<p>Regarding the color of a star, if you don't need anything precise, you can assume that the spectrum of a star is a <a href="https://en.m.wikipedia.org/wiki/Black-body_radiation" rel="nofollow noreferrer">black body</a> at an effective temperature <span class="math-container">$T_\text{eff}$</span>. Given the temperature, you can calculate a RGB representation of the color using for instance the table provided in <a href="http://www.vendian.org/mncharity/dir3/blackbody/" rel="nofollow noreferrer">this website</a></p>
<p>The last thing you need to know is how to calculate the effective temperature from the quantities in the EGDR3. I found a paper that can help you with this: <a href="https://arxiv.org/abs/2106.03882v1" rel="nofollow noreferrer">Mucciarelli et al. 2021</a></p>
<p>You just need to know the photometric color of the star, its metallicity, and then you can use equation 1 in the paper to find the effective temperature. The coefficients for the equation 1 are found in table 1.</p>

CC BY-SA 4.0
2022-09-01T14:52:19.073Z
You need to know the extinction as well if you want to calculate the temperature like this. If you just want the apparent colour of the star, that is already encoded with Bp-Rp.
ProfRob
CC BY-SA 4.0
2022-09-01T07:49:04.853Z
2022-09-01T07:49:04.853Z
Prallax
<p>Is there a way to take the Gaia Early Data Release 3 dataset and calculate a likely star size (radius and mass) (units not relevant), and emission spectra (hydrogen, helium) or light color?  Please note that this does not have to be precise or precisely accurate, just in the right ballpark (I will not be worrying about noise, errors, or error adjustments from the data set) (no +/- 0.1237610987564 luminosity will be used in the database I'm creating)</p>
<p>I'm building a star map for a future project, and I'd like to be able to assign stars at their actual locations with a size and, preferably type, but I'll settle for color.</p>
<p>Any assistance greatly appreciated as the maths is not my strong suit, although the Excel certainly is and once I know <em>how</em> to do it for one, it'll be (relatively) quick and easy to do it for all of them.</p>
<p>Please try to keep answers in plain English at just below the Calculus level, as I never started Calculus.  Thank you.</p>

CC BY-SA 4.0
2022-08-30T21:30:57.467Z
What do you mean by size and emission spectra? Do you mean radius and spectral type/classification or temperature?
ProfRob
CC BY-SA 4.0
2022-08-31T00:16:38.017Z
Edited original question to clarify, but I really want to know radius and visible light emission as if you were at or near the source.  I can convert from emission spectra to visible light and from visible light to spectral type, but if it's easier to just tell me how to calculate the spectral type using the GDR3 data, that's fine, too.
GrasshopperTaji
CC BY-SA 4.0
2022-08-31T06:46:32.980Z
The GDR3 data already tells you the star "colour". It is  $G_{Bp}-G_{Rp}$. Of course that (and the spectrum observed) are affected by interstellar extinction. It is still unclear what you expect to get as an answer when asking for the "visible light emission" or what you mean by "emission spectra (hydrogen, helium)".
ProfRob
CC BY-SA 4.0
2022-08-31T21:31:07.490Z
@ProfRob What's interstellar extinction?
I'm sorry if I'm unclear about emission spectra, let me try to explain what I'm looking for.  Our sun (Sol) has a spectral classification of G2V, a color of (B-V) of 0.63, and a Luminosity of 3.828×1026 W.  I want to convert the GDR3 data into those elements, if possible so that I can say what a given star would look like if you were in the same solar system as it.  Emission spectra can be used to determine the color of a star by taking the observed emission lines from the star and blue-shifting them back along the distance travelled.
GrasshopperTaji
CC BY-SA 4.0
2022-08-31T21:33:50.253Z
@ProfRob So...emission spectra say which elements from the periodic table have been excited into light from the source.  Take Hydrogen, and excuse the crudity, but the emission lines look something like this:      |  |   |||    |  |
If you find that pattern in the Deep Infrared, you know that the light has been red-shifted by x amount, and you can take the distance measurement and "re-align" the emission lines to where they *should* be.  With that, you can determine which other elements the star is burning and that contributes to total color.
GrasshopperTaji
CC BY-SA 4.0
2022-08-31T23:58:01.450Z
Okay...so GDR3 contains a pseudocolour # for a large number of stars.  How does that convert to actual colors?  e.g. source Gaia EDR3 23435098209438976 has a pseudocolour of 1.5506241.  Is that Red?  Is it Yellow?  Is it green?  Is it 610 nanometers?  What is it and how do I convert it to RGB / CMYK / nanometers or whatever else?
GrasshopperTaji
<star><gaia><star-maps>
Classifying stars using GEDR3
GrasshopperTaji
# Classifying stars using GEDR3

