Discovering the stars when looking at the night sky, the first question that makes a young restless mind is: what is a star? A star is a huge sphere of hot, bright, gas that produces its own energy through so-called nuclear reactions taking place in the core-Center of the star-making to reach enormous temperatures, and becoming luminous objects that accompany us in our observations of the night sky on clear nights. Stars have a life cycle as any living being: they are born, develop, evolve and grow and eventually die and disappear, for surely trigger the birth of stars. But this happens so slowly that you can not see in human time scale. The universe is a nearly infinite space where they fit millions of stars, groups of stars and galaxies. The distance to the Sun is the nearest star, called astronomical unit – UA and equates to 149.597.870 km. taking into account that the speed of light is 300,000 Km per second, visible light observed from the Sun takes eight minutes approximately to Earth. The next nearest star to the Sun, is called Proxima Centauri, and the light emitted takes over 4 years to reach Earth. This means that when looking at this star, is seeing how was more than four years ago, and is not known as is at the present time.
And indeed, when viewed in the Sun, with appropriate protection on eyes, looks how was eight minutes ago. Molecular clouds in clear nights, especially if seen in the field with a small telescope, far from cities or towns that illuminate the night sky, can also be observed nebulous areas where are born the stars, like Orion and M42, in the constellation of the same name. They are the so-called molecular clouds. Molecular clouds are huge cold and dark clouds which are formed by a gas called hydrogen (99%) and dust – matter solid – in very small proportion (1%), but enough so that under certain conditions, the stars can be born.