Stars are "born" from nebulae made up largely of gases, dust and solid particles.
Scientists explain that there is a reciprocal attraction between the particles of matter that make up the large cloud - the nebula. This attraction is called the force of gravity. Due to the force of gravity, the matter that constitutes a nebula is grouped together, forming a compact mass and forming the stars.
Some stars reach a gigantic size, and the temperature inside is very high. The pressure and heat become so intense at the center of these stars that a great deal of energy is released in the form of heat and light. This property of producing its own heat and light is what differentiates stars from planets and other stars.
The brightness of the stars is produced by their energy, which radiates through space in the form of light. The stars do not last forever. They "are born", evolve and "die". This same process occurs with the Sun, for it is also a star.
It may seem strange, but when we look at the stars, we are seeing their past. If the star is far, far away, it may not even exist as we know it today - and may even have become another celestial body. When we look at a star, we are catching the light it has emitted into space. Light is a form of energy that travels at an incredible speed of about 300,000 kilometers per second. But because the distance between the celestial bodies is also great, it may take a long time for the starlight to reach us.
See the example:
The closest star to us after the sun called Near Centaur, is at a distance of 40 trillion kilometers from Earth. This means that the light from this star takes about 4.2 years or 4.2 light years to get here. So when we look at this star, we are now seeing the light it emitted 4.2 years ago. If, at that moment, that star ceased to exist, it would only "go out", that is, its light would cease to reach us in 4.2 years. Only then would we realize that it ceased to exist.
The brightness of the stars is overshadowed during the day by sunlight that is the closest star to the earth. Therefore, we perceive the stars in the sky only at night, but they remain there during the day.
With the naked eye, it is difficult to distinguish the color of the stars. Because of the great distances they are from us, the amount of light that reaches our eyes is very small and we do not perceive colors when there is little light.
The color of stars depends on the heat coming from the core to their surface and is therefore related to their temperature. Stars with a warmer surface are white or bluish, and those with a reddish color have a less warm surface. With the telescope you can see the color of the stars more clearly.
In the less warm stars, the surface temperature reaches 3 000ºC, while in the hottest stars it reaches 50 000ºC.
The sun has a yellowish color and, compared to the other stars, has an average temperature.
Figure: O blue represents the hot interstellar gas, the stars appear the color green and the hot dust the red. The red super giant stars are the brightest stars in the center.
Why do the stars flash?
Looking at the night sky, we can see that the brightness of the stars change: they "flash". But stars are always emitting the same light. Flashing is caused by changes in the air of the atmosphere that light passes through.