Download Physics 127 Descriptive Astronomy Homework #12 Key (Chapter 6

Physics 127 Descriptive Astronomy
Homework #12 Key (Chapter 6)
Winter 2015
6-1. Describe the kinds of features that can be seen on the Moon with a small telescope.
Even a naked-eye observer can pick out broad highland (light-shaded) regions and maria (dark regions). Additionally,
with a small telescope, many large impact craters, a few surrounded by rays of scattered debris, can be easily seen.
Also evident is the roughness and jaggedness of the highland regions which are discernible to the naked-eye observers
only because of their light shades.
6-4. Rocks found on the moon are between 3.1 and 4.47 billion years old. By contrast, the majority
of the earth's surface is made of oceanic crust that is less than 200 million years old, and the
very oldest earth rocks are about 4 billion years old. If the earth and moon are essentially the
same age, why is there such a disparity in the ages of rocks on the two worlds?
The surface of the earth is constantly being worn down by erosion, mostly a consequence of water flow on the surface
and wind, neither of which are factors on the moon’s surface. Furthermore plate tectonics is responsible for constantly
reforming and repaving the earth’s surface. This also does not happen on the moon.
6-6. If Mercury is the closest planet to the Sun and has such a high average surface temperature,
how is it possible that ice might exist on its surface?
Because Mercury’s rotational axis is almost perfectly perpendicular to its orbital plane, no sunshine ever falls on the
floors of craters near its two poles. Therefore sunshine does not warm those crater floors and because there is no
atmosphere, there are no winds to transport warmth created by sunshine elsewhere on Mercury to the interiors of these
craters. They however can radiate any warmth they receive directly into space. Thus they remain forever cold.
6-9. How was water most recently discovered on Earth’s Moon?
Evidence suggests that existence of significant amounts of water ice in permanently shaded regions in several lunar
craters.