Humanity has looked up to the sky to gaze at the stars since time immemorial. In fact, we probably do it before we even become human today. These stars in the sky have been a source of inspiration for artists of all kinds, to a very important source of information on what the universe in which we live is like, to a vital guide for sailors and travelers.
What are the stars and stellar classification
Astronomy defines stars as plasma spheroids that emit light and maintain their structure thanks to the force of gravity. Our closest star is the Sun , the only one in the solar system and the one that gives us light and heat, making possible the necessary conditions for our life.
However, there are many types of stars . These can be classified by:
- Its level of light and heat.
- Its longevity.
- Its severity.
Let’s see, next, what are each of the types of these possible parts of the stellar classification . In addition, if you want to learn more information and discover curiosities about these stars.
The so-called Harvard spectral classification , which gets its name from having been developed at Harvard University in the late 19th century, is the most common of the classifications used by astronomers. Divide the stars according to their temperature and apparent luminosity , taking their color as a reference. This classification includes 7 main types: O, B, A, F, G, K and M, with colors ranging from blue to red.
However, the Yerkes spectral classification or MK system, which came later, takes into account both stellar temperature and surface gravity, which influences luminosity. Therefore, a more specific classification results. The Yerkes spectral classification divides stars into 9 types :
- 0 – Hypergigante
- Ia – Very luminous supergiant
- Ib – Supergiant of lower luminosity
- II – Bright giant
- III – Giant
- IV – Subgiant
- V – Dwarf main sequence stars
- VI – Subenana
- VII – White Dwarf
Types of stars according to their light and heat
- They are considered hypergiants stars which have up to 100 M (the mass of our Sun), approaching the theoretical maximum limit of 120 M.
- The supergiant stars , however, have a mass of between 10 and 50 M, and dimensions up to 1000 times that of our sun.
- The giant stars usually have a radius of between 10 and 100 times the solar radius.
- The subgiant stars are those that have fused all the hydrogen in their nuclei. They are brighter than the main sequence dwarfs, but less than the giants.
- The dwarf stars are part of the main sequence, which includes most of the stars of the universe. Our Sun is a yellow dwarf.
- The objects represent stars have a luminosity between 1.5 and 2 magnitudes below the main sequence but with the same spectral type.
- The white dwarf stars finally, are the remnants of stars that have run out of nuclear fuel. They are the most numerous in the universe together with red dwarfs, and it is estimated that 97% of known stars will go through this phase.
In the image below you can see the size comparison between some of the types of stars and some well-known planets, such as Earth and Jupiter. And since we have talked about the luminosity of the stars, we also encourage you to discover these other posts about Why do stars shine at night and not during day and Why do you not see stars in cities .
The classification of stars according to their life cycle ranges from the birth of the protostar from a large molecular cloud, to the death of the star in its different forms and the different stellar remnants that they can leave behind.
Phases of the star’s life
- PSP: Main Presequence
- SP: Main Sequence
- SubG: Subgigante
- GR: Red Giant
- AR: Red Crowding
- RH: Rama horizontal
- RAG: Giant asymptotic branch
- SGAz: Blue supergiant
- SGAm: Yellow supergiant
- SGR: Super giant roja
- WR: Star Wolf-Rayet
- VLA: Blue luminous variable
In addition, stars can die in different ways , which are as follows:
- EM: Brown dwarf
- NP: Nebulosa planetaria
- SN: Supernova
- HN: Hipernova
- BRG: Gamma Ray Outbreak
And finally, these are the star remnants they can leave behind:
- EB: White dwarf
- EN: Neutron star
- AN: Black hole
The gravitational classification of star types takes into account four gravitational criteria. These are relatively recent, since they were established in 2006 by the International Astronomical Union. They are as follows:
- Classification by stellar gravitational center.
- Systemic star ranking by position.
- Classification of stars by gravitational grouping.
- Star classification by planetary system.
Therefore, astronomers also classify the types of stars according to stellar gravitational center, by systemic stars by position, by gravitational grouping, and by planetary system.
How many stars are in the Milky Way and in the universe
It is unfeasible to count all the stars in the observable universe one by one. Instead, the galaxies are counted to make estimates and averages of solar masses contained in them and, therefore, of stars.
Our Milky Way galaxy is believed to contain between 150,000 and 400,000 million stars . Taking into account the number of observable galaxies, astronomers estimate a total number of stars of around 70,000 trillion stars, that is, one seven and twenty-two zeros. Of these, we are only able to observe 9,096 with the naked eye.
That said, one last note is worth leaving: shooting stars are not stars despite their name. They are meteors, small particles that disappear due to friction against the atmosphere when they enter, producing their ephemeral glow.