Lifeless space is not at all deserted. It combines a huge mass of all kinds of bodies of different nature, size and with a different name. Among them are meteors, meteorites, comets, fireballs, planets and stars. Moreover, each of the categories of cosmic bodies within itself is also divided into types, the difference between which can often only be understood by an experienced astronomer. Let’s try to understand fundamental principles, for example, how stars differ from planets.
The main difference
The very first, fundamental and unquestioned difference is the ability to shine. Any star necessarily emits light, but the planet does not possess this property. Of course, nearby planets also look like luminous spots - Venus can serve as an eloquent example. But this is not her own glow, she is just a “mirror” in which the light of the true source - the Sun is reflected.
By the way, this is a very good way to distinguish a planet from a star purely visually, without additional optical devices. If a luminous dot in the night sky “winks”, that is, flickers, be sure this is a star. If the light emanating from a celestial object is even and constant, then this planet reflects the light of the nearest luminary. And this is the very first and most obvious sign showing us how stars differ from planets.
The second difference arising from the first
The ability to emit light is characteristic only of very hot surfaces. As an example, we can consider metal, which in itself does not glow. But if it is heated to the desired temperature, the metal object is heated and emits, albeit weak, but light.
So the second thing that stars differ from planets is the very high temperature of these cosmic bodies. This is what allows the stars to shine. Even on the surface of the coldest luminary, the temperature does not fall below 2000 degrees K. Usually stellar temperatures are measured in Kelvin, in contrast to the usual Celsius.
Our Sun is much hotter, at different periods its surface heats up to 5000, and even 6000 K. That is, “in our opinion” it will be 4726.85 - 5726.85 ° C, which is also impressive.
Necessary clarification
The indicated temperatures are typical only for stellar surfaces. What makes stars different from planets is that they are much hotter inside than outside. Even the surface temperatures on some stars reach 6000 K, and in the center of the stars they are presumably surpassing millions of degrees Celsius! So far, there are no opportunities, no necessary equipment, or even a calculation formula, with the help of which one could determine the internal "degree" of stars.
Dimensions and movement
The sizes of stars and planets differ just as grandiose. Compared with the celestial "lanterns" of the planet - just grains of sand. And this applies to weight (mass), and volume. If, instead of the Sun, a medium-sized apple is placed in the middle of free space, then to indicate the position of the Earth, you need a pea, referred to hundreds of meters. A comparison of the sizes of planets and stars shows that the volumes of the second are thousands, or even millions of times, of the volume in space that the first occupy. There are other ratios with a lot of dumb. The fact is that all planets are solids. And stars are mostly gaseous, otherwise thermonuclear reactions, which provide the sky-high temperatures of the stars, would be simply impossible.
And what is the difference between a planet and a star? A planet, by definition, has a trajectory of motion called an orbit. And she necessarily surrounds the star as a more significant heavenly body. The star is motionless in the sky. If you have patience and watch a certain part of the sky for several nights, the movement of the planet can be noticed even with a slightly armed eye (but you can’t do without an amateur telescope).
Additional signs
The sizes of stars and planets cannot be determined by eye. But some of the differences that accurately characterize cosmic bodies require even more specific equipment. So, the chemical composition that can be determined by spectral analysis will tell you exactly whether a planet or a star is in front of us. After all, luminaries are gaseous giants, therefore, they consist of light elements. And the planets include mostly solid components.
An indirect sign may be the presence of a satellite (or even several). Only planets have them. However, if a satellite is not observed, this does not mean at all that we have a clear star - some planets do well without such “neighbors”.
Astronomers have another sign of determining whether a planet is a newly discovered cosmic body. The orbit in which it moves should not contain extraneous objects, roughly speaking, debris. Satellites are not considered as such, they are large enough, otherwise they would fall to the surface. This rule was adopted quite recently - in 2006. Thanks to him, Eris, Ceres and - attention! - Pluto is now considered not full, but dwarf planets.
Astronomical calculations
Scientists are distinguished by increased curiosity. Knowing perfectly how stars differ from planets, they nevertheless wondered what would happen when the massiveness of the planet exceeds, for example, the size of the sun. It turned out that such an increase in the size of the planet will lead to a sharp increase in pressure in the core of the cosmic body; then the temperature will reach a million (or several) degrees; nuclear and thermonuclear reactions will begin - and instead of the planet, we will get a newborn star.