A question about supernovas and the Crab Nebula

[soul]

It is said that supernovas can only come from red giants. If that is so then how come the supernova that occurred approximately 1000 years ago was seen to have happened from a blank piece of sky in the constellation Taurus. It was the "quest star" according to the Chinese. Wouldnt a red giant have been visible or any star for that matter but especially a red giant in that part of the sky BEFORE the supernova. I mean after all a red giant at that close proximity (the crab nebula is not that far away in cosmic terms) would have been seen would it not ? This question been on my mind some time. Please help to answer.

 

[thalion]

^<br />Good post; mine just follows up on what you did.<br /><br />IIRC, a red supergiant like Betelguese or Antares typically has an absolute magnitude of about -5.5. Using a ballpark estimate for the Crab Nebula's distance at 6500 ly (~2000 pc), and the familiar distance modulus formula of:<br /><br />m-M = 5logD-5<br /><br />where:<br /><br />D = parsecs<br />m = apparent magnitude<br />M = absolute magnitude<br /><br />--I derived a distance modulus of 11.5 magnitudes for the nebula. Assuming its progenitor had an absolute magnitude of -5.5, it would have been only magnitude 6, near the commonly-held threshold of naked-eye vision. This is of course neglecting interstellar dust absorping its light, which I'm guessing would knock it down at least another magnitude or two.<br /><br />In short--its progenitor was probably quite inconspicuous.

 

[soul]

interesting responses...im learning more everyday. I just thought because it was not all that far in cosmic terms it would have been seen being such a big red super giant star. My mistake. Thanks for the responses. <br /><br />Just curious are you both astronomers or just very informative people in this area ? You both seem to know your stuff.

 

[jurgens]

hey, if you want to learn some about astronomy, check out this site, start at week 1 and go till week 10!<br /><br />http://spiff.rit.edu/classes/phys301/phys301.html

 

[thalion]

<<Just curious are you both astronomers or just very informative people in this area ? You both seem to know your stuff. >><br /><br />"I'm just a guy." <img src="/images/icons/wink.gif" /><br /><br />I've never even taken a college astronomy course; I'm just someone who's been interested in the field for most of my life, and who has been a voracious reader of the available material. I'm also an amateur astronomer, though these days it's more armchair (hides).