<p>The term <em>brightness</em>, or <em>apparent brightness</em>, is used to describe how bright a star appears to us from Earth. The term <em>luminosity</em> is used to describe how bright the star is physically, also called <em>intrinsic brightness</em>. </p>

<p>As light spreads from a star to the viewer, it diverges inversely proportional to the square of its distance (d) from the viewer.  <span class="math-container">$\begin{equation}B \propto \frac{1}{d^2}
\end{equation}$</span>. </p>

<p>The relationship between brightness (B) and luminosity (L) is described by <span class="math-container">$\begin{equation}B = \frac{L}{4\pi d^2}
\end{equation}$</span> (1). So we have three variables, <strong>brightness</strong>, <strong>luminosity</strong> and <strong>distance</strong>. </p>

<p>So out of those three, you'd need two to acquire the third. The distance is generally the hardest to acquire. The gold standard in measuring the distance to a star is <a href="https://en.wikipedia.org/wiki/Stellar_parallax" rel="noreferrer">stellar parallax</a>. If you can't do parallax, then distance-independent properties of stars sometimes serve as clues to distance. </p>

<p>Measuring brightness is generally the easy one. <a href="https://en.wikipedia.org/wiki/Charge-coupled_device" rel="noreferrer">CCD's</a> are often used to measure apparent brightnesses. Brightness can be expressed in <a href="http://abyss.uoregon.edu/~js/glossary/stellar_magnitude.html" rel="noreferrer">stellar magnitudes</a> or absolute fluxes. </p>

<p>So to sum up, we calculate or measure distance, we measure apparent brightness and finally calculate the luminosity value from (1). </p>

CC BY-SA 4.0
2020-05-03T16:53:55.397Z
2020-05-03T16:53:55.397Z
sbjartmar
<p>How do scientists measure the brightness of so distant stars? </p>

CC BY-SA 4.0
2020-05-03T16:21:07.923Z
We can easily say their *visible limunosity*. The problem to solve: it is not easy to say, we have a star X light years away, or a star twice brighter, 2X light years away. Might read this: https://en.wikipedia.org/wiki/Cosmic_distance_ladder
peterh
<star><observational-astronomy><brightness>
How do we measure the brightness of the stars?
Sazzad Hissain Khan
# How do we measure the brightness of the stars?

(Asked by: username_0 on 2020-05-03)

How do scientists measure the brightness of so distant stars?

**Tags:** star, observational-astronomy, brightness

> **Comments:**
> **username_1**: We can easily say their *visible limunosity*. The problem to solve: it is not easy to say, we have a star X light years away, or a star twice brighter, 2X light years away. Might read this: https://en.wikipedia.org/wiki/Cosmic_distance_ladder  

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## 1 answers

### Answer by username_2 on 2020-05-03. Score: 7 | Accepted answer

The term *brightness*, or *apparent brightness*, is used to describe how bright a star appears to us from Earth. The term *luminosity* is used to describe how bright the star is physically, also called *intrinsic brightness*.

As light spreads from a star to the viewer, it diverges inversely proportional to the square of its distance (d) from the viewer. $\begin{equation}B \propto \frac{1}{d^2}
\end{equation}$.

The relationship between brightness (B) and luminosity (L) is described by $\begin{equation}B = \frac{L}{4\pi d^2}
\end{equation}$ (1). So we have three variables, **brightness**, **luminosity** and **distance**.

So out of those three, you'd need two to acquire the third. The distance is generally the hardest to acquire. The gold standard in measuring the distance to a star is [stellar parallax](https://en.wikipedia.org/wiki/Stellar_parallax). If you can't do parallax, then distance-independent properties of stars sometimes serve as clues to distance.

Measuring brightness is generally the easy one. [CCD's](https://en.wikipedia.org/wiki/Charge-coupled_device) are often used to measure apparent brightnesses. Brightness can be expressed in [stellar magnitudes](http://abyss.uoregon.edu/~js/glossary/stellar_magnitude.html) or absolute fluxes.

So to sum up, we calculate or measure distance, we measure apparent brightness and finally calculate the luminosity value from (1).


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