Asteroids Asteroids are small fragments of rock, not large enough to be classified as Planets. About 2,500 of these have been catalogued and they range from metres in diameter to hundreds of kilometres wide - although only about 250 have diameters of over 100km, most tend to be about 1km across.
Asteroids The largest asteroid is Ceres (940 km in diameter). 92.8% of all the asteroids examined were found to be made of stone 5.7% were made from a mixture of Nickel and Iron
Asteroids tendency to have irregular shapes, like pebbles and some of them actually have their own little moons Most asteroids are found in the Asteroid Belt which is in an elliptical orbit round the Sun, between Mars and Jupiter about 2.2 to 3.3 AU from the Sun
Asteroids some are found inside Earth's own orbit Quite a few also get knocked out of the belt one theory suggests that the dinosaurs were wiped out when an asteroid or comet hit the Earth near the Yucatan peninsula
Comets Many people think that comets were huge balls of fire. In fact, they're solid, frozen, lifeless cosmic icebergs when they get hot enough as they approach the sun and the nucleus unfreezes, a coma develops and the gas inside absorbs ultraviolet light, giving it a bright blue look
Comets Comets with short periodicity originate from the Kuiper belt and those with long periodicity originate from the Oort Cloud
Comets When they are near the Sun and active, comets have several distinct parts: Nucleus: relatively solid and stable, mostly ice and gas with a small amount of dust and other solids; Coma: dense cloud of water, carbon dioxide and other neutral gases sublimed off of the nucleus;
Comets Hydrogen Cloud: huge (millions of km in diameter) but very sparse envelope of neutral hydrogen; Dust Tail: up to 10 million km long composed of smoke-sized dust particles driven off the nucleus by escaping gases; this is the most prominent part of a comet to the naked eye; Ion Tail: up to 100 million km long composed of plasma and laced with rays and streamers caused by interactions with the solar wind.
Zodiacal Light The zodiacal light is a faint, roughly triangular shaped glow of light extending away from Sun It is merely sunlight reflected by dust in the plane of the ecliptic
Zodiacal Light In September and October, because the ecliptic is more nearly perpendicular to the horizon at sunrise, the zodiacal light extends more nearly vertically from the horizon and we have a better opportunity to see it shortly before sunrise than when it lies along the horizon and is lost in the dust and haze of Earth's atmosphere.
Gegenschein German for "counter-glow“ The gegenschein is a faint spot of light in the sky, diametrically opposite Sun. The gegenshein is even fainter than the zodiacal light -- fainter than the Milky Way -- so any additional light from Moon, street lights, or a nearby planet and any obscuring haze make it impossible to seethis faint glow
Gegenschein Cometary dust and dust generated by collisions among the asteroids are believed responsible for the maintenance of the dust cloud producing the zodiacal light and the gegenschein.
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