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How visible is Sirius B from Sirius A?
Hi. I'm an SF writer, and many years ago I asked a pretty basic question here in sci.astro and got some extremely helpful answers, so I thought I'd have another go!
My story's set on a planet fairly closely orbiting Sirius A. My question is: how well (on average) could the inhabitants see Sirius B? Would it be too far away to seen without a telescope, or would it shine brightly enough to be seen by the naked eye? Many thanks for any help anyone can give me! Cheers, - Kate |
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How visible is Sirius B from Sirius A?
On 02/03/2014 9:05 PM, Kate Orman wrote:
Hi. I'm an SF writer, and many years ago I asked a pretty basic question here in sci.astro and got some extremely helpful answers, so I thought I'd have another go! My story's set on a planet fairly closely orbiting Sirius A. My question is: how well (on average) could the inhabitants see Sirius B? Would it be too far away to seen without a telescope, or would it shine brightly enough to be seen by the naked eye? Many thanks for any help anyone can give me! Sirius A and B orbit each other between 8.2 to 31.5 AU, so basically the orbit ranges from around the orbit of Saturn to around the orbit of Pluto. I'd say at its closest approach, Sirius B should be more luminous than Saturn. And even at its furthest approach it should be luminous enough to be seen at least with binoculars. Usually the planets further than Saturn aren't visible to the naked eye, but this is a star after all so it generates its own light. Yousuf Khan |
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How visible is Sirius B from Sirius A?
Yousuf Khan wrote:
On 02/03/2014 9:05 PM, Kate Orman wrote: Hi. I'm an SF writer, and many years ago I asked a pretty basic question here in sci.astro and got some extremely helpful answers, so I thought I'd have another go! My story's set on a planet fairly closely orbiting Sirius A. My question is: how well (on average) could the inhabitants see Sirius B? Would it be too far away to seen without a telescope, or would it shine brightly enough to be seen by the naked eye? Many thanks for any help anyone can give me! Sirius A and B orbit each other between 8.2 to 31.5 AU, so basically the orbit ranges from around the orbit of Saturn to around the orbit of Pluto. I'd say at its closest approach, Sirius B should be more luminous than Saturn. And even at its furthest approach it should be luminous enough to be seen at least with binoculars. Usually the planets further than Saturn aren't visible to the naked eye, but this is a star after all so it generates its own light. Yousuf Khan I'm not sure how you are doing this calculation. The absolute magnitude of Sirius B is (from references) about +11.5, so at 31.5 AU, log(d) = -3.82 (d in parsec). The usual distance modulus formula m - M = 5logd -5 then gives apparent magnitude m = -12.6, roughly as bright as the average full moon from Earth. At 8 AU it should be about 15 times brighter than that. Incidentally, Sirius is around 25 times more luminous than the Sun, so if the supposed planet of the OP is meant to have Earthlike conditions, it needs to be about 5 AU from the primary, so the distance to Sirius B would range from around 3 AU to 26.5 AU at opposition (if the orbit is roughly circular). -- Mike Dworetsky (Remove pants sp*mbl*ck to reply) |
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How visible is Sirius B from Sirius A?
In article ,
"Mike Dworetsky" writes: I'm not sure how you are doing this calculation. The absolute magnitude of Sirius B is (from references) about +11.5, so at 31.5 AU, log(d) = -3.82 (d in parsec). The usual distance modulus formula m - M = 5logd -5 then gives apparent magnitude m = -12.6, roughly as bright as the average full moon from Earth. At 8 AU it should be about 15 times brighter than that. Looks right to me. Worth noticing is that Sirius B would be a point of light, not extended. Looking at it with human eyes would probably burn a blind spot in one's retina. A single spot would be tiny and therefore unnoticed in normal life, but an accumulation of blind spots would significantly decrease vision. Presumably the inhabitants of such a planet would have evolved some protection against this danger, though I'm not sure quite what. Maybe just a reflex aversion to looking at bright lights would suffice. Incidentally, Sirius is around 25 times more luminous than the Sun, so if the supposed planet of the OP is meant to have Earthlike conditions, it needs to be about 5 AU from the primary, so the distance to Sirius B would range from around 3 AU to 26.5 AU at opposition (if the orbit is roughly circular). Hard to imagine a planet 5 AU from Sirius A having a stable orbit. There must be some calculation of how small the orbit would have to be, but I don't know where to find it. Even 1 AU, where mean temperature would be about 330 deg_C, seems dubious to me. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
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How visible is Sirius B from Sirius A?
