Astronomy HW 3

| October 22, 2018

Homework 3 Astronomy 100 Dr. Warner

DUE: April 5th , 2012

Note: Unlike
the last two homework assignments there are three mandatory questions on
this assignment: Questions 9, 12 and 16 are required. These three questions are
worth 15 points. As before, you only need to get 50 points in order to have a
perfect score, and so you need to select at least another 35 points from the
remaining questions. Your score will thus consist of a score out of 15 for the
mandatory problems and a score out of 35 for the other problems. You may
attempt, and submit more problems, but if your score for these additional
problems exceeds 35, then it will be set equal to 35.

you do this homework please read the comments on page 4 of the syllabus
concerning acceptable and unacceptable levels of collaboration.

Summarize the evidence supporting the theory that the Cretaceous-Tertiary
extinction, which includes the extinction of the dinosaurs, was precipitated to
a significant degree by the impact of a


(4 points)


What are the three primary ways in
which a planet can have or acquire a Moon. What is the most

probable origin of
Earth’s Moon? Given examples of moons that probably arose by the other two


(5 points)


What is the Roche limit of a planet
and its role in the formation of ring systems? What would happen

to an astronaut who
enters the Roche limit of a planet?

(4 points)


What are the defining properties of
a dwarf planet? What extra condition must be satisfied in order

for a dwarf planet
to be a true planet?

(3 points)


Describe the position, layout and
typical inhabitants of the Asteroid Belt, the Kuiper Belt and the

Oort Cloud. What, in particular, are plutinos?

(5 points)

6. A comet often has two different tails. what determines
their direction in space?

How are they created, of
what do these tails consist and (4 points)

a) The dwarf planet, Ixion, has an orbit that ranges from 30.091AU out to
49.269 AU. Use Kepler’s Laws of Planetary Motion to calculate the orbital
period of Ixion.

b) Using the same technique, compute the maximum distance
from the Sun of a long-period comet that has an orbital period of 1,500,000
years and a perihelion at 0.5 A.U.
for a) and b): Remember that the semi -major axis is the average of the
distance at perihelion and aphelion.) (4 points)

What are the photosphere, chromosphere and corona of the Sun? Describe some
typical phenomenon observed on or in each. What are the various emission and
absorption line spectra associated with these layers of the Sun? What is the
solar wind, and of what does it consist. How is it related to the corona and
coronal holes? How is it related to aurorae on Earth? (8 points)

9.* (Mandatory)
What are sunspots and how are they related to the Sun’s magnetic field? Is the
magnetic field stronger weaker in sunspots? How does the temperature in a
sunspot relate to the temperature in the rest of the photosphere? Describe the
role of the Sun’s differential rotation in the formation of sunspots. Describe
(briefly) the 22 year solar cycle, stating its essential features.

(5 points)

At one time, the protostar that became our Sun had a surface temperature of
about 3000K and a radius about 25 times that of the present-day Sun. How much
more (or less) luminous, compared to today, was our Sun when it was a
protostar? At what distance would you have to be from the protostar for it to
have the same brightness as the Sun seen from Earth today? (5 points)

What is the Solar Neutrino problem, and what are the possible resolutions of
it? Which of these resolutions is now believed to be the most likely
explanation? (3 points)

12.* (Mandatory)
What is the mass deficit in nuclear reactions? Where does the mass go? Which
elements can fuse together to generate energy and why is iron considered
to be the most stable element? Why do thermonuclear reactions occur only in the
Sun’s core, and not in the outer parts of the Sun? Why is it more difficult to
fuse two helium nuclei than it is to fuse two hydrogen nuclei?

(5 points)

In the 19th century there was much discussion about
what could be the energy source of the Sun. Why was it evident that the Sun
could not be powered by chemical reactions? Kelvin and Helmholtz thought they
had the answer. What was their idea and what 19th
century evidence showed that they were wrong? (5 points)


A red star and a blue star have the
same size and are at the same distance from Earth. Which one

looks brighter in
the night sky? Why? (Ignore the interstellar reddening)

(3 points)


What is the fundamental explanation
(in terms of atomic physics) of why hydrogen absorption lines

weak in O and M stars and strong in A stars. Why are molecular
absorption lines strong in K and M stars but weak in O, B and A stars? (4

(Mandatory) a) Sketch a Hertzsprung-Russell diagram:
label the axes, marking off the scales. Indicate the regions on your diagram
occupied by main sequence stars, red giants, supergiants, the Sun. Discuss how
the one can determine the radius of a star from its position on the
Hertzsprung-Russell diagram – you need not go into great mathematical detail, a
short outline of the ideas will suffice.

(5 points)

a) Describe how we measure distance using parallax. What is the practical
limitation of this technique, and what is the approximate distance (in parsecs)
out to which this technique is useful.

b) Describe how we measure distance using “spectroscopic
parallax”. What is the practical limitation in using this technique, and what
is the approximate distance (in parsecs) out to which this technique is useful.

c) How do we use the spectral class and the apparent
color of a star to determine the amount of dust and gas (the “crud”) that lies
between us and the star. (8 points)

Star A and star B have the same apparent magnitude, but star B is twelve times
further away than star A. How much more luminous is star B than star A? Suppose
that star B also only has half the surface temperature of star A, what is the
energy flux from the surface of star B compared to star A? What is the ratio of
the radius of star B over the radius of star A. (6 points)

19. Describe how one
can determine the mass of a star when it a) is part of a binary system

when it is not part of a binary system. Mathematical details are not necessary
– I only want you to briefly outline the methods. (4 points)

20. Describe the
complete life cycle of the Sun and plot it on an HR diagram. What is a

nebula? What process
gives rise to such a nebula? What typically lies at the center of a planetary

nebula? (8 points)

21. The labels, “type I” and
“type II,” of different kinds of supernova come from observational astronomy
and reflect a fundamental difference in their observed spectrum. What is that
difference and, for type Ia and type II supernovae, how is it related to the
evolution that leads to the supernova explosion? Why are type Ia supernovae so
important to distance measurement in astronomy? What are the possible remnants
of a type II supernova? Where and in what process were all the heavy metals and
rare-earth elements, like gold, created? (8 points)22. What is the Chandrasekhar limit in the context of
white dwarfs and neutron stars? Give a brief explanation of the result
if the mass of the core of a star exceeds the Chandrasekhar limit. Is it
possible that one could find a black hole or a neutron star of one (1) solar
mass? Is it possible that one could find a black hole or a neutron star of ten
(10) solar masses? What happens if you keep adding mass to a white dwarf (be
careful here, the answer is not obvious from the context of this question)?
What happens if you keep adding mass to a neutron star? (6 points)

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