Jupiter - central meridian

[Langworthy]

I have no idea if this is  a silly question or not, but it's vexing me so I'd better ask it. Maybe I've misunderstood something.

I realise that since Jupiter is not solid but, for observational purposes, a big stripey ball of gas, pinpointing where something is on the swirling, shifting surface is not a straightforward matter. There are no fixed points like craters that are always in the same place in relation to other surface features and anyway the surface is turning at different speeds depending on latitude.  I also know that to deal with this there are tables to calculate the longitude of the central meridian (the line running north-south down the middle of the planet) at any given time so that we can say at what longitude a certain feature is. What I don't understand is this: if one observes something on Jupiter that isn't on the central meridian, but somewhere off to the right or left of it, how is one supposed to calculate its longitude? Or does one have to wait for the feature to cross the meridian and then use the tables based on the time it crossed the line?

I should add that I'm not an avid Jupiter watcher and don't have the kit to observe it in great detail so this central meridian issue is never likely to be of immediate relevance to me. It just irks me that I don't understand.

[brantuk]

"I also know that to deal with this there are tables to calculate the longitude of the central meridian (the line running north-south down the middle of the planet) at any given time so that we can say at what longitude a certain feature is."

Do you have a link to the tables please? With a 200P you should be able to observe a fair bit of detail on Jupiter btw.

[Langworthy]

"I also know that to deal with this there are tables to calculate the longitude of the central meridian (the line running north-south down the middle of the planet) at any given time so that we can say at what longitude a certain feature is."

Do you have a link to the tables please? With a 200P you should be able to observe a fair bit of detail on Jupiter btw.

I don't have a link but the tables are available in the British Astronomical Assoc. Handbook 2015.

Well, yes,I can see the cloud bands and the GRS.