Asteroids are the many thousands of small worlds most of which move round the Sun between the orbits of Mars and Jupiter.
By far the largest of the asteroids is Ceres, with a diameter of 485 miles. Pallas is 304 miles in diameter; no other is more than 300 miles. The asteroids are so small that they cannot have an atmosphere of any sort. They are airless and lifeless.
The asteroid you can easily see without a telescope is Vesta. It is only 214 miles across. Much less than Ceres and Pallas, but it is the brightest of the little planets that is, the asteroids. Its distance from the Sun is about 200 million miles.
One American astronomer says that there may be 44,000 asteroids, but Russian scientists believe that there are as many as 100,000.
A few asteroids have orbits that bring them very close to the Earth. In 1937, a very small asteroid called Hermes passed the earth at a distance of only 400,000 miles – less than twice the distance of the Moon. But the chances that the Earth will meet with an asteroid are very small, and astronomers do not worry about it.
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