Midterm Questions

Question 1

Why are Cepheid variables so important for measuring distances in astronomy?

Answer 1

They all have the same luminosity.

Question 2

The distribution of the mass of the Milky Way Galaxy is determined by?

Answer 2

Studying the rotation of the galaxy.

Question 3

You observe a star in the disk of the Milky Way, and you want to plot the star on an H-R diagram. You will need to determine all of the following, except the?

Answer 3

Rotation rate of the star.

Question 4

How many atoms fit across the period at the end of this sentence?

Answer 4

Millions

Question 5

Modern telescopes are capable of seeing bright galaxies up to about?

Answer 5

10 billion light-years away.

Question 6

Which of the following statements is not one of Newton’s laws of motion?

Answer 6

What goes up must come down.

Question 7

What do we mean when we say the universe is expanding?

Answer 7

Average distances are increasing between galaxies.

Question 8

How many galaxies are there in the observable universe?

Answer 8

Roughly (within a factor of 10) the same as the number of stars in our galaxy.

Question 9

What is a possible solution to the solar neutrino problem?

Answer 9

The electron neutrinos created in the Sun change into another type of neutrino that we do not detect.

Question 10

The tides on Earth are an example of?

Answer 10

Newton’s third law of motion.

Question 11

Each of the following lists two facts. Which pair can be used with Newton’s version of Kepler’s third law to determine the mass of the Sun?

Answer 11

Earth is 150 million km from the Sun and orbits the Sun in 1 year. (Distance and orbital period)

Question 12

Which of the following statements does not use the term angular size or angular distance correctly?

Answer 12

The angular distance between those two bright stars in the sky is about 2 meters. Angular distance is in degrees between two objects. Angular size is also in degrees, but is for one object.

Question 13

What quantities does angular momentum depend upon?

Answer 13

Mass, velocity, and radius

Question 14

Roughly how many stars in the Milky Way Galaxy?

Answer 14

100 billion

Question 15

What do we mean by the observable universe?

Answer 15

The part of the universe that could be observed in principle, including things that may require future technologies.

Question 16

A star’s luminosity is the?

Answer 16

Total amount of light that the star radiates each second. W = J/s

Question 17

Patterns of stars in constellations hardly change in appearance over a few thousand years. Why?

Answer 17

The stars in our sky actually move rapidly relative to us - thousands of kilometers per hour - but are so far away that it takes a long time for this motion to make a noticeable change in the patterns in the sky.

Question 18

Suppose we look at a photography of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest?

Answer 18

The one that is farthest away.

Question 19

Which of the following is not a unit of energy?

Answer 19

Kilowatt.

Question 20

You are standing on a scale in an elevator. Suddenly you notice your weight decreases. What do you conclude?

Answer 20

The elevator is accelerating downwards.

Question 21

Which scientists played a major role in overturning the ancient idea of an Earth-centered universe, and about when?

Answer 21

Copernicus, Kepler, and Galileo; about 400 years ago.

Question 22

Which of the following statements about the sunspot cycle is not true?

Answer 22

The rate of nuclear fusion in the Sun peaks about every 11 years.

Question 23

The age of the universe is?

Answer 23

Between 10 billion and 16 billion years.

Question 24

What is a spectrum binary?

Answer 24

“can’t see 2 different stars NOR oscillating
spectral lines, BUT mutually exclusive spectral lines”. It is a binary star system that cannot differentiated by spectral lines or changes in apparent brightness on a light curve, but by observing that they both have distinct sets of spectral lines.

Question 25

What four stellar parameters are used in comparing one star with another? Which is the most important and how do the others depend on this parameter?

Answer 25

Mass, luminosity, temperature, and chemical composition. Mass.

Question 26

Describe the butterfly diagram, what data it is based upon, what physical processes produces the effect, and who collect the data?

Answer 26

Quantity of sunspots and how they vary over time. Magnetohydrodynamics and twisting of magnetic field lines. Annie Mauder.

Question 27

What is Kepler’s Third Law?

Answer 27

Square of a planet’s orbital period (p) is proportional to the cube of its semimajor axis to the object it is orbiting (a). When p is in years and a is in AU, p^2 = a^3.

Question 28

What is Newton’s version of Kepler’s third law?

Answer 28

p^2 = 4pi^2a^3 / G (m1+m2). p is in seconds, a is in meters, mass is in kg.

Question 29

An earth-like planet orbits its central star at a distance of 2 AU in a time of 4 years. Determine the mass of the central star in solar masses.

Answer 29

For the Sun and the Earth, the orbital period is 1 year and the distance is 1 AU. Therefore, 4pi^2/G(Msun) is equal to 1. Given that the orbital period is 4 years (4^2 = 16) and the distance is 2 AU (2^3 = 8), the mass must be equal to 2.

Question 30

The central star in the above example is found to be an M type star. Using the typical temperature of an M type star and assuming it has the same diameter as the sun, compare its luminosity with that of the Sun.

Answer 30

Luminosity of the M type star divided by the Luminosity of the Sun means that all the variables are cancelled except for the temperature. 3000K^4 divided by 5800K^4 = 13.97

Question 31

What is the brightness of the M star as seen by this earth-like planet compared with the brightness we measure from our Sun? Express you answer in Wm^-2. What are the conditions likely to be on this planet?

Answer 31

Brightness is Luminosity / 4pi*distance^2. At 1 AU, the brightness is 1/16 of the solar irradiance. At 2 AU, the brightness is 1/64.