## Posts by Evil Dr Ganymede

28.05.2005, 01:16
Forum: Physics and Astronomy
Topic: how to calculate magnitudes?
Replies: 35
Views: 10170

### Re: how to calculate magnitudes?

OK, I think I got it. My first equation was actually correct, but I'd swapped the absolute and apparent magnitudes for Sol around. The following appears to be correct: Equation for calculating Absolute Magnitude of a star given only its Luminosity and Distance from viewer. http://www.evildrganymede....
28.05.2005, 00:26
Forum: Physics and Astronomy
Topic: how to calculate magnitudes?
Replies: 35
Views: 10170

### Re: how to calculate magnitudes?

Also, that m_sol is weird in the formula. Should be m_star, the APPARENT magnitude of the star, as seen from sol, isn't ? Should be something like this : http://nho.ohn.free.fr/celestia/Cham/Divers/equation3.jpg Don't think so. The whole point is that we don't know the apparent or absolute magnitud...
28.05.2005, 00:17
Forum: Physics and Astronomy
Topic: how to calculate magnitudes?
Replies: 35
Views: 10170

### Re: how to calculate magnitudes?

Evil, you should get everything there : http://www.physicsdaily.com/physics/Absolute_magnitude That's just what Selden quoted earlier though, it doesn't help because it doesn't include the luminosity terms. And don't forget this formula is using the base 10 log, NOT the natural log. yep, been using...
28.05.2005, 00:00
Forum: Physics and Astronomy
Topic: how to calculate magnitudes?
Replies: 35
Views: 10170

### Re: how to calculate magnitudes?

Gah! Still the result is the same - if Lstar/Lsol = 1, and d_star = 1.5844e-5 ly (1 AU), then M_star = 36.4, which is wrong. The Absolute Magnitude of the sun should be -26.74. I can get that by replacing the - sign in Cham's equation with a + sign. But if I keep Lstar/Lsol = 1, and change d_star, t...
27.05.2005, 23:53
Forum: Physics and Astronomy
Topic: how to calculate magnitudes?
Replies: 35
Views: 10170

### Re: how to calculate magnitudes?

Indeed, my equation could be simplified considerably. Sorry, I didn't took time to write it correctly. Here it is, but I can't confirm your equation was right, as I don't know the magnitude definition. http://nho.ohn.free.fr/celestia/Cham/Divers/equation2.jpg What is this damn number, 32.616 anywwa...
27.05.2005, 23:46
Forum: Physics and Astronomy
Topic: how to calculate magnitudes?
Replies: 35
Views: 10170

### Re: how to calculate magnitudes?

At least in the part of the world where I live, the general idea is that /teachers/ explain the logical steps of how to arrive at the solution, while the students are gaining practice in working things out explicitly... Yes, but if it's clear that the student can't figure it out, then you don't jus...
27.05.2005, 23:33
Forum: Physics and Astronomy
Topic: how to calculate magnitudes?
Replies: 35
Views: 10170

### Re: how to calculate magnitudes?

That's what I managed to figure out eventually, but it doesn't look like it's right. Replacing: m_sol = 4.83 I got: Ms = 4.83 - [1/0.4*log((L_star/L_sol)*((d_star/d_sol)^2))] - 5log(d_star/32.616) Which is almost the same as what you get, but the dsol/dstar is...
27.05.2005, 22:39
Forum: Physics and Astronomy
Topic: how to calculate magnitudes?
Replies: 35
Views: 10170

### Re: how to calculate magnitudes?

I give up. :roll: Can someone who can do the required mathematical jiggerypokery please just take this equation: (L_star/L_sol) = ((d_star/d_sol)^2) * 10^(0.4*(m_sol-[M_star + 5*log10(d_star/32.616)]) and make M_star the subject of the equation? Please?! B...
27.05.2005, 21:49
Forum: Physics and Astronomy
Topic: how to calculate magnitudes?
Replies: 35
Views: 10170

### Re: how to calculate magnitudes?

First of all, please remember that you did not tell anyone here what you wanted to do with the information you were asking for. So it's hard for me and others to become more specific. Sometimes I have to figure out how bright a companion star is as seen from the surface of a planet orbiting the pri...
27.05.2005, 18:02
Forum: Physics and Astronomy
Topic: how to calculate magnitudes?
Replies: 35
Views: 10170

