what does geocentric and topocentric mean?

[Astronolee]

I bought a great little android app called Galilean for phones...on this app it tracks and shows where the Galilean moons are but there are 3 settings which I have to set manually called none, geocentric or topocentric...what is this? I get its something relating to tilt...but can someone explain what this is to a newbie please and which setting should be used...I mean it only adjusts the tilt but what does it all mean...cheers Lee

[LukeSkywatcher]

I think its all about the orientation/position of the moons of Jupiter on your android device. One setting would be as you would see it with the naked eye and the other is flipped and reversed so to be how you might see it in a telescope.

[brantuk]

Topocentric is as measured/observed from a point on Earth's surface - unlike geocentric which is as measured from the center of the Earth

[LukeSkywatcher]

Topocentric is as measured/observed from a point on Earth's surface - unlike geocentric which is as measured from the center of the Earth

I googled it and could not make head nor tails of it, but your explaination makes sense.

[brantuk]

I had to look it up too Paul lol

[rowan46]

I can't understand it either

https://play.google.com/store/apps/details?id=requio.com_galilean_moons&hl=en

[andyboy1970]

Kim to the rescue!

Can't see it making a lot of difference to be honest.

[Astronolee]

Thanks Kim...I was curious as to what it meant

[mcrossley]

That app is not using the terms geocentric and topocentric in the way they are normally understood (i.e. correctly used ). It is using them in relation to the orientation of Jupiter's axis on the display which has nothing to do with geo/topocentric. The clue is in 'geo' which means Earth!

What the app is showing (as far as I can tell) is either Jupiter with its North/South axis upright, or with the user horizon horizontal, and Jupiter tilted over at its apparent angle visually (or in with a Az-Alt scope).

[brantuk]

You're welcome Lee but I only looked it up. Mcrossley seems to have a more insightful answer describing "how" the term is being used in this case - credit where due

[Astronolee]

Mcrossley blimey and thanks what an excellent answer :-)