milky Way Galaxy: 100,000 ly across and only about 2,000 ly thick > The nearest galaxy is the Andromeda Galaxy at 2,000,000 ly away

Astronomy Notes

The Local Group is a collection of 17 galaxies within 3,000,000 ly

Types of Galaxies 4 types dependent on shape: spiral

barred spiral

elliptical

irregular

Astronomy Notes

spiral

The Milky Way!

no young stars or nebulae

elliptical

barred spiral

smaller and fainter

irregular

Star Clusters

Found within galaxies – Globular Clusters: more circular – Open Clusters: more irregular

Astronomy Notes

HOMEWORK: Create 5 Test Questions from today's notes > Include: » 1 sketch » 1 short answer » 1 True/False » 2 Multiple Choice

GRAVITY

Astronomy Notes

Gravity: A force of attraction that exists between all objects, everywhere in the universe.

Weight is caused by gravity: it is the measurement of gravity's force on an object's mass

Force of Gravity Gravity of the Earth pulls objects towards the center of the planet · The pull (or gravitational force) of an object depends on the object's mass Really massive = more gravitational force

Astronomy Notes

The greater the distance between two objects, the weaker the gravitational force

Gravity & Earth's Orbit

Earth wants to keep going forward but the gravity of the Sun pulls it in. The Earth and Sun continue playing "tug of war", causing Earth to orbit the Sun

This is also why the moon orbits Earth!!!

Astronomy Notes

Will Earth ever stop orbiting the Sun? No, because of INERTIA If something is moving, it will keep moving until something stops it (Newton's First Law of Motion)

Earth's rotation is not circular. It is ELLIPTICAL

Astronomy Notes

EARTH'S

MOTIONS

It takes 365 days for the Earth to complete one revolution around the sun

· It takes 24 hours for the Earth to complete one rotation once around its axis

Astronomy Notes

Seasons

· Due to Earth's tilted axis (23.5 degrees) · NOT due to Earth's distance from the Sun

HOMEWORK: Create 10 Test Questions from today's notes > Include: » 2 Sketches » 3 Matching » 1 short answer » 1 True/False » 3 Multiple Choice

Astronomy Notes

Matching Example:

You can use pictures too!

STARS!

Astronomy Notes

Characteristics · The Star closest to Earth is the SUN · The Sun is a very ordinary star – Ordinary mass, size, temp., brightness, composition, and age

· All the stars we see with the unaided eye (3,000-5,000) are fairly close to us in the Milky Way galaxy · There are about 100,000,000 stars/galaxy and there are 100's of billions of galaxies

Astronomy Notes

COLOR

· The color of a star tells us the temperature · Colors follow the rainbow colors « ROY G BIV + white RED = <3,000 C

YELLOW = 5,500 C BLUE/WHITE = >30,000 C

· Smallest = < 20km in diameter (neutron stars) · Largest = 1000X larger than Sun · Sun's diameter is 110X larger than Earth's

SIZE

Astronomy Notes

MASS

· Smallest- 1/50 of Sun's mass · Largest- 50X Sun's mass · Sun is 330,000X more massive than Earth

COMPOSITION · Stars are mainly Hydrogen & Helium · Sun: >

75% H

>

24% He

>

1% other elements

· Stars contain small amounts of C, N, O, and Ca

« Very small amounts of all the elements can be found in stars

Astronomy Notes

Good for you

Bad for you tastes great

tastes awful

Hertzsprung-Russel Diagram

Amount of Energy t

Astronomy Notes

Classification of Stars · The H-R Diagram is a graph of the absolute magnitude of stars and their temp. · It shows the 4 general classes of stars

4 Classes of Stars:

Main  Sequence  Stars:  90%  of  stars  in  universe  > Average  brightness  for  their  color  > White  hot  stars  are  bright  and  red  cool  stars  are  dim Red  Giants:  Cool  but  bright  > Must  be  very  large  (100-­‐200X  larger  than  the  Sun) Super  Red  Giants:  Cool  but  VERY  bright  > Very  large  (1,000-­‐2,000X  larger  than  the  Sun  > Almost  as  big  as  the  Solar  System White  Dwarfs:  Hot  but  dim  > Very  small  (Earth  to  Jupiter  sized)

