## Light on distant bodies

Axel
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Location: Montreal, Quebec

### Light on distant bodies

Today's (17 January 2005) APOD mentions the '"eery orange light" on Titan but gives no idea of how much light - it can't be as much as it would be if Titan shared our orbit. I'd like to know how much light there is on a distant body when the Sun is high in the sky, taking into consideration what we know of the local atmosphere, but cannot imagine a way of conveying this helpfully to laypersons that would still be useful and semi-objective for comparative purposes. Might it be something like this: "The light at Noon here is like that on a clear Earth morning when the Sun is X degrees below the horizon"? (That wouldn't be helpful to late risers though.)

makc
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if you note that same amount of light falls on every sphere around the sun, you'll see that amounts of light falling on same facet at R1 and R2 can be connected with simple equation amt2 = amt1*R1^2/R2^2. that is, if it has same angles to coordinate axes.

makc
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### APOD 2005 January 17

Just wanned to stress on that this orange color is not real. It has been constructed from grayscale image (which, by the way, you can find here - edit by makc). So, the question is, where is real "source" data? Is it publicly available?

Christian Huygens
Were did you get that information; on what basis that image was colourized and syndicated all over the world without any warning or such, then

Axel
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Location: Montreal, Quebec

### Comparison must be empirical

The above answer would work in a vacuum; any helpful answer must be based on empirical data accounting for the atmospheres involved (including Earth's). Also, I am asking if there might be a way of approximately comparing light intensities that would be reasonably objective yet still accessible to intelligent amateurs. Knowing that there is, say, .01 times the light of an Earth Noon on planet X doesn't help me; knowing that it is like two hours before sunrise does help me - I have an idea of what that looks like.

crosscountry
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picture a very overcast day around sunrise. that's what I figure.

think about it. titan is bathed in clouds. and it's got way less sun that the earth hitting it at any moment.

makc
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Christian Huygens wrote:Were did you get that information
In photoshop. You see, when you perform auto-levels on actual color photos, you never see grayscale image as the result. Also, the fact that the rest of images are black and white, is really strong hint.
Christian Huygens wrote:on what basis that image was colourized
That's exactly my question.

Guest
anyone can do that with any image.

however in this case its true colour representation supplied in the data. more colour photos will come in later weeks. so to reply to this thread. it IS real.

Christian Huygens
Here’s ESA’s official caption accompanying the colour image:

First Color View of Titan's Surface
January 15, 2005
Full-Res: PIA07232

This image was returned yesterday, January 14, 2005, by the European Space Agency's Huygens probe during its successful descent to land on Titan. This is the colored view, following processing to add reflection spectra data, and gives a better indication of the actual color of the surface.

So, can we infer that the picture was shot in grayscale, then colourized afterwards?

makc
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absolutely no way. these two images are absolutely unrelated; one of them was taken by color camera, that broke up right after that; all other images were taken by 2nd reserve b&w camera. what a pity.

no, what I mean is that if these guys would make additional data available, perhaps someone could make better color images

name_removed

### How about more pics from titan's surface?

i have checked most official sites, and all i can see are only mosaics from the descent, all blacn and white of course
no more than 30 images, some of them pretty ugly

will be there more photographs like that color one from the mud in the surface?, i would enjoy that a lot

Christian Huygens
Absolutely unrelated?

If you position both images one on top of the other in Photoshop, you immediately notice that they were shot with EXACTLY the same perspective, angle, focals, etc.

So, one most assume that the Colour AND Black White Cameras were positioned at the same eight on the probe + had the same focal length, right?

S. Bilderback
They don't use color cameras, they take multiple photos from the same camera with different filters and superimpose the layers with color correction to create the colored image.

makc
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to Cristian: that was sort of humor.

to Bilderback: are raw images accompanied with filter curves, or is it available anywhere?
Last edited by makc on Tue Jan 25, 2005 9:12 am, edited 1 time in total.

ruidh
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S. Bilderback wrote:They don't use color cameras, they take multiple photos from the same camera with different filters and superimpose the layers with color correction to create the colored image.
Not on this probe they didn't. The original poster was right. They took a greyscale image and applied a single color to it derived from spectrometer data. The spectrometer can get a distribution of colors in the light in its field of view, but not an image. The image is intended to give an idea of what the surface looks like given the ambient light, but isn't a color photograph.