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PostPosted: Mon Feb 06, 2012 11:18 am 
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At the moment I am still working a bit on my new version of the Phalanos
setting, the fantasy - science fiction crossover with magic gates as the
means to travel between worlds.

Today I used the free Celestia planetarium program to get an impression
what the night sky of a planet Phalanos in an orbit around Tau Ceti might
look like, and whether my pseudo-medieval visitors to such a planet would
be able to recognize any of Earth's constellations and would have a chan-
ce to find out where they are now in relation to Earth.

It seems the only easily recognizable well known constellation would pro-
bably be Orion, otherwise the night sky would look rather different, and
Sol (now in Bootes near Arcturus) would be just another comparatively
bright star. With a lot of observations and the star charts built upon them
it should be possible to recognize some other very bright stars and con-
stellations, but I think only a true genius could combine the charts and
identify Sol as the Earth's sun.

Still, perhaps one of the players will find a way to solve this puzzle. :)


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PostPosted: Mon Feb 06, 2012 8:26 pm 
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Yeah, I think it's surprising how much the appearance of the constellations are broken up just by moving to a star that's 11.9 ly from Sol. They're vaguely similar, but some are severely distorted!

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PostPosted: Tue Feb 07, 2012 1:17 am 
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EDG wrote:
Yeah, I think it's surprising how much the appearance of the constellations are broken up just by moving to a star that's 11.9 ly from Sol. They're vaguely similar, but some are severely distorted!

Yeah, the distortion is dramatic enough that you can work out where you are pretty simply.

The constellations that you have moved towards (Cetus) and away from (Boötes) ought to be basically recognisable but with radial movement of the nearer stars. Find Arcturus and Spica, and there will be a new third-magnitude star near Nu Boötis. That's Sol, and it's location gives you a simple and very accurate idea of which direction you're displaced in, which even an amateur astronomer can work out.

Working out how far you've gone is a bit trickier, and probably requires an instrument and either a professional astronomer or a decent star catalogue. Your best bet for a fix is to measure how much Sirius has been displaced. It is nearby, bright, and fortunately at such a spot in the sky that the parallax of its displacement will be large. But I'd guess τ Ceti just from seeing Sol near ν Böotis.

One thing that your astronomy program probably doesn't show you, but which would be prominent in the night sky of any planet orbiting τ Ceti, is that the thick debris disk of τ Ceti would produce zodiacal light ten times as bright as in Earth's sky.

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PostPosted: Tue Feb 07, 2012 1:00 pm 
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Location: Sonthofen / Germany
I think it will depend a lot on how well the players can roleplay the
(pseudo-) medieval mindset. While our modern concept of astrono-
my makes it comparatively easy to understand what a voyage to a
the planet of another star does to the constellations, and how one
can explain the differences and estimate where one came from and
where one is now in relation to it, a (pseudo-) medieval astronomer
with his concept of the stars as lights fixed to the heavenly sphere
which revolves around the Earth should need a true genius' insight
to understand what he sees in the foreign night sky (and would en-
ter the dangerous realm of obvious heresy by doing so).

Oops, sorry for that very long sentence ...


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PostPosted: Tue Feb 07, 2012 6:00 pm 
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Ah! Sorry, I had the bull by the foot.

The first stellar parallax was not measured until 1838, with means that your mediaeval scholars don't know the distance of Sirius or Tau Ceti, and they have no hope of working out where they are displaced to. Indeed, as you say, they probably won't have the concepts that the Sun is a star or that the stars are scattered at different distances through space available to them. As late as the Sixteenth Century (late Renaissance) it was possible for a major astronomer with a great international reputation to maintain that the stars were fixed lights attached to a spherical shell surrounding the Earth at equal distance: Tycho Brahe did so.

It was Giordano Bruno in 1584 who first suggested that the stars are other suns distributed at different distances in space. He was burned at stake for heresy for thus contradicting the Bible.

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