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Old 12-04-2016, 03:12 PM
Nars Glinley Nars Glinley is offline
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If the largest known star were as close as Proxima Centauri...

Would it appear much different than any other star when viewed from Earth?
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Old 12-04-2016, 03:19 PM
Chronos Chronos is offline
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You mean, aside from being a lot brighter? And naked eye, or through a telescope?
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Old 12-04-2016, 03:21 PM
Nars Glinley Nars Glinley is offline
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Not just brightness but apparent size. I was thinking about the naked eye.
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Old 12-04-2016, 04:12 PM
Quartz Quartz is offline
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THe largest known star has a diameter measured in light-seconds. Proxima Centauri is over 4 light years away. That's a factor of millions.
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Old 12-04-2016, 04:17 PM
jtur88 jtur88 is offline
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What is the name of the largest known star, and how far away is it? What is its class, and brightness?
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Old 12-04-2016, 04:24 PM
jtur88 jtur88 is offline
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It took me more than five minutes to look it up. It's VY Canis Majoris.

It is 100,000 times less dense than the earth's atmosphere, which makes it problematic to determine where the star's "surface" is, and how far that is from the center. The star loses gravitational control of its material at the edge.

https://en.wikipedia.org/wiki/VY_Canis_Majoris

Last edited by jtur88; 12-04-2016 at 04:27 PM.
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Old 12-04-2016, 04:26 PM
Ignotus Ignotus is offline
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Here's a list.
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Old 12-04-2016, 04:47 PM
wolfpup wolfpup is offline
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Quote:
Originally Posted by Nars Glinley View Post
Would it appear much different than any other star when viewed from Earth?
In short, yes. I didn't work through any of the detailed calculations, but one can quickly see this just by taking Rigel A as an example and doing some quick guesstimates. Rigel A is described as "a blue-white supergiant that is estimated to be anywhere from 120,000 to 279,000 times as luminous as the Sun"; it's the seventh brightest star in the sky despite being 863 light-years away.

By contrast, Sirius A has 25 times the luminosity of the sun and is only twice as far away as Proxima Centauri, and the combination makes it by far the brightest star in the sky.

Anyway by my rough guesstimates, its absolute magnitude tells us that at about 32 ly, Rigel would be intense and unmistakeable -- 40 times brighter than Venus at its brightest, which itself is 15 times brighter than Sirius. At the distance of Proxima Centauri, it would dominate the night sky and, though still only visible as a point of light, would be bright enough to provide nighttime illumination and cast a shadow, comparable to the moon.
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Old 12-04-2016, 04:52 PM
Nars Glinley Nars Glinley is offline
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Quote:
Originally Posted by Quartz View Post
THe largest known star has a diameter measured in light-seconds. Proxima Centauri is over 4 light years away. That's a factor of millions.


If my math is right (and it probably isn't), it's about 6,666 light-seconds in diameter.
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Old 12-04-2016, 05:32 PM
Chronos Chronos is offline
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Which still makes it about 1/300 degree (or 12 arcseconds) across. That's resolvable with a ground-based telescope, but only an extremely good one (atop Mauna Kea, the best observing site on the surface of the planet, the atmosphere imposes a limit of at best about 0.4 arcseconds). By eye? Not a chance.

Last edited by Chronos; 12-04-2016 at 05:32 PM. Reason: Corrected math error
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Old 12-04-2016, 06:02 PM
scr4 scr4 is offline
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Quote:
Originally Posted by Chronos View Post
Which still makes it about 1/300 degree (or 12 arcseconds) across. That's resolvable with a ground-based telescope, but only an extremely good one (atop Mauna Kea, the best observing site on the surface of the planet, the atmosphere imposes a limit of at best about 0.4 arcseconds). By eye? Not a chance.
If I did my math right, it's actually about 5 arcseconds. (VY Canis Majoris: 990 million km diameter, divided by 1.3 parsec, convert to arcsecond.)

And a decent amateur telescope should show it as a finite size disk. A good quality >4" refractor can resolve 1 arcsecond on a good day.

Last edited by scr4; 12-04-2016 at 06:02 PM.
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Old 12-04-2016, 06:08 PM
Ludovic Ludovic is offline
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However, a quasi-star looks like it would make the cut at 120 arcseconds. In addition to probably frying us.
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Old 12-04-2016, 07:02 PM
LSLGuy LSLGuy is offline
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I recall an artists conception, perhaps from NASA's APoD site, that was supposedly a realistic rendering of the Sun as seen from Pluto. I just searched but did not find it.

As I recall their description was something like: no discernable disc, but almost as bright as looking into a welding arc.

Rigel A in Proxima Centuari's place would probably be similar.
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Old 12-04-2016, 07:28 PM
Nars Glinley Nars Glinley is offline
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Originally Posted by scr4 View Post
If I did my math right, it's actually about 5 arcseconds. (VY Canis Majoris: 990 million km diameter, divided by 1.3 parsec, convert to arcsecond.)

And a decent amateur telescope should show it as a finite size disk. A good quality >4" refractor can resolve 1 arcsecond on a good day.


According to the wiki above, 990 million km is the radius. So, 10 arcseconds?
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Old 12-05-2016, 06:32 AM
Darren Garrison Darren Garrison is offline
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Quote:
Originally Posted by jtur88 View Post
It took me more than five minutes to look it up. It's VY Canis Majoris.
Sorry if I' sound rude, but I'm curious what method it took to take you more than 5 minutes? The "typing 'largest known star' in Google and hitting the enter key" method takes less than 5 seconds.
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Old 12-05-2016, 07:42 AM
Clark Cello Clark Cello is offline
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Quote:
Originally Posted by Darren Garrison View Post
Sorry if I' sound rude, but I'm curious what method it took to take you more than 5 minutes? The "typing 'largest known star' in Google and hitting the enter key" method takes less than 5 seconds.
I don't want to speak for jtur88, but I don't think his point was "This was difficult", but was "I missed the edit window, which is why I have double-posted".

So, after he hit "submit" on his first part, the entire process of thinking "Hmmm, this would probably be simple to just look up myself", then googling it, then reading a few things about it, would easily cause him to miss the edit window.
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