by alter-ego » Thu Aug 28, 2014 4:56 am
Chris Peterson wrote:Nitpicker wrote:Chris Peterson wrote:The video covers about ten days, three days before the encounter to seven days after. The star fields are not static; the field before the encounter is drifting at a different rate than the one seen after the encounter.
Well, that information contradicts the Wikipedia article on Voyager 2, which describes its curved path from
very low over the North Pole of Neptune, towards Triton, over a period of less than 24 hours.
I don't think there's any contradiction. The rapid flyby was less than 24 hours. The video is made up of frames from well before to well after that.
Triton orbits Neptune with a period of about five days, I think. So, it is unclear to me how the background star field, on approach to Triton in the movie, could appear so static over a period of three days.
I agree. But the fact that it isn't rendered as static is certainly suggestive of the fact that somebody actually considered the background.
Perhaps the video is synthesized, with the actual imagery mapped onto a sphere (which is very much in the area of specialization of the author), in which case the view may reflect a different path, or a time distorted path.
First, although generally realistic in appearance, I'm convinced the video is not meant to be precise in stellar background content or dynamics during the flyby. In content I've been unable to make heads or tails out of the star background - I can't find any matching stars (searching large and small fields of view) even knowing the accurate coordinates of the receding moon. With that said, please read on.
Second, using Horizons, I plotted the
absolute value, or magnitude, of the view drift over 10 days (240 hours) in 30-min increments.
Edit:The gray bar represents star background
partial invisibility because Triton' in the way (
Note: the width of the bar is defined as when Triton
just fills is ½ the video FoV in the vertical direction). I also chose 0 hours and 0° to be at closest approach.
- Relative star field motion, full range
- Relative star field motion, visible range
The right-side plot shows that on approach, the star background (or FoV center) drifts 32° in ~70 hours, but after the flyby, the maximum drift amplitude is only 4° over the next 140 hours. This is exactly the general trend that is displayed in the video. It's the detailed background / FoV drift that's not shown. Now, as I see it, comes the creative part of the video. The image sequence appears based on the Narrow Angle camera on Voyager 2. The FoV of the camera is ~0.4° x 0.4°! Horizons data for Triton's angular size crudely, but definitively scales, the video FoV as being < 1°! The best resolution at closest approach is also consistent with the narrow camera field. So here's where the dynamics break down. I believe Paul has created a good illusion here. He as created the feel of a wide angle camera by "slowing" down the FoV view drift. Consider the post-flyby view drift of 4° on a 0.4° x 8° FoV. During the last 30 seconds or so of the video, the drift would be a dizzying 5 to 10 FoVs! Geck found 15° disorienting. An FoV <1° would be
really distracting and the video would most likely not be appreciated.
I think the purpose of the star field is to enhance the visual experience, but Paul may have purposely scaled back the background drift rate to make the experience more comfortable / palatable. It's clear he followed the general dynamical trend. Also, the primary focus of the video is intended to be Triton - to enjoy Triton's carefully recreated realism. The video could have been done without stars. Maybe that would have been better, but my opinion is the stars are an added extra. Paul addressed them in a reasonable manner I think. It's ironic though that the stars ended up being a big focus. I think he did a good job at the pseudo star-background realism; it's not trivial to show or understand clearly what's going on.
Lastly, I'm normally pretty good at star field recognition, but maybe I missed it here, maybe due to the clever scaling of the background drift rate.
If anyone has identified specific members in the star field(s), I'd appreciate hearing about it.[quote="Chris Peterson"][quote="Nitpicker"][quote="Chris Peterson"]The video covers about ten days, three days before the encounter to seven days after. The star fields are not static; the field before the encounter is drifting at a different rate than the one seen after the encounter.[/quote]
Well, that information contradicts the Wikipedia article on Voyager 2, which describes its curved path from [u]very low[/u] over the North Pole of Neptune, towards Triton, over a period of less than 24 hours.[/quote]
I don't think there's any contradiction. The rapid flyby was less than 24 hours. The video is made up of frames from well before to well after that.
[quote]Triton orbits Neptune with a period of about five days, I think. So, it is unclear to me how the background star field, on approach to Triton in the movie, could appear so static over a period of three days.[/quote]
I agree. But the fact that it isn't rendered as static is certainly suggestive of the fact that somebody actually considered the background.
Perhaps the video is synthesized, with the actual imagery mapped onto a sphere (which is very much in the area of specialization of the author), in which case the view may reflect a different path, or a time distorted path.[/quote]
First, although generally realistic in appearance, I'm convinced the video is not meant to be precise in stellar background content or dynamics during the flyby. In content I've been unable to make heads or tails out of the star background - I can't find any matching stars (searching large and small fields of view) even knowing the accurate coordinates of the receding moon. With that said, please read on.
Second, using Horizons, I plotted the [u]absolute value[/u], or magnitude, of the view drift over 10 days (240 hours) in 30-min increments. [color=#FF0000]Edit:[/color]The gray bar represents star background [color=#FF0000]partial [/color]invisibility because Triton' in the way ([b]Note:[/b] the width of the bar is defined as when Triton [s]just fills[/s] [color=#FF0000]is ½[/color] the video FoV in the vertical direction). I also chose 0 hours and 0° to be at closest approach.
[float=left][attachment=1]View Drift - Full Range.JPG[/attachment][/float] [float=right][attachment=0]View Drift - Visible Range.JPG[/attachment][/float]
The right-side plot shows that on approach, the star background (or FoV center) drifts 32° in ~70 hours, but after the flyby, the maximum drift amplitude is only 4° over the next 140 hours. This is exactly the general trend that is displayed in the video. It's the detailed background / FoV drift that's not shown. Now, as I see it, comes the creative part of the video. The image sequence appears based on the Narrow Angle camera on Voyager 2. The FoV of the camera is ~0.4° x 0.4°! Horizons data for Triton's angular size crudely, but definitively scales, the video FoV as being < 1°! The best resolution at closest approach is also consistent with the narrow camera field. So here's where the dynamics break down. I believe Paul has created a good illusion here. He as created the feel of a wide angle camera by "slowing" down the FoV view drift. Consider the post-flyby view drift of 4° on a 0.4° x 8° FoV. During the last 30 seconds or so of the video, the drift would be a dizzying 5 to 10 FoVs! Geck found 15° disorienting. An FoV <1° would be [i]really[/i] distracting and the video would most likely not be appreciated.
I think the purpose of the star field is to enhance the visual experience, but Paul may have purposely scaled back the background drift rate to make the experience more comfortable / palatable. It's clear he followed the general dynamical trend. Also, the primary focus of the video is intended to be Triton - to enjoy Triton's carefully recreated realism. The video could have been done without stars. Maybe that would have been better, but my opinion is the stars are an added extra. Paul addressed them in a reasonable manner I think. It's ironic though that the stars ended up being a big focus. I think he did a good job at the pseudo star-background realism; it's not trivial to show or understand clearly what's going on.
Lastly, I'm normally pretty good at star field recognition, but maybe I missed it here, maybe due to the clever scaling of the background drift rate.
[color=#0000FF]If anyone has identified specific members in the star field(s), I'd appreciate hearing about it.[/color]