Celestia Forums

I just have a question about apparent magnitudes. From an orbit around Rigel Kentaurus A the on-screen info states that it has an app. mag. of -26.73 and the nearby B has -18.19, yet when you view the Star Browser, it lists them as -21.13 and -19.80 respectively. I was just wondering why the numbers are different?

Looks like a bug to me!

Danial wrote:I just have a question about apparent magnitudes. From an orbit around Rigel Kentaurus A the on-screen info states that it has an app. mag. of -26.73 and the nearby B has -18.19, yet when you view the Star Browser, it lists them as -21.13 and -19.80 respectively. I was just wondering why the numbers are different?

Unlike the Absolute magnitude the apparent magnitude is dependent on the distance of observer and light source. Did you make sure that the distances under which you looked at on the canvas and in the Celestia browser were exactly equal??

Selden wrote:Looks like a bug to me!

only if the distances were the same!


Actually, in the star browser the distance is in ly and correspondingly has a truncated 0.000 entry. The distance where the app.mag is -26.73 is only 1.2407 AU! So the distance display in the browser is certainly rather nonsensical and should switch units. There might be a truncation effect at work that is responsible for the apparent difference.

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[Edit:] That trucation of the distance in the star browser seems actually to be the problem: At a distance of 1ly, where the star browser displays at full accuracy, the two app.mag numbers are identical (-3.18) . So whoever coded this might want to make the distance display in the star browser switch units appropriately!
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F.

They are:

Goto Rigel Kentaurus A
Open Star Browser
view AppMag in HUD: -28.40
view AppMag in Star Browser Menu: -21.38

selden wrote:They are:

Goto Rigel Kentaurus A
Open Star Browser
view AppMag in HUD: -28.40
view AppMag in Star Browser Menu: -21.38

I am just entering the case into the bugtracker. I am pretty sure that in the star browser the distance got calculated with the truncated distance at close approach. This is supported by the fact that at larger distances the two values agree again.

F.

t00fri wrote:

selden wrote:They are:

Goto Rigel Kentaurus A
Open Star Browser
view AppMag in HUD: -28.40
view AppMag in Star Browser Menu: -21.38

I am just entering the case into the bugtracker. I am pretty sure that in the star browser the distance got calculated with the truncated distance at close approach. This is supported by the fact that at larger distances the two values agree again.

I checked and there are two problems with the Windows star browser: the star to observer distance is being calculating at single precision (really bad anywhere except in our solar system) and the current time is not used, which is another problem for stars like Alpha Centauri A that are in multistar systems. I checked in a fix for the Qt4 star browser, which was calculating distances at high precision but still suffered from the time problem. I'll fix the Windows star browser sometime when I'm not on my Mac.

--Chris

Just did a little test and found that the 2 magnitude values don't match up until around 0.5ly distance. Not sure if that helps solve the problem or not.