<p>A typical Type II supernova has a peak absolute magnitude of -17. Betegeuse is ~170 pc away, so its supernova would be 289 times dimmer, corresponding to a magnitude increase of 6.15, so its apparent magnitude would be ~-10.85, which is slightly dimmer than the full moon, but would appear brighter as it would appear as a point source.</p>
<p>Venus, which peaks at magnitude -4.6, can cast shadows, albeit very faint ones; as it is similar to a point source, we can extrapolate to Betelgeuse to conclude that it definitely could, but not at day as the Sun would outshine it by a factor of over 1000000. Even if the Sun were behind clouds, it would not be able to cast any shadows, just like how the brighter Moon can't do so either.</p>

CC BY-SA 4.0
2022-05-31T19:06:59.630Z
2022-05-31T19:06:59.630Z
WarpPrime
<p>Popular science <a href="https://www.forbes.com/sites/startswithabang/2020/01/23/this-is-what-well-see-when-betelgeuse-really-does-go-supernova/?sh=70c2d84243a2" rel="nofollow noreferrer">articles</a> suggest that when Betelgeuse goes supernova, for some days it would appear as bright as the full moon.  But I have no intuition about a celestial <em>point source</em> that bright.</p>
<ul>
<li>Would staring at it for some time risk eye damage?</li>
<li>With the sun behind clouds and the supernova unobstructed, could it cast obvious shadows in daytime?</li>
<li>Would it affect weather forecasts' UV index (risk of sunburn)?</li>
<li>Might other analogies hint at what optical phenomena it might produce?</li>
</ul>

<supernova><betelgeuse><brightness>
How bright would Betelgeuse's supernova appear?
Camille Goudeseune
# How bright would Betelgeuse's supernova appear?

(Asked by: username_0 on 2022-05-31)

Popular science [articles](https://www.forbes.com/sites/startswithabang/2020/01/23/this-is-what-well-see-when-betelgeuse-really-does-go-supernova/?sh=70c2d84243a2) suggest that when Betelgeuse goes supernova, for some days it would appear as bright as the full moon. But I have no intuition about a celestial *point source* that bright.

* Would staring at it for some time risk eye damage?
* With the sun behind clouds and the supernova unobstructed, could it cast obvious shadows in daytime?
* Would it affect weather forecasts' UV index (risk of sunburn)?
* Might other analogies hint at what optical phenomena it might produce?

**Tags:** supernova, betelgeuse, brightness

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## 1 answers

### Answer by username_1 on 2022-05-31. Score: 3 | Accepted answer

A typical Type II supernova has a peak absolute magnitude of -17. Betegeuse is ~170 pc away, so its supernova would be 289 times dimmer, corresponding to a magnitude increase of 6.15, so its apparent magnitude would be ~-10.85, which is slightly dimmer than the full moon, but would appear brighter as it would appear as a point source.

Venus, which peaks at magnitude -4.6, can cast shadows, albeit very faint ones; as it is similar to a point source, we can extrapolate to Betelgeuse to conclude that it definitely could, but not at day as the Sun would outshine it by a factor of over 1000000. Even if the Sun were behind clouds, it would not be able to cast any shadows, just like how the brighter Moon can't do so either.


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