Monday, 14 November 2016

Supermoon - or what?

I thought I could get through without being noticed but I didn't quite.

So , what is the deal? It is in this case a full moon very near perigee, the point in the moon's orbit when it is closest to earth. Perturbations on the earth-moon system mean that both ellipses, the orbits, drift systematically in space so that - in this case - the full moon does not occur at the same position in its orbit from moonth to month. The earth is also moving around the sun so the position of full moon also moves, occurs 2-3 days later  as the moon must revolve further to "catch up" with the earth.sun alignment to be at full moon.

Full moon was at 8:52am this Monday morning. The distance between the centres of the earth and moon was at a minimum at 6:23am (All times Easttern Standard). So was that when you were closest to the moon/the moon appeared to be largest? Almost certainly not - depends a little on where you individuals were. For most mortals living in Ontario they were closest - the moon was largest - around midnight. By nearly 7000km. And here is why:

This diagram is from my friend Daniel Fischer writing for Sky and Telescope
where you can get more insight. (Daniel got me involved in the ESA-Rosetta Mission back in February 2004.)

For a better understanding of the role being played by the elliptical orbit I refer you to another excellent article in Sky&Telescope
(I have been subscribing to Sky&Telescope since the early-mid 1950s.)

I still had Halloween on the brain Saturday evening when I took these photos:

Scary? Lunatic? Lover of the (unpolluted) night sky? Astronomer? Interested?

Actually, here is another link from the Canadian "Sky News"



  1. Thanks for the excellent explanation of the super moon. And I really love the photos of it. I'm using one of them as my computer screen saver -- hope you don't mind! Your sister, Anne

  2. I need more sisters like you - too take up some of your work load!
    Your brother, Bill