PV Gap

Stacy Said:

how can we see venus and mercury in night sky- slightly confusing?

We Answered:

The orbits of Mercury and Venus carry them between Earth and the Sun but also carry them out to the side.

Because of the proximity to the Sun, Mercury can only be seen at a maximum of about 17 degrees angle from the Sun and thus at night can only be seen very near dawn or dusk.

Venus can be seen only to a maximum of about 47 degrees from the sun and can be seen at night a few hours before dawn or after dusk. Venus is so bright it can also be seen in full daylight (If you know exactly where to look).
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Beatrice Said:

Is Pluto still a planet of the solar system?

We Answered:

It looks as though a hand full of eggheads got together and have made up their minds that Pluto is no longer a planet. Who in the hell do they think they are? If the majority wants it to be a planet then as far as I'm concerned it still is.

Jeffery Said:

How do you prove the sun is the center of the solar system?

We Answered:

Hi Rider!

You're absolutely right that it's neither obvious nor easy to prove that the sun is in the center.

This is why most astronomers before Copernicus, and many after him such as Tycho Brahe, remained supporters of the earth-centered system.

The problem with any earth-centered system is that it's hard to explain things like the retrograde motion of Mars and other planets at certain times in their journeys across the sky. Copernicus discovered that by assuming the sun to be at the center instead, the math came out much simpler.

Simpler, but not perfect. Copernicus, like earlier astronomers, still needed to insert epicycles into his calculations, those little circles within circles to explain why planets moved to and fro as they sometimes did. The Church, which ran much of the educational system back then, took this to mean that Copernicanism might be a useful mathematical trick for teaching astronomy, but should not be regarded as the literal state of affairs. Besides, if the earth is moving, how do you explain why the birds don't get blown away? Why, if a person jumps into the air, does he still come down in the same spot?

Galileo showed that Venus shows phases like the moon, and for that matter it had long been obvious that Venus and the sun can never appear opposite to one another in the sky. Brahe suggested that you could explain this if all the other planets move around the sun, and the sun and all the rest orbit the earth, but no one could demonstrate that the earth moves. Galileo tried and failed.

Only much later did the proof arrive. John Kepler did away with the epicycles by the inspired discovery that planets move not in perfect circles, but ellipses. Isaac Newton's laws of motion explained the concept of inertia, showing how a person could jump into the air and land in the same spot, even on the moving earth.

By measuring carefully, astronomers were able to show that over the course of the year, some nearby stars show a parallax. If you measure the star's precise location against the celestial background, first in spring and then in autumn, you may notice that the nearer star has shifted slightly. They couldn't manage this in Galileo's time, so as far as anyone could tell then, the earth must be fixed. Today, though, astronomers using careful measurement can see the difference. Heliocentrism is true, at least within the solar system.