Wow, it is so incredibly bright tonight. Clear skies and a full moon, I don't think I have ever seen it so bright. Amazing.
Most people would rather die than think, and most people do.
- Bertrand Russell
- Bertrand Russell
i think it has something to
i think the moon's brightness has something to do with the proximity to the winter solstice.
on thursday night, it rose so huge and orange-y bright, i didn't recognise it for moment.
cool it was super bright
cool
it was super bright here but a blinding white colour
solstice
That surely contributes to some change in the brightness, but I can't imagine it being anywhere near as much of an effect as just about everything atmospheric. I have difficulty believing the percentage change would even be detectable to the human eye (in the absence of a proper analysis that shows one way or the other - something i'm too lazy to do right now).
I lied
This is actually not a very hard problem, as I later realized while trying to get to sleep and being kept awake by the fun physics of this, convincing me of my position.
First, the notion of flux. Flux is (basically) a measurement of the flow of something through an imaginary loop. In this case, we define our loop as the surface of the moon - which we will approximate as a flat surface (i'll get back to that at the end) - and then see how much the light flowing through it changes from earth's perihelion to aphelion.
To determine the change, we need to know the difference in the amount of real estate the moon takes up in the sun's sky. The sun radiates spherically, and the area of the surface of a sphere is 4 x Pi x r^2. The area of the moon is (1/2 x d)^2. 'd' will not change of course, but r will have two values. There will be a percentage change in the amount of flux based entirely on the percentage change in the amount of space the moon occupies in the sphere of flux around the sun.
r at summer solstice = 152,097,701 km + 384,403 km
r at winter solstice = 147,098,074 km + 384,403 km
d of moon = 3,474 km
Percentage of sky in summer = (Pi x 1,737km^2)/(4 x Pi x r1^2) = 3.24416 x 10^-9 %
Percentage of sky in winter = 3.46784 x 10^-9 %
Clearly the change in flux to the moon is minuscule from the sun's perspective, but from the moon's perspective that's a 6.8% increase to the amount of energy it is receiving. That's not the end though, because the moon doesn't reflect most of the light that hits it (most is absorbed and later re-radiated in IR). It's albedo is 0.12 for all of the sun's light, and for visible light that's a bit less, around 0.09. So only 9% of the light hitting it is reflected, thus the maximum visible change to an ideal observer of the moon is 0.61%.
At this point, it's not worth going further, and the number still needs to be shrunk considerably due to the fact we're not ideal observers (the moon isn't a flat circle, it's a sphere, so most of the reflected light never even reaches the earth) plus we haven't even started on the minimum interference of the Earth's atmosphere which cuts down the amount of light even more - not the percentage change mind you, but lower total light means the less actual change a percentage shift will cause and thus the more sensitive our eyes would have to be to even be physically capable of detecting a shift.
Bottom line is, most people can't even tell a 1% change of intensity on their computer screen that occupies almost all of their vision, let alone a tiny visual angle the size of the moon fully 6 months apart. It's beyond a stretch that any human could detect something probably on the order of 1/100th or 1/1,000th of a percent in a change of intensity.
interesting analysis
but I think it was brighter cause the sky was clearer than usual due to the extreme cold air at the surface of the earth that we've been suffering from lately.
cold air
Cold air is dense air. However cold air also has a LOT less water in it, however I think even this effect is largely dwarfed by one thing and one thing only which singularly can explain why winter moons appear so much clearer and brighter...
There's more night in the winter. Up here in higher latitudes, our nights get long in the winter and so by the time the full moon rises, it's a little later after sunset in a sky that is getting darker much faster. There is so much less light elsewhere in the sky compared to the moon as it is rising that it will appear much much brighter.
This effect lasts through the night as well because there is considerably less light bouncing around in the upper atmosphere during a winter night (a higher-latitude location is deeper in the umbra) making many stars more visible that we can't see in the summer.
You would think then that the moon would also be so much brighter in the tropics. And to some extent, it is, but the atmosphere is so very much thicker in the tropics that the effect is countered and the moon is actually much duller year round instead.