Chapter 1
Edwin Hubble discovered what two key observation facts?
(1) Virtually every galaxy outside our Local Group is moving away from us. (2) The more distant the galaxy, the faster it is moving away. The raisin cake analogy shows how these two facts lead to the conclusion that the universe is expanding.
If the 14 billion year history of the universe were compressed to one year, and "now" is exactly midnight December 31, approximately how long ago were your grandparents born?
0.15 second ago
Light travel time from moon
1 second
Based on observations of the universal expansion, the age of the universe is about ________.
14 billion years
Our solar system is located about 27,000 light-years from the galactic center. How far does our solar system travel in one orbit?
170,000 light-years
Part complete Our solar system is located about 27,000 light-years from the galactic center. How far does our solar system travel in one orbit?
170,000 light-years
Light travel time from Andromeda Galaxy
2.5 million years
Light travel time from sun
8 minutes
Light travel time from Sirius
8 years
One light-year is the distance light travels in one year. The speed of light is about 300,000 km/s (3×105km/s). How far is 1 light-year?
9.46 × 1012 km
Galaxy
A great island of stars in space, all held together by gravity and orbiting a common center
Sun
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.
Comet
A relatively small and icy object that orbits a star
asteroid
A relatively small and rocky object that orbits a star
Solar System
A star and all the material that orbits it, including its planets and moons
By studying distant galaxies in the 1920s, Hubble made the following important discovery that led us to conclude that the universe is expanding.
All galaxies outside the Local Group are moving away from us, and the farther away they are, the faster they're going.
Nebula
An interstellar cloud of gas and/or dust
moon/satellite
An object that orbits a planet
The greater the distance the younger the object
At great distances, we see objects as they were when the universe was much younger.
Why do the patterns of the stars in our sky look the same from year to year?
Because the stars in the constellations are so far away.
What is our place in the universe?
Earth is part of the solar system, which is in the Milky Way Galaxy, which is a member of the Local Group of galaxies in the Local Supercluster.
How do the speeds at which we are moving with Earth's rotation and orbit compare to the speeds of more familiar objects?
Earth's rotation carries most people around the axis faster than a commercial jet travels, and Earth's orbit carries us around the Sun faster than the Space Shuttle orbits Earth.
Compared to the length of its diameter, the Milky Way is more than tens of thousands of these lengths away from all other galaxies.
False
How are galaxies important to our existence?
Galaxies recycle material from one generation of stars to the next, and without this recycling we could not exist.
Relative to the age of the universe, how old is our solar system?
It is about one-third the age of the universe.
Because we live in an expanding universe, distant galaxies are farther away from us today than they were when the light we see from them started on its journey to us. So what do we mean when we say that a galaxy is 7 billion light-years away?
Its light has taken 7 billion years to reach us.
The Milky Way and Andromeda galaxies are among a few dozen galaxies that make up our ____________.
Local Group
Why can't we see a galaxy 15 billion light-years away? (Assume the universe is 14 billion years old.)
Looking 15 billion light-years away means looking to a time before the universe existed.
Our entire solar system orbits around the center of the ____________ about once every 230 million years.
Milky Way Galaxy
Using the ideas discussed in your text, in what sense are we "star stuff"?
Nearly every atom from which we are made was once inside of a star.
Using the ideas discussed in your textbook, in what sense are we "star stuff"?
Nearly every atom from which we are made was once inside of a star.
Could we see a galaxy that is 20 billion light-years away? (Assume that we mean a "lookback time" of 20 billion years.)
No, because it would be beyond the bounds of our observable universe.
How do our lifetimes compare to the age of the universe?
On a cosmic calendar that compresses the history of the universe into 1 year, human civilization is just a few seconds old, and a human lifetime is a fraction of a second
Note that an observer located at the Local Raisin would see Raisins 1, 2, and 3 all move away from her during the video. What would an observer located at Raisin 2 see?
Raisin 1 and Raisin 3 both move away from her.
Where is our solar system located within the Milky Way Galaxy?
Roughly halfway between the center and the edge of the visible disk of the galaxy
If you could count stars at a rate of about one per second, how long would it take to count all the stars in the Milky Way Galaxy?
Several thousand years
Which of the following is a general difference between a planet and a star?
Stars glow in infrared and visible light, while planets glow only in the infrared.
How big is the Milky Way Galaxy?
The Milky Way has about 100 billion stars.
How big is the Milky Way Galaxy?
The Milky Way has about 100 billion stars. On the same 1-to-10 billion scale...
How big is the universe?
The Milky Way is one of about 100 billion galaxies. 1011 stars/galaxy x 1011 galaxies = 1022 stars It has as many stars as grains of (dry) sand on all Earth's beaches.
How big is the universe?
The Milky Way is one of about 100 billion galaxies. 1011 stars/galaxy x 1011 galaxies = 1022 stars It has as many stars as grains of (dry) sand on all Earth's beaches.
Which of the following statements best describes what astronomers mean when they say that the universe is expanding?
The average distance between galaxies is increasing with time.
The following statements describe ways in which the analogy might apply to the real universe. Which statements are correct?
The average distance increases with time both between raisins in the cake and between galaxies in the universe. An observer at any raisin sees more distant raisins moving away faster, just as an observer in any galaxy sees more distant galaxies moving away faster. The raisins stay roughly the same size as the cake expands, just as galaxies stay roughly the same size as the universe expands.
we see objects as they were in the past:
The farther away we look in distance, the further back we look in time.
