Asteroids ar solid stony bodies that, like planets, move through near-solar elliptical orbits. However, the scale of those bodies is way smaller than that of standard planets, therefore asteroids wont to be known as little planets. Recently, the term "small planets" isn't counseled to use that there's no confusion with the formally accepted term "dwarf planets", the example of that was Pluto and including the biggest asteroid - Ceres.
After the separation of the dwarf planets in AN freelance cluster, among the asteroids extremely remained solely solid bodies, the inner structure of that is ready to resist attractive force compression. For this reason, asteroids area unit less vulnerable to internal evolution than planets (for example, in their depths there ought to be no attractive force differentiation of matter), however, they're less proof against external factors, like surface shock process and evolution of the orbit. During this sense, the asteroid category has become a lot of uniform. However, once describing asteroids any we are going to additionally mention Ceres, each owing to tradition and since of its borderline position, that makes it potential to contemplate this body as a transient between asteroids and dwarf planets.
Dimensions of asteroids
Diameters of asteroids range from a few tens of meters (conditionally) to about 1000 km (size of Ceres). The first asteroid - still the same Ceres - was discovered on January 1, 1801, by the Sicilian astronomer Giuseppe Piazzi. The term "asteroid" (i.e. "star-shaped") was introduced by William Herschel, wishing to emphasize the fact that when observed in the telescope asteroids look like stars. Even with the help of the best ground telescopes, it is impossible to distinguish the shape of the largest asteroids: their angular diameter does not exceed 0.5". Like large planets, asteroids in the visible spectrum shine reflected sunlight.
Diameters of some asteroids were measured by the method of covering the stars in those successful moments when the asteroids were on the same beam of vision with a sufficiently bright stars. In most cases, however, their sizes are estimated indirectly by shine, color, and distance.
Most of the known asteroids move between the orbits of Mars and Jupiter at distances from the Sun 2,2-3,2 a.u. In total, about 380 thousand asteroids were discovered by the middle of 2007. About 150 thousand of them are registered, i.e. assigned numbers, their orbits are calculated with greater accuracy so that these asteroids can no longer be "lost". About 14 thousand asteroids have received their own names. If we remember that in November 2004 it was known about 265 thousand asteroids, it is easy to see that the average rate of their discovery in recent years is about 130 asteroids per day!
What is their name?
The names of asteroids are usually given by their discoverers in accordance with international rules. Initially, they were given mythological names, continuing the tradition of naming large planets. When the ancient names ran out, asteroids began to give names to outstanding people. But recently, thanks to the automation of astronomical observations, the frequency of discovery of new asteroids has significantly exceeded the capacity of the International Astronomical Union to review applications for naming. Perhaps this tradition will soon be finally broken.
The ring region between the orbits of Mars and Jupiter, inhabited by asteroids, is traditionally called the Main Asteroid Belt (recently, some authors suggest that this region be called the Phaeton Belt). The duration of the orbital period in this zone is from 3 to 9 Earth years, depending on the distance from the Sun. Its average orbital speed is about 20 km/s. Asteroid orbital inclinations to the ecliptic plane (i) reach 70 degrees, but usually, do not exceed 10 degrees. On this basis, the asteroids of the Main Belt are divided approximately equally into flat and spherical subsystems.
Systematically measuring the luster of asteroids, astronomers have long found that almost all of it changes in a short time: from hours to weeks. From the very beginning, it was obvious that these changes are associated with the wrong shape and rotation of asteroids. This was confirmed by the first images from close range obtained by space probes: they showed that the surface of the asteroids was dug by craters and funnels of different sizes. It appears that the shape and structure of the surface of small bodies is due to their numerous collisions with each other. Since the exact form of the asteroids observed from Earth is unknown, it is usually presented as a three-axis ellipse with parameters to explain the variations in brightness.