APOD: Saturn at Opposition (2015 May 29)

[DavidLeodis]

I think you better ask him, David. I looked around the site and could find no clues.

Thanks for trying geckzilla, which is appreciated . Perhaps there were others like me that did not know but they were to enquire (or never even noticed!).

[Nitpicker]

As nobody has asked it seems reasonable to assume that their meaning is well-known but as I don't know I would be grateful if someone could please let me know what the 'I: 152 II: 302 III: 298 (42 min)' and the 'IR I: 167 II:316 III: 312 (7min)' mean? (the IR will be Infrared). I'm guessing the 'S: 7-8/10' may be the seeing conditions being 7 to 8 out of 10 (which sounds like that is OK) but what does the 'T: 3-4/5' mean? Thanks for any help . They are nice images of .

The I, II and III annotation is the Saturn central meridian apparent in the image, for three different measurement systems that have been adopted over the years. The surface of Saturn is observed to rotate at different rates at different latitudes, different again from the rotation rate of its magnetic field. More detail may be found on this page:
http://www.southastrodel.com/PageSaturn003.htm

Note that over the 42 minute period that the RGB image was recorded, Saturn would have rotated on its axis by more than 23 degrees. I am not sure if this image has been de-rotated. I don't suppose it makes a big difference unless there is an obvious storm visible.

I think you are right that "S" is for atmospheric seeing and I might guess that "T" is for atmospheric transparency. Various scales are used to describe seeing and transparency and I don't know which ones Mister Go has specified. (I haven't checked Mister Go's website in detail, but one might deduct a point for transparency from him, for not providing accessible explanations on these small matters.)

[DavidLeodis]

Thanks Nitpicker for that very helpful reply .

[Nitpicker]

On closer inspection, I would be surprised if these images hadn't been de-rotated to 14:37 and 15:02 UT, respectively. The images are too good to have not been de-rotated.

I am not sure if anyone pays close attention to Saturn's CM I and CM II system measurements anymore. CM III seems to be the most useful one these days. I imagine the de-rotating software automatically calculates all three system CMs ... to satisfy the information gluttons.