Hi Gary,

On 10/06/2013 02:04 PM, Gary Seronik wrote:
> ...I like this suggestion. And I would like to add one more. Could
> we have a way of entering the current GRS longitude manually?

I see two big issues with this: the GRS is moving pretty fast these
days, about fourteen degrees a year; and if you set Guide back to
1990, it would be stuck with the 2013 value of the GRS longitude.

However, I think there's a simple and even elegant solution to this.
When Guide shows GRS data in tables or More Info, the words "Great Red
Spot" are linked to some text describing the feature. I can, without
much effort, add this text:

The Great Red Spot moves gradually over time. You can *click here* to
have Guide download current longitude data, thereby causing the program
to display its position and compute its transit times more accurately.

"*click here*" would very simply cause Guide to download this file:

http://www.projectpluto.com/grs_lon.txt

to your Guide folder, overwriting the copy you currently have there.
I would suggest doing this; it'll keep you going until I get the "click
here" version posted. The currently posted 'grs_lon' file has been
updated using JUPOS.org data (http://jupos.privat.t-online.de/rGrs.htm)
and the extrapolated position revised. From the 'rGrs' graph, it
looks as if the GRS has accelerated a bit, and is now moving at a
pretty steady 14 degrees/year. (I also revised an error I made in the
explanation at the end of the file, in which I suggested that perhaps
we could find data going back to Galileo. I mis-remembered my history;
Cassini probably observed the GRS, but then there's a gap until 1831.
So I don't expect us to be able to extend the table before then.)

> (I just did this yesterday, as it happens, and I believe Guide
> was giving a longitude of around 182 whereas the actual longitude
> is 201 or something close to that.)

I didn't think it was _that_ far off. But I see that with the
default file with a last "known position" of 168 degrees in August 2011,
back when the GRS wasn't moving at its current breakneck speed, you
get something around 182 degrees... definitely something that needs
fixing!

-- Bill