Means star-like. They are not like stars though, only
their appearance in a small telescope is star-like.
Asteroids come in many varieties. Some large, some small. Most are located
in orbits between mars and jupiter. However, other orbits exist. Some cross
the earth's orbit, and are called 'apollo asteroids'. One unusual asteroid
called chiron orbits between saturn and uranus. It may even be a very large
The asteroids (or minor planets) are very small. Most only several kilometers
across. The largest (Ceres) may be about 470 kilometers. Most of the asteroids
are not round, just a lump of rock and metal in space. They are heavily cratered
and may be left over from the solar system's beginning. It is believed the
main asteroid belt failed to form a planet because giant jupiter disrupts
their orbits and prevents them from coalescing.
It should be pointed out that although the asteroids are numerous, they are
not close together. The image (see below) shows positions for most asteroids.
although they seem bunched, remember that the sun earth distance is 150 million
kilometers. Most asteroids are millions of kilometers from each other. The
'Empire Strikes Back' scene where the heros navigate an asteroid field is
not really factual. This close together over long time spans would have the
asteroids constantly hitting each other resulting in either one big mass
or a bunch of dust.
The most frightening aspect of asteroids is the possibility that one could
strike the earth. The odds are not high but we could not see a small asteroid
until it is very close. The Tunguska event in Russia, in 1908 was
likely a small asteroid. It devastated the Russian forests in Siberia. If
it had struck a major city it could have killed hundreds of thousands. Since most of the earth is water, an asteroid would most likely hit the ocean causing
great tidal waves devastating coastal areas. There is continuing evidence
that an asteroid impact may have led to the dinosaurs extinction. We have
no way of knowing whether these asteroid impacts, have periods of increased
activity, and when we would be entering such a period.
The first in 1801. There are now thousands cataloged.
In 1937 asteroid Hermes was discovered, passing less than
a million kilometers from earth proving we are always in
some danger from these interlopers.
In 1977, Chiron the strange asteroid/comet was discovered.
It seems some asteroids have moons. Little attendant asteroids.
OBSERVING - NAKED EYE
A couple asteroids may be seen with the naked eye under very
OBSERVING - TELESCOPE
There isn't much to see telescopically. Just a little dot which
can be followed from night to night. Advanced amateurs
could participate in plotting and computing orbits.
A diagram of asteroid locations, seen from above our solar system.
Asteroid gaspra from the Galileo spacecraft which passed it on route to Jupiter.
the colors are enhanced.
Asteroid Ida from Galileo.
Images of Mars' moons Phobos and Deimos. Their appearance suggests
they are captured asteroids.
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