Moonlight vs Sunlight

[Norm Nason]

Is moonlight actually bluer than sunlight, as it appears to the naked eye?. Does anyone know where I may find a spectral analysis of each?

[Faultline]

Not sure. It doesn't seem to harm vampires, so I suppose there is a significant difference between the two.

:roll:

[Elyk]

XD true, vampires don't seem to mind it haha. That is funny, I've never thought of asking people who believe in vampires, "Wouldn't moonlight hurt them too?"

[Elyk]

Um anyway, I think it just looks blue because it isn't so bright, since it's just a reflection. Probably something having to do with the atmosphere filtering it in a weird way. I wonder if moonlight out in space is just white, or whatever true color the sun is.

[hhEb09'1]

George! here's another one!

[Ken G]

I've wondered about this myself, and still don't really know the answer. I think part of the problem is that our eyes are conditioned to try and see the prevailing light as white, and I think this applies both in sunlight and in moonlight-- they both appear very white (as you can see by looking at a white sheet of paper, or a white house). But your question remains, does the albedo of the Moon depend on wavelength?

[Fortis]

This guy has had fun taking photos at night, just using the Moon for illumination, but increasing the exposure times to boost the illumination to the solar equivalent. Beautiful images, and strangely eerie thanks to the star trails in what looks like a normal, daytime, blue sky.

[Matherly]

"Wouldn't moonlight hurt them too?"

Well, according to the Book of Nod, the Sun specificaly hurts vampires because of the curse place on Caine by the Archangel Raphael.

:shakes head: I am such a geek.

[Ken G]

But why does bouncing it off the Moon remove the sunlight curse-- can vampires withstand scattered sunlight indoors in the daytime? Or is it an intensity issue, where the Moon is only uncomfortable but not fatal? And is this good or bad astronomy?

[Van Rijn]

First, a welcome to Norm Nason. This appears to be your first post. That is an interesting question! Unfortunately, I can't add much, though the images Fortis dug up are suggestive that the reflected spectrum isn't too different from the sun's.

On the completely irrelevent mythical vampire subissue: A common modern interpretation is that vampires are extremely sensitive to ultraviolet. Any light without UV wouldn't harm them. Now I'm wondering if there is any detectable UV at night.

[Fortis]

This link contains a measurement of the lunar spectral reflectance in the vis/NIR/SWIR. To do it properly you'd need the BRDF, which tells you how the viewing and illumination geometry affects it, but it does appear to drop off as you go towards the blue end.

[Matherly]

But why does bouncing it off the Moon remove the sunlight curse-- can vampires withstand scattered sunlight indoors in the daytime? Or is it an intensity issue, where the Moon is only uncomfortable but not fatal? And is this good or bad astronomy?

Well, obviously I'm quoting a fictional source so the creators can make up any rules they want. Withing the confines of the White Wolf "World of Darkness" role-playing games, the curse on vampires is mystical in nature and sunlight and moonlight are diffrent mystically, if not scientifically.

Oh, and no, generally WoD vampires cannot withstand scattered sunlight. Although a small amount of sunlight creates proportially smaller burns.

(And I just keep geeking it up )

[mahesh]

This guy has had fun taking photos at night, just using the Moon for illumination, but increasing the exposure times to boost the illumination to the solar equivalent. Beautiful images, and strangely eerie thanks to the star trails in what looks like a normal, daytime, blue sky.

Fortis hi

thanks for the link.....it just blew me away...beautiful

(i have used infrared ektachrome for daylight photography...some really eerie results, nice though)

thanks again

[Grey]

This guy has had fun taking photos at night, just using the Moon for illumination, but increasing the exposure times to boost the illumination to the solar equivalent. Beautiful images, and strangely eerie thanks to the star trails in what looks like a normal, daytime, blue sky.

Those are pretty cool. But now I'm perplexed. These seem to be exposures of only a few minutes, yet I've seen many shots of the night sky with star trails over several hours still showing a black sky. Or were those shots all specifically taken on nights with no moon, and nobody before now has bothered to mention that if you don't pick the right night to take such a photo, you'll end up with it looking like daytime?

[Elyk]

Those are pretty cool. But now I'm perplexed. These seem to be exposures of only a few minutes, yet I've seen many shots of the night sky with star trails over several hours still showing a black sky. Or were those shots all specifically taken on nights with no moon, and nobody before now has bothered to mention that if you don't pick the right night to take such a photo, you'll end up with it looking like daytime?

I'm wondering the same thing...Because they leave the shutter open a long time but its still dark as night in those pictures.

[Fortis]

Good question. According to this page the illumination from a full moon is 1-2 lux, whereas that from starlight alone is ~0.0001 lux.
I guess it may well be that people avoid taking star-trail images around full moons because even at short exposures you get reduced contrast, and so they never go the whole hog and take a really long exposure?
I'm going to give this one a try.

[Jeff Root]

A few years ago a film crew set up down the block and shot night
scenes all night long. I suspect that they intended it to appear
to be moonlit, and that it was no coincidence that it was right
at full Moon, with the Moon high in the sky at midnight. They
also had a fairly bright movie light, though, on a crane 35 or
40 feet above the street. It was much brighter than any street
light, but not as bright as a searchlight. They cut off a tree
branch and stuck it in front of the lamp so it would cast shadows
like moonlight through the trees.

From where I was watching, the Moon and the movie lamp were
side-by-side. The Moon looked very yellow compared to the lamp,
which was blue-white.

