I am trying to figure out Voyager's NAC resolution at 251,000 km, 435,000 km, and 708,000 km. I have always calculated this in the past, but my numbers seem wrong and I am nervous...

I understand this kind of paranoia!

The Voyager NAC pixel FOV is 0.000530 degrees (source: Voyager 1 NAC instrument description)

0.000530 degrees = 0.00925 millradians

251,000 km x 0.00925 millradians = 2.32 km/pixel
435,000 km x 0.00925 millradians = 4.02 km/pixel
708,000 km x 0.00925 millradians = 6.55 km/pixel

--Emily

Thanks - That's what I thought, but 2.32 seemed too high and was making me nervous - I have a tendency to make silly mistakes with things like this and was having a pre-LPSC panic moment - thanks!

Calculations with lots of zeros scare me. My calculus professor used to have great laughs showing my work on the overhead projector (I felt cool!). He claimed I was the only student he ever had who could do the calculus with ease but routinely screwed up the arithmetic! I always leave out, add or transpose a number somewhere.

To complicate matters a bit, there is significant geometric distortion in the Voyager images so the pixel scale really isn't completely uniform across the image. Once the images have been geometrically corrected they look like this:

Click to view attachment

This is a Voyager 1 image of Rhea from the calibrated and geometrically corrected Voyager volumes at the PDS Rings Node.

I don't think this is usually taken into account when the resolution is specified and the effect is small. Where the image above is widest (top/bottom), the FOV ~0.438 degrees if you omit the black 'frame' around the image and 0.424 degrees near the center because the image edge is 'curved'.

Well, for this purpose, I simply needed a ballpark number. But yes, for mapping, that is important.