What are asteroids? First of all, I would like to say that this is the name for stony solid bodies that move along the circumsolar orbits of an elliptical shape like planets. However, space asteroids are much smaller than, in fact, the planets themselves. Their diameter is conditionally located in the following ranges: from several tens of meters to up to a thousand kilometers.
When wondering what asteroids are, a person involuntarily thinks about where this term came from, what it means. It translates as “star-like”, and introduced it in the XVIII century by an astronomer named William Herschel.
Comets and asteroids can be seen as point sources of a certain light, more or less bright. Although in the visible range, these celestial bodies do not radiate anything - they only reflect the sunlight that falls on them. It should be noted that comets are different from asteroids. The first is their different appearance. The comet is easily recognizable by its brightly glowing core and tail, which comes from it.
Most of the asteroids known to astronomers today move between the orbits of Jupiter and Mars at a distance of about 2.2-3.2 a. e. (that is, astronomical units) from the sun. To date, scientists have discovered about 20 thousand asteroids. Of these, only fifty percent are registered. What are registration asteroids? These are celestial bodies that have been assigned numbers, and sometimes even their own names. Their orbits are calculated with very high accuracy. It should be noted that these celestial bodies usually have the names assigned to them by their discoverers. Names for asteroids are taken, as a rule, from ancient Greek mythology.
In general, from the above definition it becomes clear what asteroids are. However, what else is characteristic of them?
As a result of observations made with celestial bodies through an telescope, an interesting fact was discovered. The brightness of a large number of asteroids can change, and in a very short time - it takes several days, or even several hours. Scientists have long suggested that these changes in the brightness of asteroids are associated with their rotation. It should be noted that they are caused - first of all - by their irregular shapes. And the first photographs in which these celestial bodies were captured (images were taken using spacecraft) confirmed this theory, and also showed the following: the surfaces of asteroids are completely pitted with deep craters and craters of various sizes.
The largest asteroid discovered in our solar system was previously considered the celestial body of Ceres, whose dimensions were about 975 x 909 kilometers. But since 2006, she received a different status. And it became known as the dwarf planet. And the other two large asteroids (under the names Pallas and Vesta) have a diameter of 500 kilometers! Another interesting fact should be noted. The fact is that Vesta is the only asteroid that can really be observed with the naked eye.