Read Chapter 15
1.)
a.)
Proxima Centauri is the nearest star in the sky. It is
"only" 1.3 parsecs (i.e. 4.2 light years) away. Using the
parallax angle formula, calculate the parallax angle for
observing Proxima Centauri.
b.)
Another star, Lalande 21185, is approximately twice
as far away as Proxima Centauri. For the sake of argument,
let us treat it as if it were exactly twice as far away
as Proxima Centauri. Is its parallax angle half as large
or twice as large as that of Proxima Centauri?
2.) Sirius is the brightest star in the night sky, but
if we moved it 10 times further away it would look
a.) just as bright as it is now
b.) 1/10 as bright
c.) 1/100 as bright
d.) 1/1000 as bright
3.)
a.) What is a binary?
b.) What are the differences between visual binaries, eclipsing binaries,
and spectroscopic binaries?
Dear Students: we didn't have as much time for this topic as
I had planned, so you can see this problem as a practice problem,
rather than as a HW problem
4.) Suppose that you want to calculate the mass of a binary
(i.e. you want the sum of the masses of the stars,
but don't necessary
need to know the individual masses)
Describe how you propose to learn the sum of the masses. You can use a
hypothetical binary, whose observable properties you
dream up, as long
as they are realistic. Note, there are a lot of steps in the explanation,
so be sure to list them all
(i.e. you will need a lot of information,
so be sure to consider everything you need and how you plan to
determine it).
For brevity, you don't need to describe the steps in great detail.
5.) Which one of these statements is true? (Note that if you
"directly measure" something, that means
that you use a ruler, thermometer, or other measurement tool
to measure the object. It is the opposite
of calculating the answer from other information that you know.)
a.) Astronomers find the distances to nearby stars
by directly measuring how much their angle on the sky
varies throughout
the year and then calculating the distance from that information
b.) Astronomers find the apparent brightness of stars
by directly measuring their luminosities and
temperatures and then
calculating their apparent brightnesses from that information
c.) Astronomers find the temperatures of stars by directly
measuring how much their angle on the sky
varies throughout
the year and then calculating the temperature from that information
d.) Astronomers find the masses of stars by directly measuring their
luminosities and calculating their masses
from that information
6.) As you go through the stellar sequence (OBAFGKM), what
characteristic of the star changes and how?
7.) Table of stars and questions from textbook:
Star Name..........Absolute magnitude..........Apparent magnitude
..........Spectral Type..........Luminosity Class
Aldebaran..........-0.2
..................................+0.9
....................................K5
.........................III
Alpha Centauri A...+4.4
..............................0.0
....................................G2
.........................V
Antares..............-4.5
..................................+0.9
....................................M1
.........................I
Canopus............-3.1
...................................-0.7
....................................F0
..........................II
Fomalhaut.........+2.0
.................................+1.2
....................................A3
.........................V
Regulas.............-0.6
..................................+1.4
....................................B7
.........................V
Sirius.................+1.4
..................................-1.4
....................................A1
.........................V
Spica.................-3.6
.............................. ....+0.9
...................................B1
.........................V
a.) Which star appears brightest in our sky?
b.) Which star appears faintest in our sky?
c.) Which star has the greatest luminosity?
d.) Which star has the least luminosity?
e.) Which star has the highest surface temperature?
f.) Which star has the lowest surface temperature?
g.) Which star is most similar to the Sun?
h.) Which star is a red supergiant? (use Table 15.2 to decode the Luminosity Class)
i.) Which star has the largest radius? (use Table 15.2 to decode the Luminosity Class)
j.) Which stars have finished burning hydrogen in their cores? (use Table 15.2 to decode the Luminosity Class)
k.) Among the main-sequence stars listed (use Table 15.2 to decode the Luminosity Class), which one is the most massive?
l.) Among the main-sequence stars listed (use Table 15.2 to decode the Luminosity Class), which one has the longest lifetime?
8.)
a.) What material do main sequence stars burn and where in
the stars is it burned?
b.) Do white dwarf stars burn material (by fusion)?
If so, where in the stars is it burned and if not,
why are they able to give off energy in the form of photons?
9.) There are many more low-mass main sequence
stars than high-mass main sequence stars.
One reason for this is that more low mass stars are born. What
is the other reason?
10.)
a.) What observable property of a Cepheid Variable star varies?
b.) Why does it vary?
c.) What other property of the star can be determined from the variation?
11.) Regarding globular clusters and open clusters:
a.) Which are older?
b.) Which type is often found in the Galaxy's halo?
c.) Which has more stars in it?
d.) Could our Galaxy contain a globular cluster that contains A stars?
e.) Could our Galaxy contain an open cluster that
no longer contains K stars?
f.) Bonus question: in which type of cluster are the stars more
attracted to their cluster than to the galaxy?
12.)
Suppose that you are studying a cluster of stars.
Most of the stars in the cluster are main sequence stars.
But, of the main sequence stars, there are no O, B, or A stars, even
though there are F, G, K, and M main sequence stars.
How old is the cluster?
a.) less than 10 million (107) years
b.) between 10 million and 100 million (108) years
c.) between 100 million and a billion (109) years
d.) between a billion and 10 billion (1010) years
e.) between 10 billion and 100 billion (1011) years
f.) more than 100 billion years