Astronomy UNIT 3

Astronomers have concluded that the Sun's activity varies in an 11-year cycle. Which of the following statements about this cycle is TRUE:

The number of sunspots gets larger and smaller over the course of 11 years

Which of the following statements about the Sun's photosphere is NOT TRUE?

The photosphere is significantly hotter than all the layers of the Sun beneath it (further inward)

When astronomers discuss a nebula, what are they talking about?

a giant cloud of gas and dust between or among the stars

The Orion Nebula is

a large cloud of gas and dust illuminated by the light of newly formed stars within it

Who pays the bill for the energy generated by nuclear fusion in the Sun? In other words, where does the energy pouring out of the Sun come from ultimately?

a little bit of mass is lost in each fusion reaction and is turned into energy (the Sun is losing mass

Physicists Kelvin and Helmholtz in the last century proposed that the source of the Sun's energy could be:

a slow contraction

A charming friend of yours who has been reading a little bit about astronomy accompanies you to the campus observatory and asks to see the kind of star that our Sun will ultimately become, long, long after it has turned into a white dwarf. Why is the astronomer on duty going to have a bit of a problem satisfying her request?

after a white dwarf cools off it becomes too cold and dark to emit visible light

One of your good friends who is on a diet asks you to point out the stars with the smallest mass on an H-R diagram that you are studying. Where are you sure to find the stars with the lowest mass on any H-R diagram?

among the stars at the bottom right of the main sequence

Solar wind particles can be captured by the Earth's magnetosphere. When these particles spiral down along the magnetic field into the atmosphere, they are responsible for:

aurorae (northern and southern lights)

Imagine that a brilliant but quirky scientist in the biology department manages to put you in a deep freeze and you wake up in a million years. Which of the following statements about the sky you would see in that future time is correct?

because of proper motion, a number of the familiar constellations will look somewhat different in a million years

Why can a star with a mass like our Sun not fuse (produce) further elements beyond carbon and oxygen?

because they just cannot get hot enough for the fusion of heavier nuclei

When great currents of hot material rise inside the Sun (and cooler material sinks downward), energy is being transferred by a process known as:

convection

Astronomers use the term interstellar matter to refer to:

gas and dust that lies between stars

When an astronomer rambles on and on about the luminosity of a star she is studying, she is talking about:

how much energy the star gives off each second

The most common element in the Sun is

hydrogen

Which of the following statements about interstellar matter is FALSE?

if the matter were spread out evenly, it would be about as dense as the Earth's atmosphere

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?

it must be quite large in size

Ninety percent of all stars (if plotted on an H-R diagram) would fall into a region astronomers call:

main sequence

When two light elements collide to undergo nuclear fusion

some of the energy in their mass is released

A type of star that has turned out to be extremely useful for measuring distances is

the Cepheid variables

A friend (who does not have the new awareness which you have gained from this course) suggests that the mechanism that keeps the Sun shining as brightly as it does is the burning of coal. You brilliantly challenge his theory! Your challenge comes in several related steps; which of the following is one of those steps?

the dating of radioactive rocks show that the Earth and thus the Sun are billions of years old

When an astronomer measures a color index for a star, what is she measuring?

the difference between how bright a star looks at two different wavelength regions

If observations of supernovae in other galaxies show that such an explosion happens in a spiral galaxy like the Milky Way on average every 25 to 100 years, why have astronomers on Earth not seen a supernova explosion in our Galaxy since 1604?

the disk of our Galaxy contains a great deal of dust, which tends to block the light of supernova explosions from more distant parts of our Galaxy

Which of the following is a characteristic of degenerate matter in a white dwarf star?

the electrons get as close to each other as possible and resist further compression

The measurement of cosmic distances was helped tremendously by the discovery, in the early part of the 20th century, that in Cepheid variable stars, the average luminosity was related to

the length of time they took to vary

On an H-R diagram of a cluster of stars, which characteristic of the diagram do astronomers use as a good indicator of the cluster's age?

the point on the main sequence where stars begin to "turn off" -- to move toward the red giant region

Your sweetheart gives you a piece of gold jewelry as a present to celebrate your passing your astronomy class. Where did the gold atoms in that gift originally come from (where were they most likely made)?

they were built up from smaller nuclei during a supernova explosion

A light curve for a star measures how its brightness changes with

time

In a planetary nebula, the shell of expelled material is glowing intensely. What is the main source of energy for this glow?

ultraviolet radiation from the collapsing hot star at the center

Astronomers identify the "birth" of a real star (as opposed to the activities of a protostar) with what activity in the star?

when nuclear fusion reactions begin inside its core

Which of the following can astronomers NOT learn from studying the spectrum of a star?

you can't fool me, all of the characteristics listed can be learned from studying the spectrum