Sunday, March 20, 2011

March 19, 2011 Super Moon (not really)

I can always tell when an astronomical phenomenon is getting media attention, as friends start sending me notices. This month was a "super moon", a term I hadn't heard before. It describes a full moon occuring near the moon's perigee -- it's closest point to Earth. Therefore, the full moon at perigee should appear larger than any other full moon. As full moon occured at 11:10 am my time (Pacific Daylight Time), and perigee at 12:09 (PDT), I had no chance of seeing the super moon. But what I would have seen, had I been under clear skies at the other side of the Earth, would not have been much different from what I  see every few years when the full moon is within a day or two of perigee.

Below are some photos I took in the days before and after the super moon to which I added a blue outline for ease of comparison.

Thurs., 17 March, about 40 hours before the full moon (evening photo):

March 18, about 34 hours before perihelion (morning photo; so the moon appears upside down)

March 18, 14 hours before perihion (look closely, this one appears larger than the previous two):

Hint: Look closely at the right side. The moon 14 hours before perigee fills the box and extends into the blue line on the right side, where the previous two images leave a few pixel gap.

Weather interfered with my next opportunity, the morning of March 19, when I could have photographed the moon perhaps 8 hours before perihelion. Weather interfered again the following night 7 hours past perigee. I was able to photograph the moon, but the conditions clearly show my image as unreliable or comparison:

And here is my last photo in the series, taken 10 hours past perigee under a cloudy sky:

We see little difference in size from 40 hours to 14 hours before perigee, suggesting that another14 hours later wouldn't have shown much increase in size, had I been able to photograph then. I can always photograph a gibbeous near and at perihelion to confirm my guess, a project I'll enjoy doing when perigee occurs in evening hours at my location.

So, the super moon most of us missed appears just as big and just as bright as the more frequent "almost super moons" we see every couple years. This October, however, full moon will appear near apogee, the moon's farthest point from Earth. Weather permitting, I'll photograph that one too. The difference in size with this one should be striking.


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