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Re: OT: Celestial maps

From:Andreas Johansson <andjo@...>
Date:Tuesday, January 15, 2008, 19:49
Quoting caeruleancentaur <caeruleancentaur@...>:

> >"Mark J. Reed" <markjreed@...> wrote: > > >This is getting seriously OT, but since I didn't explain it very > >well, I thought I'd try again. > > Who cares? :-) As long as it's marked OT, those not interested can pass > it by. I find it fascinating. > > >Depends on what you mean by "different". The Moon is receding from > >the Earth at a rate of about 38mm/year. So, for instance, back at the > >start of the Pleistocene it was about 40,000 miles closer to us than > >it is now. > > Math is not my strong suit. Can you tell us how much larger the moon > appeared then than it is now? Twice as large? Thrice as large, etc.? > It must have been truly beautiful.
Mark's math appears to be off by a factor thousand - 38mm/yr for 1.8 million years adds up to 68.2 km or roughly 40 miles. That's much less than the monthly variation in distance caused by the ellipticity of the Moon's orbit, which people don't ordinarily notice, so the Moon won't have looked appreciably larger at the start of the Pleistocene. It *will* however have looked much larger in the distant youth of our planet. The Internet is being unhelpful in giving an estimate for how distant the Moon was when it first formed (from debris smashed into space when a Mars-sized protoplanet collided with the proto-Earth, according to current theory), but it at a tenth of present distance it would look ten times larger and a hundred times brighter (well, actually more like 70 times brighter, because the Sun wasn't as bright then). It must indeed have been a spectacular sight - a pity that eyes wouldn't evolve until some four billion years later. Andreas


Mark J. Reed <markjreed@...>