Space help - Comets/meteors/asteroids etc

sparkypants said:

Hi team,

Anyone help with a bit of clarification?

From my own research, as I understand it:

• A comet (usually rock, and ice, and crap etc) is an object that passes us, in an orbit that does not change (or at least not much).

• An asteroid is huge and only passes once.

• A meteor is little bits of rock that sometimes hit the earth.

Is this correct??

Also, is it plausible for a comet to pass us that has never been seen before in recorded history, and if so, how far in advance would we spot this?

Is it reasonable to suggest that a comet could be spied as early as 12 months prior to it properly "passing" earth?

Would it then be as visible for as many months before it passes as after? How much in size would it grow as each month progressed?

Does this post make an sense?

Lol. Any help much appreciated all.

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That is not correct.
Comets are leftovers from the beginning of the Solar System. There are many comets in the cometary halo outside of the orbit of Pluto. Some comets wander into the inner system after their orbits are perturbed by a planet, or something else. Most comets that enter the inner system develop multi-decade orbits.

Asteroids are mostly in the Asteroid Belt between Mars and Jupiter, but there are some that have other orbits.They are thought to be fragments of a planet that was destroyed or didn't finish forming. There is one group of asteroids that have orbits that cross the Earth's orbit.

Meteors are rocky things that enter the Earth's atmosphere, where they burn. They have their origins as parts of comets or asteroids, or any old thing.

Comets are sometimes visible with telescopes for months, and some are visible to the naked eye forquite a while. Comets shrink with every passage to the inner system, because material boils off to form the tail. The apparent size would increase in proportion to the proximity to the observer. New comets appear from time to time. How soon it would be visible is an open question. I believe that comets are sometimes detected around the orbit of Jupiter.

There is a difference between meteors and meteorites also.

Meteors are small enough to burn up in the atmosphere and often come in showers - more commonly known as shooting stars.

Meteorites are bigger and although they do burn up somewhat as they enter the atmosphere, there is enough of them left to land on the surface.

New comets show up all the time and many amateur astronomers compete to find them as they may get the comet named after them.
Here's one guy's website http://thecomethunter.com/

All the definitions of celestial bodies are old and out date .The original name of comet was referring an object, with a tail, that moved across the sky.Asteroids ,once called planetoids ,have been defined as, rocky bodies orbiting the sun, but too small to be planets.Meteoroids was anything smaller than ten meters across.But, as observation techniques have improve the mystery to the origin and the makeup of the thousands objects in space has only deepened.So to answer your questions ,it's a yes and it would depend how big the thing is. Question two is the same as question one part two, so yes it could be possible.Question three ,yes. and finally ,no.

Under the cloud, I would imagine. About a second before it hits.

It would be possible. You'd have to figure out how close yourself, based on how large the comet is. I'd say it would need to appear visually a similar size to the Moon (as you can sometimes see the moon through cloud cover). Which would mean passing inside the Moon's orbit, unless it's larger than the Moon (not very likely).

I'm assuming an albedo similar to the Moon's here, since it's mostly ice I think that should be about right.

sparkypants said:

Another quick question, how close/big would comet have to be for it to be seen through cloud cover? (As in the light emitted/reflected) Would this even be possible?

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With real cloud cover the comet wouldn't be visible until it came through the clouds, but I can imagine a comet being as bright as the Moon, which can be seen through thin clouds.

sparkypants said:

From my own research, as I understand it:

• A comet (usually rock, and ice, and crap etc) is an object that passes us, in an orbit that does not change (or at least not much).

Click to expand...

No. A comet is a body made up primarily if ices (which can be water, carbon dioxide, nitrogen or others, and passes close enough to the sun in its orbit for those ices to volatilize and be ejected as a visible tail of gases. A comet's orbit can be changed dramatically by passage near the sun or near one of the planets, such as the 1994 passage of the Shoemaker-Levy comet past Jupiter, its breakup and subsequent collision with the planet.

Some comets have known orbits, but many appear from very distant portions of the solar gravitational influence, and may never be seen again. Some have been known to crash directly into the sun and are, obviously, long gone.

sparkypants said:

An asteroid is huge and only passes once.

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No. Asteroids are rocky bodies with no obvious volatile material, and they can range in size from several hundred miles in diameter (Ceres, Vesta) to things the size of a school bus or smaller. They may have various orbits. Most known asteroids are confined to an orbital belt between Mars and Jupiter, but many are known that pass much closer to the sun, and some have the potential for intersecting with Earth in their orbits.

sparkypants said:

A meteor is little bits of rock that sometimes hit the earth.

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A meteor is a space rock, of varying size, that collides with Earth. Most are tiny and burn up in the atmosphere. We see these at night as "shooting stars". They are usually of stony (silicate) composition, but some are dominantly iron-nickel amalgams. A few large enough ones may survive passage through the atmosphere and make it to the ground. There, when found, they are called meteorites.

caw

Drachen Jager said:

I'd say it would need to appear visually a similar size to the Moon (as you can sometimes see the moon through cloud cover). Which would mean passing inside the Moon's orbit, unless it's larger than the Moon (not very likely).

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Bear in mind that most of a comet's visibility comes from sunlight reflecting from the coma and tails. The size of these phenomena should give a comet a lot more relative visibility than the moon, given equal distance.

Drachen Jager said:

I'm assuming an albedo similar to the Moon's here, since it's mostly ice I think that should be about right.

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Comets tend to be much darker than the moon: ~3% albedo versus 12%, but again, the coma and tails are going to be a bigger factor than the body itself at realistic distances.

This page has some interesting notes on the appearances of near-earth comets.

Drachen Jager said:

It would be possible. You'd have to figure out how close yourself, based on how large the comet is. I'd say it would need to appear visually a similar size to the Moon (as you can sometimes see the moon through cloud cover). Which would mean passing inside the Moon's orbit, unless it's larger than the Moon (not very likely).

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Incorrect. In 1996 Comet Hyakutake made, for a comet, a relatively close pass of the Earth, about 9 million miles, and at its peak had a visible diameter of about 4 times that of a full moon. The reason for this is that we don't actually see the cometary body. We see the vast cloud of gases and dust that are ejected from it via solar heating. Hyakutake was actually a relatively small comet, compared to Hale-Bopp, which became visible a few weeks later. H-B was a much larger cometary body, but passed a great deal farther away. I saw both of these things through several nights. Hyakutake was larger to the eye, but more diffuse, and had a distinctly green hue. H-B was more compact, white, and brighter.

caw