Astronomy 1040: Chapter 1 HW
Shown here are six galaxies, each labeled with its approximate distance from Earth. Rank the galaxies from left to right based on the amount of time it has taken their light to travel to Earth, from the longest time to the shortest time.
-10 billion light-years -5 billion light-years -2 billion light-years -800 million light-years -230 million light-years -70 million light-years
Consider again the galaxies you ranked in Part A. This time, rank them from left to right based on the age of the universe at the time these galaxies emitted the light we receive from them today, from oldest (closest to today) to youngest (furthest back in time).
-70 million light-years -230 million light-years -800 million light-years -2 billion light-years -5 billion light-years -10 billion light-years
The following statements describe ways in which the analogy might apply to the real universe. Which statements are correct?
-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 average distance increases with time both between raisins in the cake and between galaxies in the universe. -The raisins stay roughly the same size as the cake expands, just as galaxies stay roughly the same size as the universe expands.
Which of the following are real motions of our "spaceship Earth"?
-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. -Earth orbits the Sun.
Represents 1 astronomical unit (1 AU)
-Earth's average distance from the Sun -Jupiter lies about 5.2 of these from the Sun -about 150 million kilometers
Largest 2nd Largest 3rd Largest Smallest
-Galaxy -Solar System -Sun -Earth
Observations
-James is wearing a yellow shirt. -The plastic melted when I held it near the light bulb. -The defendant's DNA was found at the crime scene. -The defendant's calendar says he was at lunch when the crime occurred.
Classified as an observation, meaning something we have directly observed or measured
-More distant galaxies are moving away from us faster than nearby galaxies. -Stars can shine brightly for billions of years. -All planets orbit the Sun in the same direction and nearly the same plane. -The Andromeda Galaxy is similar in structure to our own Milky Way.
Rank the following items according to their size (diameter) from left to right, from largest to smallest.
-The Universe -The local supercluster -The Local Group -The Milky Way Galaxy -Our solar system -The Sun -Jupiter -Earth
Explanations
-The defendant only intended to scare the victim. -James wears a yellow shirt when his other shirts are dirty. -Plastic melts when it reaches a temperature that breaks bonds that hold its structure intact.
Rank the following items that describe distances from longest distance (left) to shortest distance (right). (If two distances are equal, drag the second item on top of the first item.)
-The distance from the Milky Way Galaxy to the Andromeda Galaxy -The distance from the Sun to the center of the Milky Way Galaxy -The distance from Earth to Alpha Centauri -One light-year -The distance across our solar system(to Neptune) -The average distance from Earth to the Sun & one astronomical unit (AU)
Classified as an explanation, meaning something that we infer from observational or experimental evidence even though we cannot observe it directly.
-The universe is expanding because it began with a Big Bang. -The Andromeda and Milky Way galaxies formed in the same way. -The orderly orbits of planets arose from their formation in a rotating gas cloud. -Stars shine with energy generated by nuclear fusion in their cores.
Represents 1 light-year
-about 10 trillion kilometers -the star Sirius lies about 8 of these from the Sun -the distance light travels in 1 year
Consider again the objects you ranked by distance in Part A. Suppose each object emitted a burst of light right now. Rank the objects from left to right based on the amount of time it would take this light to reach Earth, from longest time to shortest time.
-star on far side of Andromeda Galaxy -star on near side of Andromeda Galaxy -star on far side of Milky Way Galaxy -star near center of Milky Way Galaxy -Orion Nebula -Alpha Centauri -Pluto -The Sun
Look once more at the objects you ranked in Parts A and B. This time, rank the objects from left to right based on how much they have aged since they emitted the light we see today, from greatest to least.
-star on far side of Andromeda Galaxy -star on near side of Andromeda Galaxy -star on far side of Milky Way Galaxy -star near center of Milky Way Galaxy -Orion Nebula -Alpha Centauri -Pluto -The Sun
Shown here are astronomical objects located at different distances from Earth. Rank the objects based on their distances from Earth, from farthest to nearest.
-star on far side of Andromeda Galaxy -star on near side of Andromeda Galaxy -star on far side of Milky Way Galaxy -star near center of Milky Way Galaxy -Orion Nebula -Alpha Centauri -Pluto -The Sun
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.
-the 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
Represents NEITHER 1 AU or 1 light-year
-the diameter of Earth -Mars's average distance from the Sun
Light received from a galaxy at the far end of the Local Supercluster was emitted roughly ____________.
10_8 years ago
An astronomer looks at the Andromeda galaxy (the other large galaxy in the Local Group) through her telescope. How long ago did that light leave Andromeda?
2.5 million years
Which of the following lies in the ecliptic plane?
Earth's orbital path around the Sun
Which sequence is correctly ordered from smallest to largest?
Earth, Moon's orbit, the Sun, Neptune's orbit
Which of the following correctly lists our "cosmic address" from small to large?
Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe.
By how many orders of magnitude is the distance to the nearest stars greater than the orbital radius of Neptune?
Four
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 earliest radio broadcasts on Earth were emitted about 100 years ago. Approximately where are these initial radio waves now? (Radio waves are a type of radiation, so they travel at the speed of light)
Just passing relatively local stars in our galaxy.
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 Milky Way and Andromeda galaxies are among a few dozen galaxies that make up our _____
Local Group
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
Our entire solar system orbits around the center of the _____ about once every 230 million years.
Milky Way Galaxy
Could we see a galaxy that is 50 billion light-years away?
No, because it would be beyond the bounds of our observable universe.
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.
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.
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.
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.
The fact that nearly all galaxies are moving away from us, with more distant ones moving faster, helped us to conclude that:
The universe is expanding.
In what sense are telescopes like time machines?
They allow us to see distant objects as they were long in the past.
In January, Earth's rotation axis points in the direction of the star Polaris. Where does it point in July?
Toward the star Polaris
If stars existed but galaxies did not:
We would not exist because we are made of material that required recycling in galaxies.
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.
Mars is _____ from the Sun.
about 1.5 AU
The diameter of the Milky Way Galaxy is _____
about 100,000 light-years
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
Jupiter is _____ from the Sun.
about 5 AU
The star Sirius is _____ from the Sun.
about 8 light-years
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
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
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 distance from Earth to the Moon is _____
less than 0.01 AU
The age of our solar system is about:
one-third of the age of the universe.
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
What is the "Raisin Cake model" intended to explain?
that every raisin in a raisin cake moves farther away from every other raisin: there is no special central raisin (and no special central 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
Our solar system consists of _________.
the Sun and all the objects that orbit it
What do astronomers mean by the Big Bang?
the event that marked the beginning of the expansion of the universe
If we represent the solar system on a scale that allows us to walk from the Sun to Pluto in a few minutes, then:
the planets would all be marble size or smaller and the nearest stars would be thousands of miles away.
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
The star Betelgeuse is about 600 light-years away. If it explodes tonight,
we won't know about it until 600 years from now.
What do we mean when we say that the universe is expanding?
Average distances between galaxies are increasing with time.
