Posted: Jul 03, 2012 9:12 am
campermon wrote:twistor59 wrote:Talking of which, from the Guardian:
(I've pasted a quote, because surely they'll correct it?)Supermoon makes photographers go crazy
Perigee moon appears 14% bigger and 30% brighter as planet passes closer to Earth
Now I'm not an expert astronomer but.....
http://www.guardian.co.uk/science/2012/may/06/supermoon-makes-photographers-crazy?CMP=twt_fd
From here; http://www.fourmilab.ch/earthview/moon_ap_per.html
The angular size;
Perigee - Angle subtended: 0.5548°
Apogee - Angle subtended: 0.4923°
So at perigee it appears to be about 14% wider than at apogee.
Not sure about the moon been 30% brighter.
edit - the same link also says that it's about 30% brighter.
We can apply some basic geometry here.
Let us approximate the appearance of the Moon by a disc. This disc will have a certain radius, r. This disc will have a certain surface area, said surface area being given by A = 4πr2. The apparent brightness will be proportional to the surface area - a larger reflecting surface will appear brighter than a smaller surface, because it's reflecting more incident light rays in our direction, and the number of incident light rays reflected in our direction will be proportional to the area.
So, let us increase the radius by 14%. This means that the radius is now 114r/100. Feeding this into the equation for area, we have that the new area is 4π[114r/100]2
= 4πr2 × (114/100)2
= 4πr2 × (129.96/100)
So the new area is 29.96% greater than the old area - approximately 30%.
QED.