por What are the celestial bodies?
The celestial bodies They are all those natural objects that belong to the universe, have a measurable size and have mass, which is why they are capable of gravitational interaction with each other. Designating astronomical objects as celestial bodies derives from the fact that they can be seen from Earth, occupying different positions in the sky.
Some authors consider that a celestial body is an entity or individual body, different from an astronomical object. Others even affirm that the celestial bodies are only those that belong to the solar system. In this case, only one star would be considered a celestial body: the Sun, the others would not.
In this sense, the beautiful cluster of the Pleiades (the Seven Goats or the Seven Sisters) would not be a celestial body, although we can see it from Earth. But an individual star in the cluster would be a celestial body, unless we limit ourselves to the solar system.
Throughout this article we will consider as celestial bodies those that can be distinguished with the naked eye, with instruments or are detected by their effects on other known bodies, that have an individual character and that also possess the characteristics described at the beginning: tener mass and measurable size. With mass comes the ability to gravitationally interact with other celestial bodies.
types of celestial bodies
We will classify the celestial bodies into two large groups:
Those that emit their own light.
Those that reflect the light emitted by other stars.
In the first group we have the stars, while in the second there is a great variety of bodies that includes: planets, natural satellites, dwarf planets, asteroids, meteoroids, comets and trans-Neptunian objects.
Except for planets, satellites, and dwarf planets, all other objects are classified as minor bodies of the solar system.
stars
They are gigantic balls of gas, mainly hydrogen and helium, the lightest elements that exist, inside which there is a nuclear reactor that continuously transforms them into heavier elements.
Thanks to these reactions, the star releases enormous amounts of energy, in the form of light and heat.
During their lives, the stars remain in equilibrium thanks to the action of the force of gravity that compresses them, and the pressure of the constituent gases, which tends to expand them.
There are all kinds of stars, from supergiants to dwarfs, as well as colors, which are determined by the temperature of the stellar atmosphere.
The life of stars depends on their initial mass: smaller stars, whose mass is equal to or less than that of our Sun, are stable and have longer lives. Very massive stars, on the other hand, have short lives and usually end up in catastrophic events of the supernova type.
planets
Planets are bodies that lack their own light, since they do not have a fusion reactor at their center. They orbit around the central star, which in the case of the solar system is the Sun.
The planets of the solar system are divided into two categories: rocky planets terrestrial type and the giant planets, also called Jovian planets, because Jupiter is the prototype. The former are dense and small, the latter are light and much larger.
For a long time the only known planets were the 8 planets that orbit the Sun, Earth included.
But in 1992, an extrasolar planet was detected for the first time, and more are being discovered with each passing year. Almost all of them are of the Jovian type, that is, gas giants in which life as we know it is unlikely to be found.
However, terrestrial-type planets are known, with planet Kepler-438b, 473 light-years away, being the most Earth-like to date.
natural satellites
Almost all the planets in the solar system have natural satellites, rocky bodies that orbit around the planet, instead of around the Sun. Only Mercury and Venus, the closest to the Sun, lack satellites.
Rocky planets like Earth and Mars have few satellites, but giant planets number in the dozens.
The largest of all is Ganymede, one of Jupiter’s four Galilean moons, named after Galileo, who first saw it through his telescope.
Tiny planets
It is a more recent category of celestial bodies, whose best-known member is the ancient planet Pluto.
Although they possess almost all the characteristics of the major planets, it is considered that the dwarf planets lack a «clean» orbit, that is, one exclusively dominated by the gravity of the star king.
So far the dwarf planets are, in addition to Pluto, Ceres, ancient asteroid, Eris, Makemake and Haumea. Of them, only Ceres is close to Earth, since it belongs to the asteroid belt. The others lie beyond the orbit of Neptune, the farthest planet from the Sun.
asteroids
An asteroid is a rocky body in the solar system, larger than a meteoroid, but smaller than a planet. Most of them are located in the asteroid belt, the border that separates the terrestrial planets from the Jovian planets.
The rest are scattered around the orbit of Jupiter and to a lesser extent around the other planets. Neptune’s orbit forms the natural confines.
They are very numerous, around 600,000 are known to date, of which about 10,000 have orbits close to that of the Earth.
Their shapes and sizes are diverse. Pallas and Vesta are the largest, with a diameter of about 500 km. That is why they can rarely be seen with the naked eye, unless they pass close to Earth.
meteoroids
They are rocky celestial bodies, smaller than asteroids, but larger than cosmic dust. At most they reach 50 m in diameter.
These include fragmented asteroid and comet remnants, debris from the formation of the solar system, or rocks ejected from planets by colossal impacts.
When they come close to Earth or any other planet and enter the atmosphere they are called meteors. Friction with atmospheric molecules heats and vaporizes them, due to the great speed with which they enter. The fragments that manage to impact the surface are known as meteorites.
kites
They are stars made of rock, ice, gas and dust that orbit around the Sun following a conical trajectory, almost always elliptical with great eccentricity, which means that they move considerably away from the Sun.
When their orbits bring them closer to the king sun, the heat of the Sun and the solar wind give rise to the characteristic hair and tail, but at the same time they fragment the comet.
Much of the debris they leave behind during their visits remains in Earth’s orbit. This is how many meteor showers of periodic appearance in the night skies originate.
trans-Neptunian objects
As their name implies, they are rocky celestial bodies found after the orbit of Neptune.
Pluto and its satellite Charon, the plutinos, the plutoids, which are the dwarf planets like Eris, Makemake and Haumea, are also trans-Neptunian objects.
In addition there are Sedna, one of the most distant objects in the solar system known so far, and the bodies that populate the Kuiper belt, the Oort cloud and the scattered disk.