Astro homework

Question 1

A lightyear is

Answer 1

the distance that light travels in one year

Question 2

Which of the following is most abundant in the Universe?

Answer 2

Helium

Question 3

When an atom has lost one or more electrons, it is said to be:

Answer 3

ionized

Question 4

Newton showed that to change the direction in which an object is moving, one needs to apply:

Answer 4

a force

Question 5

As astronomers have learned more about the structure of the Sun, they have found that it

Answer 5

is made entirely of hot gas

Question 6

The most common element in the Sun is

Answer 6

hydrogen

Question 7

You are out on the beach, enjoying the warm sunshine with friends. As you glance up at the Sun, the part of the Sun that you can see directly is called its:

Answer 7

photosphere

Question 8

The antimatter version of an electron is called a

Answer 8

positron

Question 9

Which magnitude looks the brightest in the sky?

Answer 9

a star with magnitude -1

Question 10

Which of the following characteristics of a single star (one that moves through space alone) is it difficult to measure directly?

Answer 10

its mass

Question 11

I am measuring the spectrum of the stars in a spectroscopic binary system. When one of the stars is moving toward the Earth in its orbit, we observe

Answer 11

that the lines in its spectrum show a blue-shift

Question 12

For what type of star can astronomers measure the diameter with relative ease?

Answer 12

eclipsing binary stars

Question 13

Measurements show a certain star has a very high luminosity (100,000 x the Sun’s) while its temperature is quite cool (3500o K). How can this be?

Answer 13

it must be quite large in size

Question 14

Where on the H-R Diagram would we find stars that look red when seen through a telescope?

Answer 14

only on the right side of the diagram and never on the left.

Question 15

Astronomers use the term interstellar medium to refer to:

Answer 15

gas and dust that lies between stars

Question 16

An HII region is

Answer 16

a zone around a hot star where hydrogen atoms are ionized

Question 17

If you want to find stars that are just being born, where are the best places to search?

Answer 17

in giant molecular clouds

Question 18

A star whose temperature is increasing but whose luminosity is roughly constant moves in what direction on the H-R diagram?

Answer 18

to the left

Question 19

Which of the following types of stars will spend the longest time (the greatest number of years) on the main sequence?

Answer 19

K

Question 20

A type of star cluster that contains mostly very old stars is

Answer 20

a globular star cluster

Question 21

The event in the life of a star that begins its expansion into a giant is

Answer 21

almost all the hydrogen in its core that was hot enough for fusion has been turned into helium

Question 22

As a cluster of stars begins to age, which type of star in the cluster will move off the main sequence of the H-R diagram first?

Answer 22

the O and B type stars

Question 23

what will happen after the life of a star with a mass like the Sun?

Answer 23

as the star is dying, a considerable part of its mass will be lost into space.

Question 24

When a single star with a mass equal to the Sun dies, it will become a

Answer 24

white dwarf

Question 25

The most stable (tightly bound) atomic nucleus in the universe is:

Answer 25

iron

Question 26

In a supernova like SN1987A, once the crisis of iron fusion has begun, roughly how long does it take the star’s core to collapse?

Answer 26

less than a second

Question 27

If you are in a freely falling elevator near the top of a tall building, as the elevator falls, your weight would be:

Answer 27

equal to zero – you would be weightless

Question 28

To predict whether a star will ultimately become a black hole, what is the key property of the star we should look at?

Answer 28

mass

Question 29

The region around a black hole where everything is trapped, and nothing can get out to interact with the rest of the universe, is called

Answer 29

an event horizon

Question 30

Wearing a very accurate watch, you volunteer to go on a mission to a black hole in a spaceship that has powerful rockets. You are able to orbit the black hole and stay a little distance outside of the event horizon. Compared to watches on Earth, your watch near the black hole will run:

Answer 30

more slowly

Question 31

Objects orbiting around the center of the Milky Way obey Kepler’s 3rd Law. This means that:

Answer 31

a cloud of gas or star that is further from the center will generally take more time to orbit

Question 32

For the Milky Way, compared to the sun stars in the inner central bulge have:

Answer 32

slower Galactic orbital velocities

Question 33

Order the following regions of the Galaxy from youngest mean stellar age to oldest:

Answer 33

thin disk, thick disk, halo

Question 34

Order the following in order of total mass:

Answer 34

thin disk, halo, thick disk

Question 35

If I want to find a sizeable collection of Population II stars in the Milky Way Galaxy, where would be a good place to look?

Answer 35

in a globular cluster high above the Galaxy’s disk

Question 36

Which type of galaxy is observed to contain mostly older stars?

Answer 36

giant elliptical

Question 37

Which is one reason that the typical galaxy’s mass-to-light ratio (in units of the Sun’s mass over the Sun’s luminosity) generally greater than 1?

Answer 37

galaxies contain many more stars that shine much less brightly than the Sun

Question 38

What method would astronomers use to find the distance to a galaxy so far away that individual stars are impossible to make out (resolve)?

Answer 38

finding the red­shift and using Hubble’s Law

Question 39

According to our current understanding, giant elliptical galaxies form:

Answer 39

by the merger (or swallowing) of a number of smaller galaxies in a cluster of galaxies

Question 40

The Andromeda Galaxy (our nearest spiral neighbor) has spect­ral lines that show a blue shift. From this we may conclude that:

Answer 40

this particular nearby galaxy is moving toward us

Question 41

According to Hubble’s Law, if two galaxies are not part of our Local Group, and galaxy B is three times farther away from us as Galaxy A, then Galaxy B will

Answer 41

move away from us three times faster than A

Question 42

If the Hubble Constant is currently 68 km/s/Mpc and a distant galaxy is 1 Gpc away, approximately what is its redshift?

Answer 42

.22

Question 43

When we determine the age of the universe using the Hubble Time, what important simplifying assumption goes into our calculations?

Answer 43

that the expansion of the universe has been happening at the same rate – neither speeding up or slowing down

Question 44

The Hubble constant is measured to be 68 km/s/Mpc at time A.

At another point in time, B, it was measured to be 90 km/s/Mpc.

At another point in time, C, the Hubble Time was measured to be 18 billion years.

Order the age of the Universe at times A, B, and C from LEAST to MOST.

Answer 44

Time B, Time A, Time C

Question 45

Based on many surveys of the average density of matter in the universe (regular matter and dark matter), astronomers now conclude that the average density of the universe is

Answer 45

less than the critical density

Question 46

Today, we believe that only a small number of elements were actually formed during the Big Bang. what are they(3)

Answer 46

helium, lithium, hydrogen

Question 47

After the Big Bang, in order for the universe to become transparent to light and other electro-magnetic radiation, what had to happen?

Answer 47

free electrons needed to bind to nuclei

Question 48

The rich galaxy cluster that is closest to our Local Group of galaxies is the

Answer 48

Virgo Cluster

Question 49

When astronomers say that the groups of galaxies are distributed isotropically, they mean that

Answer 49

the way galaxies are arranged in space looks the same in all directions