Steve Willner wrote:
In article , "Mike Dworetsky" writes: I'm not sure how you are doing this calculation. The absolute magnitude of Sirius B is (from references) about +11.5, so at 31.5 AU, log(d) = -3.82 (d in parsec). The usual distance modulus formula m - M = 5logd -5 then gives apparent magnitude m = -12.6, roughly as bright as the average full moon from Earth. At 8 AU it should be about 15 times brighter than that. Looks right to me. Worth noticing is that Sirius B would be a point of light, not extended. Looking at it with human eyes would probably burn a blind spot in one's retina. A single spot would be tiny and therefore unnoticed in normal life, but an accumulation of blind spots would significantly decrease vision. Presumably the inhabitants of such a planet would have evolved some protection against this danger, though I'm not sure quite what. Maybe just a reflex aversion to looking at bright lights would suffice. Yes, I was aware of this issue, but it pales into insignificance compared to the next one. Incidentally, Sirius is around 25 times more luminous than the Sun, so if the supposed planet of the OP is meant to have Earthlike conditions, it needs to be about 5 AU from the primary, so the distance to Sirius B would range from around 3 AU to 26.5 AU at opposition (if the orbit is roughly circular). Hard to imagine a planet 5 AU from Sirius A having a stable orbit. There must be some calculation of how small the orbit would have to be, but I don't know where to find it. Even 1 AU, where mean temperature would be about 330 deg_C, seems dubious to me. I agree, but I did want to go into all those details at once. The period of the 5AU hypothetical would be fairly short (rough Kepler's third law calc yields around 6-7 years) compared to the longer Sirius B orbit. But an occasional regular peri-sirion by a massive companion star (around 1 solar mass for B) ought to make stability difficult and a circular orbit impossible. So a close orbit is required for stability but makes the surface conditions approach those of Venus. The evolutionary state of the Sirius system would make habitability questionable anyways--Sirius B evolved first, and would have been a red giant, cooking any planet in the system some time in the past few hundred million years. -- Mike Dworetsky (Remove pants sp*mbl*ck to reply) |
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How visible is Sirius B from Sirius A?
On 04/03/2014 4:13 AM, Mike Dworetsky wrote:
Steve Willner wrote: Hard to imagine a planet 5 AU from Sirius A having a stable orbit. There must be some calculation of how small the orbit would have to be, but I don't know where to find it. Even 1 AU, where mean temperature would be about 330 deg_C, seems dubious to me. I agree, but I did want to go into all those details at once. The period of the 5AU hypothetical would be fairly short (rough Kepler's third law calc yields around 6-7 years) compared to the longer Sirius B orbit. But an occasional regular peri-sirion by a massive companion star (around 1 solar mass for B) ought to make stability difficult and a circular orbit impossible. So a close orbit is required for stability but makes the surface conditions approach those of Venus. The evolutionary state of the Sirius system would make habitability questionable anyways--Sirius B evolved first, and would have been a red giant, cooking any planet in the system some time in the past few hundred million years. Actually, the entire evolutionary timeline of the Sirius system would make it difficult for a native race of sentients to evolve on it. It's only a quarter of a billion years old, it's main sun has already undergone a red giant transition a few million years ago, and it's current main sun only has another 1 billion years left before it too goes red giant. However, it's possible that an emigrant race of sentients could've settled on a planet in that system and terraformed it. Yousuf Khan |
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How visible is Sirius B from Sirius A?
