Alpha Centauri is 15,000 Astronomical Units away

I think offhand Alpha Centauri miht appear a bright as Venus in the night sky, though I'm not sure about that. It will be like another planet to the ancients, except one that does not move - much.

I think history would not be affected much, though certain Greek myths might be altered to give centaurs a greater prominence.

OK, let´s consider it.

If Toliman is 16 times closer than in OTL, then it is about 6 magnitudes brighter. -6 for Toliman A is plainly and unmistakably brighter than any star or planet - Sirius is -1,43, Venus is -4,3 at brightest. It is not, however, close to Moon: full moon is -12,7.

The distance? The maximum physical distance, 36 au, would at 15 000 au, span 8 arc minutes. One quarter of the diameter of Moon´s disc. Clear to resolve, and B which is only 3,5 times (1,4 magnitudes) dimmer than A would not be lost in glare either. I am not quite sure what the inclination of orbit is, though.

Regarding the speed: if it is orbiting, its speed would be in the region of 400 m/s and period close to 1 million years.

That means a degree in 3000 years - similar to the proper motion of fixed stars.

If, however, Toliman is freely passing Sun by, near its OTL relative speed of 40 km/s, then the proper motion would be in the region of a degree in 30 years. Plainly visible over a lightyear. Over historic period of a few millennia, it would cover most of the sky, change its luminosity and inclination...
 
Well one thing that might happen is a more focused space development. If Alpha Centauri is .24 ly away than NASA and other space agencies (assuming this ATL is as close to OTL as possible) might attempt to create a continuous reaction engine so to travel to and from that system. Yes the time for radio contact would be 6 months round trip but you could probably get out there and back in a decade. Another change for being that close in comparison is if there was actually a habitable planet as it might be possible to construct a fleet of ships containing a 1000 settlers to these other planets.
 

Tom Kalbfus

Banned
OK, let´s consider it.

If Toliman is 16 times closer than in OTL, then it is about 6 magnitudes brighter. -6 for Toliman A is plainly and unmistakably brighter than any star or planet - Sirius is -1,43, Venus is -4,3 at brightest. It is not, however, close to Moon: full moon is -12,7.

The distance? The maximum physical distance, 36 au, would at 15 000 au, span 8 arc minutes. One quarter of the diameter of Moon´s disc. Clear to resolve, and B which is only 3,5 times (1,4 magnitudes) dimmer than A would not be lost in glare either. I am not quite sure what the inclination of orbit is, though.

Regarding the speed: if it is orbiting, its speed would be in the region of 400 m/s and period close to 1 million years.

That means a degree in 3000 years - similar to the proper motion of fixed stars.

If, however, Toliman is freely passing Sun by, near its OTL relative speed of 40 km/s, then the proper motion would be in the region of a degree in 30 years. Plainly visible over a lightyear. Over historic period of a few millennia, it would cover most of the sky, change its luminosity and inclination...
It would be easier to pick out the planets orbiting A and B at this distance, we'd probably have a good idea by now what sorts of planets are orbiting it. Lets assume there is at least one Earthlike planet orbiting one of those stars. A solar sail starship could reach the A/B part of the system in 33 years, instead of 1350 years OTU. Solar Sail starships seem the easiest to build without major technological breakthroughs, basically they just unfurl their sails vary close to the Sun and accelerate away ar around 14gs, the strands of the sails would have to be very strong to sustain this acceleration, on the order of carbon nanotubes or diamond. I could imagine a civilization which build a space elevator undertaking this journey, and I could imagine this space elevator existing by mid 21st century. The launch date for the mission would probably be on 2060 at the soonest, and it would take nearly the remainder of the 21st century for the starship to approach the A/B components and slow down via the light pressure of Alpha Centauri A at another 14gs. A return journey could be made just as easily.

Basically you can have two-way traffic between Alpha Centauri A & B and Sol with each journey taking about a third of a century. The time it takes to send a message from the Solar System to Alpha Centauri would be 86.63 days at exactly 15,000 AU. A round trip communication would take 173.26 days. It possible for different nations to establish colonies in the Alpha Centauri system and maintain some sort of delayed control over them, it would be much like a European Colonial power governing its overseas colonies in the16th and 17th centuries, communication being sent via letter onboard wooden sailing ships.
 

Penelope

Banned
This is actually really intresting, but at that distance, we wouldn't have a few of the outer planets...

I imagine that Pluto and Eris would be gone, problably wandering in space, drug into the Centauri system, or on a highly eccentric orbit around Sol.

Neptune and Uranus would probably have much more eccentric orbits than they do know, just because of the gravitational effect Centauri would have. I would imagine the Oort cloud, most of the Kuiper belt, and maybe even Pluto and Eris would have been ejected out of the system. The Ice Gaints, Neptune and Uranus, probably have orbits as eccentric as Pluto does.
 

Tom Kalbfus

Banned
Well one thing that might happen is a more focused space development. If Alpha Centauri is .24 ly away than NASA and other space agencies (assuming this ATL is as close to OTL as possible) might attempt to create a continuous reaction engine so to travel to and from that system. Yes the time for radio contact would be 6 months round trip but you could probably get out there and back in a decade. Another change for being that close in comparison is if there was actually a habitable planet as it might be possible to construct a fleet of ships containing a 1000 settlers to these other planets.
I think the easiest sort of ship to build would be a Solar Sail Ark, but instead of it being multiple generations or 1350 years , it would take only 73 years! A Solar Sail ark requires building only the Ark and the Solar Sail attached to it, about one human lifetime would pass onboard the ark enroute. Easy to build, compared to other starship options. The other calculation above assumed the stars were 0.1 light years away.

Colonies in the Centauri system would be on their own with 6 months two-way communication.

A Dyson Starship requiring fusion bombs to propel itself can reach a velocity of 0.005c with a specific impulse of 100,000 seconds and an overall mass ratio of 4.6, a trip to Proxima OTU one-way fly through would take 860 years without slowing down, square the mass ratio to 21.16 and you can slow down, it would take 860 years one-way with a slow down OTU, but only 48 years in this timeline, while using up a lot of hydrogen bombs, you basically need 21.16 tons of hydrogen bombs for every ton of starship structure and payload delivered to Alpha Centauri.
 
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