Stars And Classification

 Do you know, how many types of stars are there?..

As the summer starts, we start to think about the temperature we feel although the sun is so far from the earth. Then think what if we got closer to the sun! And I want to tell you that billions of stars have more temperature than our sun. 

Our sun is a very normal and general star in the universe like us. There are so many stars that are greater than our sun, so much greater than the sun, thousands of times hotter than the sun. It is said that there are a total of 200000000000000000000000 (200 billion trillions) stars present in the universe. Then how to remember all these stars? The question has an answer. Same as we can classify the human population in the upper class, middle class or lower class depend upon resources they have and how they live, same like that we have classified stars into O, B, A, F, G, K and M.

But only a few people know that Indian astrophysicists have contributed to studying the sun and based on their equations stars can be studied and classified. Indian astrophysicist M. N. Shaha studied sunlight and its spectrum in 1920 and told that our sun is made up of hydrogen, helium and some carbon. 

25 Brightest Stars in the night sky
credit- Tregoovhitr Jittasaiyaoan

O- type stars:

These types of stars are the most massive stars with the highest surface temperature. These are called Blue types of stars because of their high temperature. The mass of these stars is greater than 16 solar masses  ( M☉) or more. Radius is 7 times the radius of the sun (R☉) and surface temperature is 25,000 to 40,000K. Because of their high size and temperature, their luminosity is 30,000 times that of the sun ( these are 30,000 brighter than the sun, 30000L☉). But they are in the least population with 0.00003% of abundance.

B- type stars:

This class of stars have a surface temperature between 11,000 to 25,000K and is known as blue/white stars. Their mass range is 2 M☉ to 16 M☉ and their radius ranges between 1.8 R☉ to 6.6 R☉. Their luminosity is having a wider range of 25 L☉ to 30,000 L☉. The percentage in the total population is greater than O-type stars and is about 1%.

Ex. Some stars in the constellation of Orion belongs to this class

A-type stars:

These are stars with 1.4 M☉ to 2M☉, Their surface temperature can be between 7,500 to 11,000K. They are known as white colour stars and their radius is between 1.4 R☉ to 1.8 R☉. A type of star shines 5 to 25 times brighter than the sun.

Ex." Hydrogen stars", Vega and Sirius are of this type.

A Dark Winter Sky over Monfrague National Park in Spain
You, too, can see a night sky like this. That is because Monfrague National Park in Spain, where this composite image was created, has recently had its night sky officially protected from potential future light pollution. Icons of the night sky that should continue to stand out during northern winter -- and are visible on the featured image -- include very bright stars like Sirius, Betelgeuse, and Procyon, bright star clusters like the Pleiades, and, photographically, faint nebulas like the California and Rosette Nebulas. Even 100 years ago, many people were more familiar with a darker night sky than people today, primarily because of modern light pollution. Other parks that have been similarly protected as dark-sky preserves include Death Valley National Park (USA) and Grasslands National Park (Canada). Areas such as the city of Flagstaff, Arizona and much of the Big Island of Hawaii also have their night skies protected.
Image Credit & Copyright: José Luis Quiñones (Entre Encinas y Estrellas)

F- type stars:

These are known as yellow/ white stars. This class of have a mass of 1.04 to 1.40 M☉ and radius ranges between 1.15 to 1.5 R☉. Their surface temperature is from 6000 to 7000K. The luminosity is 1.5 to 5 L☉.

Ex. Procyon is typical of this type.

G- type stars:

These stars are found in only yellow colour. Our sun comes under this type. The surface temperature of these stars is between 5,200 to 6,000K with mass ranging from 0.8 to 1.04 M☉. radius 0.96 to 1.15 R☉ and luminosity is from 0.6 to 1.5 L☉. These are also known as main-sequence stars. Their percentage is about 3% of the total population.

Ex. Sun belongs to class G2 and the notable star is Capella.

K- type stars:

These stars are having a population of 12% and are known as orange stars. Surface temperature is from 3,700 to 5,200K. Mass is from 0.4 to 0.8 solar masses. Radius is 0.7 to 0.96 R☉ and they are very faint with luminosity 0.08 to 0.6 L☉. 

Ex. Examples are Arcturus and Aldebaran.

M- type stars:

These stars have the highest population of 76% with a very weak hydrogen line (I will write about these lines later). These are also known as red stars. This type of star is characterized by 2,400 to 3,700 K surface temperature. Mass is 0.08 to 0.45 solar masses. and radius less than 0.7 solar radii. They are the faintest stars with 0.08 or even less luminosity.

Ex. Stars like Betelgeuse, Antares belongs to this class.