# Sun ,Barnards star ,Sirius A and hot blue Supergiant Rigel

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#### remcot

##### Guest
As seen from a Hypothetical planet at 1 lightyear. Can you explain with kind of visible magnitude they shine at the so called planet or moon at 1 lightyear distance? I like this question because they are a totally different kind of stars. Thanks. remcot.

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#### doubletruncation

##### Guest
1 light year = 0.307 pc, so if you know the absolute magnitude (Mv) of the star the apparent magnitude from 1 light year would be Mv + 5log(0.307) - 5 = Mv - 7.57<br /><br />So here are the absolute magnitudes (found from various sources on the internet) and the corresponding apparent mag from 1 light year:<br /><br />[star] [abs-mag] [app-mag from 1 ly]<br />Sun 4.8 -2.8<br />Barnard's star 13.2 5.6<br />Sirius 1.4 -6.2<br />Rigel -8.1 -15.7<br /> <div class="Discussion_UserSignature"> </div>

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#### doubletruncation

##### Guest
Just to put a sense of scale to these numbers, if each of these stars were 1 light year away from us, then Rigel would be almost 20 times brighter than the full moon, Sirius would be about 6 times brighter than Venus at its brightest (or as bright as a crescent moon), the Sun would be about as bright as Jupiter, and Barnard's star would be barely visible to the naked eye from a very dark site. <div class="Discussion_UserSignature"> </div>

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#### remcot

##### Guest
Is Rigel at 1 lightyear distance shining as bright as Venus is shining in our morning or evening sky? He was shining like a (very) bright star at previous years autumm.

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#### remcot

##### Guest
Can you tell me that truncation? Thanks.

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#### doubletruncation

##### Guest
If it were 1 light year away from us, Rigel would actually be much much brighter than Venus (imagine taking all the light from the full moon, compressing it into a point of light like a star, and multiplying it by 20). As crazzyeddie mentioned, it would almost be too bright to look at. If Sirius were only 1 light year away from us, it too would also be brighter than Venus ever gets (but only 6 times brighter than it). <div class="Discussion_UserSignature"> </div>

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#### remcot

##### Guest
At this moment one of the voyager spacecraft has reached twice Plutos distance from the Sun. If we place the voyager spacecraft at the (same) distance of the (surface) from Rigel as it is at this moment from the surface of our little Sun ,will it be in near darkness then? Will Rigel be bright enough to illuminate the Voyager spacecraft then or will it be absolute dark then? Can you explain that? Big thanks. remcot.

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#### doubletruncation

##### Guest
If voyager were a light year away from Rigel, it would be lit up quite nicely (if you're ever out in the middle of nowhere on nights with and without the full moon you can really see that the full moon lights things up quite a bit). In fact voyager is nowhere near 1 light year away from the sun. It is more like 0.1% of a light year away from the Sun (0.00039 parsecs). If voyager were that same distance away from Rigel, it would have an apparent magnitude of<br />-8.1 + 5*log(0.00039) - 5 = -30<br /><br />That's brighter than the Sun is when viewed from the Earth. So yes, definitely the voyager spacecraft would be lit up quite a bit if it were 0.1% of a light year from Rigel. <div class="Discussion_UserSignature"> </div>

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#### remcot

##### Guest
What if you have travelled to Rigel in a (hypothetical)spaceship and you get out of the spaceship for a spacewalk at a distance from Rigel like Venus is to the Sun (less than 1 astronomical unit) will that be dangerous or not? Will it be warm then? Can you try to explain that? Thanks.

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#### qso1

##### Guest
It would be dangerous enough to do that around the sun assuming current or near term projected technology were employed by the craft and crew. Far more dangerous to do around Rigel I would think.<br /><br />But if one can travel to Rigel in the first place, one may have overcome the barriers currently associated with something like taking a spacewalk at Venus distance from Rigel.<br /><br />For one thing, with a diameter over 60 million miles, you would only be 7 million miles from Rigels surface on average. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

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#### remcot

##### Guest
I have 2 last questions:1 Will it ever be possible to go to the surface of the hot supergiant stat Rigel ,and make a spacewalk there? 2: How will it be on a (hypothetical) planet that is orbiting Rigel at 0,13 AU distance from the surface of Rigel (2 times more close than Mercury is to the Sun) What kind of experience will it be to land and walk on such a (hypothetical) planet at 0,13 au from the surface of Rigel? Will it be cold or hot then? Can you try and explain this questions? Lot of thanks. remcot

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#### qso1

##### Guest
Nobody can answer that question today. Thats one to be answered well into the future first by pointing out that we have to be able to first get there. If we can do that, it may well be possible but the next question might be, why? As it stands right now, nobody in the space business I'm aware of even seriously thinks humans will go into Jupiter or Saturns atmospheres.<br /><br />I expect on a planet at .13 au from Rigels surface, that it would be extremelly hot and bright. The planet would be tidally locked at that distance so there would be a perpetual night side as well. But even that would be hot due to lack of atmosphere, and an atmosphere would have boiled away if it ever got the chance to form at all under those conditions. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

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#### agnau

##### Guest
I have read several good Sci-Fi series (including Piers Anthony's Bio of a Space Tyrant and Proteus in the Underworld) over the years with floating cities in the atmospheres of both planets.

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#### qso1

##### Guest
Thanks, I'll have to check those out. Imagine if New Orleans had been a floating city or rather a levitated city. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

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