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Astronomy/Planets with dark/light sides

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Expert: - 2/12/2010


Question
Hi there,
I'm writing a science fiction story about a world with a 'sunny side' from which the sun appears to simply hang motionless in the sky. From what I understand, this is possible because, from the moon, the Earth appears to be immobile... doesn't it?
What I do not know is the term for such an orbit.
In my story, all indigenous life is subterranean (on the assumption that surface moisture would be evaporated and drawn to the dark side).
But, for the sunny side to have a climate that could be reasonably tolerated by humans, how far away from its sun would it have to be?

This is very soft science fiction but I'd still like a minimal level of believability.

Answer
The term is synchronous rotation... the moon keeps one side facing the Earth because it
rotates once for every one revolution.
As far as distance, that would depend on the planet's size, internal core (molten or frozen?),
internal radioactivity, atmospheric composition, distance from the sun, etc.
Just as a guess, I would estimate somewhere between Mars and Earth distance would keep the
sunward side of the planet relatively warm, but very cold on the non-sun-facing side.
And I would guess that the surface inhabitants would naturally migrate close to the equatorial terminator edges (where the sun would only be a few degrees above the horizon at all times) to take advantage of a moderately temperate environment.
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA  

Astronomy

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Tom Whiting

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Astronomy has been my hobby/pasttime for over 50 years.  Currently own 3 telescopes, the largest of which is a 30 inch Newtonian truss Dob that is portable.I taught Astronomy/Meteorology at the University Level for 13 years before retiring in 1995. Being retired and home most of the time, I am able to answer all questions relatively quickly, unless it's a new moon weekend with good observing conditions.  No astrology questions please, or questions about alleged UFO picture identifications.

Experience

Experience: Astronomy has been my hobby and study for over 50 years. We currently now own a 30 inch portable telescope (Updated - Pennsylvania`s largest portable telescope). It can be seen on our website at:http://www.velocity.net/~bwhiting and also attend several regional starparties during the year, and have been on 5 total solar eclipse expeditions.

Organizations: President, Erie County Mobile Observers Group for over 15 years.

Publications: Wrote the "Over Erie Skies" newspaper article in our local newspaper for 11 years (1975-86).

Education: Masters Degree- Taught at the University level for 13 years. Retired 20 years -USAF Pilot - KC-135 with 180 combat missions;  Also Eagle Scout, Philmont staff 2 Yrs, Order of Arrow Lodge Chief, Ham Radio (inactive).

Awards: two discoveries: The mini-coathanger asterism in Ursa Minor (the little dipper) And the mini-ladle- another asterism in the bowl of Ursa Minor. Clients: Currently President of the ECMOG as mentioned above.

Education/Credentials
BS  Metallurgical Engineering Grove City College, PAMaster's Degree, Gannon University, Erie, PA Also retired USAF pilot, 20 years.

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