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Stars brightness

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Stars brightness was created by Bill_H

Hope I'm in the right place. While the sky is not permitting viewing, as usual, I'm spending time on Astrosuite spherical projection. I'm currently looking at two stars, Sirius and Rigel. It tells me that Sirius has a mag of -1.4 and a distance of 7 light years, while Rigel has a mag of .12 and a distance of 913 light years. Obviously the difference in distance isn't the reason for a comparatively small difference in magnitude - or is it? What is the cause of the difference. I'm assuming here that Rigel must be a huge star of sorts? If so what type is it and what type is Sirius?
Astronomers do it with the lights off.
18 years 3 weeks ago #7463

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Replied by Bill_H on topic Re: Stars brightness

Sorry folks, I stupidly hit the submit button twice :oops:
Bill.
Astronomers do it with the lights off.
18 years 3 weeks ago #7465

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Replied by James Butler on topic Re: Stars brightness

Stars have two magnitudes. The first being the apparent magnitude as viewed from the earth. The second is the absolute magnitude, that is the magnitude of the star if it were 10 parsecs from the earth. The absolute magnitude tells you how bright the star really is.

You are correct in noting that Sirius is very close in astronomical terms and is therefore the brightest star in the sky. Sirius is only twice the mass of the Sun and is a double star.

Rigel is a super giant and these have diameters hundreds of times bigger than the sun. Rigel is also a triplet of three stars which might account for added brightness and its variability. Super giants are fast burners and go out with a bang in the form of a super nova.
James Butler

Astronomy Diary - astronomy-diary.blogspot.com/
18 years 3 weeks ago #7467

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Replied by Bill_H on topic Re: Stars brightness

Many thanks James.
Astronomers do it with the lights off.
18 years 3 weeks ago #7469

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Replied by Keith g on topic Re:

Bill, adding on to what James has said, If Rigel was located at the same distance that Sirius is, it probably would blaze at about magnitude -5 or so, even brighter that Venus! :shock:

It's like looking at a cars headlight about half a mile away and looking straight into your light at your front door!, the light at the front door appears brighter because of your short distance from it, the headlight is overall dimmer from your perspective, even though it is many times brighter than the door light!

Imaginr wearing sunglasses at night when rigel rises over the horizon from 7 lightyears away!, you could probably cook yourself a nice slice of toast!! :P

Keith..
If a telescope can fit into your backyard it's too small. If you can't move it, it's too big." -- John Dobson
18 years 3 weeks ago #7575

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