<p>The spectral classes (O, B, A, F, G, K, M) and their 10 subtypes (0 to 9) were <em>initially</em> meant only as differentiators of spectral type. <a href="https://en.wikipedia.org/wiki/Annie_Jump_Cannon" rel="nofollow noreferrer">Annie Jump Cannon</a> was the creator of this system. Through her work for/with <a href="https://en.wikipedia.org/wiki/Edward_Charles_Pickering" rel="nofollow noreferrer">Edward Pickering</a>, she ended up classifying nearly a third of a million stars over a few decades. She (and many others) did not realize that this was actually a temperature scale - the classifications were based on the spectral lines that Cannon observed and sorted into categories. It wasn't until Cecilia Payne's work, and, most notably, <a href="https://en.wikipedia.org/wiki/Cecilia_Payne-Gaposchkin#Doctoral_thesis" rel="nofollow noreferrer">her doctoral thesis</a>, that anyone realized that the OBAFGKM system (and the sub-classes it came with) was actually a temperature scale.</p>
<p>Payne's work showed that the difference in spectral type was not due to differing amounts of elements, but mainly due to the <em>temperatures</em> of stars. This also led to the realization that stars were made of far more helium and hydrogen than other elements. However, the professor who reviewed her thesis, <a href="https://en.wikipedia.org/wiki/Henry_Norris_Russell" rel="nofollow noreferrer">Henry Russell</a>, dismissed her findings as impossible, since at the time, the implications went against much of contemporary knowledge. After a few years, Russell realized that Payne was right, and praised her work, crediting her with the discovery.</p>
<p>(Side note: there's an amazing episode of the TV series <em>Cosmos</em> - the new one with Neil DeGrasse Tyson - called &quot;Sisters of the Sun&quot; that dives into this story quite well. If you have the time, I'd definitely recommend it - it's a great watch.)</p>

CC BY-SA 4.0
2020-11-17T23:58:06.017Z
2020-11-18T07:54:14.637Z
2020-11-18T07:54:14.637Z
sforsingh
<p>The spectral type of stars has an OBAFGKM class, along with a number, from 0 to 9. According to Wikipedia, (sample shown below), the lower the number, the hotter and more massive the star, but absorption lines are not included. Then looking at the second image, we can see that different spectral types have different absorption lines. So I am wondering, are the sub-spectral types (numbers) based off of <strong>temperature and/or mass</strong> or <strong>absorption/spectral lines?</strong></p>
<p><a href="https://i.sstatic.net/3V7M3.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/3V7M3.png" alt="Characteristics of G-type stars" /></a>
<a href="https://i.sstatic.net/w6H7I.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/w6H7I.png" alt="Comparison of spectra" /></a></p>

<star><spectral-type>
Are the sub-spectral types (1,...9) based on temperature or spectral lines?
WarpPrime
# Are the sub-spectral types (1,...9) based on temperature or spectral lines?

(Asked by: username_0 on 2020-11-17)

The spectral type of stars has an OBAFGKM class, along with a number, from 0 to 9. According to Wikipedia, (sample shown below), the lower the number, the hotter and more massive the star, but absorption lines are not included. Then looking at the second image, we can see that different spectral types have different absorption lines. So I am wondering, are the sub-spectral types (numbers) based off of **temperature and/or mass** or **absorption/spectral lines?**

[![Characteristics of G-type stars](https://i.sstatic.net/3V7M3.png)](https://i.sstatic.net/3V7M3.png)
[![Comparison of spectra](https://i.sstatic.net/w6H7I.png)](https://i.sstatic.net/w6H7I.png)

**Tags:** star, spectral-type


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## 1 answers

### Answer by username_1 on 2020-11-17. Score: 4 | Accepted answer

The spectral classes (O, B, A, F, G, K, M) and their 10 subtypes (0 to 9) were *initially* meant only as differentiators of spectral type. [Annie Jump Cannon](https://en.wikipedia.org/wiki/Annie_Jump_Cannon) was the creator of this system. Through her work for/with [Edward Pickering](https://en.wikipedia.org/wiki/Edward_Charles_Pickering), she ended up classifying nearly a third of a million stars over a few decades. She (and many others) did not realize that this was actually a temperature scale - the classifications were based on the spectral lines that Cannon observed and sorted into categories. It wasn't until Cecilia Payne's work, and, most notably, [her doctoral thesis](https://en.wikipedia.org/wiki/Cecilia_Payne-Gaposchkin#Doctoral_thesis), that anyone realized that the OBAFGKM system (and the sub-classes it came with) was actually a temperature scale.

Payne's work showed that the difference in spectral type was not due to differing amounts of elements, but mainly due to the *temperatures* of stars. This also led to the realization that stars were made of far more helium and hydrogen than other elements. However, the professor who reviewed her thesis, [Henry Russell](https://en.wikipedia.org/wiki/Henry_Norris_Russell), dismissed her findings as impossible, since at the time, the implications went against much of contemporary knowledge. After a few years, Russell realized that Payne was right, and praised her work, crediting her with the discovery.

(Side note: there's an amazing episode of the TV series *Cosmos* - the new one with Neil DeGrasse Tyson - called "Sisters of the Sun" that dives into this story quite well. If you have the time, I'd definitely recommend it - it's a great watch.)


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