Curve of the shadow on the Moon

Factual Questions
21

See here for a good description of how the ancient Greeks used eclipses to estimate the distance to the Moon, and how they less successfully attempted to estimate the distance to the Sun.

The quote in the OP, of course, is complete hogwash. The church in Magellan’s time did not maintain that the Earth was flat. No educated person had maintained that since the time of the Greeks.

22

Well, this site
http://www.earlychurch.org.uk/creation_flatearth.html
has links to those who argue that the early church did/didn’t think the earth was flat. In particular
http://www.ethicalatheist.com/docs/flat_earth_myth_ch2.html
lists seven early Christian writers who say (or imply?) that the earth is flat. It doesn’t give quotes, so who knows if these are “four corners of the earth” things that could be purely figures of speech, or actual statements/defenses of the flat earth. Even this site, which claims that the chruch-flat earth connection is incorrect, admits two early Christian writers defended the idea:
http://www.christiananswers.net/q-aig/aig-c034.html

From a quick glance over these sites, it seems clear that

  1. up until the 6th century AD there were several opinions on the matter, and no official Church view.
  2. after that time, the spherical earth is universal (among educated writers, at least - who knows what the average-slob-in-the-street thought)
  3. there was an effort in the 19th century to tar the Church with the flat-earth brush
  4. that modern Christians go the other direction, and downplay evidence of flat-earth thinking among early Christians, calling it a myth invented by anti-Church forces.

Can anyone define objectivity for me, class?

23

Which doesn’t help you. All that gives you is the ratio of the Moon’s diameter to its distance, which again, is much easier to find from just observing its angular size.

But you can measure the distance to the Moon fairly accurately using parallax, from different points of observation on the Earth.

24

I’ve seen modern folk that exhibit flat-earth thinking, so I dunno why that’s such a surprise.

25

jklann posted a nice link explaining how to use the Earth’s penumbra to get a fairly accurate measure of the Moon’s distance. This technique works for an observer in just one location.

26

You can only get that result by excluding penumbral eclipses.

Of course, a penumbral eclipse isn’t going to demonstrate the effect the OP was talking about, but it’s still an eclipse.

27

Okay, so the quote is probably made up, which is a shame. Google couldn’t give me a decent cite, nor do any really reputable sites have it.

But you’re telling me the concept does work, which is nice. And thata not only is it a lot older than I thought, but that lunar eclipses are a lot more common than I thought. Hey ho.

(I’m not interested in the whole religion angle, I’d just like a nice answer to anyone who says that you can’t prove the Earth is a sphere without going up into orbit, or flying around it, or whatever).

So thanks all. I’ll have to try it for myself.

28

Next lunar eclipse, Nov. 9, and it’s early evening (USA)

29

I’m reminded of a bit Steve Martin did called “What I Believe,” which included* this:

“I believe that a total eclipse of the sun is a beautiful and moving experience, but an eclipse of the moon is a cheap and degrading spectacle.”

  • As I recall it, at least. Several Web sources on the sketch don’t include this one, which I think is the best of the lot. Well, if he doesn’t take credit for it, I will.