October 13, 2008

Aria -- engineer's disease


I don't think that Phobos or Deimos look anything like that.

Just did some calculations. At its closest approach, when directly overhead, Phobos has a disc of 0.2 degrees. From earth, Luna is a disk of about 0.5 degrees.

But because Phobos has a smaller orbit, then when it's on the horizon its disk would be about 0.15 degrees, or about one eleventh the area. Visible? Yeah. But it wouldn't look like that image.

And since its orbital period is only 7 hours, it would visibly move.

OK, Steve, put down that slide rule and back away slowly...

UPDATE: Not only would Phobos have only 1/11th of the apparent disc, but illumination by the sun would be 43% as bright on average, which means as a night-sky light illuminating things on the ground, Phobos would only cast 4% of the amount of light that Luna does on "Manhome" when full.

Posted by: Steven Den Beste in Engineer's Disease at 05:43 PM | Comments (7) | Add Comment
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1 Cosmetic astrography?  "Don't like the look of your moon?  Terraform one planet with our services, and get a free moon upgrade!"

Posted by: metaphysician at October 13, 2008 06:03 PM (h4nEy)

2 I felt a disturbance... as if millions of catgirls cried out, and were silenced.

Posted by: Wonderduck at October 13, 2008 07:12 PM (AW3EJ)

3 Gravitational lensing? ;p "Hey, let's make the moon look bigger too!"

Posted by: Avatar_exADV at October 13, 2008 07:30 PM (pfysU)

4 As long as we're picking... Phobos is very small and thus not actually round: "Phobos is highly nonspherical, with dimensions of 27 × 22 × 18 km." - Wikipedia.

Posted by: Jeremy Bowers at October 13, 2008 07:43 PM (7LWnd)

5 Actually, I think Metaphysician may have it right. Perhaps there had to be some serious demolition work on the planet when they first began the terraforming project, and they knocked away enough mass into orbit to create a reasonable moon, one that is much larger than Phobos. (In fact, that's how Luna was created, though not as a result of technology.)

Posted by: Steven Den Beste at October 13, 2008 07:50 PM (+rSRq)

6 I like that answer. My policy, even as a nit-picking engineer, is always to try to look for the explanation that makes sense.

Posted by: Jeremy Bowers at October 14, 2008 09:53 AM (FXfNF)

7 Well, if they were using asteroid impacts for some of the early excavation, then maybe they collected a few extra asteroids into the same orbit and let them coalesce into a larger body.

Posted by: Steven Den Beste at October 14, 2008 11:54 AM (+rSRq)

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