(Asked by: username_0 on 2022-08-30)

Is there a way to take the Gaia Early Data Release 3 dataset and calculate a likely star size (radius and mass) (units not relevant), and emission spectra (hydrogen, helium) or light color? Please note that this does not have to be precise or precisely accurate, just in the right ballpark (I will not be worrying about noise, errors, or error adjustments from the data set) (no +/- 0.1237610987564 luminosity will be used in the database I'm creating)

I'm building a star map for a future project, and I'd like to be able to assign stars at their actual locations with a size and, preferably type, but I'll settle for color.

Any assistance greatly appreciated as the maths is not my strong suit, although the Excel certainly is and once I know *how* to do it for one, it'll be (relatively) quick and easy to do it for all of them.

Please try to keep answers in plain English at just below the Calculus level, as I never started Calculus. Thank you.

**Tags:** star, gaia, star-maps

> **Comments:**
> **username_1**: What do you mean by size and emission spectra? Do you mean radius and spectral type/classification or temperature?  
> **username_0**: Edited original question to clarify, but I really want to know radius and visible light emission as if you were at or near the source.  I can convert from emission spectra to visible light and from visible light to spectral type, but if it's easier to just tell me how to calculate the spectral type using the GDR3 data, that's fine, too.  
> **username_1**: The GDR3 data already tells you the star "colour". It is  $G_{Bp}-G_{Rp}$. Of course that (and the spectrum observed) are affected by interstellar extinction. It is still unclear what you expect to get as an answer when asking for the "visible light emission" or what you mean by "emission spectra (hydrogen, helium)".  
> **username_0**: @username_1 What's interstellar extinction? I'm sorry if I'm unclear about emission spectra, let me try to explain what I'm looking for.  Our sun (Sol) has a spectral classification of G2V, a color of (B-V) of 0.63, and a Luminosity of 3.828×1026 W.  I want to convert the GDR3 data into those elements, if possible so that I can say what a given star would look like if you were in the same solar system as it.  Emission spectra can be used to determine the color of a star by taking the observed emission lines from the star and blue-shifting them back along the distance travelled.  
> **username_0**: @username_1 So...emission spectra say which elements from the periodic table have been excited into light from the source.  Take Hydrogen, and excuse the crudity, but the emission lines look something like this:      |  |   |||    |  | If you find that pattern in the Deep Infrared, you know that the light has been red-shifted by x amount, and you can take the distance measurement and "re-align" the emission lines to where they *should* be.  With that, you can determine which other elements the star is burning and that contributes to total color.  
> **username_0**: Okay...so GDR3 contains a pseudocolour # for a large number of stars.  How does that convert to actual colors?  e.g. source Gaia EDR3 23435098209438976 has a pseudocolour of 1.5506241.  Is that Red?  Is it Yellow?  Is it green?  Is it 610 nanometers?  What is it and how do I convert it to RGB / CMYK / nanometers or whatever else?  

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## 1 answers

### Answer by username_2 on 2022-09-01. Score: 1

Regarding the color of a star, if you don't need anything precise, you can assume that the spectrum of a star is a [black body](https://en.m.wikipedia.org/wiki/Black-body_radiation) at an effective temperature $T\_\text{eff}$. Given the temperature, you can calculate a RGB representation of the color using for instance the table provided in [this website](http://www.vendian.org/mncharity/dir3/blackbody/)

The last thing you need to know is how to calculate the effective temperature from the quantities in the EGDR3. I found a paper that can help you with this: [Mucciarelli et al. 2021](https://arxiv.org/abs/2106.03882v1)

You just need to know the photometric color of the star, its metallicity, and then you can use equation 1 in the paper to find the effective temperature. The coefficients for the equation 1 are found in table 1.

> **Comments:**
> **username_1**: You need to know the extinction as well if you want to calculate the temperature like this. If you just want the apparent colour of the star, that is already encoded with Bp-Rp.  

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