On Sunday, March 2, 2014 6:05:16 PM UTC-8, Kate Orman wrote:
Hi. I'm an SF writer, and many years ago I asked a pretty basic question here in sci.astro and got some extremely helpful answers, so I thought I'd have another go! My story's set on a planet fairly closely orbiting Sirius A. My question is: how well (on average) could the inhabitants see Sirius B? Would it be too far away to seen without a telescope, or would it shine brightly enough to be seen by the naked eye? Many thanks for any help anyone can give me! Cheers, - Kate Sirius(b) is mostly emitting photons in the UV spectrum, so don't expect any human visual capability of even telescope aided views of that one. |
#8
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How visible is Sirius B from Sirius A?
How about the Dogon who indicate that there is a Sirius C? If it exists it
must be very dim and orbiting far from Sirius A+B. I would think it would have been found by now if it exists. But you never know. I doubt if Astonomers have spent a lot of large telescope observatory time looking. As far as I know the Dogon don't give much detail on this star since their religion shrouds it in mystery. "Brad Guth" wrote in message ... On Sunday, March 2, 2014 6:05:16 PM UTC-8, Kate Orman wrote: Hi. I'm an SF writer, and many years ago I asked a pretty basic question here in sci.astro and got some extremely helpful answers, so I thought I'd have another go! My story's set on a planet fairly closely orbiting Sirius A. My question is: how well (on average) could the inhabitants see Sirius B? Would it be too far away to seen without a telescope, or would it shine brightly enough to be seen by the naked eye? Many thanks for any help anyone can give me! Cheers, - Kate Sirius(b) is mostly emitting photons in the UV spectrum, so don't expect any human visual capability of even telescope aided views of that one. |
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How visible is Sirius B from Sirius A?
On Tuesday, March 4, 2014 4:11:21 PM UTC-8, Bernard Isker wrote:
How about the Dogon who indicate that there is a Sirius C? If it exists it must be very dim and orbiting far from Sirius A+B. I would think it would have been found by now if it exists. But you never know. I doubt if Astonomers have spent a lot of large telescope observatory time looking. As far as I know the Dogon don't give much detail on this star since their religion shrouds it in mystery. "Brad Guth" wrote in message ... On Sunday, March 2, 2014 6:05:16 PM UTC-8, Kate Orman wrote: Hi. I'm an SF writer, and many years ago I asked a pretty basic question here in sci.astro and got some extremely helpful answers, so I thought I'd have another go! My story's set on a planet fairly closely orbiting Sirius A. My question is: how well (on average) could the inhabitants see Sirius B? Would it be too far away to seen without a telescope, or would it shine brightly enough to be seen by the naked eye? Many thanks for any help anyone can give me! Cheers, - Kate Sirius(b) is mostly emitting photons in the UV spectrum, so don't expect any human visual capability of even telescope aided views of that one. Supposedly some efforts have been made to discover Sirius(c), or anything else associated with Sirius(a) and (b). At least so far, no luck. What's needed is a good StarShade. http://en.wikipedia.org/wiki/New_Worlds_Mission http://www.newscientist.com/article/...l#.Uxa0_vldV0w However, we should be capable of getting a very good look-see at the photosphere of Sirius(a), because more than sufficient optics with ample magnification and optical filters have existed for more than a decade, and yet not one example of that enormous photosphere can be found (seems a bit odd). |
#10
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How visible is Sirius B from Sirius A?
Brad Guth wrote:
Sirius(b) is mostly emitting photons in the UV spectrum, so don't expect any human visual capability of even telescope aided views of that one. Which of course does not explain why Sirius B was discovered visually in the 1860s during testing of a new Alvan Clark refractor, and I myself saw it through the Mt Wilson 60-in telescope in the 1970s. It's faint, but the main viewing difficulty is its proximity to bright Sirius, not its low luminosity. -- Mike Dworetsky (Remove pants sp*mbl*ck to reply) |
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