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   17.4Phases

3. (Exercises 6 and 7) What would be the maximum altitude of the full moon as seen by an observer in northern Florida (29°, 82°), and what time of year will this maximum altitude occur? Since we are dealing with a full moon, it must be 180° away from the Sun (that is, on the opposite side of Earth), and it will also be highest in the sky when the Sun is the lowest. The lowest declination of the Sun is 23.5 degrees south of the equator, at which time the Moon is 23.5 degrees north of the equator in its full phase. The angle between the zenith for this latitude and the declination of the Moon at this time will be 29° - 23.5° = 5.5°, which is called the zenith angle. The difference between this zenith angle and 90 degrees will give the altitude. Hence 90° - 5.5° = 84.5°, so the full moon will appear at an altitude of 84.5° when it is at its maximum height in the sky. Since this can only occur when the Sun is at 23.5°, and this happens on or about December 21st each year, the full moon will have its maximum altitude right around Christmas time.


Section   17.5Eclipses

4. (Exercises 15 and 16) 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 can 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 17 and 18) New York City (41°, 79°) 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° (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°, and the other at 79° - 90° = -11°, or 11 degrees on the other side of the zero degree meridian, at 11°

Return to Previous Page