You know how some nights you can see the missing bite from the moon as a shade lighter than the black sky behind? I understand that’s the surface of the moon illuminated by light reflected from Earth, right?
My question is, does that change in any perceptible way depending on location? Would it look brighter in Central Asia during the winter (all snow and ice with high Albedo) than in the middle of the Pacific (all dark ocean water with low albedo).
I understand that we are all seeing the same moon and it looks equally bright no matter where you are, so it would not be your location but whatever location is currently reflecting sun light to the moon.
When is the best time to see this and what does that mean in terms of what location is influencing what you see?
Does it change with season? snow cover vs forest or crops?
Yes, a true blue moon can be caused by weather, and (I’ve heard, no cite) whether the moon is getting a lot of reflected light from the Pacific Ocean right then.
But definitely by the weather and recent geologic phenomena.
Yes, but as described in the previous link, you’ll need precision instruments to measure it. It isn’t something you’ll notice by casual observation, because the exact brightness of the earthshine will be overwhelmed by variation in the width of the sunlit crescent on the Moon, the angle at which the Moon sets from your location, and local weather and sky transparency.
Viewing the earthshine is a trade-off–as the new moon “ages”, it moves farther from the sun, so you can view it higher in the sky and against a darker background. But conversely, as the crescent gets thicker, the earth is getting less full as seen from the moon, so the earthshine gets fainter, and it gets overwhelmed by the fattening sunlit crescent. In general earthshine is best two to three days before or after new moon.
Beyond that, polar ice has the highest albedo, so I suppose the earthshine is a little brighter in winter, when the Sun is shining on Antarctica. And it’s brighter when the daylight half of earth is shrouded in clouds. But again, you won’t notice by casual observation.
Come to think of it, there’s another reason why earthshine would be brighter in January–the Earth is near perihelion and receiving and reflecting 7% more light than in July.
Another factor is the distance of the Moon from the Earth. Near perigee = more earthshine; near apogee = less.
When it all comes together–a crescent Moon near perigee, in January, when the daylight hemisphere is mostly cloudy except for Antarctica–mmm yeah, that’s good earthshine.
Yes and no. The exact math is beyond me, because of the perigee/apogee thing . . . The earthshine is brighter at perigee, but it’s also spread over a larger surface area, so I’m not sure how the brightness per unit of sky varies.
But still, putting it together . . . the earthshine under the perigee/perihelion/high-albedo combo is at least 20% brighter than the reverse, and that’s a pretty significant difference. I have no doubt that if you were to line up two moons in the sky, and dial up the earthshine brightness on one by 20%, you’d be able to tell the difference.
However . . . in real life, you don’t get to line up two moons in the sky. You get brief glimpses of earthshine, now and again, with the moon at a different age and different elevation and under different sky conditions each time.
By way of analogy, some full moons are 10% wider and 20% brighter than other full moons. That’s a pretty significant difference. If I show you two circles, you can tell if one is 10% wider. But do you feel like you notice the difference in moon size? Probably not; memory is imperfect from one month to the next.
So if you were to tell me, “The earthshine looked brighter this month than last month”, I’d be skeptical. Did you see the moon at the exact same age each month? There’s a big difference between earthshine on a two-day-old moon and a three-day-old moon–enough to drown out the other effects. Was the moon at the same elevation above the horizon? Were sky conditions comparable?
Blue (and more commonly., green )moons do indeed result from atmospheric scattering under unusual conditions. I’ve written a piece about them. But I seriously doubt that you get a “blue moon” from reflections from the Pacific. And I’ve never heard of such a thing.
Take a total lunar eclipse, which can range from a bright red/white to so dark you almost don’t notice its the moon sitting there, with the only difference being atmospheric conditions on the Earth.
It would not surprise me that Earthshine on the moon, which is still somewhat a function of the atmospheric conditions on Earth, could vary an observable amount.
My WAG is that a well used and calibrated eyeball could tell a difference. My eyeball and brain think they can (maybe/possibly). But IMO it would be fairly subtle.
As noted by others, other variables such as exact location in the sky, phase of the moon, and local observing conditions would be hard to filter out from such an observations.
You are joking, right? My memory is imperfect from one hour to the next, never mind a month. Point well taken, though. Maybe a photo is all it would take (assuming you fix your camera settings).