Alien skies

This video's making the rounds, but I'll share it here because it just makes my heart go thumpity-thump watching it. Brad Goodspeed has created a video in Adobe After Effects showing what several of our solar system's planets might look like if they were orbiting the Earth at the same distance as our moon (or, perhaps, if we were orbiting them, as I imagine the barycenter of an Earth-Jupiter dynamic wouldn't be anywhere inside our little chunk of rock).

"Scale":

Scale from Brad Goodspeed on Vimeo.

This could be the reason that I loved Star Wars more than Star Trek, when I think about it: that Lucas had the budget and know-how to do what Trek couldn't do in its original television incarnation: desert planets with several moons and multiple suns, an inhabited jungle world that was actually the moon of an enormous gas giant that hung in the sky over the trees. These were the vistas I wanted to see, still want to see, though I never will except in my mind and as rendered by artists in various media--film or computer model or paint, whatever they might be using. And watching Goodspeed's film brings that same feeling that same rush: what would a gas giant 240,000 miles (give or take) away from the Earth look like, hanging in our sky (or completely filling it, in Jupiter's case)?

All this reminded me of an old video game, Firaxis' 1999 Sid Meier's Alpha Centauri: it was a good game in its own right, but maybe my very favorite thing was actually in the rulebook, in an appendix where the game designers and their science consultant tried to convey where a habitable planet might be found in a three-star system and what such a planet's sky might look like:

There are limits on the radius at which a planet habitable to mankind might orbit a star. The brighter and hotter the star, the farther out a planet must be to be habitable; the dimmer the star, the closer a planet must be. Alpha Centauri C can have no habitable planets--any planet close enough for life-sustaining sunshine would be quickly ripped apart by gravitational forces. Both Alpha Centauri A and B could have habitable planets, if they weren’t part of a binary system.

But what effect might the two stars have on each other’s habitable planets? As it happens, very little. If a planet were within either star’s habitable zone, it would never come close enough to the other star to be materially affected by it--its orbit would be stable. Take a look at the illustration of our solar system, with the Alpha Centauri binary system superimposed on it. Mentally replace the Sun with Alpha Centauri A. Alpha Centauri A’s habitable zone does not reach much beyond the orbit of Mars, and any planet that close to Alpha Centauri A is always too far from Alpha Centauri B to be affected by it.

Now mentally replace the Sun with Alpha Centauri B. Since Alpha Centauri B is cooler than the Sun or Alpha Centauri A, its habitable zone is even closer to Alpha Centauri B. Again, Alpha Centauri A would never come close enough to perturb a habitable planet around Alpha Centauri B.

The same can not be said for planets at greater distances from either of the binaries. Neither star can have a planet with the orbital radius of Jupiter, Saturn, Uranus or Neptune. In fact, once beyond the radius of Mars, the only stable orbits are those that circle both stars.

Even if neither star would perturb each other’s habitable planets, they would still be clearly visible. From a planet circling Alpha Centauri A, Alpha Centauri B would be a tiny, dazzlingly-bright yellow-orange light in the sky. It will be a tiny dot, but not quite a point, and it would be far brighter than any full moon--easily bright enough to read by. It would light up the night sides of any moons in the sky, as Earth does to the Moon’s dark side if you look carefully when the Moon is a crescent. Depending on the geometry at any given time, soon after sunset or before sunrise you night even see "double crescent" moons! Alpha Centauri C would be just barely visible at darkest night as a red
naked-eye star from either Alpha Centauri A or B.

I can't vouch for how accurate that description was or still is eleven years later, I just love trying to get my head around that star in the sky that's so bright you can read by it. Maybe that doesn't seem like much to be excited over, I don't know. To me, though, it's a wonder I can't even describe. When the interwebs were stirred by announcements that Betelgeuse might go nova soon, my first reaction was excitement over the prospect of a spectacular night sky (sadly, all the kerfluffle is "oh noes 2012 Mayan prophecies" related, and Betelgeuse's chances of blowing up remain exactly what they have been, which is the star could blow up tomorrow or any other time over the next million years, which is to say Betelgeuse might have blown up 643 years plus-or-minus up to 146 years or any time in the next million years and it would eventually come to our attention).¹

So, anyway, my thanks to Mr. Goodspeed, for feeding my dreams a sight they'd want to see, for offering a view of a strange sky.

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¹My second reaction when I saw the stories, seriously: "Poor Ford."

The third thing that crossed my mind: "That's really going to screw up Orion, too."

Yep, I'm a geek.