Astronomy 110-03:   Midterm Exam (Sample)
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Please keep your answers brief, and to the point. For multiple choice questions, chose and circle one and only one answer.

1. Is the "dark side of the Moon" always in the dark? Why, or why not?

The Moon is tidally locked to the Earth, which means that the same side of the Moon always faces the Earth. The "dark side of the Moon" is thus the side of the Moon that always points away from the Earth (called dark because it is always hidden to us on Earth), not the side of the Moon which is shadowed from the Sun. As the Moon goes around the Earth each month, the dark side points towards the Sun during the new moon phase and then away from the Sun during the full moon. Thus the dark side of the Moon can be fully illuminated, and it is not always dark.

2. What are two observations, possible with the naked eye, which contradicted the Ptolmeic model? How did they do so?
      [a] the observed phases for the planet Venus, which could not be explained if Venus orbited the Earth
      [b] the moons of Jupiter, which orbit Jupiter rather than the Earth

3. The Terrestrial planets in our solar system that have substantial atmospheres are:
      [a] the Moon and Mercury
      [b] Mercury, Venus, and the Earth
      [c] Mars, Venus, and the Earth
      [d] Mars, Jupiter, and the Earth

4. The more __________ an object is, the further back in time we look when we observe it. Why?
      [a] bright
      [b] faint
      [c] nearby
      [d] distant

Light takes time to travel to Earth from distant objects, so we observe the most distant objects not as they are today, but as they were in the past (when the light that we see from them was emitted).

5. If the radius of the Earth's orbit was decreased to a third of its current size, then what would happen to parallax angles?

The parallax effect is caused by the change in the Earth's position over the course of a year, which causes nearby stars to appear to change position relative to distance ones. If the Earth's orbit decreased in radius by a factor of three, the parallax effect would be a third of its current state, and parallax angles would decrease by a factor of three.

6. Procyon is 11 light-years away, while Hadar is 525 light-years away. Which star has the greater parallax angle?

The parallax effect is strongest for the nearest objects, and so Procyon would have a significantly larger parallax angle than Hadar.

7. Sketch the solar system, under the following conditions. First, draw a circle to indicate the position of the Sun (placing the letter "S" near to it). Second, draw four large dashed circles to indicate the orbits of Earth, Jupiter, Mars, and Venus. Third, place Earth anywhere on its orbital path, by drawing a small circle with the letter "E" near to it; place Jupiter so it would appear in the "full" phase from Earth; place Mars where it would rise at midnight, as viewed from Earth. Fourth, add two circles for Venus, at the locations where it could most easily be observed from Earth by eye.

This sketch of the solar system drawn from above the North Pole shows a central Sun surrounded by three circles representing the orbits of Venus, Earth, and Mars. To the right is drawn a portion of the larger circle for the orbit of Jupiter, so much larger that only part of it appears on the figure. Jupiter is drawn as a large dot on the horizontal line intersecting both the Sun and Earth, at opposition where it will appear overhead around midnight. Venus is drawn twice at maximum elongation, where it appears furthest from the Sun in the sky, near dawn and near dusk. Mars is drawn high along a vertical line intersecting Earth.

Jupiter will be in the full phase when the side facing Earth is also pointed directly toward the Sun (and thus overhead at midnight). If Mars rises at midnight, it will be overhead at 6 am. Venus is best viewed with the naked eye at dusk and dawn, and most easily found when it is as far as possible from the Sun, as viewed from Earth.

8. What phase would Mars appear to have from Earth, in your diagram?

Mars would appear just before the third quarter phase (slightly gibbous).

9. What is the maximum separation between Earth and Jupiter, in units of A.U.? What is the minimum? Jupiter lies 5.2 A.U. from the Sun.

Earth lies 1 A.U. from the Sun, while Jupiter lies 5.2 A.U. from the Sun. When the two planets line up on the same side of the Sun, their separation is

S = 5.2 - 1.0 = 4.2 A.U.

and when the two planets are on either side of the Sun their separation is

S = 5.2 + 1.0 = 6.2 A.U.

10. If the planet Neptune has a year 165 Earth years long, at what radius does it orbit the Sun? Remember that the Earth has an orbital radius of 1 A.U., and takes one Earth year to go once around the Sun.
      [a] less than one A.U.
      [b] one A.U.
      [c] more than one A.U.
      [d] We need more information to answer this question.