How do scientists determine what is a star a moon or a planet?

Answer 1

In the most simplest definition a Star would produce its own light where as planets would not. A star burns heavy fuel for instance in the case of sun you have hydrogen fusion to produce heavy compounds and at the same time release energy by the process of nuclear fusion there by producing light. In the case of planets this process of nuclear fusion does not take place and hence they do not produce light so to speak of and only reflect light by receiving it from their nearest star system.

Moon's are also called natural satellietes since they revolve in orbits around their respective planets. Their sizes are much smaller generally speaking in contrast to the planets they revolve around. Where as Stars on the other hand are much bigger than the planets.

Hope that helps !!

Answer 2

If you look up at the night sky, you will see stars and maybe some planets. The only moon you can see with the naked eye is our own, and that stands out pretty strongly!

You may be able to see that planets don't 'twinkle' as much as stars. That is because they are little discs of light instead of points (the planets are much closer than the stars) and so the light is less disrupted by the earth's atmosphere.

Over a period of days or weeks, you will also see the planets move against the background of stars. The word 'planet' comes from a Greek word meaning 'wanderer'. This is how the first scientists discovered planets - because of their movement in the sky.

In a telescope, you can clearly see the disk shape of the planets in our solar system, while stars always remain as points.

When Galileo pointed his brand new telescope at Jupiter, he saw that it had four companions that appeared to orbit around the planet. They appeared first on one side, then the other, with a regular motion. This motion led him to understand that Jupiter had moons. There were clearly not stars, or other planets, because they belonged to Jupiter.

They were the first things seen that did not appear to go around the Earth. This annoyed a lot of people who though that the bible said that the earth was the center of everything. It turns out that it isn't. Hey - that's life!

Answer 3

Some good answers above, but just to add to the difference between planets and stars. basically, in any body that had sufficient mass, its internal gravity would crush its atoms and a nuclear fusion reaction would start.

It used to be believed that Jupiter was a very low energy star, but now believed you need at least 10 times its mass for nuclear fusion to start.

The point is that many stars have small companion stars in what they call binary systems. In reality, there must be a level at which a planet could be called a planet or a small companion star to its "sun". If the planet is large enough to have nuclear fusion happening inside it, it will radiate a certain amount of energy, though it may not necessarily be enough to make it "shine" of its own.

So, you see, a big planet could be a small star. But ordinarily, planets only shine by reflected light from their star (their sun).

Answer 4

I just read the answer in a Scientific American Article.

Stars are basically giant gas balls glowing from the nuclear fusion that occurs inside them

Planets are objects that orbit stars, but they also have to be large enough to sweep up 99% of the total mass that crosses it's orbit around the sun. Seeing as how Pluto is in the Kupier Belt, a lot of particulate matter crosses it's orbit (including Neptune) and this excludes it from planethood. But even if Neptune did not cross Pluto's obit or vice versa, the small matter that crosses Pluto from the KB still excludes it.

Moons are objects that orbit planets.

Answer 5

A planet turns on itself (and around the sun for our galaxy). A moon turns around the planet. Stars are balls of gas.

Answer 6

Well a star is gas, and planets are rock like matter. Also, planet vs. moon is dependent on size. Pluto was discredited as a planet because most of its mass was ice.

Answer 7

You can trace the patterns of their orbits in the sky. Each has a characteristic "pattern". One of the revolutionary ideas in early astronomy was realizing that Earth was not at the center of the Universe, and that by observing the orbits of objects in the nighttime sky, it could be shown that we were "heliocentric", not "geocentric".