29:50 Modern Astronomy
First Hour Exam
September 27, 2002
Form A

1. The astronomical unit is defined as
   (a) the diameter of the planet Earth.
   (b) the average diameter of the Jovian planets.
   (c) the mean distance of the Sun from the center of the Milky Way galaxy.
   (d) the mass of the Sun, which is used as a scale for stellar masses.
   (e) the average distance between the Earth and Sun.
2. Consider the size of the Sun relative to the Earth. Which of the following gives an accurate, approximate value for the size relationship.
   (a) The diameter of the Sun is 37 % that of the Earth.
   (b) The Sun has a diameter roughly 10 times that of the Earth.
   (c) The Sun is about 10 thousand times the diameter of the Earth.
   (d) The Sun is roughly 100 times the diameter of the Earth.
   (e) The diameter of the Sun is approximately times that of the Earth.
3. The seasons are caused by
   (a) annual variations in the distance between the Earth and Sun.
   (b) the tilt of the Earth's axis relative to its orbital plane.
   (c) a ``heartbeat'' of the Sun which causes its brightness to change during a year.
   (d) the rotation of the Earth on its axis.
   (e) the revolution of the Earth about the Sun.
4. A star transits (crosses the meridian) at midnight in January. At what time of the day or night will it be highest in the sky in June?
   (a) midnight
   (b) sunrise
   (c) sunset
   (d) the middle of the morning
   (e) noon
5. On any given day, there may be sunspots present on the surface of the Sun. If observations of the Sun are made regularly over a long period of time, what will an observer see?
   (a) The size of sunspots has been steadily increasing since observations began in the 19th century.
   (b) The number of spots increases and decreases in a cycle, with a maximum every 11 years.
   (c) Sunspots are absent except for periods every 7 years, when they may be seen for a few months. This year is one such time.
   (d) Sunspots disappear when the Sun's diameter increases to 15 % above its mean value.
   (e) The number of spots on the Sun's surface is constant to a very high degree.
6. Direct distances to stars are measured using the technique of
   (a) trigonometric parallax.
   (b) inverse square law.
   (c) Faraday rotation.
   (d) spectroscopy
   (e) proper motion measurement.
7. How far away are the nearest stars relative to the Sun?
   (a) The nearest stars are 0.20 to 0.78 astronomical units from us.
   (b) They are several hundred thousand times more distant than the Sun.
   (c) They are five hundred to one thousand times more distant than the Sun.
   (d) Even the nearest stars are more distant than the Sun.
   (e) We will never be sure how distant the stars are, since they ceased to exist before their light has reached us.
8. Which of the following is a unit used to describe distances to stars?
   (a) light year
   (b) astronomical unit
   (c) nanometer
   (d) micron
   (e) SRU (stellar remoteness unit)
9. The absolute magnitude is a measure of what stellar property?
   (a) how bright a star appears to us
   (b) how distant a star is
   (c) intrinsic brightness
   (d) stellar color
   (e) the chemical composition of a star
10. If one examines the characteristics of the nearest stars (think of looking at a table with the properties of the nearest stars), a striking and curious property is noticed, which was discussed in lecture. What is it?
    (a) Nearly all of them are spectral class O stars.
    (b) The percentage of stars like the Sun is far higher than among stars in general.
    (c) All stars in the vicinity of the Sun are moving away from us.
    (d) Nearly all (80 %) are at a distance of approximately 750 au.
    (e) Some of these are among the brightest stars, but most are too faint to see with the eye.
11. Stars are grouped into classes according to their spectra. To which class does the Sun belong?
    (a) G
    (b) O
    (c) M
    (d) A
    (e) Wolf-Rayet
12. When you look at the stars in the night sky, you can see that they differ in color. Many are red, others are yellow, still others white or bluish-white. What characteristic of these stars is causing the color differences?
    (a) temperature
    (b) mass
    (c) distance
    (d) apparent magnitude
    (e) absolute magnitude
13. What planet has been prominent in the evening sky this semester?
    (a) Mars
    (b) Jupiter
    (c) Venus
    (d) Saturn
    (e) Mercury
14. An important result about the nature of stars is revealed when one plots stars on a graph in which the temperature (or equivalent parameter) is on the abscissa (x axis) and the luminosity (or equivalent) is on the ordinate (y axis). This graph is called
    (a) Hertzsprung-Russell diagram
    (b) Hubble diagram
    (c) Curie plot
    (d) Plasma Dispersion relation
    (e) spectrum
15. One of the laws of physics that is highly useful in astronomy is Wien's Law. Wien's Law says that there is a mathematical relation between
    (a) where absorption lines are seen and the chemical nature of the object.
