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View Full Version : Full Moon at Perigee - 2011 MAR 19



Centaur
2011-Mar-14, 04:46 PM
The Full Moon of 2011 MAR 19 will occur near the time of perigee. The Moon was most recently closer during the Full Moon of 2008 DEC, not 1993 as reported in the popular media. Unfortunately for us North Americans, it will be daytime with the Moon beneath the horizon when it is most fully illuminated and at the time of perigee. For us the nights of March 18/19 and March 19/20 will serve as equally good consolation.

Full Moon at perigee occurs once every 14 synodic months (lunar months of 29.53 days). I’ve created a chart illustrating various factors for the next 15 Full Moons, the first and last occurring near perigee. It can be seen at http://www.curtrenz.com/moon

Although this month’s Full Moon will appear particularly large due to its occurrence near the time of perigee, the previous two Full Moons were actually brighter. That’s because the Earth/Moon duo was closer to the Sun, and the Moon was nearer to the ecliptic thus enhancing the opposition flash. These factors increased the number of photons being reflected back toward us.

The brightness factor on my Full Moon chart gives a value of 1.00 when both the Sun and Full Moon are at their mean distances from Earth, and the Moon is on the ecliptic. Of course that would be during a total lunar eclipse, but for the standard it is assumed that sunlight passes unimpeded through the Earth. For a Full Moon that actually goes into eclipse, the brightness factor is an average for the moments just before and after the Moon touches the Earth’s penumbra.

Photos and discussions of this month’s especially large Full Moon would be welcome additions to this thread. Below is the picture I took of the rising Hunter’s Moon on 2010 OCT 22.

http://www.curtrenz.com/FM101022.jpg

elizabeth25
2011-Mar-15, 10:47 AM
wow that looks beautiful, i am looking forward to seeing the moon on the march 19th, as i live in the UK, it will be dark, but hopefully we will also have a perfect clear sky, i will try and get a picture and upload it on here so everyone can see. fingers crossed for a clear sky.

Centaur
2011-Mar-22, 05:25 AM
Thank you, Elizabeth. Did you get a picture?

There seems to be some confusion in the popular media regarding the factors that produce lunar perigee and apogee. The shape of the orbit is irrelevant. Itís a virtual circle that is only slightly elliptical, i.e. the mean semi-major axis is only 1.0015 times the length of the mean semi-minor axis. And the semi-minor axis plays no role in perigee, since perigee and apogee occur at opposite ends of the major axis. The significant factor resulting in perigee and apogee is the mean orbital eccentricity of 0.055, i.e. on average the Earth is separated from the orbital center by 0.055 times the length of the mean semi-major axis.

A = Semi-major axis of ellipse
B = Semi-minor axis of ellipse
C = Distance between a focus of the ellipse and its center
D = Ellipticity (non-circularity)
E = Eccentricity (focus off-centeredness)

In the case of the lunar orbit, A is half of its longer axis. B is half of its shorter axis. C is the distance of the Earth's center from the orbital center.

E = C/A

D = A/B = 1 / Square Root(1 - E≤)

Mean E for lunar orbit = 0.055 (varies between 0.026 and 0.077 during as little as 3 months)
Mean D for lunar orbit = 1.0015

The ellipticity D is barely different from circular, as seen in my diagram below. It is only at large eccentricities that the ellipticity would be obvious in a diagram.


http://www.curtrenz.com/LunarOrbit.JPG

elizabeth25
2011-Mar-23, 07:56 PM
wow very interesting, thanks. erm well i went to the park to see it as it is much darker there, but the camera on my phone is rubbish so all the pictures i have looks just like a ball of light, but as i was driving home that night about 7pm the moon was just coming up behind the hill and it was huge, the most amazing beautiful thing i have ever seen. i was speechless. did you get to see it?

Hornblower
2011-Mar-23, 08:53 PM
wow very interesting, thanks. erm well i went to the park to see it as it is much darker there, but the camera on my phone is rubbish so all the pictures i have looks just like a ball of light, but as i was driving home that night about 7pm the moon was just coming up behind the hill and it was huge, the most amazing beautiful thing i have ever seen. it had the orange glow to it from the earths shadow. i was speechless. did you get to see it?

My bold. No, the orange glow was caused by atmospheric dimming and reddening. There was no eclipse this time.