OBAFGKM is a classification system that’s designed to help astronomers and scientists identify different types of stars. To the naked eye, the stars all appear to be white. In low light conditions affected by things like light pollution, our eyes can’t distinguish the unique colors that stars produce.
However, upon closer inspection in prime conditions, you can see that the universe is filled with colorful stars. The wavelengths of light they produce differ, producing distinct spots of color against the dark backdrop of deep space.
Being able to distinguish stars based on their color is important. You see, all of the stars in space are special. While they may look like simple dots, each one varies quite a bit in terms of size and temperature. They’re also made up of different gases. It’s those unique identifiers that help us get more in-depth information about the star from millions and millions of miles away.
We can learn a lot about what a star is made of just by taking a look at its color. Not only that, but stars are constantly evolving. They can get bigger with time and change temperatures. With that knowledge, you can even determine the approximate age of stars.
So, where does OBAFGKM come into the equation? Well, OBAFGKM is the classification system. Each letter represents a class, which provides a closer glimpse at the temperature and composition of the star.
O Class
The O class stars take on a bluish hue. They are superhot stars with temperatures above 31,000 degrees Kelvin. The gas spectrum that makes up these celestial bodies include weakened hydrogen, neutral helium, and ionized helium.
B Class
Stars in the B class are slightly cooler, lying somewhere between 9,750 and 31,000 degrees Kelvin. They are made up of neutral helium and stronger hydrogen than what’s found on O Class stars. As for color, these stars take on a softer blue-white shade.
A Class
A class stars are easier to identify thanks to their staunch white color. They are made up of strong hydrogen and a collection of ionized metals. Typically, temperatures are between 7,100 and 9,750 degrees Kelvin.
F Class
As we reach the F class, temperatures start to dip even more. These stars are 5,950 to 7,100 degrees Kelvin. They have a soft yellow hue and are made up of weaker hydrogen along with ionized metals.
G Class
G class stars are made of even weaker hydrogen. They’re also comprised of ionized and neutral metals. As for temperature, these stars are between 5,250 and 5,950 degrees Kelvin. They take on that iconic yellow color.
K Class
With a soft orange color, K class stars have a much lower temperature than some of the other classes. They are between 3,800 and 5,250 degrees Kelvin. K class stars have very low levels of hydrogen and a collection of neutral metals.
M Class
Finally, there are M class stars. Despite their fiery red color, these stars have the lowest temperature range. They are between 2,200 and 3,800 degrees Kelvin. When it comes to the composition and gas spectrum, these stars have a trace amount of hydrogen or none at all. They also have neutral metals and molecules.
Within these individual OBAFGKM classes, stars are separated even further into more specific groups. In case you are wondering, our sun falls into the G class. It’s a G2 star, so there’s plenty of time for it to grow and climb up the ladder.
If you’re having trouble remembering the classes, many people use mnemonic phrases. One of the most popular is, “Oh, Be A Fine Girl Kiss Me.”