<p>Since age is not a direct observable for a star (and in most cases, neither is mass) you would have to look up your answers using evolutionary tracks from a stellar model. In principle, the answer may also depend on the initial chemical composition of the star and its rotation rate. The maximum luminosity of a red giant may also depend on it mass loss rate.</p>
<p>There are lots and lots of publicly available stellar evolution tracks. For example the <a href="http://stev.oapd.inaf.it/PARSEC/tracks_v2.html" rel="noreferrer">PARSEC</a> or <a href="https://www.unige.ch/sciences/astro/evolution/fr/recherche/geneva-grids-stellar-evolution-models/#grids92" rel="noreferrer">Geneva</a> models.</p>
<p>A possible empirical alternative is just to use observations of star clusters of known age. Since these contain stars at a range of masses then you get an observational measurement of their luminosity (usually in a restricted wavelength band). The trick then is to also estimate the mass of these stars, which can be done from their colours and <span class="math-container">$T_{\rm eff}$</span> for main sequence stars or is just a little higher than the main sequence turn off mass for giants.</p>

CC BY-SA 4.0
2024-12-02T08:17:24.397Z
2024-12-02T08:17:24.397Z
ProfRob
<p>I am really confused on how to estimate the luminosity of a made-up star through its lifetime, like say a star with the mass of 0.902 suns, how would I find the luminosity of it say, 6.5 billion years into its life? Or when it's in its red giant phase? What's the max luminosity it will reach in both red giant phases, and how would I calculate that? I've looked it up everywhere and I cannot get a solid answer, so I decided to come and ask here. I really like making up star systems evolution and finding the luminosity over the millions to billions of years of its life have always been really frustrating. I hope y'all can answer my question to help me out a little. Thanks! - some random guy</p>

CC BY-SA 4.0
2024-12-02T06:18:48.707Z
You might be interested in this Worldbuilding.SE question and answer: [What sets of stellar models are freely available for reference when worldbuilding?](https://worldbuilding.stackexchange.com/questions/175697/what-sets-of-stellar-models-are-freely-available-for-reference-when-worldbuildin/175698#175698) Generally, the idea if you don't want to run physical simulations yourself is to look up a similar mass/metallicity/age combination in a big table made by someone who did.
parasoup
CC BY-SA 4.0
2024-12-02T23:21:47.110Z
There is probably some empirical formula to this, but I am not so sure.
Polaris5744
CC BY-SA 4.0
2024-12-03T00:21:09.747Z
Can you say what you mean by a 'made-up' star, please? Is that something fictional, or what?
Robbie Goodwin
CC BY-SA 4.0
2024-12-03T03:19:05.320Z
Just a random Zero-Age star.
Sayon Meares
<star><mass><luminosity><size><radius>
How do I find the luminosity of a star as it evolves through its entire lifetime
Sayon Meares
# How do I find the luminosity of a star as it evolves through its entire lifetime

(Asked by: username_0 on 2024-12-02)

I am really confused on how to estimate the luminosity of a made-up star through its lifetime, like say a star with the mass of 0.902 suns, how would I find the luminosity of it say, 6.5 billion years into its life? Or when it's in its red giant phase? What's the max luminosity it will reach in both red giant phases, and how would I calculate that? I've looked it up everywhere and I cannot get a solid answer, so I decided to come and ask here. I really like making up star systems evolution and finding the luminosity over the millions to billions of years of its life have always been really frustrating. I hope y'all can answer my question to help me out a little. Thanks! - some random guy

**Tags:** star, mass, luminosity, size, radius

> **Comments:**
> **username_1**: You might be interested in this Worldbuilding.SE question and answer: [What sets of stellar models are freely available for reference when worldbuilding?](https://worldbuilding.stackexchange.com/questions/175697/what-sets-of-stellar-models-are-freely-available-for-reference-when-worldbuildin/175698#175698) Generally, the idea if you don't want to run physical simulations yourself is to look up a similar mass/metallicity/age combination in a big table made by someone who did.  
> **username_2**: There is probably some empirical formula to this, but I am not so sure.  
> **username_3**: Can you say what you mean by a 'made-up' star, please? Is that something fictional, or what?  
> **username_0**: Just a random Zero-Age star.  

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## 1 answers

### Answer by username_4 on 2024-12-02. Score: 10

Since age is not a direct observable for a star (and in most cases, neither is mass) you would have to look up your answers using evolutionary tracks from a stellar model. In principle, the answer may also depend on the initial chemical composition of the star and its rotation rate. The maximum luminosity of a red giant may also depend on it mass loss rate.

There are lots and lots of publicly available stellar evolution tracks. For example the [PARSEC](http://stev.oapd.inaf.it/PARSEC/tracks_v2.html) or [Geneva](https://www.unige.ch/sciences/astro/evolution/fr/recherche/geneva-grids-stellar-evolution-models/#grids92) models.

A possible empirical alternative is just to use observations of star clusters of known age. Since these contain stars at a range of masses then you get an observational measurement of their luminosity (usually in a restricted wavelength band). The trick then is to also estimate the mass of these stars, which can be done from their colours and $T\_{\rm eff}$ for main sequence stars or is just a little higher than the main sequence turn off mass for giants.


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