A Star Is Born (Part I)

Source: European Space Agency (ESA/Hubble)

Even in the most ancient civilizations we know about, stars played a crucial role, be it through religion or navigation, making astronomy one of the oldest sciences, if not the oldest. The invention of a telescope, followed by the invention of photography and spectroscopy, allowed for a closer research of the stars themselves, and to determine their composition and movement, giving birth to another science in the process: astrophysics. The biggest breakthrough yet came in the shape of the Hubble Space Telescope, the first space-based optical telescope, which allowed scientists the obtain the most detailed, deepest analysis of the universe within the visible-light spectrum.

Of course, we don’t live in the ancient times, so we know that the stars are giant glowing spheres of plasma. There are approximately two billions stars in the Milky Way Galaxy, including our own Sun. Taking into account that there are billions of galaxies in the universe should give you a good idea about the total number of stars. Also, scientists have been able to determine that there are hundreds of stars that have planets orbiting around them, as it the case with our Sun. Stars are developed from a large cloud that consist mostly of hydrogen and helium, which slowly rotates. The cloud begins to collapse onto itself over time due to its gravitational pull, and as it becomes smaller, begins to spin faster and faster, its outer parts forming a disk, while the middle becomes a spherical clump. This material forms a ball called the protostar. When the heat and the pressure inside the protostar reach about 1 million degrees Celsius, the atom nuclei that would normally repel each other being to fuse together, igniting the star.

Source: NASA, ESA, AURA/Caltech, Palomar Observatory (


The stars can be categorized based on several criteria, such as brightness, color, surface temperature, size, mass, magnetic field, metallicity and many others. Astronomers describe the stars in terms of magnitude and luminosity. Astronomers refer to a star’s brightness as it can be seen from Earth as its apparent magnitude, but seeing as the distance between the Earth and the star can affect the light one sees from it, there is also the actual brightness which is described by using the term absolute magnitude, which is defined as apparent magnitude at a distance of 32.6 light years from Earth. Although the magnitude scale previously used to go from one to six, it now spans to more than six and less than one, even all the way down to negative numbers. The brightest star in the night sky is Sirius, with an apparent magnitude of -1.46.

Luminosity on the other hand is the power of a star, or to be more exact, the rate at which it emits energy. Even though power is usually measured in watts, they are not used as measure because our Sun, for example, has the power of 400 trillion trillion watts, so the luminosity of the star is determined by using the Sun as a reference point. Alpha Centauri is about 1.3 times as luminous as the Sun.

To be continued…

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