[Drow (OP)]

Hi, I am doing an assignment for my astronomy class and am stuck at one of the questions. Can anyone help me with this. The question is:

"Describe three ways in which the relative configuration of a planet, the Earth and the Sun affect the planet's appearance, as viewed from Earth. Explain your reasoning."

Any help in solving this question will be greatly appreciated. Thanks.

[Titanscape]

The earth's spin affects where looking up shows a view and it's turn around the sun too. Distant plants move as well but less fast around the sun in terms of their years. So the earth is behind then in front of the sun often compared to Saturn...

Titanscape

[qpan]

I'm thinking simpler - how about planets looking bigger and brighter when the earth's orbit passes close to them and looking smaller and fainter when they are on the opposite side of the sun?

Also how about planets making crescents like the moon due to the earth viewing the planet from side on in relation to the sun?

"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe

[gsmollin]

This question is a little vague. Your teacher may be fishing for three things that were in your textbook or his lecture, so you should be careful taking advice from the outside.

That being true, I can think of the three most basic things about the relationship between the Sun, Earth, and another planet.

1. The planet is in an inferior orbit, e. g. Mercury and Venus. Then they are always near the sun, and show strong phases. They may also be eclipsed, or perform transits of the sun. There are three already...

2. The planet is in a nearby superior orbit, e. g. Mars. Then then still show phases, but weaker than inferior planets. The motion of mars can also be retrograde, as earth overtakes it in its orbit. Mars can be eclipsed by the sun, but will not transit.

3. The outer superior planets, e. g. Jupiter, Saturn, Uranus, Neptune, and Pluto, show little or no phases, because they are so far from Earth and Sun. Their orbital motion is rather constant, as they move through the constellations at great distances. They are rarely eclipsed, although it can happen.

[LordRaidis]

gsmollin, a weird question, perhaps you are able to interpret:

If the earth is in superior in orbit to mars--which is of course, superior to all the other "outside" inferior orbiting bodies, AND if mars can be viewed as "retrograde" then can one deduce that The light coming from Mars (or ANY light for that matter, originating beyond the earth's solar orbital apogee) IS actually running on a timeline opossite of that in which we experience here on the earth? Or even venus? RELATIVELY speeking ;-)

"Science is the belief in the ignorance of experts."

-DR. RICHARD P. FEYNMAN

[gsmollin]

I think you are mis-interpreting what I said. The terms "inferior" and "superior" refer to orbital positions, inferior orbits are inside of superior orbits. So the orbital numbering, from most inferior to most superior is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto. (Pluto is in a highly eliptical orbit, and is sometimes inferior to Neptune.)

Earth and Mars are close together, as planets go. Earth has an inferior orbit to Mars, so it orbits considerably faster than Mars. At times, Earth overtakes Mars and passes it by on the inside. These events are called "oppositions". As the Earth passes by Mars, there are a lot of parallax-effects between Earth and Mars, and the stars behind Mars. It appears that Mars slows down, and reverses direction in the sky, moving backwards (i. e. retrograde) for a time. Then it slows, stops, and goes forward again. This retrograde motion is an illusion caused by Earth's relative motion to Mars. We are moving fast enough to make Mars look like it is going backwards against the stars, for a time.

The velocities of orbiting planets are not relativistic, and there are no significant time dilations between Earth and Mars as a result of their relative orbital motions. On a microscopic level, a clock on Earth will run slower than a Martian clock, since Earth moves faster in its orbit than Mars.