* * * *

Here's an image of the ASTRO-1 telescope mounted on the Space Shuttle
payload bay, with Orion in the background. The telescope is illuminated
by moonlight:

http://science.ksc.nasa.gov/mirrors/...5/10063952.jpg

-- Jeff, in Minneapolis

[The Mangler]

Those are pretty cool. But now I'm perplexed. These seem to be exposures of only a few minutes, yet I've seen many shots of the night sky with star trails over several hours still showing a black sky. Or were those shots all specifically taken on nights with no moon, and nobody before now has bothered to mention that if you don't pick the right night to take such a photo, you'll end up with it looking like daytime?

I'm not a professional, but this is the basic concept that will explain this (I think):

Shutter speed (exposure time) controls the speed of the shutter (duh)
ISO speed is the sensitivity to light.
Higher ISO speed means high sensitivity to light.
If the ISO speed was high enough (my camera goes from 100 to 1600, in 1 stop increments. Don't know how high it needs to be for this [EDIT: the captions on the pictures say it was at ISO 200 & ISO 400 on one of them. I would have thought it would be higher than that.], I've never tried those kind of pics. Maybe I will now though...) and you had shutter speeds like the ones used in those pictures I guess it could work.
Shutter speed doesn't necessarily have anything to do with light gathering.

Next full moon (12/15) I'll try it and see what happens (I might not wait that long though... If it works I'll post it on here ).

[The Mangler]

Mars 12-3-05 small file.jpgI didn't think there was enough moonlight tonight, but I still wanted to play around... This is either a 15 or 30 second exposure (I can't believe I forgot ) of Mars at ISO 1600.

I'm not very impressed with the picture quality (plus, I had to compress it to make it small enough to post here, making the quality even worse), but I think it's kinda cool how it made the rest of the sky red. A lower ISO speed would have made it less grainy, but my battery was going dead, so I came back inside to charge up. I don't know if mars is actually moving fast enough that a 30 second exposure would show movement like this (maybe I bumped it), but it doesn't look like any of the stars moved. Plus, it looks like it moved the wrong direction (I was facing east, so it should be moving up, not down right?

To do exposures longer than 30 seconds on my camera, you have to actually hold the shutter button down for as long as you want it to stay open, which means I have to get a much sturdier tripod before I try those 10 minute long shots.

[Kiwi]

...now I'm perplexed. These seem to be exposures of only a few minutes, yet I've seen many shots of the night sky with star trails over several hours still showing a black sky. Or were those shots all specifically taken on nights with no moon, and nobody before now has bothered to mention that if you don't pick the right night to take such a photo, you'll end up with it looking like daytime?

Black-sky photos will be either without moon or with suitable filtering, and blue-sky photos will be with moonlight. Nobody really needs mention it because anyone who has a go at it will quickly learn. Most people who want only stars and deep-sky objects take their photos on moonless nights, well away from light pollution.

Not enough people take landscapes and other scenes by moonlight, which can produce wonderful effects because of the long exposures. E.g.: waves, running water and wind-blown objects will appear as mist, and "ghosts" and "UFOs" can be easily added. Flash can be added to the foreground too, with time for multiple exposures on the one frame, or you can paint light with a torch. And you don't need a full moon -- less than a quarter moon is bright enough and it just means longer exposures. Record all the exposure details so you can learn from them.

It can be really confusing to people who view a landscape with lights or stars in it, yet it looks like it was taken by sunlight.

I stopped off one moonlit night to photograph New Zealand's Mount Ruapehu with Orion lying on it's side and setting just above the snowy top of the mountain. I cradled my camera with wide-angle lens in a bean-bag on the bonnet of my car and, using a cable release, took exposures of 30 seconds at f4 on 200 ISO film. Everything came out perfectly, the sky coming out light to deep blue and the land, foliage and mountain looking sunlit. Even the pink Orion nebula showed up, and the photo lab reprinted a few shots through thinking that the stars were dust.

Earlier in the evening I took a photo of Lake Taupo with the lit-up town in the background, moonlight glinting off the lake, and Jupiter up in the sky.

[Fortis]

[QUOTE=The ManglerI'm not very impressed with the picture quality (plus, I had to compress it to make it small enough to post here, making the quality even worse), but I think it's kinda cool how it made the rest of the sky red.
[/quote]
Nice.

I suspect that at least some of the redness may come from light polution. I've yet to give this one a go myself, but am looking forward to it.

To do exposures longer than 30 seconds on my camera, you have to actually hold the shutter button down for as long as you want it to stay open, which means I have to get a much sturdier tripod before I try those 10 minute long shots.

If you can get a remote for your camera (the guy in the article used an IR remote), that might help. I'm stuck with a max of 30 seconds so I'm planning on just using the timer delay to trigger the shutter, and hopefully cut down on vibration.

[hhEb09'1]

Those are pretty cool. But now I'm perplexed. These seem to be exposures of only a few minutes, yet I've seen many shots of the night sky with star trails over several hours still showing a black sky. Or were those shots all specifically taken on nights with no moon, and nobody before now has bothered to mention that if you don't pick the right night to take such a photo, you'll end up with it looking like daytime?

Messier marathons (where one tries to see all Messier objects in one night) are done during the part of the year when the sun is in that part of the sky that is more devoid of Messier objects, on a weekend (for obvious reasons) nearest the new moon, for the reason Kiwi gave.

Shutter speed doesn't necessarily have anything to do with light gathering.

I suppose it doesn't but in general, twice the shutter speed (if speed is given in seconds ) gives twice the light gathering