PHY 110: Astronomy and Cosmology: Stars and Galaxies
Spring 2004 Prof. Cote's Website " Astronomy at Rutgers " Department of Physics & Astronomy " Rutgers University
Last updated March 11, 2004
Solutions to Midterm
Correct answers are given in bold. Note that the order of the questions and answers may differ from that on your exam.
1) Rutgers is a partner in the consortium of institutions that is building an 11m telescope in South Africa (SALT). This telescope will be used to carry out observations in what wavelength region?
Optical.
Radio.
Gamma Rays.
X-Rays.
Ultraviolet.
2) The belief that every action or event has a cause is a belief in
authority.
actuation.
causality.
instrumentality.
superstition.
3) The mass of the Milky Way is about 200 billion solar masses. The nearby Virgo Cluster has a mass of about 2x1014 solar masses. By how many orders of magnitude does the mass of the Virgo Cluster exceed that of the Milky Way?
25.
11.
3.
1000.
14.
4) You look to the eastern horizon and see the full moon rising. What is the approximate time of day?
6 am.
Noon.
Midnight.
6 pm.
It depends on your latitude and longitude.
5) In New Jersey, it is hottest in June because
the Sun shines more brightly then.
the Sun has a northerly declination then.
the Earth is closest to the Sun then.
the ozone layer is thinnest then.
the ozone layer is thickest then.
6) Suppose that the Sun instantly turned into a black hole, with no loss or gain in mass. What effect would this have on the Earth? [HINT: Recall that, in its complete form, Kepler's Third Law says P2 = 4pi2 a3 / G(M1 + M2).]
Earth would leave its orbit along a tangent.
Earth would fall directly towards the black hole.
Earth would slowly spiral into the black hole.
Earth would drift slowly outwards.
Earth would continue in its current orbit.
7) A moving object has no forces acting on it. According to Newton's First Law, it should
move in a circular orbit once per day.
slow to a stop.
speed up with constant acceleration.
move in a straight line.
none of these answers are correct.
8) Planet A has four times the mass as Planet B; its radius is twice as large as Planet B. How would your weight on the surface of Planet A compare to that on Planet B?
the same.
2 times lower.
2 times greater.
4 times greater.
4 times lower.
9) Compared to other forms of electromagnetic radiation, radio waves have
the shortest wavelengths and photons of the lowest energies.
the longest wavelengths and photons of the lowest energies.
the shortest wavelengths and photons of the highest energies.
the longest wavelengths and photons of the highest energies.
the same wavelengths and photons of the same energy.
10) Which of the following is the same for all types of electromagnetic waves in a vacuum?
Energy.
Wavelength.
Color.
Speed.
Frequency.
11) When an excited atom emits a photon, how does the photon's energy compare to the energy of the electron's orbital levels in the atom?
The photon energy must equal the energy difference between the levels.
The photon energy must exceed the energy difference between the levels.
The photon energy must be less than the energy difference between the levels.
The photon energy must equal the energy of the electron in the lower orbit.
The photon can have any energy.
12) Two stars have identical radii. The surface temperature of Star A 6000 K, while that of Star B is 3000 K. How do their luminosities compare?
They have the same luminosities.
The luminosity of Star B is twice that of Star A.
The luminosity of Star A is 4 times that of Star B.
The luminosity of Star A is 16 times that of Star B.
The luminosity of Star B is 4 times that of Star A.
13) What is the most important function of a telescope?
Magnification.
Resolution.
Light gathering ability.
To reduce atmospheric blurring.
To disperse light.
14) NASA recently launched Spitzer, an infrared space telescope. It joins two other "Great Observatories" already in space, which are designed to observe in the optical and X-ray spectral regions. What are they?
Hubble and Chandra.
Chandra and Pathfinder.
Clementine and Chandra.
Stardust and Pathfinder.
Hubble and Clementine.
15) How does the light gathering ability of the 10m Keck telescope compare to that of the 0.5m telescope atop the Physics and Astronomy building?
10 times greater.
100 times greater.
20 times greater.
400 times greater.
4 times greater.
16) Why do astronomers want to observe and measure neutrinos from the Sun?
Neutrinos are more energetic than photons from the sun.
Neutrinos are easier to detect than photons.
Neutrinos give direct information about the photosphere.
Neutrinos give direct information about the Sun's core.
Neutrinos tell us about magnetic fields inside the Sun, allowing solar flares to be predicted with high precision.
17) How do we measure the radius of the Sun?
From its Doppler shift.
From its gravity.
From its distance and angular size.
From its spectrum.
From its temperature.
18) Protostars radiate most of their energy in
X-rays.
visible light.
ultraviolet.
infrared.
radio.
19) Most stars in our Galaxy are
cooler and brighter than the Sun.
cooler and fainter than the Sun.
hotter and brighter than the Sun.
hotter and fainter than the Sun.
This is a trick question. All stars have the same temperature and luminosity.
20) The orbit of Saturn has a semimajor axis of 9.5 AU, whereas that of Uranus has a semimajor axis of 19 AU. How does the apparent brightness of the Sun at the distance of Uranus compare to that at the distance of Saturn?
Four times brighter.
Two times fainter.
Eight times fainter.
The same brightness.
Four times fainter.
21) You measure the parallax of a star to be 0.25 arcseconds. How far away is it?
4 pc.
13 pc.
1.2 pc.
1 pc.
0.25 pc.
22) Emission nebulae appear _________. Reflection nebulae appear __________.
blue, pink.
yellow, green.
green, pink.
green, yellow.
pink, blue.
23) The balance between pressure and gravity in a main-sequence star is known as
the mass-luminosity relation.
Kirchoff's law.
hydrostatic equilibrium.
solar oscillations.
the neutrino problem.
24) The Hertzsprung Russell diagram is a plot of
parallax versus radius.
mass versus color.
absolute magnitude versus composition.
luminosity versus temperature.
apparent brightness versus distance.
25) Fusing two nuclei together requires high temperatures to
overcome the force of gravity acting on the nuclei.
remove the electrons which surround the nuclei.
overcome the electromagnetic repulsion of the nuclei.
ensure the nuclei thoroughly mix when they collide.
force the nuclei to expand.
26) The globular clusters in our Galaxy are roughly the same age as the Universe itself. How old are they?
4 billion years.
2 million years.
14 billion years.
200 billion years.
100 million years.
27) The Russell Vogt Theorem states that the structure of a star is determined by its
mass and chemical composition.
temperature and luminosity.
radius and mass.
radius and chemical composition.
distance and temperature.
28) The maximum mass for a white dwarf is about ____________, and is known as the ___________ limit.
2 solar masses; Chandrasekhar.
1.4 solar masses; Chandrasekhar.
1.4 solar masses; Eddington.
3 solar masses; Eddington.
2 solar masses; Eddington.
29) What is the only way that a white dwarf can suddenly explode as a Type I supernova?
If it finally cools off to under 2000 K and collapses as a black dwarf.
If it is a member of a mass-transfer binary.
If it passes through a large dust cloud.
If another star collides with it.
This is a trick question. There is no way that a white dwarf can explode as a Type I supernova.
30) What was the very first signal to arrive from supernova 1987A?
A burst of gamma rays.
A burst of X-rays.
A burst of neutrinos.
A burst of cosmic rays.
A burst of optical photons.
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