## ASTR 1210 (O'Connell) ANSWERS TO SAMPLE EXAM QUESTIONS

In which direction does the Sun appear to move from one day to the next with respect to the stars? A) north; B) south; C) east; D) west. C) east

A healthy, fruit-based model of the nearby stars in which the Sun was the size of an orange would have to be how large in size just to contain the next nearest star? A) 100 feet; B) 100 yards; C) 1 mile; D) 10 miles E) thousands of miles. E) thousands of miles.

(T/F) A particular constellation rises at the same time every night. False [because the sun moves eastward through the constellations at a rate of about 1 degree a day, a given group of stars rises 4 minutes earlier each night.]

An alien visitor from a planet with a slow rotation period becomes nostalgic for long nights. Where on the Earth's surface would you recommend that she goes? A) to the poles; B) to the equator; C) to Las Vegas; D) sorry: all places on Earth have days with equal lengths. A) to the poles.

This sketch shows the Sun, Earth, and the Moon at a particular point in its orbit. In what "phase" will the Moon be at this time as viewed from Earth? A) Full; B) First quarter; C) Crescent; D) New. C) Crescent.

The retrograde motion of Mars can best be explained as: A) Mars reversing its motion in its orbit; B) the Earth reversing its motion in its orbit; C) the Earth overtaking and passing Mars; D) the stars reversing their motion. C) Earth overtaking

The "obliquity of the ecliptic" is defined to be the angle between the Earth's rotation axis and a direction perpendicular to the plane of the ecliptic. This angle is presently 23.5 degrees. If it were 60 degrees instead, seasonal changes would be A) the same as now, since seasons depend only on the Earth's distance from the Sun; B) more extreme; C) less extreme. B) more extreme

Which of the following has the more complicated path in the sky with respect to the stars, as seen with the naked eye? A) the Sun; B) the Moon; C) Venus. C) Venus.

Kepler's Second Law implies that when a planet is nearer the Sun, its speed in its orbit A) increases; B) decreases; C) stays the same. A) increases

This sketch represents the orbit of the Earth seen from a point above its North pole. If the Earth is presently at the point labeled "now". at which point will it be in 3 months? Point A. [As seen from above its North pole, the Earth moves counterclockwise in its orbit. It moves 1/4 of the distance around the sun in 3 months.]

Of which of the following did the Greeks not have an appreciation? A) size of Earth; B) nature of lunar phases; C) shape of Earth; D) Jupiter's satellites; E) approximate distance to sun. D) Jupiter's satellites---requires a telescope to detect these.

[Brief answer question---2-3 sentences.] Why was the {\it accuracy} of Tycho's observations of the planets important in the resolution of the controversy over the structure of the solar system? Kepler knew and respected the accuracy of Tycho's observations. He insisted his model orbits fit Tycho's data for Mars to the known uncertainty in Tycho's observations. This led him to discard other models and realize that Mars' orbit was an ellipse with the Sun at one focus.

[Harder question:] If a full Moon occurs on March 21, you know that the Moon's location in the sky must be: A) near the celestial equator; B) about 23 degrees from the celestial equator; C) near the North Pole; D) in the constellation Cygnus. A) near the celestial equator. [At full moon, the Moon is 180 degrees away from the Sun. The Moon's orbit is almost in the plane of the ecliptic (maximum distance only 5 degrees.) Since the Sun is on the celestial equator at March 21 (the vernal equinox), then the Moon must be 180 degrees away and on the ecliptic, which means it is near the celestial equator at the autumnal equinox. The Moon can never be near the North Pole or Cygnus since those points are not near the ecliptic plane.]

[Fill in.] With his telescope, Galileo made a remarkable discovery about the appearance of the planet Venus. What was it? It shows phases.

If the Moon were twice as far away from Earth as it is today, the "month", as defined by the cycle of lunar phases, would be (A) longer; (B) shorter; (C) the same length as today. A) longer [because, according to Kepler's third law, it would take the Moon longer to complete one orbit around the Earth.]

An object launched at twice the escape velocity from the Earth will be moving with respect to the Earth in A) a circular orbit; B) a bound orbit; C) an unbound orbit; D) an elliptical orbit. C) an unbound orbit

(T/F) "Experiment is the sole source of truth" is the kind of quotation which one finds in the work of Greek philosophers like Plato and Aristotle. False. [The Greeks favored deduction from abstract postulates over experiment.]

The astronomical alignments at Stonehenge are associated with the positions of celestial objects A) at noon; B) at rise or set; C) at midnight. B) at rise or set.

Jupiter's orbit has a radius of approximately 5 Astronomical Units. If the Earth were moved to Jupiter's orbit, how strong would be the gravitational force exerted on the Earth by the Sun ? Express the answer as a ratio to the force exerted at present: A) 1/100; B) 1/25; C) 1/5; D) the same; E) 5 times larger; F) 25 times larger. B) 1/25 [according to Newton's inverse-r-squared force law for gravity]

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