<p>Try plotting absolute G magnitude (i.e. corrected for the fact tthat all the stars are at different distances) on the y-axis.</p>

CC BY-SA 4.0
2020-02-26T09:22:30.743Z
2020-02-26T09:22:30.743Z
ProfRob
<p>I was looking at the <a href="https://gea.esac.esa.int/archive/visualization/" rel="nofollow noreferrer">visualization tools of Gaia</a>, and tried plotting a color-magnitude diagram. On the right hand side of the image, <code>photGMeanMag (mag)</code> (the amount of light) is plotted as a function of <code>BpRp (mag)</code> (the color). </p>

<p><a href="https://i.sstatic.net/RHbbG.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/RHbbG.png" alt="enter image description here"></a></p>

<p>I was surprised by the distribution of the points in the plot, since I was expecting to see something like the main sequence of the HR diagram, like in <a href="https://www.cosmos.esa.int/web/gaia/gaiadr2_hrd" rel="nofollow noreferrer">this plot</a>: </p>

<p><a href="https://i.sstatic.net/Uswxd.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Uswxd.png" alt="enter image description here"></a></p>

<p>Why are the points distributed in a sort of wedge, rather than along a diagonal line? </p>

CC BY-SA 4.0
2020-02-26T08:33:49.370Z
Excellent question. That is possibly the problem. I shall investigate.
usernumber
<star><definition><variable-star><hr-diagram>
Why does the Gaia color-magnitude diagram have this shape?
usernumber
# Why does the Gaia color-magnitude diagram have this shape?

(Asked by: username_0 on 2020-02-26)

I was looking at the [visualization tools of Gaia](https://gea.esac.esa.int/archive/visualization/), and tried plotting a color-magnitude diagram. On the right hand side of the image, `photGMeanMag (mag)` (the amount of light) is plotted as a function of `BpRp (mag)` (the color).

[![enter image description here](https://i.sstatic.net/RHbbG.png)](https://i.sstatic.net/RHbbG.png)

I was surprised by the distribution of the points in the plot, since I was expecting to see something like the main sequence of the HR diagram, like in [this plot](https://www.cosmos.esa.int/web/gaia/gaiadr2_hrd):

[![enter image description here](https://i.sstatic.net/Uswxd.png)](https://i.sstatic.net/Uswxd.png)

Why are the points distributed in a sort of wedge, rather than along a diagonal line?

**Tags:** star, definition, variable-star, hr-diagram

> **Comments:**
> **username_0**: Excellent question. That is possibly the problem. I shall investigate.  

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## 1 answers

### Answer by username_1 on 2020-02-26. Score: 2

Try plotting absolute G magnitude (i.e. corrected for the fact tthat all the stars are at different distances) on the y-axis.


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