Originally posted by quater14
Why, when the moon is moving away from the earth every year, is it closest to earth on this Perigee? , closest to earth today for 18 years?
The moon is both
- drifting away from the Earth slowly, centimetres a year, and
- wobbling in and out in its orbit, over several years, by much larger amounts.
Over the small period of a century, the latter is much more noticable.
Over the geological ages, the former starts adding up, because it's not cyclical.
Get a plotting calculator (there used to be one in the PowerPack for MS Windows, don't know if there still is) to plot the graph of sin(x)+x/100. View this graph first from x=-5 to x=5, and then from x=-100 to x=100. You'll get the idea.