ASTR 109 HOMEWORK #2 (Hamilton)
1. Earth's Seasons Website.
2. Changing Perspectives: A view from the Moon.
- a) In mid-summer (Dec. 21), Christchurch gets 15.25 hours of sunlight; in
mid-winter (Jun. 21) it gets only 8.75 hours.
- b) In mid-summer (Jun. 21), Anchorage gets 18.50 hours of sunlight; in
mid-winter (Dec. 21) it gets only 5.5 hours.
- c) The equator gets 12 hours of sunlight per day all year round!
- d) Poleward of the Antarctic Circle a summer day can have 24
hours of sunlight (and a winter's day can have no
sunlight). Equatorward of the Tropic of Capricorn it is possible for
the Sun to be directly overhead.
- e) If Earth were tilted like Mercury (2 degrees) then most of the
planet would have nearly 12 hours of sunlight per day over most of the
year. At 43.5 degrees South, for example, we'd have 12.5 hours of
sunlight in mid-summer. Seasons would be extremely mild. If Earth
were tilted like Uranus (97.8 degrees), then most of the planet would
have 0 or 24 hours of sunlight for much of the year. At 43.5 degrees
South, we'd have the midnight Sun from October 28th through Feb. 18,
and no sunlight at all from April 28 through Aug. 18. Seasons would be
- f) The Tropic of Capricorn would coincide with the Antarctic
circle if Earth were tilted by 45 degrees. For larger tilts, the
Antarctic circle would be closer to the equator than the Tropic of
3. Explore the Solar System.
- a) Earth would be straight above you at the furthest possible distance from the horizon.
- b) The Earth would not move very much! It would oscillate back
and forth a little, but would remain nearly overhead. It would never
- c) If the Earth appears full to you on the Moon, then the Moon
would be "new" to an Earth based observer (who would be looking at the
unlit side of the Moon). Your picture should show the three bodies in
a straight line: Sun, then Moon, then Earth.
- d) If the Earthers see a full Moon, then you would sew a "new" or
unlit Earth. Your picture should show the three bodies in a straight
line with the Earth in the middle.
- e) During a total lunar eclipse, the shadow of the Earth
completely covers the Moon. So from the Moon you'd see the Earth
block out the Sun - a solar eclipse. As seen from the Moon, the Earth
is much larger than the Sun so a solar eclipse would last around an
hour rather than the normal 5 minutes on Earth.
- a) All of the planets orbit counterclockwise in the simulation,
along nearly circular orbits. This is a pattern that we would like to
be able to explain!
- b) Mercury (no moons), Venus (no moons), Earth (one moon), Mars
(two moons). All of these moons orbit counterclockwise along nearly
- c) The giant planets have many more moons than the terrestrial
planets, and many of the most distant ones orbit clockwise. Some of
these orbits are not circular.
- d) Pluto has three moons and so is more like a terrestrial planet
than a giant planet in this regard.
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