What are the stars?

We explain what the stars are, the types that exist and their characteristics. Also, shooting stars and rain of stars.

1. What are the stars?

When we talk about the stars, we certainly refer to those bright spots that are observed in the sky when night falls. In reality they are large luminous spheres composed of plasma . Despite being in continuous combustion, they retain their own shape thanks to the enormous force of gravity they generate.

The star we know best is the Sun, to which we owe natural light . However, there are billions of stars in the observable universe , apparently dispersed but forming galaxies , orbiting a large common center of gravity.

Although all emit different types of light and heat , only a small percentage can be captured by the human eye, even with the help of a telescope . Around many of them also turn, as in our solar system , opaque stars such as planets , meteorites or comets, hooked on their enormous gravity.

The humanity the stars has been observed since time very remote, and wanted to see in them forms, hidden messages or evidence of their gods. So much so that the stars in the sky have been named according to the formation of mythological figures called constellations.

Since ancient times they have been used for the preparation of the first calendars, as well as for cartography and navigation . In much closer times, astronomical observation has understood much more about them, classifying them and learning about their destinies, their constitution and their various ways of emitting energy.

2. Types of stars

There are very different criteria to classify the stars of the universe , according to some of its specific characteristics, such as:

• According to its life cycle . They are classified according to the moment of their life cycles in which they are: protostars, red giants, white dwarfs, black dwarfs or neutron stars (or, failing that, black holes).
• According to its luminosity and temperature . Depending on how bright and intense they are, they are classified into (from least to greatest intensity and brightness): white dwarfs, sub-dwarfs, dwarf stars (like our Sun), sub-giants, giants, luminous giants, supergiants, luminous supergiants or hypergiants.
• According to the nature of its light . According to the predominant electromagnetic emission type , we can talk about: stars type O (violet), type B (blue), type A (blue-white), type F (yellow-white), type G (yellow, like the Sun), type K ( yellow-orange), type M (red-orange).

3. Characteristics of the stars

Stars originate from molecular clouds , that is, regions of high density of space that contain mainly hydrogen, helium and other elements. Due to the forces of gravity or the collision with other similar clouds, even more dense regions are produced inside, which begin nuclear atomic fusion reactions.

As it begins to grow in mass and density, temperature and light are produced. The magnitude of these explosions is enormous, but the star is held together due to the brutal gravitational attraction it exerts on itself .

Chemically, the stars are formed by hydrogen (71%) and helium (27%), with a small percentage (2%) of heavier elements , from iron and nitrogen, to chromium and rare earths, all of which They are the result of continuous fusion inside.

That is to say that the simplest elements of the universe are composed. In fact, the fusion of stars is the origin of all atoms of matter , so we can understand stars as large space furnaces of matter.

4. Star Examples

Some of the most common stars in the sky are:

• Sirius ( Sirius ) , also called Alfa Canis Maioris , is the brightest star in the Earth’s night sky, located in the constellation Canis Maior . It is actually a two-star system, Sirius A and Sirius B, and even a Sirius C is supposed to exist.
• Canopo ( Canopus ) , the second brightest star in the night sky, is located in the constellation of the keel, 309 light years from us, and has a luminosity of 13300 times our modest Sun. That is, it is brighter than Sirius, but it is also much further.
• Arturo ( Arcturus ) , also called Alpha Bootis , is the third brightest star in the night sky, found in the constellation of the boyero, in the northern celestial hemisphere. It is an orange giant located 36.7 light years from our solar system.
• Vega , also called Alfa lyrae , since it is in the constellation of the lyre, is relatively close to Earth: just 25 light years away. And although it has a tenth of the age of the Sun, it is 2.1 times more massive, and quite poor in elements heavier than helium. Vega was the first star to be photographed and analyzed spectroscopically.
• Betelgeuse , from the constellation Orion, hence called Alpha orionis , is a red supergiant star, the ninth in brightness of the entire sky. It is an old star, which has already used up its main fuel (hydrogen), so its temperatures are relatively low (3,000 K) and emits significant amounts of red and infrared light.
• Aldebaran , also called Alpha tauri , is the main star of the constellation of Taurus, orange-red and 425 times brighter than our Sun, despite having just 1.7 times its mass . The Pionerr 10 probe is en route to Aldebaran, and it is estimated that it will reach it in about 1,690,000 years.

5. Shooting Stars

Contrary to what its name indicates, shooting stars are not properly stars . It is more about waste and astronomical objects of small size that, upon entering the earth’s atmosphere , are victims of friction and light up, giving off light and generating a visible phenomenon from the surface.

Shooting stars are really meteorites or meteors , only of a very small size (between a millimeter and several centimeters), so they do not usually reach the ground , but fade and disintegrate as they fall.

6. Meteor shower

In a shower of stars no stars really fall from the sky. On the contrary, this phenomenon is due to the fact that our planet has momentarily entered the orbit of a comet , receiving part of the gases and fragments that emerge from its coma over thousands of kilometers long.

These rains of material, which are very similar to meteor showers, when they are very abundant, penetrate the atmosphere where friction ignites them and generates light in their path. Since this usually occurs with some frequency (depending on the period of the comets ), the rains of stars can receive specific names, as is the case of the Leonids or the Perseids.