[IW]: How to get Different Stars/Constellations?

[Flyndaran]

Originally Posted by Drifter

That is the secret of happy, childhood memories - NEVER go back and watch old shows you loved as a kid. The day they put Space:1999 on Netflicks is the day the last bit of child in me dies.

Even as a child, I knew it was cheese. My family lightly mocked me for enjoying it, being a born lover of real science and all.

[BaHalus]

Originally Posted by Drifter

Axial precession would put the constellations in somewhat different positions, and would be an easy way to judge the approximate date if time traveling.

Due to the wobble in the earth's rotation the pole star shifts. The cycle is 26k years. The current 'pole star' or star closest to the apparent celestial north pole, is Polaris. About 5 thousand years ago it was Thuban. Before that it was Vega. 26 thousand years ago it would have been Polaris - if Polaris was in that same location in the sky.

The positions of the stars in the constellations themselves will change over time, but usually by a smaller amount. Some stars, like Arcturus, are just speeding along and will change positions quickly - another way to gauge the date.

so, every 26ky the stars are back to the place we know today. Then about 13ky would be the best call or 39ky or 65ky or 91ky or 13ky+n*26ky. I think this periodic shift produces a bigger effect then the real movement of stars themselves.

Other thing: if you return in time, days become shorter, if you advance, days become longer (it is related with the moon running away from earth. I read somewhere that in mesozoic days only lasted 18 hours.

[Whyte]

Originally Posted by BaHalus

so, every 26ky the stars are back to the place we know today. Then about 13ky would be the best call or 39ky or 65ky or 91ky or 13ky+n*26ky. I think this periodic shift produces a bigger effect then the real movement of stars themselves.

Other thing: if you return in time, days become shorter, if you advance, days become longer (it is related with the moon running away from earth. I read somewhere that in mesozoic days only lasted 18 hours.

Length of day: Not quite that dramatic. The day was about 22h in 620 million years before now. That was way before the dinosaurs; even before the Cambrian explosion of life. But you are correct in the broad terms that if the time traveller has access to an accurate wrist watch and times the noons, he should be able to suss out if he is several millions years in the past or in the future. (Of course, if he has Absolute Timing he can do much better. :) )

As for the precession of the Earth's axis, that only messes up the Polaris=North alignment and the equatorial coordinates. The constellations are still there, just shifted on the sky (in comparison to the Earth's axis) from what you saw last night ten thousand years ago.

[cptbutton]

Originally Posted by Drifter

The book "A World Out of Time" by Larry Niven, more or less hard science fiction, features a trip 3 million years in the future, but for one reason or another the sun is a red giant, the Earth orbits Jupiter (which itself is a red hot dwarf 'star') and the solar system is generally messed up.

As I recall it, there was a giant vertical tube floating in the atmosphere of Jupiter or one of the other gas giants that was used to move it around on a centuries or millenia time scale.

This was used to drag other planets around, dropping one of them into the sun, making it swell up. And making Earth a moon of Jupiter.

[johndallman]

Originally Posted by cptbutton

As I recall it, there was a giant vertical tube floating in the atmosphere of Jupiter or one of the other gas giants that was used to move it around on a centuries or millenia time scale.

Uranus. Some examples of how to mess this kind of operation up are supplied in this Schlock Mercenary storyline.

[oldgringo2001]

As for the precession of the Earth's axis, that only messes up the Polaris=North alignment and the equatorial coordinates. The constellations are still there, just shifted on the sky (in comparison to the Earth's axis) from what you saw last night ten thousand years ago.

Actually, not quite. Proper motion changes the apparent positions of stars in our sky as time passes, although it's only been measured for three centuries. The apparent position of Alpha Centauri has changed about two degrees since Hipparchos first plotted it around two millenia ago. The important thing seems to be that for most Earths that Homeline knows is that the night sky looks about the same.

If you're familiar with GDWs other SF RPG, 2300 AD (aka Traveller 2300), it's set in the space near earth and uses data from the second edition of the Gliese catalog of nearby stars--data that had already been superceded by the third edition by the time it was published. That turned out to be pretty important because the universe set a strict limit on how far you could stutterwarp between stars--7.7 light years. A whole lot of background depended on stars staying put. Later observations have made a mess of this version of interstellar space--but only for our universe. If one were to hop into the 2300 AD universe (or one of its echoes, say, during the Twilight War), those stars would be in the "right" places after all.

[dcarson]

If the place is/was high enough tech the reflections and glow from orbital industry, space solar power satellites etc can make it hard to see the stars.

[Fred Brackin]

Something that occurred to me was in relation to this.

http://en.wikipedia.org/wiki/Galactic_year

Even a significant part of this period could have familiar stars or even star clusters being moved behind an opaque nebula. That would make significant differences in the constellations.

The necessary scale might be between a Galactic week (5,000,000 years to a month (20,000,000) rather than the whole Galactic Year (230,000,000 years)

[David Johnston2]

Originally Posted by Fred Brackin

Something that occurred to me was in relation to this.

http://en.wikipedia.org/wiki/Galactic_year

Even a significant part of this period could have familiar stars or even star clusters being moved behind an opaque nebula. That would make significant differences in the constellations.

The necessary scale might be between a Galactic week (5,000,000 years to a month (20,000,000) rather than the whole Galactic Year (230,000,000 years)

As I said early on, because stars move in different directions at different speeds anything more than a hundred thousand years would be unrecognizable to anything except an expert.