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Githyanki
2014-Jun-07, 09:02 PM
Just how bright would Betelgeuse be if it were to go supernova? (from our perspective in the night-sky)

Hornblower
2014-Jun-07, 09:24 PM
Somewhere about -10, about the brightness of the Moon at half phase, but in the form of a dazzling point of light. The glint of the Sun on a 4-inch silver ball at a distance of some 100 feet would be a rough approximation of the appearance.

antoniseb
2014-Jun-07, 09:31 PM
I get that it would be about magnitude -10. This is based on a chart showing that a type II SN will get up to about -17 absolute magnitude, and that Betelgeuse is 640 light years away.
That would make it about 1/6th as bright as a Full Moon. It would stand out in the sky very distinctly, but it wouldn't throw much of a shadow or blind you, or look like a second Sun.

StupendousMan
2014-Jun-07, 11:23 PM
I agree on the magnitude, but I do think that it would cast a distinct shadow. Under very good conditions, I've seen a shadow cast by Venus, and this would be, oh, roughly 250 times brighter than Venus.

Githyanki
2014-Jun-08, 12:20 AM
Thanks; I have done some reading on it and Betelgeuse is part of the Orion Association which includes some of the stars in the belt. They are extremely massive being type O and **; Betelgeuse got ejected and is falling at 30KM/second leaving a shock in the interstellar wind.

Also, I like the train-station at West Falls Church. I used to use it a lot when I was in D.C. (Herndon).

Edit: the number of posts I have is how many light-years Betelgeuse is from us!

chornedsnorkack
2014-Jun-08, 08:09 AM
I get that it would be about magnitude -10.

That would make it about 1/6th as bright as a Full Moon.
Um, my standard number for full Moon is -12,74, and -10 is less than 1/12th of that.
Best table of Moon brightness I could find is the 1916 one from Russell:
http://articles.adsabs.harvard.edu//full/1916ApJ....43..103R/0000114.000.html
1/6 of full Moon is about 70...80 degrees, so slightly gibbous (the sides of Moon are different albedo because of seas)
half Moon is 1/9 full when waxing, and 1/10 when waning
-10 should be about 100 degrees from full, so almost half moon
Moon at 30 degrees elongation is about -6,7
Unfortunately Russell does not pursue Moon further towards new (remember, Mercury never passes 28 degrees elongation, and its visible, and people boast of having seen Venus through conjunction at 8 degrees elongation)

It would stand out in the sky very distinctly, but it wouldn't throw much of a shadow
As pointed out, Venus throws shadows.
Look at it this way: combined starlight is estimated at -5 or so. Skyglow is similar magnitude, so normal night illumination is about -6 over sky.

Light of Venus at -4,5 would add something like 25 % to normal darkness of night. Supposedly people can perceive the contrast with shadows.
But Moon at 30 degrees elongation and -6,7 would add 200 % light to the proposed -6 (What is your precise number for the magnitude of darkness of night due to stars and skyglow?). So that should be clear shadows.

In the absence of twilight, against background of stars and skyglow, at which phase and magnitude does a narrow crescent Moon start to cast shadows? -6 (2 nights from new)? -7 (3 nights from new)?

or blind you
-10 would be 1/12 of full Moon. But that full Moon is an extended object... say 900 pixels of eye. A supernova is point light source, so 1 pixel. You would arrive at 75 times the surface brightness of Moon, which is about 10 times surface brightness of sunlit snow. Is it safe, after all?

-10 is 8,5 magnitudes brighter than the -1,46 of Sirius A. So youd have to collect 2500 times light - not counting light loss in telescope. 50 times the aperture of the eye is 300 mm. But 400+ mm reflectors are among large Dobsonians which amateurs boast of, and professional telescopes as well.
If you magnify Sirius A by 8,5 magnitudes then B reaches -0,2, because the contrast is 9,7 magnitudes. Procyon A and B contrast is 10,4 magnitudes (+0,34 and +10,7).

What do you regard as safe magnitude to intently stare at a bright star through a big telescope, for example in search of dim companions?

Marakai
2014-Jun-08, 09:54 AM
Would it be thread hijacking to ask, by extension, who of known candidates would produce the brightest SN?

Meaning, if we took star size and distance, etc, which of the giants that actually *would* go supernova would produce the the equivalent of [moon|sun|venus]?

If I remember the chapter in Phil's "This is the way the world will end", none of the candidates are close enough that the brightness would be terminal.

antoniseb
2014-Jun-08, 12:57 PM
... who of known candidates would produce the brightest SN?... if we took star size and distance, etc, which of the giants that actually *would* go supernova would produce the the equivalent of [moon|sun|venus]? ...
Probably Betelgeuse, however it is possible that an object further away that Betelgeuse has gone undetected but would still be brighter. If a pair of massive enough in-spiraling white dwarf were to merge, that would result in a Type Ia SN, which tend t be about 3 magnitudes brighter than the Type II that Betelgeuse would be, but unlike Betelgeuse, before the explosion they would be a dim unremarkable object in the sky.

antoniseb
2014-Jun-08, 01:09 PM
... As pointed out, Venus throws shadows. ...
I have read that Venus throws shadows, but try as I might, even on dark mountain tops on Moonless nights, with white paper on the ground, *I* have never seen my shadow from Venus. I'm not saying it doesn't happen, but I have tried and not seen it. I've also looked for my shadow from a half Moon. It is there, but as I said in my post (#3 above), it is not much of a shadow.
Concerning whether it would be 1/6 or 1/12 (or some other number) of the full Moon, you gave the apparent magnitude of the full Moon to 4 significant digits, but variations in the Moon's distance from the Earth mean you should only use 2. Further, I gave 10 as the guessed brightness, but anywhere from 9.5 to 10.4 is plausible, and outside that range a bit is possible.

