<p>They can, and some do. These stars are called <a href="https://en.wikipedia.org/wiki/Variable_star" rel="noreferrer">variable stars</a>, because their luminosities <em>as observed from Earth</em> vary over time, often (though not always) in a regular period. Here are some broad categories:</p>

<ul>
<li><a href="https://en.wikipedia.org/wiki/Stellar_pulsations" rel="noreferrer"><strong>Pulsating stars</strong></a>, where fluctuations lead to increases and decreases in size or temperature, which in turn produce changes in the star's brightness. Example: The oft-cited <a href="https://en.wikipedia.org/wiki/Cepheid_variable" rel="noreferrer">Cepheid variables</a>.</li>
<li><a href="https://en.wikipedia.org/wiki/Binary_star#Eclipsing_binaries" rel="noreferrer"><strong>Eclipsing binary stars</strong></a> involve two stars orbiting each other. When one passes between the other and Earth, the combined luminosity of the system appears to decrease, even though the stars' intrinsic luminosities are probably constant. Example: <a href="https://en.wikipedia.org/wiki/Algol" rel="noreferrer">Algol</a>.</li>
<li>So-called <a href="https://en.wikipedia.org/wiki/Variable_star#Eruptive_variable_stars" rel="noreferrer"><strong>eruptive variables</strong></a> (often lumped together with <a href="https://en.wikipedia.org/wiki/Cataclysmic_variable_star" rel="noreferrer"><strong>cataclysmic variables</strong></a>, which are different) may have irregular outbursts caused by flares or other phenomena. Example: <a href="https://en.wikipedia.org/wiki/Luminous_blue_variable" rel="noreferrer">Luminous blue variables (LBVs)</a>.</li>
</ul>

<p>The change in brightness and the length of the variations depend on the type of variable star in question. The luminosity can vary by anywhere from a fraction of a magnitude to many magnitudes. Likewise, the period (if there is one) can range from hours to years.</p>

CC BY-SA 3.0
2017-04-10T17:22:43.540Z
2017-04-10T17:22:43.540Z
HDE 226868
<p>Looking at the question longer-term, a star's brightness also changes as it evolves:</p>

<ul>
<li><p>starting possibly with some brightness of its initial accretion disc,</p></li>
<li><p>then as nuclear burning begins it becomes a true star (check out the Hertzsprung Russell diagram showing stellar evolution)</p></li>
<li><p>later in its life, depending mainly on its mass it can either evolve 
into a near-dead dwarf, which will be increasingly dim</p></li>
<li><p>alternatively, heavier stars go supernova and become so bright as to 
briefly outshine galaxies before becoming dimmer again as neutron stars or black holes.  </p></li>
</ul>

<p>So to answer your question broadly - stars during their lifetimes do vary in brightness on a vast scale.</p>

<p>If interested further, I suggest you look up: </p>

<p><a href="https://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram</a></p>

<p><a href="https://en.wikipedia.org/wiki/Stellar_evolution" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Stellar_evolution</a></p>

CC BY-SA 3.0
2017-04-10T20:21:35.283Z
+1, though this is probably not what the OP had in mind.
pela
CC BY-SA 3.0
2017-04-10T22:36:06.263Z
Maybe not, but other readers might; and as it's worded I think the OP deserves to be shown that there's more to his question than he might have anticipated...?
iSeeker
CC BY-SA 3.0
2017-04-11T06:54:02.817Z
Good point [:](http://dof.dk))
pela
CC BY-SA 3.0
2017-04-11T07:26:01.677Z
It's a great answer! i love getting lost on wikipedia
Dan Wears Prada
CC BY-SA 3.0
2017-04-10T18:35:13.450Z
2017-04-13T12:13:26.027Z
2017-04-13T12:13:26.027Z
iSeeker
<p>All I could find on the internet was about how stars vary in brightness depending on their distance to Earth, temperature, type of star...</p>

