<p>The zero point luminosity L<sub>0</sub> is the luminosity of a star whose absolute <a href="https://en.wikipedia.org/wiki/Absolute_magnitude#Bolometric_magnitude" rel="nofollow noreferrer">bolometric magnitude</a> M<sub>bol</sub> is 0.
<a href="https://arxiv.org/abs/1510.06262" rel="nofollow noreferrer">IAU recommends</a> the value
L<sub>0</sub> = 3.0128 &times; 10<sup>28</sup> W.
If the Sun's M<sub>bol</sub> is +4.74, then
L<sub>0</sub> / L<sub>sun</sub> = 10<sup>4.74 / 2.5</sup> = 78.7,
which is consistent with L<sub>sun</sub> = 3.828 &times; 10<sup>26</sup> W.</p>

<p>Your understanding that L<sub>sun</sub> &equiv; L<sub>&#9737;</sub> is correct.
Maybe there was an accidental substitution of L<sub>&#9737;</sub> for L<sub>0</sub> at some point.
Curiously, the number 3.75 &times; 10<sup>28</sup> appears in the <a href="https://en.wikipedia.org/wiki/Sun" rel="nofollow noreferrer">Wikipedia:Sun</a> sidebar as the Sun's luminous flux in <em>lumens</em>, a quantity more applicable to a light bulb than to a star.</p>

CC BY-SA 4.0
2019-08-16T17:35:28.823Z
2019-08-16T17:35:28.823Z
Mike G
<p>I was doing some research and found that the zero-point luminosity was <span class="math-container">$L_\odot = 3.75\times 10^{28} $</span>, while the sun's reported luminosity was <span class="math-container">$L_{Sun} = 3.828\times 10^{26}$</span>, according to <a href="https://en.wikipedia.org/wiki/Sun" rel="nofollow noreferrer">Wikipedia</a>. Why isn't it the same value? Doesn't the symbol <span class="math-container">$\odot$</span> represent the value of our sun?  </p>

<p>Furthermore, when Googling the Luminosity of the sun, it gives <span class="math-container">$1L_\odot$</span>, which suggests that <span class="math-container">$L_{Sun} = L_\odot$</span> when it is evidently not. What's going on here? I'm very confused.</p>

<p>For background, I have little to no background knowledge of astrophysics, and I'm trying to learn about it.</p>

<p>Thanks.</p>

CC BY-SA 4.0
2019-08-16T11:26:02.527Z
Could you link/clarify what the 'zero point luminosity' is? I'm not familiar with the concept myself. Also units should always be added for any physical quantities.
AtmosphericPrisonEscape
CC BY-SA 4.0
2019-08-16T12:59:48.410Z
@Anurag Do you mean the zero point of the absolute magnitude scale?
SpaceCore
CC BY-SA 4.0
2019-08-16T14:11:26.290Z
$L_{\odot}$ is the bolometric luminosity of the Sun. I don't know where you get $3.75 \times 10^{28}$ W from?
ProfRob
CC BY-SA 4.0
2019-08-16T15:34:30.487Z
What units are these two values in? Are they both in Watts? If not, they could be equivalent, but using different unit systems.
HDE 226868
<the-sun><luminosity>
Why is the Sun's Luminosity not equal to the Zero Point Luminosity?
Anurag
# Why is the Sun's Luminosity not equal to the Zero Point Luminosity?

(Asked by: username_0 on 2019-08-16)

I was doing some research and found that the zero-point luminosity was $L\_\odot = 3.75\times 10^{28} $, while the sun's reported luminosity was $L\_{Sun} = 3.828\times 10^{26}$, according to [Wikipedia](https://en.wikipedia.org/wiki/Sun). Why isn't it the same value? Doesn't the symbol $\odot$ represent the value of our sun?

Furthermore, when Googling the Luminosity of the sun, it gives $1L\_\odot$, which suggests that $L\_{Sun} = L\_\odot$ when it is evidently not. What's going on here? I'm very confused.

For background, I have little to no background knowledge of astrophysics, and I'm trying to learn about it.

Thanks.

**Tags:** the-sun, luminosity

> **Comments:**
> **username_1**: Could you link/clarify what the 'zero point luminosity' is? I'm not familiar with the concept myself. Also units should always be added for any physical quantities.  
> **username_2**: @username_0 Do you mean the zero point of the absolute magnitude scale?  
> **username_3**: $L_{\odot}$ is the bolometric luminosity of the Sun. I don't know where you get $3.75 \times 10^{28}$ W from?  
> **username_4**: What units are these two values in? Are they both in Watts? If not, they could be equivalent, but using different unit systems.  

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## 1 answers

### Answer by username_5 on 2019-08-16. Score: 2 | Accepted answer

The zero point luminosity L0 is the luminosity of a star whose absolute [bolometric magnitude](https://en.wikipedia.org/wiki/Absolute_magnitude#Bolometric_magnitude) Mbol is 0.
[IAU recommends](https://arxiv.org/abs/1510.06262) the value
L0 = 3.0128 × 1028 W.
If the Sun's Mbol is +4.74, then
L0 / Lsun = 104.74 / 2.5 = 78.7,
which is consistent with Lsun = 3.828 × 1026 W.

Your understanding that Lsun ≡ L☉ is correct.
Maybe there was an accidental substitution of L☉ for L0 at some point.
Curiously, the number 3.75 × 1028 appears in the [Wikipedia:Sun](https://en.wikipedia.org/wiki/Sun) sidebar as the Sun's luminous flux in *lumens*, a quantity more applicable to a light bulb than to a star.


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