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-   -   If the largest known star were as close as Proxima Centauri... (http://boards.straightdope.com/sdmb/showthread.php?t=812873)

Nars Glinley 12-04-2016 02:12 PM

If the largest known star were as close as Proxima Centauri...
 
Would it appear much different than any other star when viewed from Earth?

Chronos 12-04-2016 02:19 PM

You mean, aside from being a lot brighter? And naked eye, or through a telescope?

Nars Glinley 12-04-2016 02:21 PM

Not just brightness but apparent size. I was thinking about the naked eye.

Quartz 12-04-2016 03:12 PM

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.

jtur88 12-04-2016 03:17 PM

What is the name of the largest known star, and how far away is it? What is its class, and brightness?

jtur88 12-04-2016 03:24 PM

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

Ignotus 12-04-2016 03:26 PM

Here's a list.

wolfpup 12-04-2016 03:47 PM

Quote:

Originally Posted by Nars Glinley (Post 19828941)
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.

Nars Glinley 12-04-2016 03:52 PM

Quote:

Originally Posted by Quartz (Post 19829050)
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.

Chronos 12-04-2016 04:32 PM

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.

scr4 12-04-2016 05:02 PM

Quote:

Originally Posted by Chronos (Post 19829208)
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.

Ludovic 12-04-2016 05:08 PM

However, a quasi-star looks like it would make the cut at 120 arcseconds. In addition to probably frying us.

LSLGuy 12-04-2016 06:02 PM

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.

Nars Glinley 12-04-2016 06:28 PM

Quote:

Originally Posted by scr4 (Post 19829249)
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?

Darren Garrison 12-05-2016 05:32 AM

Quote:

Originally Posted by jtur88 (Post 19829084)
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.

Clark Cello 12-05-2016 06:42 AM

Quote:

Originally Posted by Darren Garrison (Post 19830003)
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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