Dawn at Ceres Thread

[-Velocity-]

Amazing. I didn't assume it will be this tall.

Now we know what it is.

?

An ice-capped cryovolcano? Something must be continuously producing the water vapor they've supposedly detected, because the gravity sure isn't strong enough to hold onto it.

And I still disagree with you on whether these spots are grey or white. Remember, the 40% albedo measurement was taken before they resolved the spots. The reflected light was spread over a larger area than it actually subtends. So the reflectivity must in fact be much higher than 40%- so these spots are probably, in fact, "white".

[Kryten]

The idea that 40% albedo means something isn't 'white' is completely ludicrous. Have you looked at the moon lately? 14% albedo.

[Bill Phil]

I thought 100% Albedo was the black side of the scale?

[Kryten]

No. Clue's in the name, it's latin for 'whiteness'.

[Bill Phil]

You never know with them science guys...

I figured it was the opposite.

The moon being 14% white doesn't mean it's not bright. Even a solid black planet would have a reflection. If you had a monolith, that wouldn't be bright at all. Even in full sunligt.

[Newt]

Albedo of 1 means 100% of light reflected.

As for Moon, if you take a piece of dark material, say that absorbs 99.9999% of all the light that hits it, there still is a tiny bit of light reflected. Shoot enough light at the thing, and it will be really bright anyway. Moon is dark, absorbing 86% of the light that hits it (about), but as it is hit by so much light generally, low albedo regolith looks light grey. We do not have some high albedo surface to compare in the same conditions, so it is not really put into perspective as it is when dealing with objects close by. I hope that clears up some of the confusion.

(Wishing to post something more about Macula Mons (just a name I came up with, by no means official), but needing to do some more investigation first)

[moronwrocket]

The moon is visible in the day time. Pick up a rock, and hold it up against it in the sky. They will have similar illumination by the Sun. You'll have to subtract the effect of the blue sky between you and the Moon, but it does give you an idea just how "dark" the surface is compared to Earth rocks.

[-Velocity-]

The idea that 40% albedo means something isn't 'white' is completely ludicrous. Have you looked at the moon lately? 14% albedo.

I disagree. The "colors" white, black, and gray are entirely determined by albedo. While the word "white" isn't exactly well-defined, generally, it's going to mean a high albedo, like, I donno, 75% or higher. Gray can in fact appear white, if you compare it to something very dark, like the night sky, but if it was compared to something that was truly white under the same illumination, its grayness would be immediately obvious.

[Kibble]

I disagree. The "colors" white, black, and gray are entirely determined by albedo. While the word "white" isn't exactly well-defined, generally, it's going to mean a high albedo, like, I donno, 75% or higher. Gray can in fact appear white, if you compare it to something very dark, like the night sky, but if it was compared to something that was truly white under the same illumination, its grayness would be immediately obvious.

Common white asphalt shingles have an albedo of .2

[-Velocity-]

Common white asphalt shingles have an albedo of .2

So what? I'm sure white Labrador retrievers have an albedo of something like 0.3, but are actually called "yellow" labs. "Black" people are actually brown. Gray foxes are not actually gray, and they're not even in the Vulpes family (though they are closely related), so is even really correct to call them foxes? "Fisher cats" do not fish and are a species of marten, so they are as distantly related to cats as your dog is. Might as well call your cat a "flying weasel", it would be just as accurate.

Want me to bring up more unrelated examples of poor naming?

Edited March 4, 2015 by |Velocity|

[Camacha]

Want me to bring up more unrelated examples of poor naming?

I think the point is that white shingles are actually quite white, though their albedo is low, not that they are not aptly named.

[PlonioFludrasco]

That picture gives a very good idea of how long low-thrust burns can be: http://www.nasa.gov/sites/default/files/images/552784main_trajectory_new-full.jpg

[Frozen_Heart]

That picture gives a very good idea of how long low-thrust burns can be: http://www.nasa.gov/sites/default/files/images/552784main_trajectory_new-full.jpg

Yet people seem to still want that level of thrust in KSP...

[-Velocity-]

I think the point is that white shingles are actually quite white, though their albedo is low, not that they are not aptly named.

This is a ridiculous discussion. Things with an albedo of 0.2 are not white on any reasonable scale where white-gray-black are defined by their albedos. All you have to do is put something next to it that has an albedo of 0.9 and you will see that they do no longer appear white.