Suppose we observe a galaxy that is 13 billion light-years away. Which of the following can we conclude?
The galaxy formed before the universe was 1 billion years old.
How did we come to be?
The matter in our bodies came from the Big Bang, which produced hydrogen and helium. All other elements were constructed from H and He in stars and then recycled into new star systems, including our solar system.
Which statement about motion in the universe is not true?
The mysterious "dark matter" is the fastest-moving material in the universe.
How big is the universe?
The observable universe dwarfs our Milky Way Galaxy, which in turn dwarfs our solar system. Scale models can help with visualizing such distances.
Suppose we make a scale model of our solar system, with the Sun the size of a grapefruit. Which of the following best describes what the planets would look like?
The planets are all much smaller than the Sun. Four planets are within about 20 meters of the Sun, while the rest planets are spread much farther apart.
universe
The sum total of all matter and energy; that is, everything within and between all galaxies
In what sense are telescopes like time machines?
They allow us to see distant objects as they were long in the past.
The distance light can travel in 1 year is about 10 trillion kilometers. So it would be 6 trillion miles.
This photo shows the Andromeda Galaxy as it looked about 2 1/2 million years ago. Question: When will we be able to see what it looks like now?
Earth rotates on it axis each day, the Moon orbits Earth in a little less than one month, and Earth orbits the Sun each year.
True
Today, the evidence that we live in an expanding universe is extremely strong because astronomers have measured the motions of millions of galaxies. Nevertheless, in science, we must always remain open to the possibility that some future observation could call even our most strongly supported theories into question. Which of the following hypothetical observations would NOT be consistent with what we expect in an expanding universe?
You discover an extremely distant galaxy that is moving toward us.
Which of the following has your "cosmic address" in the correct order?
You, Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe
A galaxy is ________.
a collection of a few hundred million to a trillion or more stars, bound together by gravity
Part complete The number of stars in the Milky Way Galaxy is approximately ________.
a few hundred billion
The number of stars in the Milky Way Galaxy is approximately ________.
a few hundred billion
Suppose you tried to count the more than 100 billion stars in our galaxy, at a rate of one per second...
a few thousand years
Light travels at....
a finite speed (300,000 km/s).
The Dark Matter Halo of our galaxy is
a massive non-luminous cloud of material that surrounds the galaxy, providing the dominant source of gravity in our galaxy.
Let's reduce the size of the solar system by a factor of 10 billion; the Sun is now the size of a large grapefruit (14 cm diameter).
a tip of a ballpoint pen
According to current scientific estimates, when did the Big Bang occur?
about 14 billion years ago
The Andromeda Galaxy is faintly visible to the naked eye. When you look at the Andromeda Galaxy, the retina of your eye is absorbing light that has traveled through space for ______ to reach you.
about 2 ½ million years
Hubble discovered that...
all galaxies outside our Local Group are moving away from us. the more distant the galaxy, the faster it is racing away.
When we look at an object that is 1,000 light-years away we see it _________.
as it was 1,000 years ago
Suppose that someone in the Andromeda galaxy had a super-telescope through which they were looking at Earth right now. They would see Earth ______.
as it was about 2 ½ million years ago
Astronomers infer that the universe is expanding because distant galaxies all appear to _________.
be moving away from us, with more distant ones moving faster
On the cosmic calendar, which compresses the history of the universe into a single year, about when did life arise on Earth?
in September
On the cosmic calendar, which compresses the history of the universe into a single year, about when did Earth form?
in early September
On the cosmic calendar, which compresses the history of the universe into a single year, about when did early humans first walk on Earth?
just a few hours before midnight on December 31
You are one year older each time Earth ___________ about the Sun.
orbits
The Sun appears to rise and set in our sky because Earth _________ once each day.
rotates
Our __________ is moving toward the star Vega at about 70,000 km/hr.
solar system
A person located on the equator is orbiting the center of the Earth to the East at 1670 km/s. Relative to the center of the Earth, a person on the North Pole is
stationary, except spinning in-place once per day.
Our solar system consists of _________.
the Sun and all the objects that orbit it
On our 1-to-10 billion scale, it's just a few minutes' walk to Pluto. How far would you have to walk to reach Alpha Centauri?
the distance across the United States (2500 miles)
The total number of stars in the observable universe is about _________.
the same as the number of grains of sand on all the beaches on Earth
Suppose we imagine the Sun to be about the size of a grapefruit. How big an area would the orbits of the eight planets of the solar system cover?
the size of a typical college campus
Which of the following best describes what we mean by the universe?
the sum total of all matter and energy
Based on what you've learned from the raisin cake analogy, which two properties of distant galaxies do astronomers have to measure to show that we live in an expanding universe?
their distances and speeds
On average, galaxies are getting farther apart with time, which is why we say our _________ is expanding.
universe
Suppose we look at two distant galaxies: Galaxy 1 is twice as far away as Galaxy 2. In that case _________.
we are seeing Galaxy 1 as it looked at an earlier time in the history of the universe than Galaxy 2
Suppose we look at two distant galaxies: Galaxy 1 is twice as far away as Galaxy 2. In that case, ________.
we are seeing Galaxy 1 as it looked at an earlier time in the history of the universe than Galaxy 2
Rotation of the Earth
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.
If we imagine the history of the universe compressed into one year ending today, dinosaurs became extinct ________.
yesterday morning
If we imagine the history of the universe compressed into one year, with the present as the stroke of midnight at the very end of that year, dinosaurs became extinct _________.
yesterday morning