    (b) the mass of a star and its luminosity.
    (c) the wavelength of light and its frequency.
    (d) the radius of an object and its mean density.
    (e) the temperature of an object and the wavelength at which it is brightest.
16. The corona of the Sun is a gas of low density and high temperature. If you take a spectrum of the light emitted by the corona, what would you expect to see?
    (a) Emission at certain wavelengths, but darkness over much of the spectrum.
    (b) A spectrum which smoothly varies with wavelength.
    (c) A continuous spectrum, but with dark ``absorption lines'' characteristic of the material the corona is made of.
    (d) Pure white light.
    (e) Emission at a single wavelength, which depends on the phase of the rotation of the Sun.
17. The term absolute zero refers to
    (a) the temperature at which molecular motion ceases.
    (b) the position of zero radius at the center of the Sun.
    (c) The center of the system which includes the Sun and all stars we see.
    (d) The very beginning of time (refers to zero time elapsed since the start of the universe).
    (e) your roommate.
18. What we perceive as visible light corresponds to
    (a) electromagnetic waves with a very narrow range of wavelengths, from about 0.1 to 0.35 meters.
    (b) electromagnetic waves with a very narrow range of wavelengths, from about to meters.
    (c) electromagnetic waves with a broad range of wavelengths from to meters.
    (d) subatomic particles with electrical charge, and whose energy determines our sensation of color.
    (e) pressure waves in the atmosphere, which cause vibrations in the cornea of the eye.
19. The Sun and (almost) all other stars are predominantly composed of one of the following elements. Which is it?
    (a) oxygen
    (b) hydrogen
    (c) helium
    (d) nitrogen
    (e) carbon dioxide
20. Planets like the Earth are called the terrestrial planets. Which of the following sets gives correct characteristics of the terrestrial planets?
    (a) Location far from the Sun, primarily hydrogen composition, masses substantially larger than that of Jupiter.
    (b) rocky composition, locations in the inner solar system, masses much less than the Jovian planets.
    (c) rock and ice composition, location in the outer solar system, masses less than the Jovian planets.
    (d) locations in the inner solar system, liquid water common property of all, masses 10 - 15 % that of the Sun.
    (e) composition primarily of helium, location in the inner solar system, relatively small masses.
21. At different times of the year, different constellations are visible in the evening sky. The astronomical reason for this is
    (a) the tilt of the Earth's axis with respect to its orbital plane.
    (b) parallax as the Earth changes its position in space.
    (c) the rotation of the Earth on its axis.
    (d) the orbital motion of the Earth around the Sun.
    (e) the motion of the Sun through the Milky Way galaxy.
22. The age of the Sun and solar system is
    (a) 95 billion years
    (b) 1.3 billion years
    (c) about 375 million years
    (d) 20 billion years
    (e) 4.5 billion years .
23. The star Deneb (brightest star in the constellation Cygnus) is one of the 20 brightest stars in the sky, and is at a distance of 430 parsecs. Without doing any calculations, but recalling what you know about ``ballpark'' stellar properties, what can you say about Deneb?
    (a) It is rather faint compared to the stars in other constellations.
    (b) It must be a spectral class M star.
    (c) It is a star of average luminosity.
    (d) A star with those characteristics must be a binary (double) star.
    (e) It is an extremely luminous star .
24. As a source of light moves further away from an observer, the observer sees it become fainter (technically, the flux of radiation becomes smaller). What law of physics describes how this happens?
    (a) Wien's law
    (b) Kirchoff's law
    (c) Newton's law of motion
    (d) the inverse square law
    (e) Ohm's law
25. You see two stars in the night sky. Both are spectral class F Main Sequence stars. Star A has an apparent magnitude of 2.5, while star B has an apparent magnitude of 5.5. What can you say about the similarities and differences of these two stars?
    (a) star A is more distant than star B.
    (b) star A is more luminous than star B.
    (c) star B is more distant than star A.
    (d) star B is more luminous than star A.
    (e) star A has a higher surface temperature than star B.

• About this document ...