Motion of the planets as seen from earth
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As seen from the Earth, the Sun, Moon, and planets all appear to move along the ecliptic. More precisely, the ecliptic is the Sun's apparent path among the stars over the course of a year. (Of course, it's actually the Earth that moves about the Sun, and not the other way around, but because of our orbital motion, the Sun seems to move across the backdrop of distant stars.) The planets don't remain exactly on the ecliptic, but they always stay fairly close to it.
Unlike the Sun, however, the planets don't always make steady progress along the ecliptic. They usually move in the same direction as the Sun, but from time to time they seem to slow down, stop, and reverse direction! This retrograde motion was a great puzzle to ancient astronomers. Copernicus gave the correct explanation: all planets, including the Earth, move around the Sun in the same direction; retrograde motion is an illusion created when we observe other planets from the moving planet Earth.
It's easiest to understand the retrograde motion of the inner planets, Mercury and Venus. These planets are closer to the Sun than we are, and they orbit the Sun faster than we do. From our point of view, the Sun trundles along the ecliptic (due, of course, to our orbital motion), while Mercury and Venus run rings around the Sun. So at some times we see these planets moving in the same direction as the Sun, while at other times we see them moving in the opposite direction.
For the outer planets, Mars, Jupiter, Saturn, and so on, the explanation is a bit more subtle. These planets are further from the Sun than we are, and they orbit the Sun more slowly than we do. From time to time we pass one of these planets, and when that happens, the planet seems to be moving backwards because we're moving faster than it is. At such times we naturally see the Sun and the planet in opposite parts of the sky; the planet is said to be in opposition to the Sun. Opposition is a good time to observe an outer planet; it's above the horizon all night, and relatively close to the Earth.
An outer planet's apparent motion is alwaysretrograde for a month or more before and after opposition. The duration of retrograde motion depends on the planet; it's shortest for Mars, and generally longest for Pluto. The moment when a planet's apparent motion changes direction is called a stationary point, because at that instant the planet appears to be more or less stationary with respect to the stars. An outer planet always has one stationary point before opposition, and another stationary point after opposition.
Venus and Mars are the two planets that come nearest to the Earth. As all three planets orbit the Sun, the view of our neighbors will constantly change in various ways. By watching the apparent motion, change in distance, and change in phase of these two planets, we can see that many different effects are explained by the one basic idea that all planets orbit the Sun.
THE BIG PICTURE
Fig. 1 shows the orbits of Venus, Earth, and Mars and their positions in Fall 2005. From this diagram we can predict several interesting observational results.
Fig. 1. Orbits of Venus, Earth, and Mars. This view looks `down' on the plane of Earth's orbit from the North, so all planets orbit counter-clockwise. Small filled circles show positions on 9/28; small open circles show positions 4 weeks earlier (8/31), 4 weeks later (10/26), and 4 weeks later (11/23).
Apparent Motions
Venus is catching up with Earth, but will not pass us before the end of the semester (see Fig. 2). For most of the semester, Venus is heading more or less toward us. As a result, it will appear in the roughly same position with respect to the Sun -- prominent in the West at sunset -- for several months. Venus appears to be moving along the ecliptic in the same direction as the Sun (West to East); this is called direct motion.
Fig. 2. Triangles connecting Earth, Venus, and Sun on the dates indicated in Fall 2005. The line from Earth to Venus turns in the same direction (counter-clockwise) as the line from Earth to Sun, so Venus's motion is direct; also, the angle between Venus and the Sun as seen from Earth is roughly constant, so Venus will appear about the same distance above the horizon each night. The distance between Venus to the Earth steadily decreases, so Venus will appear larger and larger. At the same time, the angle of sunlight falling on Venus changes; by the end of the semester Venus
Unlike the Sun, however, the planets don't always make steady progress along the ecliptic. They usually move in the same direction as the Sun, but from time to time they seem to slow down, stop, and reverse direction! This retrograde motion was a great puzzle to ancient astronomers. Copernicus gave the correct explanation: all planets, including the Earth, move around the Sun in the same direction; retrograde motion is an illusion created when we observe other planets from the moving planet Earth.
It's easiest to understand the retrograde motion of the inner planets, Mercury and Venus. These planets are closer to the Sun than we are, and they orbit the Sun faster than we do. From our point of view, the Sun trundles along the ecliptic (due, of course, to our orbital motion), while Mercury and Venus run rings around the Sun. So at some times we see these planets moving in the same direction as the Sun, while at other times we see them moving in the opposite direction.
For the outer planets, Mars, Jupiter, Saturn, and so on, the explanation is a bit more subtle. These planets are further from the Sun than we are, and they orbit the Sun more slowly than we do. From time to time we pass one of these planets, and when that happens, the planet seems to be moving backwards because we're moving faster than it is. At such times we naturally see the Sun and the planet in opposite parts of the sky; the planet is said to be in opposition to the Sun. Opposition is a good time to observe an outer planet; it's above the horizon all night, and relatively close to the Earth.
An outer planet's apparent motion is alwaysretrograde for a month or more before and after opposition. The duration of retrograde motion depends on the planet; it's shortest for Mars, and generally longest for Pluto. The moment when a planet's apparent motion changes direction is called a stationary point, because at that instant the planet appears to be more or less stationary with respect to the stars. An outer planet always has one stationary point before opposition, and another stationary point after opposition.
Venus and Mars are the two planets that come nearest to the Earth. As all three planets orbit the Sun, the view of our neighbors will constantly change in various ways. By watching the apparent motion, change in distance, and change in phase of these two planets, we can see that many different effects are explained by the one basic idea that all planets orbit the Sun.
THE BIG PICTURE
Fig. 1 shows the orbits of Venus, Earth, and Mars and their positions in Fall 2005. From this diagram we can predict several interesting observational results.
Fig. 1. Orbits of Venus, Earth, and Mars. This view looks `down' on the plane of Earth's orbit from the North, so all planets orbit counter-clockwise. Small filled circles show positions on 9/28; small open circles show positions 4 weeks earlier (8/31), 4 weeks later (10/26), and 4 weeks later (11/23).
Apparent Motions
Venus is catching up with Earth, but will not pass us before the end of the semester (see Fig. 2). For most of the semester, Venus is heading more or less toward us. As a result, it will appear in the roughly same position with respect to the Sun -- prominent in the West at sunset -- for several months. Venus appears to be moving along the ecliptic in the same direction as the Sun (West to East); this is called direct motion.
Fig. 2. Triangles connecting Earth, Venus, and Sun on the dates indicated in Fall 2005. The line from Earth to Venus turns in the same direction (counter-clockwise) as the line from Earth to Sun, so Venus's motion is direct; also, the angle between Venus and the Sun as seen from Earth is roughly constant, so Venus will appear about the same distance above the horizon each night. The distance between Venus to the Earth steadily decreases, so Venus will appear larger and larger. At the same time, the angle of sunlight falling on Venus changes; by the end of the semester Venus
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Heya ya ur answer is here
the motion of the earth as seen from the earth is that to be in rotation of clock wise to the earth in the direction i t was totally opposite to the direction earth
I hope this answer may help u
the motion of the earth as seen from the earth is that to be in rotation of clock wise to the earth in the direction i t was totally opposite to the direction earth
I hope this answer may help u
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