Your point is non-existant because you're comparing apples and oranges. In our normal everyday experience, white-vs.-gray-vs.-black is comparative to a well illuminated background. You cannot apply your normal everyday experience to astronomy. In astronomy, the background- space- is extremely dark. So even something with an albedo of 0.001 could appear white (if it was color neutral), while on Earth, it would appear jet black. If you want the words "black", "gray", and "white" to have any meaning at all in an astronomical context, you have to define a range of albedos that correspond to these colors. Any reasonable range is not going to put an albedo of 20% as "white", because then most color neutral objects would be "white". Ice would be the same "color" as most rocks. That would be silly. In my experience, I have only ever seen things with very high albedos are called white.

Edited March 4, 2015 by |Velocity|

[Rakaydos]

This is a ridiculous discussion. Things with an albedo of 0.2 are not white on any reasonable scale where white-gray-black are defined by their albedos. All you have to do is put something next to it that has an albedo of 0.9 and you will see that they do no longer appear white.

I'm pretty sure an albedo of .9 would be silver, not white.

[vger]

I think some people need to open up a paint program, and play around with the HLS color picker. "Brown" is just a dark shade of orange, for example.

Hue does not equal saturation, which does not equal luminance. And that's not even getting into reflectivity. Common understanding of how "color" actually works is VERY poor.

[Camacha]

Your point is non-existant because you're comparing apples and oranges.

Please do not pretend I am an active part of this discussion, I was just trying to help. I am not the target of your zeal, I was just trying to fix some of the mutual lack of understanding there seems to be.

I think some people need to open up a paint program, and play around with the HLS color picker. "Brown" is just a dark shade of orange, for example.

Hue does not equal saturation, which does not equal luminance. And that's not even getting into reflectivity. Common understanding of how "color" actually works is VERY poor.

It appears so. Colour, reflection and refraction are rather complicated subjects which can hardly be summarized in one metric. The sheer number of colour profiles, standards, technologies and whatnot shows there is a lot to be said and done

[Newt]

Kindly requesting that albedo discussion move along elsewhere. Feel free to start a new thread, and I will contribute, but this thread is meant to be about Ceres, not about shingles and asphalt.

A thought occurred to me that one of the spots could be elevated as it is on a crater central peak. The height we could get from the image (not excellent resolution) makes it hard to tell how high up it would be, but that is a possibility. There are similarly sized craters on Ceres with apparent peaks.

[lajoswinkler]

I'm pretty sure an albedo of .9 would be silver, not white.

Not at all. This is all there is to know about the difference.

Compare with sugar. Sucrose in its pure state is a transparent, colorless crystal. Crush it or just pile it on one place and you get this.

Not so transparent anymore, eh? It's the same thing white flowers' petals do. They don't possess color, only structure which disperses light.

[Nuke]

so its settled, the white spot is a giant funnel cake!

[vger]

so its settled, the white spot is a giant funnel cake!

My Kerbals tell me it didn't taste like funnel cake.

[Vanamonde]

Seriously, guys? You're getting into an argument about the definition of "white"?

Please, just talk about Ceres, okay?

[Rakaydos]

Not at all. This is all there is to know about the difference.

http://math.hws.edu/eck/cs424/notes2013/images/09/reflection1.png

Compare with sugar. Sucrose in its pure state is a transparent, colorless crystal. Crush it or just pile it on one place and you get this.

Not so transparent anymore, eh? It's the same thing white flowers' petals do. They don't possess color, only structure which disperses light.

My point is that powdered silver would have a higher albedo than powdered sugar- silver has a higher albedo than white.

[magnemoe]

Not at all. This is all there is to know about the difference.

http://math.hws.edu/eck/cs424/notes2013/images/09/reflection1.png

Compare with sugar. Sucrose in its pure state is a transparent, colorless crystal. Crush it or just pile it on one place and you get this.

http://img.ehowcdn.com/615x200/ehow/images/a04/vk/ec/alternatives-powdered-sugar-800x800.jpg

Not so transparent anymore, eh? It's the same thing white flowers' petals do. They don't possess color, only structure which disperses light.

If you work with textures for 3d models you learn a lot about this, difuse is the actual color, specular is how shiny something is. Compare black wool and a black leather jacket, you you have polished shoes you get reflection too, and this is just three layers.

[peadar1987]

so its settled, the white spot is a giant funnel cake!

To Ceres!