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Jack Koumi - 11 August 2014 10:49am
Regarding perigee and apogee (item 7 of the video clip)), the narrator said "the actual difference in size is about 40% bigger than when the moon is furthest away". In fact the sizes are proportional to the perigee/apogee sizes, 405/363 = 1.1157, so the difference is 11.57% bigger
Jack Koumi - 11 August 2014 11:21am
Linear difference in moon apparent size apogee vs perigee is 11.5%, which does mean volume would be 39% bigger, but the volume is not what observers experience. So narrator should not have said "40 percent" And in the next myth (number 8) tidal force difference between perigee and apogee is 38.9%, not 18%.
Are my calculations correct?
OpenLearn Moderator - 11 August 2014 1:54pm
Hi Jack, I've sent your comments off to the team to pass onto the academic. As soon as they come back with an answer I'll let you know.
Many thanks Jack.
Best wishes
OpenLearn Moderator
David Rothery - 11 August 2014 2:31pm
Hi Jack
I've checked the transcript,and it reads 'about 14%', though I agree the sound track sounds more like 'about 40%', which as you say would be wrong. I have asked if a link to the transcript can now be added to this site. The graphic does show the relative sizes correctly.
Tide-producing force is inversely proportional to the cube of distance. We are quoting the combined effect of lunar and solar tides in two situations. I believe our values are correct, but I do not have time to check details. The important point is that tides at 'supermoon' are not dramatically out of the ordinary.