# Thread: fun facts about the M82 supernova

1. ## fun facts about the M82 supernova

(Assuming current apparent magnitude of 11, and a distance of 12 million light years.)

If this supernova was right in the middle of the Oort cloud, about 1/3 light years away from Earth, it would appear as bright as the Sun.

At 200 light years away (a bit closer than Spica) it would appear as bright as the full Moon.

At 40k light years (near half-way across our galaxy) it would appear as bright as Sirius.

Its luminosity in absolute terms is 1/2 billion times greater than the Sun.

2. ## The Following 5 Users Say Thank You to Florin Andrei For This Useful Post:

Alantracy (01-31-2014),galileo36 (01-30-2014),Lowjiber (02-05-2014),mandomom (02-04-2014),tkeles (02-04-2014)

3. ## Re: fun facts about the M82 supernova

Crazy.....thanks for the info!

5. ## Re: fun facts about the M82 supernova

I haven't been able to find any sources for luminosity calculations. Can you tell me how that was calculated or let us know where you got this info? just curious,
Thanks,
Julie

6. ## Re: fun facts about the M82 supernova

Sure. Once you know the apparent magnitude and the distance, you can calculate the absolute magnitude.

Absolute magnitude - Wikipedia, the free encyclopedia

For the supernova, the absolute magnitude is about -16.8, assuming an apparent magnitude of 11 (it peaked at 10.5 actually) and a distance of 12 million ly.

Plug that data into the inverse formula and you get the distance required to obtain various apparent magnitudes. E.g., the distance where this absolute magnitude would look like the apparent magnitude of the Sun (it turns out it's about 1/3 ly).

Or you could use an easy online calculator:

CalcTool: Magnitude and Luminosity calculator

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Rosetta (02-05-2014)

8. ## Re: fun facts about the M82 supernova

Of course, these are the theoretical apparent magnitudes. In the real universe supernovae are nearly always subject to considerable extinction from the intervening gas and particularly dust between them and us. This is often cited as the reason why very few supernovae in our own galaxy have ever been directly observed from Earth. Even the current supernoa in M82 suffers from and is distinctly reddened, loosing a couple of magnitudes to extinction. Were it not so, it might have approached the faint end of 8th magnitude, rather than 10th.

Brooksobs

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Rosetta (02-05-2014)

10. ## Re: fun facts about the M82 supernova

Thanks for your comments. One other thing I was uncertain about was that shortly after it was observed, it was predicted that the maximum magnitude would be within a week or so. Do you know how that could be predicted?
Julie

11. ## Re: fun facts about the M82 supernova

Originally Posted by Rosetta
Thanks for your comments. One other thing I was uncertain about was that shortly after it was observed, it was predicted that the maximum magnitude would be within a week or so. Do you know how that could be predicted?
Julie
Once a few initial spectra of SN2014J were obtained it was possible to determine several aspects of the supernova. First off, the spectra was typical of a type Ia supernova about a week from maximum. The distance modulus to M82 is pretty well established; the maximum brightness of type Ia supernovae is well known; the reddening of the supernova's spectra gave a key to the amount of absorption between us and it, allowing for a correction. Thus, citing a rough date of maximum, as well as probable peak magnitude, became rather straight forward for the pros.

BrooksObs

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