<p>But my question is, can a star can change its brightness.</p>

CC BY-SA 3.0
2017-04-10T15:34:44.340Z
Wikipedia has an extensive list of the mechanisms of [variable stars](https://en.wikipedia.org/wiki/Variable_star).
pela
CC BY-SA 3.0
2017-04-10T17:35:32.100Z
This is either a one word "yes" or requires coverage of the full range of variable stars, which is too broad.
James K
CC BY-SA 3.0
2017-04-10T19:22:03.980Z
@JamesK Disagree, it is not too broad, as if the answer is not known to be "yes" you can just leave the question unanswered. That may be dissatisfying, but in this case the answer is "yes", so it doesn't matter.
called2voyage
<variable-star>
Do stars vary their own brightness?
Dan Wears Prada
# Do stars vary their own brightness?

(Asked by: username_0 on 2017-04-10)

All I could find on the internet was about how stars vary in brightness depending on their distance to Earth, temperature, type of star...

But my question is, can a star can change its brightness.

**Tags:** variable-star

> **Comments:**
> **username_1**: Wikipedia has an extensive list of the mechanisms of [variable stars](https://en.wikipedia.org/wiki/Variable_star).  
> **username_2**: This is either a one word "yes" or requires coverage of the full range of variable stars, which is too broad.  
> **username_3**: @username_2 Disagree, it is not too broad, as if the answer is not known to be "yes" you can just leave the question unanswered. That may be dissatisfying, but in this case the answer is "yes", so it doesn't matter.  

---

## 2 answers

### Answer by username_4 on 2017-04-10. Score: 4 | Accepted answer

They can, and some do. These stars are called [variable stars](https://en.wikipedia.org/wiki/Variable_star), because their luminosities *as observed from Earth* vary over time, often (though not always) in a regular period. Here are some broad categories:

* [**Pulsating stars**](https://en.wikipedia.org/wiki/Stellar_pulsations), where fluctuations lead to increases and decreases in size or temperature, which in turn produce changes in the star's brightness. Example: The oft-cited [Cepheid variables](https://en.wikipedia.org/wiki/Cepheid_variable).
* [**Eclipsing binary stars**](https://en.wikipedia.org/wiki/Binary_star#Eclipsing_binaries) involve two stars orbiting each other. When one passes between the other and Earth, the combined luminosity of the system appears to decrease, even though the stars' intrinsic luminosities are probably constant. Example: [Algol](https://en.wikipedia.org/wiki/Algol).
* So-called [**eruptive variables**](https://en.wikipedia.org/wiki/Variable_star#Eruptive_variable_stars) (often lumped together with [**cataclysmic variables**](https://en.wikipedia.org/wiki/Cataclysmic_variable_star), which are different) may have irregular outbursts caused by flares or other phenomena. Example: [Luminous blue variables (LBVs)](https://en.wikipedia.org/wiki/Luminous_blue_variable).

The change in brightness and the length of the variations depend on the type of variable star in question. The luminosity can vary by anywhere from a fraction of a magnitude to many magnitudes. Likewise, the period (if there is one) can range from hours to years.


---

### Answer by username_5 on 2017-04-10. Score: 3

Looking at the question longer-term, a star's brightness also changes as it evolves:

* starting possibly with some brightness of its initial accretion disc,
* then as nuclear burning begins it becomes a true star (check out the Hertzsprung Russell diagram showing stellar evolution)
* later in its life, depending mainly on its mass it can either evolve
  into a near-dead dwarf, which will be increasingly dim
* alternatively, heavier stars go supernova and become so bright as to
  briefly outshine galaxies before becoming dimmer again as neutron stars or black holes.

So to answer your question broadly - stars during their lifetimes do vary in brightness on a vast scale.

If interested further, I suggest you look up:

<https://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram>

<https://en.wikipedia.org/wiki/Stellar_evolution>

> **Comments:**
> **username_1**: +1, though this is probably not what the OP had in mind.  
> **username_5**: Maybe not, but other readers might; and as it's worded I think the OP deserves to be shown that there's more to his question than he might have anticipated...?  
> **username_1**: Good point [:](http://dof.dk))  
> **username_0**: It's a great answer! i love getting lost on wikipedia  

---

