<p>The Wikipedia article <a href="https://en.wikipedia.org/wiki/Stellar_classification" rel="nofollow noreferrer">Stellar Classification</a> has a subsection <a href="https://en.wikipedia.org/wiki/Stellar_classification#%22Early%22_and_%22late%22_nomenclature" rel="nofollow noreferrer">&quot;Early&quot; and &quot;late&quot; nomenclature</a>.</p>
<p>It says:</p>
<blockquote>
<p>Stars are often referred to as early or late types. &quot;Early&quot; is a
synonym for hotter, while &quot;late&quot; is a synonym for cooler.</p>
</blockquote>
<p>My lecture notes say:</p>
<blockquote>
<p>O and B stars are sometimes referred to as ‘early-type’, while K and M
are ‘late-type’.</p>
</blockquote>
<p>If I look at a <a href="https://upload.wikimedia.org/wikipedia/commons/6/6b/HRDiagram.png" rel="nofollow noreferrer">HR diagram</a>, I see that main sequence O, B stars are hotter than main sequence K, M stars. So they are burning their fuel at a greater rate than K, M stars, so they run out of it early. So the stars which we are still able to observe now from the <em>early</em> universe are K, M stars, rather than O, B, which presumably formed rather *late**ly. Yet this is not consistent with the terminology above, so something is obviously wrong here.</p>
<p><strong>What is wrong with my argument that the <em>early</em> and <em>late</em> words should be used in the other way round?</strong></p>

CC BY-SA 4.0
2020-11-10T17:51:22.563Z
oh alright, thanks.
zabop
<stellar-evolution><stellar-classification><hr-diagram>
"Early" and "late" nomenclature regarding O, B & K, M stars
zabop
# "Early" and "late" nomenclature regarding O, B & K, M stars

(Asked by: username_0 on 2020-11-10)

The Wikipedia article [Stellar Classification](https://en.wikipedia.org/wiki/Stellar_classification) has a subsection ["Early" and "late" nomenclature](https://en.wikipedia.org/wiki/Stellar_classification#%22Early%22_and_%22late%22_nomenclature).

It says:

> Stars are often referred to as early or late types. "Early" is a
> synonym for hotter, while "late" is a synonym for cooler.

My lecture notes say:

> O and B stars are sometimes referred to as ‘early-type’, while K and M
> are ‘late-type’.

If I look at a [HR diagram](https://upload.wikimedia.org/wikipedia/commons/6/6b/HRDiagram.png), I see that main sequence O, B stars are hotter than main sequence K, M stars. So they are burning their fuel at a greater rate than K, M stars, so they run out of it early. So the stars which we are still able to observe now from the *early* universe are K, M stars, rather than O, B, which presumably formed rather \*late\*\*ly. Yet this is not consistent with the terminology above, so something is obviously wrong here.

**What is wrong with my argument that the *early* and *late* words should be used in the other way round?**

**Tags:** stellar-evolution, stellar-classification, hr-diagram

> **Comments:**
> **username_0**: oh alright, thanks.  

---

## 0 answers

