In Terra Nova episode 2 they show this image of the Moon: The big moon

They mention that being 85,000,000 years in the past the Moon is much closer to the Earth, citing that every year it moves half a centimeter away from the Earth. I was curious just how much this equated to, and if it could really cause the Moon to appear so much closer. Thus, with this information the Moon would have been approximately 42,500,000 centimeters closer during this period. This equates to 264.08 miles closer. The moon is currently 238,900 miles away from the Earth. Thus, 264.08 is .11% of this distance. So for example, if we are talking about a mile this would only be 5.8 feet. So would such a small relative distance really have made the moon appear so much closer?


No; assuming that Maddy (I think that's who said it) has her facts right, their moon wouldn't be anywhere near that much bigger 85 million years ago. In fact, it would be in practically the exact same spot as it was in their present day.

Our moon is moving away from the Earth, right now, by about an inch and a half a year (about 3.5 cm). If Terra Nova's moon really did movie only .5 cm / year, then it's moving much slower than ours by a factor of about 1/7.

At the rate their moon is moving, 85,000,000 years ago it would have been approximately 425 km closer to us, which would be something like 0.08% closer. (Yes, that's eight hundreths of a percent closer). With that little change, the moon would barely look a tenth of a percent bigger.

We don't know what else might be "different" about Terra Nova's moon, but our moon's elliptical orbit causes it's distance to fluctuate about 43,000 km every month, and we barely notice the difference. It's almost certain that Terra Nova's moon would look exactly the same 85 million years in the past as it did in present day.

For a more thorough analysis, you can also read the Bad Astronomy review of Terra Nova here.

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    You should be aware that the rate of recession varies in time. It is driven by the tidal angular momentum transfer and that depends on how the oceans resonate at the tidal driving frequency which depends on where the continents are. On time scales where continental drift counts, there can be large variation in the recession rate. I don't know if that cast doubt on your answer, however. – dmckee --- ex-moderator kitten Aug 14 '15 at 18:15
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    The recession rate does vary over time and is slowing down, so yes the moon moved away faster early on and fluctuated during that period. Over the timescale of 85myr, though I don't think the numbers vary enough to matter. (That's like 2% of the moons lifetime) – KutuluMike Aug 14 '15 at 21:08
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    thanks. My math's right, I think, I just typed it wrong :) – KutuluMike Aug 15 '15 at 14:46

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