### Re: how to calculate magnitudes?

Ack. This is getting circular. So you're saying that in order to find the absolute magnitude of an object (which is far more useful than the apparent magnitude for my purposes), I have to first figure out its apparent magnitude, but that's only determined by observation? (which is not useful, since ...
27.05.2005, 00:41
Forum: Physics and Astronomy
Topic: how to calculate magnitudes?
Replies: 35
Views: 10170

### Re: how to calculate magnitudes?

Hm, well absolute magnitude may be useful (I'm very rusty on this, in case you haven't noticed). So if Abs Mag is how bright the object is if it's placed at a distance of 10 pc from the viewer, then how is that calculated? I've scoured websites looking for this and I can't find a decently explained ...
26.05.2005, 18:19
Forum: Physics and Astronomy
Topic: how to calculate magnitudes?
Replies: 35
Views: 10170

### Re: how to calculate magnitudes?

So magnitude is an entirely relative scale? i.e. it's all referenced to the magnitude of the sun?

And this doesn't help to explain how to calculate the magnitutes of non-stellar bodies based on the light they reflect. I haven't found anything to help with that yet.
25.05.2005, 20:53
Forum: Physics and Astronomy
Topic: how to calculate magnitudes?
Replies: 35
Views: 10170

### how to calculate magnitudes?

How does Celestia figure out the apparent and absolute magnitudes of stars? Sometimes I have to figure out how bright a companion star is as seen from the surface of a planet orbiting the primary - I use Celestia to give me a quick answer, but I'd still like to know how it calculates them :). And Ce...
23.05.2005, 00:15
Forum: Physics and Astronomy
Topic: Mars Global Surveyor sees Mars Odyssey
Replies: 3
Views: 1554

### Re: Mars Global Surveyor sees Mars Odyssey

Wow. Now THAT sort of thing is very cool .

(almost as good as the pictures from Apollo 12 with the astronauts tinkering with a Surveyor lander in the foreground, with the Apollo lander in the background).
13.05.2005, 22:30
Forum: Scripting
Topic: Any way to output orbital parameters in Celestia?
Replies: 3
Views: 3551

### Re: Any way to output orbital parameters in Celestia?

Hm, well I guess the lack of a mass parameter would preclude the calculation of a lot of that stuff.

I was thinking more along the lines of just saying where the planet was at that particular time, the orientation of its orbit, etc.
13.05.2005, 21:43
Forum: Physics and Astronomy
Topic: tidally locked moons
Replies: 5
Views: 2351

### Re: tidally locked moons

How about an isolated brown dwarf with two largeish moons, which heat each other up by tidal interactions? The innermost planet might develop life in its ocean depths, but be quite cold on the surface, lit by the miniscule amount of radiation that comes directly from the dwarf. That's certainly pos...
13.05.2005, 19:47
Forum: Scripting
Topic: Any way to output orbital parameters in Celestia?
Replies: 3
Views: 3551

### Re: Any way to output orbital parameters in Celestia?

anyone?
12.05.2005, 23:49
Forum: Development
Replies: 7
Views: 2473

### Re: Orbit Radius of Moons

If you could educate me what "Aryth" "Ebersun/Eberron" and "Vult" "Ebersun/Eberron" are and where I can see them with my biiiiiiiiiiiiiiiiiiiiiig telescope, I would be grateful. Bye Fridger They're fictional. Eberron is a tabletop roleplaying game (based on D&D), these are the moons and its sun.
12.05.2005, 20:44
Forum: Scripting
Topic: Any way to output orbital parameters in Celestia?
Replies: 3
Views: 3551

### Any way to output orbital parameters in Celestia?

Is there a way to output - as a text file - the orbital parameters of everything in a system at any given time in Celestia? (or could one be programmed as a script?). i.e. arguments of pericentre, orbital longitude, mean motion, all that jazz... (i'm guessing you'd have to add some terms to incorpor...
12.05.2005, 09:53
Forum: Physics and Astronomy
Topic: tidally locked moons
Replies: 5
Views: 2351

### Re: tidally locked moons

Well, to be clear , I said that a moon orbiting a planet can't be tidally locked to a star. If you want the heat to come from the body it's orbiting, you would have to replace the Superjovian with a full-on Brown Dwarf. One problem is that brown dwarfs probably put out a lot of high energy radiation...