Conversation started Feb 9, 2016 at 22:53.
Sir Cumference
Sir Cumference
Feb 9, 2016 22:53
All right, second question: is geometric albedo constant or does it change as the planet rotates? Also, is bond albedo constant?
By "constant", I mean it doesn't change when the planet rotates
duzzy
duzzy
I'm not even going to be able to participate in this one. :P
Hohmannfan
Hohmannfan
That does not change, that is for sure
Sir Cumference
Sir Cumference
Bond or geometric?
Hohmannfan
Hohmannfan
Both of them
Sir Cumference
Sir Cumference
Really?
Isn't geometric albedo the brightness when illumination comes from directly behind the observer?
So wouldn't it make a difference as the planet rotates, and light reflects off land, then ice, etc.?
Hohmannfan
Hohmannfan
Feb 9, 2016 22:58
But it averages out over one revolution
Sir Cumference
Sir Cumference
Oooh
So it's the average!
So wait, how is it different from Bond albedo?
Hohmannfan
Hohmannfan
Geometric is reflection towards the light source, Bond is in all directions
Sir Cumference
Sir Cumference
Oh yeah
All right, thanks
Wait, then what is geometric good for? Wouldn't Bond give us a better idea of the temperatures and surfaces of planets?
Hohmannfan
Hohmannfan
That is correct
Sir Cumference
Sir Cumference
So...?
Hohmannfan
Hohmannfan
Feb 9, 2016 23:04
Geometric predicts what you actually observes
Sir Cumference
Sir Cumference
All right, and what would it tell us?
Hohmannfan
Hohmannfan
"If I shine a bright light at this object, how bright would the surface look like from my point of view?"
Sir Cumference
Sir Cumference
So geometric and bond have two completely different uses?
Hohmannfan
Hohmannfan
yeah...
Sir Cumference
Sir Cumference
Cool
Hohmannfan
Hohmannfan
Feb 9, 2016 23:07
And confusing
Sir Cumference
Sir Cumference
And what would we use that data for?
How would it tell us about the planet?
Besides how shiny it is?
Hohmannfan
Hohmannfan
Geometric is "how shiny". Bond for calculating things like the surface temperature
Sir Cumference
Sir Cumference
Er, okay...
But do we need to know how shiny something is? Would it tell us the distance, or anything?
Does it help us find the Bond albedo?
Hohmannfan
Hohmannfan
They are two different measures, but not independent
Sir Cumference
Sir Cumference
Any formula relating them?
Hohmannfan
Hohmannfan
Feb 9, 2016 23:12
Only for perfect Lambertian surfaces and that kind of things. e.g. Not for any real objects. Then you do only have approximations.
Welcome to the insane world of optics!
Sir Cumference
Sir Cumference
Wait wait, if we're only using Lambertian surfaces, how does geometric albedo help us get any info in the slightest?
It's purely idealistic
Hohmannfan
Hohmannfan
But approximations can be good too
Sir Cumference
Sir Cumference
Yeah, but no surface can reflect and diffuse light like a Lambertian surface
Hohmannfan
Hohmannfan
Sure, but it is like using the black body radiation laws for approximating real emission.
Sir Cumference
Sir Cumference
GRAAAAH
Hohmannfan
Hohmannfan
Feb 9, 2016 23:15
Or patched conics for the n-body problem
Sir Cumference
Sir Cumference
So...geo albedo only tells us how a Lambertian surface would reflect light at that distance?
Hohmannfan
Hohmannfan
No, no, geo is a real thing
Sir Cumference
Sir Cumference
And Bond?
Hohmannfan
Hohmannfan
Is a real thing too
Sir Cumference
Sir Cumference
So...
Hohmannfan
Hohmannfan
Feb 9, 2016 23:17
You can not just be sure how they are related
Sir Cumference
Sir Cumference
OOOooooohhhh
Unless you have a Lambertian surface...
Hohmannfan
Hohmannfan
Or complete knowledge of the optical properties of the object in question
Sir Cumference
Sir Cumference
Ahhh...okay, makes sense :D
Thanks!
 
Conversation ended Feb 9, 2016 at 23:18.