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Chapter 1 Our Place in the Universe. Star. A large, glowing ball of gas that generates heat and light through nuclear fusion. Planet. A moderately large object that orbits a star; it shines by reflected light. Planets may be rocky, icy, or gaseous in composition. Mars. Uranus.

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slide2
Star

A large, glowing ball of gas that generates heat and light through nuclear fusion

planet
Planet

A moderately large object that orbits a star; it shines by reflected light. Planets may be rocky, icy, or gaseous in composition.

Mars

Uranus

moon or satellite
Moon (or satellite)

An object that orbits a planet

Ganymede (orbits Jupiter)

asteroid
Asteroid

A relatively small and rocky object that orbits a star

Mathilde

comet
Comet

A relatively small and icy object that orbits a star

solar star system
Solar (Star) System

A star and all the material that orbits it, including its planets and moons

nebula
Nebula

An interstellar cloud

of gas and/or dust

galaxy
Galaxy

A great island of stars in space, all held together by gravity and orbiting a common center

M31, the Great Galaxy

in Andromeda

M31, the great galaxy in Andromeda

slide10

One difference between the terms solar system and galaxy is that:

  • the solar system contains only one star but the galaxy contains many billions.
  • the solar system contains planets, but the galaxy does not.
  • other galaxies are rare, but other solar systems are common.
  • other solar systems are rare, but other galaxies are common.
slide11

One difference between the terms solar system and galaxy is that:

  • the solar system contains only one star but the galaxy contains many billions.
  • the solar system contains planets, but the galaxy does not.
  • other galaxies are rare, but other solar systems are common.
  • other solar systems are rare, but other galaxies are common.
universe
Universe

The sum total of all matter and energy; that is, everything within and between all galaxies

key definition light year
Key Definition: Light-Year

The distance light can travel in 1 year

About 10 trillion kilometers (6 trillion miles)

put these objects in the correct order from nearest to farthest from earth
Put these objects in the correct order, from nearest to farthest from Earth:
  • The Sun, the Milky Way, Alpha Centauri, Pluto, the Andromeda galaxy
  • The Sun, Alpha Centauri, Pluto, the Andromeda galaxy, the Milky Way
  • The Sun, Pluto, Alpha Centauri, the Milky Way, the Andromeda galaxy
  • Pluto, the Sun, Alpha Centauri, the Milky Way, the Andromeda galaxy
put these objects in the correct order from nearest to farthest from earth1
Put these objects in the correct order, from nearest to farthest from Earth:

C. The Sun, Pluto, Alpha Centauri, the Milky Way, the Andromeda galaxy

The sun – a star

~93 million miles away

~150 million kilometers

~ 8 light-minutes

put these objects in the correct order from nearest to farthest from earth2
Put these objects in the correct order, from nearest to farthest from Earth:

C. The Sun, Pluto, Alpha Centauri, the Milky Way, the Andromeda galaxy

Pluto – a “dwarf planet”

~3 billion miles away

~48 billion kilometers

~ 4.5 light hours

put these objects in the correct order from nearest to farthest from earth3
Put these objects in the correct order, from nearest to farthest from Earth:

C. The Sun, Pluto, Alpha Centauri, the Milky Way, the Andromeda galaxy

Alpha Centauri – a star

~26,000 billion miles away

~4.2 x 1013 kilometers

~ 4.5 light years

put these objects in the correct order from nearest to farthest from earth4
Put these objects in the correct order, from nearest to farthest from Earth:

C. The Sun, Pluto, Alpha Centauri, the Milky Way, the Andromeda galaxy

Milky Way – a galaxy

~200 billion stars

~100,000 light years across

~ 27,000 light years to center

put these objects in the correct order from nearest to farthest from earth5
Put these objects in the correct order, from nearest to farthest from Earth:

C. The Sun, Pluto, Alpha Centauri, the Milky Way, the Andromeda galaxy

Andromeda – another galaxy

~400 billion stars

~2.5 million light years away

slide20

Which is farther, the distance from San Francisco to Los Angeles, or the distance from you to the International Space Station, when it passes directly overhead?

  • San Francisco – LA is further
  • The space station is further
slide21

Which is farther, the distance from San Francisco to Los Angeles, or the distance from you to the International Space Station, when it passes directly overhead?

  • San Francisco – LA is further!!
  • The space station is further
slide22
In a scale model solar system that used a grapefruit to represent the Sun, how large would the Earth be?
  • The size of an orange
  • The size of a marble
  • The size of the point of a ballpoint pen
  • The size of a bacterium
slide23
In a scale model solar system that used a grapefruit to represent the Sun, how large would the Earth be?
  • The size of an orange
  • The size of a marble
  • The size of the point of a ballpoint pen
  • The size of a bacterium
slide24
In a scale model solar system that used a grapefruit to represent the Sun, how large would the Earth be?
  • The size of an orange
  • The size of a marble
  • The size of the point of a ballpoint pen
  • The size of a bacterium
slide25
In a scale model solar system that used a grapefruit to represent the Sun, how far away would the Earth be?
  • 6 inches
  • 1 foot
  • 5 feet
  • 40 feet
  • 1 mile
slide26
In a scale model solar system that used a grapefruit to represent the Sun, how far away would the Earth be?
  • 6 inches
  • 1 foot
  • 5 feet
  • 40 feet
  • 1 mile
slide27
In a scale model solar system that used a grapefruit to represent the Sun, how far away would Pluto be?
  • 100 feet
  • 200 feet
  • 2,000 feet
  • 10 miles
slide28
In a scale model solar system that used a grapefruit to represent the Sun, how far away would Pluto be?
  • 100 feet
  • 200 feet
  • 2,000 feet
  • 10 miles
slide29
In a scale model solar system that used a grapefruit to represent the Sun, how far away would Pluto be?
  • 100 feet
  • 200 feet
  • 2,000 feet
  • 10 miles
slide30

In a scale model solar system that used a grapefruit to represent the Sun, how far away should you put another grapefruit to represent Alpha Centauri, the next nearest star?

