Stellarium inaccurate, what have I done wrong?

[Alkaid]

Hi all,

I checked Stellarium last night and saw that at 23:45, Io was going to re-appear from behind Jupiter. So when observing I waited, and waited.......and waited. Still nothing at 00:15, despite the program showing Io now definitely re-appeared.

I've got the time and date set correctly on the program, but think this may be something to do with daylight savings and British summer time. But I couldn't find the link to check if this was set properly.

Any advice? Where do I look?

Cheers!

By the way a lovely clear night last night wasn't it? Had a great time exploring the craters around Mare Crisium.

[PRG]

If you go into the sky and viewing options window [F4], and tick simulate light speed in planets and satelites, this should sort it out.

By default Stellarium shows Jupiter as it is at the time and does not account for the time it takes for the light to reach earth, unless you tick simulate light speed.

[Merlin66]

I don't think it takes light >30 mins to travel from Jupiter to the Earth.......

[Simms]

I don't think it takes light >30 mins to travel from Jupiter to the Earth.......

It takes light 43 minutes to travel from the sun to Jupiter, - 8 minutes from the sun to earth, so depending where jupiter is in its orbit relative to Earth, it could actually take well over 30 minutes.

[Merlin66]

Hmmmm

Point made!

[Vargojones]

It takes 33 minutes for light to return back from jupiter, which would account perfectly for your delay

[Earl]

This issue is was what started the whole debate that light travelled at a speed and was not instant. (a moon not been where is should be)

[Merlin66]

No, the issue that started it was the timing didn't match... one of the reasons given was that the "light time" had not been taken into account...

[PRG]

Coincidentally, the speed of light was measured in the 17 century using observations of the eclipses of Io.

[cantab]

Galileo tried to measure the speed of light but only determined it was too fast for him to measure. Observing the moons of Jupiter did indeed give the first actual measurement of the speed (albeit a figure 25% too slow), but the question of whether light had a finite speed was ancient.

[Alkaid]

Well I'll be. Thanks everyone, I did not think of this. How clever the program is to take this into account!

Cheers!