Astrophysical Laws and Formula

[Rassilon]

This has not been done yet and I think it would help me and alot of others out if there was a post "stickied maybe' of all formulas in computing planetary calculations.... I suppose Ill be the first to contribute, mind you it might not be correct...

One I find easy to implement when I generate ssc files is finding the period of revolution by:

period = sqrt(distance??)

Now thats when the mass of the star equals that of our sun... Could someone add to this to make it complete?

[Malenfant]

This has not been done yet and I think it would help me and alot of others out if there was a post "stickied maybe' of all formulas in computing planetary calculations.... I suppose Ill be the first to contribute, mind you it might not be correct...

One I find easy to implement when I generate ssc files is finding the period of revolution by:

period = sqrt(distance??)

Now thats when the mass of the star equals that of our sun... Could someone add to this to make it complete?

Try:

Code: Select all

T = SQRT(((D^3)*(4*(PI()^2)))/(G*M))

Where D is distance from primary in metres, M is the mass of primary in kg, and T is the orbital period in seconds. (and G is the gravitational constant G). That'll give you a much more accurate answer

[Rassilon]

Thanks!

Thats what I was looking for... Also I was wondering the proper calculation for minimal roche limit of moons.... I used to guess they were 3 times the radius of the parent body but I suppose it also would have to do with the size of the moon...

[Malenfant]

Thanks!

Thats what I was looking for... Also I was wondering the proper calculation for minimal roche limit of moons.... I used to guess they were 3 times the radius of the parent body but I suppose it also would have to do with the size of the moon...

That's correct only if the densities of the primary and the satellite are the same.

It's approximately equal to:

Roche limit = 3*[(planet density/satellite density)^(1/3)]

where the roche limit is in planetary radii, and densities are in kg/m3

[Rassilon]

That's correct only if the densities of the primary and the satellite are the same.

Would this also apply to the distances between each moon? Is there a roche limit there? If so is there a way to compute this?

[Malenfant]

That's correct only if the densities of the primary and the satellite are the same.

Would this also apply to the distances between each moon? Is there a roche limit there? If so is there a way to compute this?

Actually you might be better off looking here:
http://en.wikipedia.org/wiki/Roche_limit

That explains everything a bit better. I'll have to check my notes again, not sure where I got that 3 multiplier from... it seems to be nearer 2.5 in reality.

[Rassilon]

Thanks! That actually helps alot...

Ok I think this may have been discussed before but I cannot remember... Sunset color...

How is sunset color determined exactly? Ive seen discussions on scattering effects of sunlight and came to the conclusion that if you take the color of the star add it to the atmosphere and invert it you come up with the sunset color... Is this true? Also/Or does it depend on the color of the atmosphere? And if so how is atmosphere color determined based on star color?

[Malenfant]

How is sunset color determined exactly? Ive seen discussions on scattering effects of sunlight and came to the conclusion that if you take the color of the star add it to the atmosphere and invert it you come up with the sunset color... Is this true?

IIRC the shorter (bluer) wavelengths are absorbed by the thicker atmosphere nearer the horizon (the light has to pass through more atmosphere there than when the sun is high up). The simplest way to simulate that would be to just remove the bluer colour. I'd imagine for example that if we orbited an F or A V star then sunsets would be more yellow than red, while in normal daylight the sun would look whiter.

Also/Or does it depend on the color of the atmosphere? And if so how is atmosphere color determined based on star color?

That I'm not sure of... I thought I saw something that said that regardless of the atmosphere composition the default sky colour would still be a shade of blue - it's just dust and particulates and aerosols (which there are usually a lot of) that change the colour. e.g Mars would have a dark blue sky if it wasn't for the suspended dust making it reddish. I think selden or grant talked about this at some point here...

[Rassilon]

I found this article on Rayleigh scattering

http://www.faqs.org/faqs/astronomy/faq/ ... on-17.html

It seems that the majority of planets will have a blue atmosphere unless the particles that make up the gases are larger than the particles that make up the light wave...

And on sunsets... It would be pretty cool to see green flashes and other sunset distortions such as swell etc when viewing the sunsets on Celestia...

http://mintaka.sdsu.edu/GF/explain/simu ... ockSS.html

I think that someone could implement a billboard that could be seen only on a planets surface that simulated this swelling... But thats for another discussion...

Now to truly vaporise my illusions on this I read somewhere that A class stars can sometimes exhibit a greenish hue... Is this true?