  • 10 feet
  • 1,000 feet
  • 1 mile
  • 10 miles
  • 1,500 miles
slide31

In a scale model solar system that used a grapefruit to represent the Sun, how far away should you put another grapefruit to represent Alpha Centauri, the next nearest star?

  • 10 feet
  • 1,000 feet
  • 1 mile
  • 10 miles
  • 1,500 miles
how can we know what the universe was like in the past
How can we know what the universe was like in the past?
  • Light travels at a finite speed ( 186,000 miles/second = 300,000 km/s).
how can we know what the universe was like in the past1
How can we know what the universe was like in the past?

We see objects as they were in the past:

The farther away we look in distance, the further back we look in time.

Look far enough away, and we look back in time to when the universe was much younger…

example
Example:

This photo shows the Andromeda Galaxy as it looked about 2 ½ million years ago.

how big is the universe
How big is the universe?
  • The Milky Way is one of about 100 billion galaxies.
  • 1011 stars/galaxy  1011 galaxies = 1022 stars

It has as many stars as grains of (dry) sand on all Earth’s beaches.

how is earth moving in our solar system
How is Earth moving in our solar system?

Contrary to our perception, we are not “sitting still.”

We are moving with the Earth in several ways, and at surprisingly fast speeds.

earth rotates on its axis
Earth rotates on its axis:
  • Once a day
  • Once a week
  • Once a month
  • Once a year
  • Once every 250,000 years
earth rotates on its axis1
Earth rotates on its axis:
  • Once a day
  • Once a week
  • Once a month
  • Once a year
  • Once every 250,000 years
how is earth moving in our solar system1
How is Earth moving in our solar system?

Earth rotates around its axis once every day.

earth revolves around the sun
Earth revolves around the Sun:
  • Once a day
  • Once a week
  • Once a month
  • Once a year
  • Once every 250,000 years
earth revolves around the sun1
Earth revolves around the Sun:
  • Once a day
  • Once a week
  • Once a month
  • Once a year
  • Once every 250,000 years
earth orbits the sun revolves once every year
Earth orbits the Sun (revolves) once every year…
  • at an average distance of 1 AU ≈ 150 million km.
  • with Earth’s axis tilted by 23.5º (pointing to Polaris).
  • and rotates in the same direction it orbits, counter- clockwise as viewed from above the North Pole.
the moon revolves around earth
The Moon revolves around Earth:
  • Once a day
  • Once a week
  • Once a month
  • Once a year
  • Once every 250,000 years
the moon revolves around earth1
The Moon revolves around Earth:
  • Once a day
  • Once a week
  • Once a moonth
  • Once a year
  • Once every 250,000 years
earth revolves around the milky way galaxy
Earth revolves around the Milky Way Galaxy:
  • Once a day
  • Once a week
  • Once a month
  • Once a year
  • Once every 230 million years
earth revolves around the milky way galaxy1
Earth revolves around the Milky Way Galaxy:
  • Once a day
  • Once a week
  • Once a month
  • Once a year
  • Once every 230 million years
our sun moves randomly relative to the other stars in the local solar neighborhood
Our Sun moves randomly relative to the other stars in the local solar neighborhood…
  • attypical relative speeds of more than 70,000 km/hr
  • but stars are so far away that we cannot easily notice their motion

… and it orbits the galaxy every 230 million years.

are we ever sitting still
Are we ever sitting still?

Earth rotates on axis: > 1,000 km/hr

Earth orbits Sun: > 100,000 km/hr

Solar system moves among stars: ~ 70,000 km/hr

Milky Way rotates: ~ 800,000 km/hr

Milky Way moves

in Local Group

Universe

expands

why do we not feel or sense the various motions of earth in the universe
Why do we not feel or sense the various motions of Earth in the universe?
  • They are not real, they are just models
  • They are too slow to sense
  • They are nearly uniform, and you can not sense uniform velocity, only acceleration, which is a change of velocity or direction
why do we not feel or sense the various motions of earth in the universe1
Why do we not feel or sense the various motions of Earth in the universe?
  • They are not real, they are just models
  • They are too slow to sense
  • They are nearly uniform, and you can not sense uniform velocity, only acceleration, which is a change of velocity or direction
slide52

Suppose that, at this very moment, students are studying astronomy on planets in Andromeda. Could they know that we exist here on Earth?

  • Yes, because we can see stars in Andromeda, so they can see us in the Milky Way.
  • No, the light from the solar system has not yet reached Andromeda.
  • No, the light from the solar system that has reached Andromeda came from a time before Earth hadformed.
  • No, radio signals from terrestrial civilizations have not yet reached Andromeda.
  • Yes, in principle. With sufficiently powerful telescopes, they should be able to see man-made features such as the Great Wall of China on Earth’s surface.
slide53

Suppose that, at this very moment, students are studying astronomy on planets in Andromeda. Could they know that we exist here on Earth?

D. No, radio signals from terrestrial civilizations have not yet reached Andromeda.