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Date: 15 Nov 2006 19:17:03
From:
Subject: Brightest stars, past and future
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Presently Sirius is the brightest star in our night sky, shining at
magnitude -1.4.
Disregarding novae, supernovae, and other variable stars, what star
preceded Sirius as the brightest in our night sky, before Sirius
approached near enough to claim the top spot? And which will take its
place in the future, perhaps thousands of years from now?
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Date: 16 Nov 2006 04:12:12
From: Sam Wormley
Subject: Re: Brightest stars, past and future
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allisonki@IGNmail.com wrote:
> Presently Sirius is the brightest star in our night sky, shining at
> magnitude -1.4.
>
> Disregarding novae, supernovae, and other variable stars, what star
> preceded Sirius as the brightest in our night sky, before Sirius
> approached near enough to claim the top spot? And which will take its
> place in the future, perhaps thousands of years from now?
>
Sirius B was once much brighter than Sirius A... some time ago.
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Date: 15 Nov 2006 20:53:05
From: Mij Adyaw
Subject: Re: Brightest stars, past and future
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> Sirius B was once much brighter than Sirius A... some time ago.
How long ago, and how do we know?
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Date: 16 Nov 2006 05:44:17
From: Sam Wormley
Subject: Re: Brightest stars, past and future
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Mij Adyaw wrote:
>> Sirius B was once much brighter than Sirius A... some time ago.
>
> How long ago, and how do we know?
>
>
Serious background about the Sirius system
http://www.astro.uiuc.edu/~kaler/sow/sirius.html
http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=sirius
http://en.wikipedia.org/wiki/Sirius
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Date: 17 Nov 2006 11:22:26
From: Llanzlan Klazmon the 15th
Subject: Re: Brightest stars, past and future
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"Mij Adyaw" <mij@TheBitBucket.com > wrote in news:R8S6h.12015$lv2.2089
@newsfe06.phx:
>
>> Sirius B was once much brighter than Sirius A... some time ago.
>
> How long ago, and how do we know?
>
>
The combination of the white dwarf's mass and current temperature allow an
estimate to be made based on the Stefan-Boltzmann law of radiation. This
would estimate the time since Siruis B threw off a planetary nebula to the
current time. I have seen estimates of around 120 million years for Sirius
B to have cooled to its' current temperature.
Klazmon.
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Date: 16 Nov 2006 06:05:34
From:
Subject: Re: Brightest stars, past and future
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Robert Welch wrote:
> S&T April 1998, p.59 "Once and Future Celestial Kings"
>
> In brief, Canopus was the brightest star until about 90000 years ago when
> Sirius took over the top spot. In about 210000 years, Sirius will be
> replaced by Vega.
>
> What I thought was especially interesting was that there were numerous times
> when Canopus was brightest, interspersed with periods when some other star
> got close enough to be brighter.
Thanks Robert, that's very interesting!
I am surprised that the "reigns" are so long - I would have thought
they would last just a few thousand years each.
I am also surprised to hear that S&T actually ran an interesting
article that recently.
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Date: 15 Nov 2006 22:21:51
From: Robert Welch
Subject: Re: Brightest stars, past and future
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I recall there being an article in Sky & Telescope which discussed that very
question. It took a while for me to track it down, but I found it.
S&T April 1998, p.59 "Once and Future Celestial Kings"
In brief, Canopus was the brightest star until about 90000 years ago when
Sirius took over the top spot. In about 210000 years, Sirius will be
replaced by Vega.
What I thought was especially interesting was that there were numerous times
when Canopus was brightest, interspersed with periods when some other star
got close enough to be brighter.
--
Robert Welch
Alameda, CA
<allisonki@IGNmail.com > wrote in message
news:1163647023.284689.69970@m73g2000cwd.googlegroups.com...
> Presently Sirius is the brightest star in our night sky, shining at
> magnitude -1.4.
>
> Disregarding novae, supernovae, and other variable stars, what star
> preceded Sirius as the brightest in our night sky, before Sirius
> approached near enough to claim the top spot? And which will take its
> place in the future, perhaps thousands of years from now?
>
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Date: 16 Nov 2006 06:50:44
From: Sam Wormley
Subject: Re: Brightest stars, past and future
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Robert Welch wrote:
> I recall there being an article in Sky & Telescope which discussed that very
> question. It took a while for me to track it down, but I found it.
>
> S&T April 1998, p.59 "Once and Future Celestial Kings"
>
> In brief, Canopus was the brightest star until about 90000 years ago when
> Sirius took over the top spot. In about 210000 years, Sirius will be
> replaced by Vega.
>
> What I thought was especially interesting was that there were numerous times
> when Canopus was brightest, interspersed with periods when some other star
> got close enough to be brighter.
Thanks Robert.
-Sam
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Date: 16 Nov 2006 15:29:21
From: Brian Tung
Subject: Re: Brightest stars, past and future
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Robert Welch wrote:
> What I thought was especially interesting was that there were numerous
> times when Canopus was brightest, interspersed with periods when some
> other star got close enough to be brighter.
That is because Canopus is relatively far away but intrinsically bright.
It's about 310 light-years away, so even if it were moving at the fairly
brisk rate of 100 km/s relative to us *and* doing so either directly
toward us or away from us, it would still take the sizable part of a
million years for it to either brighten or dim by a magnitude. In fact,
I don't think it is either moving at 100 km/s relative to us *or* doing
so either directly toward us or away from us.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 18 Nov 2006 09:42:28
From: Paul Schlyter
Subject: Re: Brightest stars, past and future
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In article <ejis8h$6mq$1@praesepe.isi.edu >, Brian Tung <brian@isi.edu> wrote:
> Robert Welch wrote:
>> What I thought was especially interesting was that there were numerous
>> times when Canopus was brightest, interspersed with periods when some
>> other star got close enough to be brighter.
>
> That is because Canopus is relatively far away but intrinsically bright.
> It's about 310 light-years away, so even if it were moving at the fairly
> brisk rate of 100 km/s relative to us *and* doing so either directly
> toward us or away from us, it would still take the sizable part of a
> million years for it to either brighten or dim by a magnitude. In fact,
> I don't think it is either moving at 100 km/s relative to us *or* doing
> so either directly toward us or away from us.
It's moving 20.5 km/s away from us. Since its distance is 310 light-years,
it would have to move away 180 light-years, to 490 light-years distance,
before having dimmed one magnitude. Moving away that much at 20.5 km/s
would take some 2.6 million years.
Bright massive stars such as Canopus evolve rapidly, in millions
rather than billions of years. Perhaps Canopus will change its apparent
brightness significantly due to its own evolution rather than by moving
away from us?
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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Date: 18 Nov 2006 08:29:35
From: Brian Tung
Subject: Re: Brightest stars, past and future
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Paul Schlyter wrote:
> Bright massive stars such as Canopus evolve rapidly, in millions
> rather than billions of years. Perhaps Canopus will change its apparent
> brightness significantly due to its own evolution rather than by moving
> away from us?
I have heard estimates that Canopus's mass is about eight solar masses.
If that is true, then its lifetime should be in the tens of millions of
years. But being a supergiant, it may not get much instrinsically
brighter than it is now (except as a supernova). Perhaps we'll be
better able to answer this question in a couple of more decades, as we
learn more about similar stars.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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