Anyway, thanks for your efforts to give improved numbers.


Concerning blindness... you can't get that light to focus in your eye to better than 3 arcseconds. Unless you were to somehow hold your eye dead-still (which it won't do without training), you will be illuminating a stream of rods and cones, but never long enough to damage them.

chornedsnorkack
2014-Jun-08, 01:34 PM
Meaning, if we took star size and distance, etc, which of the giants that actually *would* go supernova would produce the the equivalent of [moon|sun|venus]?

If I remember the chapter in Phil's "This is the way the world will end", none of the candidates are close enough that the brightness would be terminal.

There are now no supernova precursors near enough to be equivalent of Sun. The standard candle brightness of type I supernova is -19,3. Which means type I supernova would match the brightness of Sun at 1 lightyear. There are no stars so near.

Sirius B, should it explode as a Type I supernova, would be 70 times dimmer than Sun. It is not, however, suspected of being anywhere ready to explode as a supernova.

In order to be brighter than full Moon, a type I supernova would have to be nearer than Betelgeuse.

Of course, it need not be conspicuous. But would a type I supernova precursor within the distance to Betelgeuse be detectable at present?

Romanus
2014-Jun-08, 05:47 PM
Antares is (probably) a little closer than Betelgeuse, so its SN would be slightly brighter. Then again, after SN 1987A told us that red supergiants are not the only possible massive-star progenitors, I think we should keep an open mind.\

In my op, the next bright galactic SN in the night sky will probably be some neglected distant supergiant that'll have us scratching our heads. Note that if the progenitor to the Crab Nebula was a typical red supergiant star, it was only about 5th magnitude at the nebula's distance, and that's neglecting interstellar absorption.

chornedsnorkack
2014-Jun-08, 08:44 PM
Antares is (probably) a little closer than Betelgeuse, so its SN would be slightly brighter. Then again, after SN 1987A told us that red supergiants are not the only possible massive-star progenitors, I think we should keep an open mind.\


How many Type II supernovae since 1987A have had known progenitors?

StupendousMan
2014-Jun-08, 09:54 PM
How many Type II supernovae since 1987A have had known progenitors?

The progenitors of at least 17 core-collapse SNe have _some_ sort of constraint based on pre-explosion imaging, according to

http://adsabs.harvard.edu/abs/2014arXiv1405.6626W

Marakai
2014-Jun-08, 11:10 PM
There are now no supernova precursors near enough to be equivalent of Sun. The standard candle brightness of type I supernova is -19,3. Which means type I supernova would match the brightness of Sun at 1 lightyear. There are no stars so near.

Sirius B, should it explode as a Type I supernova, would be 70 times dimmer than Sun. It is not, however, suspected of being anywhere ready to explode as a supernova.

In order to be brighter than full Moon, a type I supernova would have to be nearer than Betelgeuse.

Of course, it need not be conspicuous. But would a type I supernova precursor within the distance to Betelgeuse be detectable at present?

Thanks for the info. Yet, I feel vaguely disappointed. No kaboom, an earth-shattering kaboom...

Ara Pacis
2014-Jun-09, 04:26 AM
How would WR 104 (http://en.wikipedia.org/wiki/WR_104) compare if and when it pops?

chornedsnorkack
2014-Jun-09, 07:22 AM
The progenitors of at least 17 core-collapse SNe have _some_ sort of constraint based on pre-explosion imaging, according to

http://adsabs.harvard.edu/abs/2014arXiv1405.6626W

But these look like being constraints on the age of star cluster where the supernova exploded.

How many supernova progenitors have a known spectral class? Sanduleak -69 202 was B3 Ia. Any others?

StupendousMan
2014-Jun-09, 11:31 AM
Go to the Astrophysics Data Service search site:

http://adsabs.harvard.edu/abstract_service.html

Enter the words "supernova progenitor HST" into the "Abstract words" box. Click on the "Send query" button.

You can read just as well as I can.

chornedsnorkack
2014-Jun-09, 12:49 PM
As of May 2014 (http://arxiv.org/pdf/1405.4863v2.pdf), there were 4 known "IIb" supernova progenitors. SN1993J, 2008ax, 2011dh and 2013dh.
1993J was about K0, with uncertainty due to reddening from G2 to K5. M can be ruled out.

SN2013ej (IIP), is suspected of having been M.
SN2008bk (also IIP) also was a "red giant".

WayneFrancis
2014-Jun-11, 06:48 AM
You'd be surprised at the shadows we can see. A few months ago I was walking on the beach with my friend and on the way back we sat down on a bench for a while just talking while looking at the ocean and that was the first time I've notice that Venus produced a very visible glitter path on the water. I would think that if the moonlight wasn't also coming from the same direct that just as I could see shadows from the moonlight I'd be able to detect a faint shadow from the light reflected off of Venus.

Githyanki
2014-Jun-20, 06:24 PM
Technically, everything casts a shadow; whether or not we see it is another matter.

Did I read it right? A supernova at one LY is as bright as our sun? That negates a lot of science-fiction. SNs are no threat to life save for an gamma-ray blast.