Thursday, August 30, 2012

If you do science fiction, please do it right

I'm watching Outland,  a 1981 film directed by Peter Hyams and starring Sean Connery.

In one of the first scenes (the second, actually) you see Jupiter as seen from Io. It occupies most of Io sky. So, I asked myself if it really looks like that.

Simple trigonometry yields the angle under which  Jupiter is seen:

r = radio of Io
R = radio of Jupiter
d = distance of the center of Io from the center of Jupiter

angle = 2 * arcsin (R / (d - r))

Looking up the data on the Wikipedia the result is

r = 1821 Km
R = 71492 Km
d = 41700 Km

angle = 19 degrees.

Note. If you don't feel at ease measuring size with angles, well, consider that Hellenistic Greeks already did it in the 3rd century B.C.. The approach was long misunderstood later, to be rediscovered and re-understood during the Scientific Revolution. The idea is that the angle is the apparent size: if you also know the distance than you'll know the real size too.

Which is a little less the one fourth of the angle (90 degrees) from the horizon to the point in the sky above you head.

So I think the movie is wrong. And, if you do science fiction, please do it right.

PS. This is how Jupiter should be seen from Io. Supposing you're watching the screen from 50 cm far, doing trigonometry the other way round, yields about 17.5 cm for the apparent diameter of Jupiter (I assembled three images using GIMP and did a perspective transformation of an Io image).

PSS. I asked Celestia, an open source 3D astronomical object visualization software. Here is the result. I was wondering if Europa and Ganymede, other two nearby Jovian satellites, could contribute to an even more appealing picture, but Celestia showed me that they actually appear as tiny spots from Io.

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