If the Universe is endless how come the same comets come back over and over?

Question

I just thought of that they said that the universe is ever exspanding but if a comet goes continuously in one direction forever and ever and there is no end to space, how come we see the same one over and over again every 75 years. or is it a different one every 75 years. I'm confused and its unusual for me to be confused.

unless the end of space is actually the beginning of the other side of space. either that or the end of space just starts another deminsion to where the coment starts all over again. OOOOOooooooooooooooooooo, I'm smart. not really .

in that case the end of space is the port for time travel and the comet gets sent back another 75 years into the past at the same place it started again.

dummy me I knew that. and I just blanked that out of my head because I was to bessy thinking of weird stuff. lol but what I said would of been cool right.

Answer 1

Comets are part of the solar system, just like the planets and asteroids. Some are in short orbits, always staying closer than Pluto. The famous Comet Hally, that comes back every 76 years is one such periodic comet. Most comets don't come back though. They come from far beyond Pluto, pass the Sun once, and disappear back into deep space out past Pluto. Orbital plots show that they do not come from interstellar space though. They are still bound to the Sun by gravity. They just have REALLY large, long orbits.

You seem to think space is a lot smaller than it really is. It would take an object moving at the speed of a comet WAY more than 76 years to even get to the nearest star. It would take many millions of years to make it all the way out of the Milky Way galaxy. It would take trillions of years or more to reach the most distant galaxies that we can see with telescopes.

Answer 2

1. Periodic comets are in orbit around the Sun. Since the ones we see today come (most of them) from a "reservoir" of comets beyond the orbit of Neptune, then they have orbits near a hundred years.

Some come from further and have even longer periods.

Comets are small compared to planets (especially Jupiter); their orbits can be affected by the planets. This can make their periods shorter (like 76 years for Halley's comet: the same one every 76 years), or even much shorter.

In some rare cases, the encounter puts them in orbit around a planet (like Shoemaker-Levy-9 around Jupiter; that's the one that broke up and crashed on Jupiter a dozen years ago).

Some can see their speed increased by the effect of planets, to the point where they exceed the escape speed (they never come back).

2) The expansion of the Universe affects distances between galaxies. It has no measurable effect within the Solar system (the solar system is small compared to the Galaxy; the Galaxy is a mere dot compared to the Universe).

3) It is possible that space (the entire universe) is "curved" in such a way that something going always in the same direction ends up back where it started. Just like (in two-dimensions), the surface of Earth is "closed": If you start off in a direction, you will go all around the sphere and pass over the point you started from.

Except that the Earth is finite in size: a great circle takes you back to your starting point after 40,000 km (25,000 mi). It is possible that the Universe is infinite in size, in which case it would take you an infinite time to make it all the way around. But even if not infinite, the Universe is much bigger than Earth. 75 years would be way too short for a round trip around the universe.

4) The Sun takes 220 million years to orbit our Galaxy (the Milky Way). The Galaxy is just a dot in the Universe, measuring a mere 100,000 light-years in diametre; the part of the Universe that we can observe measures approximately 13,000,000,000 light-years in radius... as the kids say: you do the math...
(do they still say that or am I really that old?)

Answer 3

Comets are left-over debris from when the sun first formed out of dust and gas. They are in fact in orbit around the sun, whose gravity extends to what's called the heliopause, where the sun's gravity is cancelled out by the gravity from nearby stars. Most comets have long, long orbital periods that extend way out past Pluto. Out there the comets are likely not moving much faster than you can walk but as they fall inward toward the sun they pick up speed until they whip around the sun and head back out into deep space. This can take a few years or several thousand years. Most comets are in what is called the Oort Cloud (pronounced "oart"), which may contain as many as a trillion comets and forms a sphere which the sun is the center of.

Answer 4

The comets that come back are in orbits close to the solar system -- not more than 0.5 light-years from the sun. Most are only a few light-days from the sun.

The universe, on the other hand, is over 14,500,000,000 light-years across, and that's just the part we can see now.

So comparing the orbits of comets to the whole universe is like comparing a small fraction of an inch to the size of the United States.

Answer 5

There are two things you need to get into your mind.

1. the scale of things - the Solar System and its entourage of Sun, planets, moons, comets, asteroids is a pinpoint in the galaxy, and our galaxy is a pinpoint in the universe. get that in your head, first.

2. Then, you have to understand that just about everything in the galaxy is in orbit around another body. Therefore you can see that the "keep coming back" of the periodic comets is simply that they are in captured orbits around the sun.

The nearest star is 10,000s times as far away as an average periodic comet like halley's even when Halleys is at its farthest point from the sun. Therefore, the sun "owns" these comets, as the stars are much too far away to capture them into their own gravitational field.

That is the only reason they keep coming back - they are captured. In the Galaxy there will be trillions and trillions of comets that belong to other star systems.

Most people's concept of space does not take in the sheer scale, or the fact that gravity is universal, and nothing escapes its hold, to greater or lesser extent.

Answer 6

Keep in mind that as theses objects hurl through space they are effected by the gravitational pull that is present in larger foreign bodies. While the pull my not be enough to pull them into said body it will alter their trajectory. Newton has a great many verse on these type of questions. Specifically trajectory and gravitational slingshots. You are probably considering that there was a big bang and that every thing shot straight out. All of this matter that blew, acted on its self curving and ricocheting off of each other and found an orbit. There are absolutely objects out there are in an orbit that would or will take million's of years to go around. Some have never made their full orbit yet.

Answer 7

"Mathematical theory suggests that most comets may come to the solar system from very far away, as far away as 100,000 AU. In this picture, the solar system is buried deep within the cloud.

An AU is the distance from the earth to the sun and is equivalent to about 100,000,000 miles. Mars is 1.5 AU from the sun, Jupiter is 5 AU from the sun, and Pluto is 39 AU from the sun. So comets come from very far away indeed.

Comets are observed to come to the solar system from all directions, therefore the place where the comets come from is thought to be a giant sphere surrounding the solar system. This sphere is called the Oort cloud after Jan Oort who suggested its existence in 1950. Thus comets are said to come from the Oort cloud. "

"some comets may come to the solar system from closer in. The place where these comets come from is called the Kuiper Belt, which is located past the orbit of Pluto."


A picture of the Oort cloud and the solar system's position within it can be seen at the following website (where this information came from)

Answer 8

I am not an astronomer. The same comet keeps coming back because of the 'same sun.' The universe is expanding and all comets, planets etc. are traveling with the expanding universe.

Answer 9

Because those comets are gravitationally locked into elliptical orbits around the sun, just like the planets. Those orbits may take hundreds or thousands of years, but they are orbits nonetheless.

Answer 10

Because they are trapped in orbit. The speed at which they were traveling toward an object, depening on the materials of the objects and electircal fields and the mass of the object. Also not every comment gets trapped in orbit depending on the qualities i listed above.