homework 2 astronomy
Which of the following are real motions of our "spaceship Earth"?
-Earth orbits the Sun. -Earth and our solar system moves with the Milky Way galaxy relative to other galaxies in our Local Group. -Earth moves with the Sun on an orbit around the center of the Milky Way galaxy.
Consider the indicated events in the history of the universe that have helped make human life possible. Rank the events based on when they occurred, from longest ago to most recent. To rank items as equivalent, overlap them. Note: If two events occurred within seconds of each other, rank them as equivalent.
-big bang+the universe begins to expand -elements such as carbon and oxygen first exist -nuclear fusion begins in the sun -earliest life on earth -dinosaurs go extinct -earliest humans
Approximately how fast is a person located at the Earth's equator traveling due to the rotation of the Earth?
1,700 km/hr
The Earth has a radius of about 6,000 km. How long would it take for an object traveling at the speed of light to circle the earth? (Recall that the speed of light is 300,000 km/s.)
1/8 of a second (0.0125 s)
The farthest galaxies that modern telescopes are capable of seeing are up to
10 billion light-years away.
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
How much of the hydrogen and helium of the universe had been converted into heavier elements when the universe was 1/3 its current age (when Earth formed)?
2%
How long does it take our solar system to complete one orbit around the Milky Way Galaxy?
230 million years
Astronomer Alan says the universe is expanding at one rate and Astronomer Wendy says it is expanding at a faster rate. All other things being equal, which astronomer would say that the universe is OLDER?
Alan
What do we mean when we say that the universe is expanding?
Average distances between galaxies are increasing with time.
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.
The total energy of the universe is now thought to be dominated by
Dark Energy.
What makes dark matter and dark energy so mysterious?
Dark matter and dark energy are mysterious because we don't know exactly what they are.
What makes dark matter and dark energy so important?
Dark matter and dark energy make up the majority of the total energy in the universe.
Dark matter can be detected only by its gravity, that affects other objects we can see. Why can't we see it directly by means of telescopes?
Dark matter does not emit light.
Briefly explain Earth's daily rotation and annual orbit, defining the terms ecliptic plane and axis tilt.
Earth rotates once each day on its axis and orbits the Sun once each year. The ecliptic plane is the plane defined by Earth's orbit around the Sun. Axis tilt of a planet is the amount that its axis is tipped relative to a line perpendicular to the ecliptic plane.
Which of the following lies in the ecliptic plane?
Earth's orbital path around the Sun
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.
The observable universe is the same size today as it was a few billion years ago.
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.
What does this photograph show?
It is a picture of the Andromeda galaxy, located about 2.5 million light-years away.
Relative to the age of the universe, how old is our solar system?
It is about one-third the age of the universe.
What is the significance of this photograph?
It shows a person standing on the most distant world ever visited by a human being.
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.
Regarding the history of the universe, which of the following is true?
Key elements of which Earth and life are made, including carbon, oxygen, and iron, did not exist when the universe was born and were created later in stars.
The table in the video shows you the speeds of Raisins 1, 2, and 3 as measured from the Local Raisin. Suppose instead that you measured speeds as seen from Raisin 2. An observer at Raisin 2 would measure __________.
Local Raisin speed = 4.0 cm/hr; Raisin 1 speed = 2.0 cm/hr; Raisin 3 speed = 2.0 cm/hr
Where does it reside in our galaxy?
Most dark matter resides in the halo of the 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.
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.
These photos show two different astronomical objects. Which object is bigger, and by about how much?
Object 2 is more than a trillion times as large as Object 1. Submit
Notice that Earth's axis is shown with an arrowhead in this diagram. What does the arrow point to?
Polaris, the North Star
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.
These diagrams show a raisin cake before it is put in the oven and again one hour later after it has expanded during baking. Suppose you lived in Raisin 3 (the raisin labeled "3"). What would you have noticed about Raisin 2 during baking?
Raisin 2 is moving away from you at a speed of 2 cm/hr.
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 Submit
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.
Suppose we made a scale model of our Milky Way Galaxy in which the disk of the galaxy is the size of a football field. Which (if any) diagram represents the Sun on the same scale?
The Sun on this scale would be microscopic and too small to see on the screen. Submit
When we say the universe is expanding, we mean that:
The average distance between galaxies is growing with time.
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.
This painting represents the Sun and planets (and two dwarf planets) of our solar system. What is not to scale in this painting?
The distances between the planets are not shown to scale.
This diagram represents Earth's rotation and orbit. What do we call the flat blue plane shown in this diagram?
The ecliptic plane
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.
Which statement about motion in the universe is not true?
The mysterious "dark matter" is the fastest-moving material in the universe.
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. Submit
Why don't star systems, galaxies and galaxy clusters themselves expand as the universe around them expands?
Their inter-gravitational attraction is strong enough to keep them bound together against the expansion of space.
In what sense are telescopes like time machines?
They allow us to see distant objects as they were long in the past.
Earth is made mostly of metals and rocks. Where did the elements (carbon, silicon, iron, etc.) that make up these materials form?
They were produced by nuclear fusion in stars.
In January, Earth's rotation axis points in the direction of the star Polaris. Where does it point in July?
Toward the star Polaris
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 Submit
Which of the following best describes the Milky Way Galaxy?
a disk-shaped galaxy about 50,000 light-years in radius and containing between 100 billion and 1 trillion stars
The planet Mars is, on average, about 228 million km from the Sun. How long does it take light from the Sun to reach Mars? (Recall that the speed of light is about 300,000 km/s.)
about 12.7 minutes
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
The universe is defined as
all material, space, and energy that exist: everything.
The fact that the expansion of the universe is seen to be accelerating suggests
an unknown repulsive force, called "Dark Energy", is present in the universe.
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 Submit
Nearly all of the objects that you can see in this photograph are _____________.
galaxies
What is the Sun mainly made of?
hydrogen and helium
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
The mysterious Dark Energy
is believed to be the dominant form of energy in the universe.
A television advertisement claiming that a product is light-years ahead of its time does not make sense because _________.
it uses "light-years" to talk about time, but a light-year is a unit of distance
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
The age of our solar system is about:
one-third of the age of the universe.
How many galaxies are there in the observable universe?
roughly (within a factor of 10) the same as the number of stars in our galaxy
The term observable universe refers to ________.
that portion of the universe that we can see in principle, given the current age of the universe
What do astronomers mean by the Big Bang?
the event that marked the beginning of the expansion of the universe
From your location on Earth right now, your trajectory through space is the combination of many different motions. Which motion adds the most velocity to total?
the orbit of the solar system around the center of the galaxy
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
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
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
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
