# If the largest known star were as close as Proxima Centauri... **URL:** \ **Category:** Factual Questions\ **Created:** [December 4, 2016, 8:12pm UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861 "2016-12-04T20:12:24Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Nars\_Glinley](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nars_glinley/32/8177_2.png) [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)\ **Post date:** [December 4, 2016, 8:12pm UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/1 "2016-12-04T20:12:24Z")
Would it appear much different than any other star when viewed from Earth? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 4, 2016, 8:19pm UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/2 "2016-12-04T20:19:22Z")
You mean, aside from being a lot brighter? And naked eye, or through a telescope? ---
**Author:** ![Nars\_Glinley](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nars_glinley/32/8177_2.png) [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)\ **Post date:** [December 4, 2016, 8:21pm UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/3 "2016-12-04T20:21:58Z")
Not just brightness but apparent size. I was thinking about the naked eye. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [December 4, 2016, 9:12pm UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/4 "2016-12-04T21:12:03Z")
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. ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [December 4, 2016, 9:17pm UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/5 "2016-12-04T21:17:51Z")
What is the name of the largest known star, and how far away is it? What is its class, and brightness? ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [December 4, 2016, 9:24pm UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/6 "2016-12-04T21:24:46Z")
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. > **[VY Canis Majoris](https://en.wikipedia.org/wiki/VY_Canis_Majoris)** > > VY Canis Majoris (abbreviated to VY CMa) is an extreme oxygen-rich (O-rich) red hypergiant (RHG) or red supergiant (RSG) and pulsating variable star 1.2 kiloparsecs (3,900 light-years) from the Solar System in the slightly southern constellation of Canis Major. It is one of the largest known stars, one of the most luminous and massive red supergiants, and one of the most luminous stars in the Milky Way. > No evidence has been found that it is part of a multiple star system. Its great infrared (... ---
**Author:** ![Ignotus](https://avatars.discourse-cdn.com/v4/letter/i/ecc23a/32.png) [@Ignotus](https://boards.straightdope.com/u/Ignotus)\ **Post date:** [December 4, 2016, 9:26pm UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/7 "2016-12-04T21:26:02Z")
[Here’s](https://en.wikipedia.org/wiki/List_of_largest_stars) a list. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [December 4, 2016, 9:47pm UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/8 "2016-12-04T21:47:09Z")
> [@Nars\_Glinley](#): > > 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](https://en.wikipedia.org/wiki/Rigel) “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. ---
**Author:** ![Nars\_Glinley](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nars_glinley/32/8177_2.png) [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)\ **Post date:** [December 4, 2016, 9:52pm UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/9 "2016-12-04T21:52:19Z")
> [@Quartz](#): > > 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. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 4, 2016, 10:32pm UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/10 "2016-12-04T22:32:13Z")
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. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [December 4, 2016, 11:02pm UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/11 "2016-12-04T23:02:01Z")
> [@Chronos](#): > > 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. ---
**Author:** ![Ludovic](https://avatars.discourse-cdn.com/v4/letter/l/7ab992/32.png) [@Ludovic](https://boards.straightdope.com/u/Ludovic)\ **Post date:** [December 4, 2016, 11:08pm UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/12 "2016-12-04T23:08:40Z")
However, a [quasi-star](https://en.wikipedia.org/wiki/Quasi-star) looks like it would make the cut at 120 arcseconds. In addition to probably frying us. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 5, 2016, 12:02am UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/13 "2016-12-05T00:02:01Z")
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. ---
**Author:** ![Nars\_Glinley](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nars_glinley/32/8177_2.png) [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)\ **Post date:** [December 5, 2016, 12:28am UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/14 "2016-12-05T00:28:10Z")
> [@scr4](#): > > 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? ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [December 5, 2016, 11:32am UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/15 "2016-12-05T11:32:08Z")
> [@jtur88](#): > > It took me more than five minutes to look it up. It’s VY Canis Majoris. [URL=“[VY Canis Majoris - Wikipedia](https://en.wikipedia.org/wiki/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. ---
**Author:** ![Clark\_Cello](https://avatars.discourse-cdn.com/v4/letter/c/58f4c7/32.png) [@Clark\_Cello](https://boards.straightdope.com/u/Clark_Cello)\ **Post date:** [December 5, 2016, 12:42pm UTC](https://boards.straightdope.com/t/if-the-largest-known-star-were-as-close-as-proxima-centauri/773861/16 "2016-12-05T12:42:28Z")
> [@Darren\_Garrison](#): > > 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.