Full-disk multiwavelength extreme ultraviolet image of the Sun via NASA

We all know scientists like to classify and categorize things, especially in space where everything is unfamiliar. This unfamiliarity makes it hard to convey information accurately. On top of this, there’s a seemingly infinite amount of stars in the universe. Fortunately, astrophysics has come up with a snazzy system to tell them apart.


As we all know, stars are huge, bright spheres of gas spinning through space at incredible speeds. Stars provide the energy which makes (almost) all life on Earth possible. Even in death, stars provide us with life -- giving us the heavy elements necessary for our existence. By sorting out the differing types of stars in the universe we (the science community) can start to observe trends and similarities that will inevitably lead to a better understanding of the universe around us.


One way science classifies stars is by the light it gives off. By observing the color of the star, we can make a pretty good guess at the star’s temperature. As a general rule, the blue end of the spectrum is the hottest. At the other end of the spectrum there is red, which is coolest. A second part of studying a star’s color is finding its emission and absorption lines. Every element, when heated, gives off light at a specific and individual wavelength; these are the emission lines – and they tell us what elements are in stars. When “cold” light is passed through a gas, some of the light is blocked, thus creating absorption lines in the spectrum. Using these two techniques we can decode exactly what chemical elements are within stars. This gives us the ability to create the first part of a star’s classification; it’s spectral type. There are seven spectral types of stars, ranging from type O (the hottest and bluest) to type M (much cooler and very red).


Here is some more information on spectral types.


To be even more exact, scientists put a numerical value on these spectral letters. Numbers ranging from 1-9 describe a star’s position between one spectral type and another. For instance our Sun is a type G2 star, meaning it falls within the G range but is 20% down the path to being a K star (each number corresponds with a percentage; 1=10%, 5=50%, and so on).


Since science likes to beat things to death, there’s one more part to a classification of a star, and that’s a roman numeral describing size and luminosity of the star. This ranges from supergiants (I) to dwarfs (V). This makes the Sun’s type a G2V star, stating that it’s a main sequence, yellow star with a temperature between 5,000 and 6,000 degrees that’s 20% on its way to being an orange type star.


As a general rule this can describe most stars in the universe (so far). There has, however, been additions to these scales to compensate for an ever weirder universe.

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