Astronomy Notes

Star Motion · Stars are actually moving very fast through space · Most stars are moving within galaxies and galaxies are moving away from each other

The Sun is moving 2,000,000 mph as it spins around the milky way galaxy every 200,000,000 years

Astronomy Notes

· Since the distance between stars is great, we have difficulty seeing this motion · Using a principle called the Doppler Effect we can detect the motion

mimic the noise of a plane flying by

· Blue  Shi):  stars  are  moving  towards  us · Red  Shi(:  stars  are  moving  away  from  us Almost  all  stars  and  galaxies  are  red  shi1ed,  so   the  universe  is  ge5ng  larger  (expanding)

Astronomy Notes

HOMEWORK: Create 10 Test Questions from today's notes > Include: » 3 Matching with H-R Diagram » 2 short answer/Fill-in-the-Blank » 2 True/False » 3 Multiple Choice

STELLAR EVOLUTION

Astronomy Notes

An average star (like our Sun), goes through a life cycle of birth, youth, mid-life, old age, and death > Sun: mid-life stage « 5 billion years old « 5 billion years left to live

5 Stages of a Star's Life • outlined on the H-R Diagram

Astronomy Notes

Stage 1: NEBULA STAGE • Huge clouds of gas and dust between stars called nebula are the birth place of stars > 70% Hydrogen Gas > 28% Helium & 2% other elements • The cloud probably came from an exploded star called a supernova

Stage 2: Proto-Star STAGE • Each nebula is about 25 ly across and begins to be pulled together by gravitational compaction into a more and more dense cloud • The nebula will begin to glow as a red protostar due to the heat

Astronomy Notes

Stage 3: Main Sequence (Stable Star) STAGE

• As gravity pulls the protostar tighter and tighter, it will get hotter and hotter • When the star reaches a temp. of 10,000,000 C, NUCLEAR FUSION begins

NUCLEAR FUSION • Process which turns Hydrogen into Helium and creates a huge amount of energy >

Same process which fuels the Hydrogen bomb

• Once it begins, it is a stable main sequence star and will stay that way for billions of years • Our Sun will be a main sequence star for about 10 billion years

Astronomy Notes

Stage 4: Red Giant or Supergiant STAGE • When the star has "burned" most of its Hydrogen, nuclear FUSION OF HELIUM will begin > A much hotter process > Star expands into a red giant or a super red giant • Our Sun will expand into a red giant in about 5 billion years and melt the Earth

Stage 5: White Dwarf STAGE • After burning as a red giant for a few million years, the star will use up all of its fuel and shrink into an Earth-sized white dwarf • During shrinking, it may illuminate the outer layer of gases briefly creating a planetary nebula

Astronomy Notes

• It will glow dimly for about a billion years then fade into a brown or black dwarf > This is dark remains of a burnt out star • Occasionally, the white dwarf will flare into a brighter nova but fade in a few days back into the white dwarf

Astronomy Notes

Massive stars will end their lives very differently than the Sun

Supernovas • Massive stars will not fade into a white dwarf, but will explode as a violent supernova • In a supernova, there is fusion of Carbon into Iron which will quickly create both an explosion and implosion of matter

Astronomy Notes

Neutron Stars • The core of a "small" supernova will form a neutron star which is made of just neutrons • These stars are very small, spin very fast, and are very dense • Some neutron stars produce beams of radiation that are "heard" by radio telescopes and care called pulsars

Black Holes

• In very large stars, the supernova creates an area of matter so dense at its center that is called a black hole > So dense it won't let light escape • We can't see black holes, so we examine the pattern of x-rays given off as matter is pulled into the black hole • The center of Milky Way= massive black hole

Astronomy Notes

HOMEWORK: Create 5 Test Questions from today's notes > Include: » 5 Multiple Choice