Section   17.1General Features

1. (Exercises 1 and 2) A lunar roving vehicle weighs 1860 lb on Earth. What will be the weight of the vehicle on the surface of the Moon?

The textbook tells us that the gravity on the Moon produces a force on an object on its surface that is just 1/6 of the weight of that object on the surface of Earth.

Weight_{on Moon} = 1/6 (Weight_{on Earth})

Weight_{on Moon} = 1/6 (1860 lb)

Weight_{on Moon} = 310 lb

Section   17.3Lunar Motions

2. (Exercises 3 and 4) A lunar mission is scheduled to last for 3 sidereal lunar months. Approximately how many days is this?

Each sidereal lunar month represents the time for one lunar rotation with respect to any other star than the Sun, and one sidereal lunar month lasts for 27.33 days. Three sidereal lunar months is, therefore, equivalent to 3 x 27.33 days = 82 days.

Section   17.5Eclipses

4. (Exercises 11 and 12) Describe the relative positions of the Sun, Moon, and Earth during: (a) a total lunar eclipse; (b) a total solar eclipse.

(a) During a total lunar eclipse, Earth must be between the Sun and the Moon so that the Moon will be in the shadow of Earth as it blocks the light from the Sun that normally illuminates the surface of the Moon. Not only that, but the Moon must be in the umbra portion of Earth's shadow for a total eclipse to occur. If all or part of the Moon is in the penumbra portion of Earth's shadow, a partial lunar eclipse will be seen. (b) For a total solar eclipse to occur, the Moon must be between Earth and the Sun to prevent sunlight from reaching the area on Earth that is experiencing the eclipse. Again, the observer on Earth must be in the umbra portion of the Moon's shadow for a total eclipse to be seen.


Section   17.6Ocean Tides

5. (Exercises 13 and 14) New York City (41°N, 79°W) experiences high tide on a certain spring day. (a) What other longitude will be experiencing a high tide at the same time? (b) Where will low tide conditions be occurring when the tide is highest in New York?


(a) High tides are paired such that they occur on opposite sides of the planet from each other. Thus the other high tide would be 180° around from the longitude of New York City, which would place it at 180° - 79° = 101°E. (b) Low tides are also paired and occur 180° apart, and in addition are 90°, or 1/4, of the way around the planet from the current high tide. This places one low tide location at 79° + 90° = 169°W, and the other at 79° - 90° = -11°, or 11°E on the other side of the zero degree meridian, at 11°.

Return to Previous Page