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22.2
The Earth-Moon-Sun System
| Term | Definition |
|---|---|
| Rotation | the turning, or spinning, of a body |
| Revolution | the motion of a body along a path around some point in space. |
| What are the three motions of earth? | rotation, revolution and precession |
| Precession | a very slow motion, the slight movement over a period of 26,000 years, of earth's axis. |
| What are the main results of earth's rotation? | day and night |
| What are the ways we can measure earth's rotation? | Mean solar day and the sidereal day |
| Mean solar day | the time interval from one noon to the next, which averages about 24 hours. |
| Zenith | Noon, when the sun is the highest point in the sky |
| Sidereal day | the time it takes for earth to make one complete rotation (360 degrees) with respect to a star other than our sun. It is measured by the time required for a star to reappear at the identical position in the sky where it was observed the day before. It h |
| Which day is shorter, the mean solar day or the sidereal day? Why? | The sidereal solar day is almost 4 minutes shorter than the mean solar day. This difference results because the direction to distant stars barely changes because of earth's slow revolution along its orbit. The direction to the sun, on the other hand, ch |
| Which "day" do we use as a measurement of our day? | The mean solar day. |
| How does the earth revolve around the sun? | In a elliptica orbit at an average speed of 107,000 kilometers. |
| Perihelion | When earth is closest to the sun, about 147 million kilometers away. Occurs about January 3 each year. |
| Aphelion | When earth is farthest from the sun, about 152 million kilometers away. Occurs about July 4th. |
| When is the earth closest and furthest from the sun? | Earth is furthest from the sun in July and closest to the sun in January. |
| Ecliptic | The apparent annual path of the sun against the backdrop of the celestial sphere. |
| Plane of the ecliptic | The imaginary plane that connects earth's orbit with the celestial sphere. |
| What is earth's axis of rotation? | The earth's axis of rotation is tilted about 23.5 degrees |
| What degrees do the sun and the celestial equator intersect each other? | an angle of 23.5 degrees |
| Does precession have a major or minor effect on the seasons? | a minor effect because the angle of tilt changes only slightly. It does cause the seasons to move slightly each year among the stars. |
| What is earth's one natural satellite? | The moon |
| How long does it take the moon to orbit earth? | About 1 month |
| Perigee | When the moon is closest to the earth |
| Apogee | When the moon is farthest from earth |
| What causes the phases of the moon? | The motions of the earth-moon system constantly change the relative positions of the sun, earth and moon. This results in changes in the appearance of the moon. |
| Phases of the moon | changes in the amount of the moon that appears lit |
| Crescent phase | About two days after the new moon, a thin sliver appears low in the western sky just after sunset. |
| First-quarter phase | After the crescent phase, the lighted portion of the moon visible from earth increases (waxing) to a half circle and can be seen from noon to midnight |
| Full-moon phase | A week after the first quarter phase, the complete disc can be seen rising in the east as the sun is sinking in the west. |
| New moon phase | The percentage of the moon that can be seen steadily declines (waning) until the moon disappears. |
| What are lunar phases a result of? | The motion of the moon and the sunlight that is reflected from its surface |
| How long does it take moon to cycle through its phases? | 29 1/2 days, synodic month |
| How often does the moon rotate on its axis? | Once every 27 1/3 days |
| Why do we sometimes see the moon in daytime? | During phases of the lunar cycle other than the full moon, the moon and sun are not directly opposite each other. This makes it possible to see the moon during daylight hours. |
| Solar eclipse | Occurs during new moon phases. When the moon moves in a line directly between earth and the sun, it casts a shadow on the earth. |
| Lunar eclipse | Occurs during full-moon phases. When the moon moves within the earth's shadow. |
| What must happen for an eclipse to take place? | During a new moon or full moon phase, the moon's orbit must cross the plane of the ecliptic for an eclipse to take place. |
Created by:
jclicurse
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