Zoomed in on D solution
Zoomed in on R solution
Solution; 54 seconds duration is not possible given the known dimensions and albedo of the asteroid. Indeed, the D looks too early by eye, despite PyOTE decision.
This is a bright event, but only R=0.18 magnitude depth. Do-able but will require lowering the gain and being at 2x to get unsaturated data. Unfortunately, no comparison stars will be available at the required gain. Max duration and for me, is 36 seconds long. However, the oblong nature of Vesta means it could be as much as +-4s shorter or longer than the mean.
Alt=31 in the west and this is high enough to clear the trees so it's do-able from my driveway.
I was so late in getting this one noticed and then charted and posted, that I didn't have time to notify Kirk or Karl. I was the only one to get data, from the base of my driveway. At 2x, gain=19. Clear skies but with some light cirrus that didn't seem noticable.
First analysis: Take very wide D and R regions to be sure I captured it. Unfortunately, it settled on a duration which is implausibly large: 54 seconds. However, it looks to me like there was a gradual increase in atmospheric opacity to the middle of the event, which then cleared. The event looks suspiciously round-bottomed and not squarewave. On the light curve then, there seems was a bit of haze that seems to have affected the last 30sec of the recording too. The atmospherics were high humidity, city light pollution. No apparent clouds of any kind, but cloudiness had only recently cleared from earlier in the evening and a bit of condensation in the sky might have still remained as high pressure slowly built in?
magDrop report: percentDrop: 10.3 magDrop: 0.118 +/- 0.009 (0.95 ci)
DNR: 0.82
D time: [06:51:06.8280]
D: 0.6800 containment intervals: {+/- 0.2392} seconds
D: 0.9500 containment intervals: {+/- 0.8964} seconds
D: 0.9973 containment intervals: {+/- 2.1690} seconds
R time: [06:52:00.8276]
R: 0.6800 containment intervals: {+/- 0.2392} seconds
R: 0.9500 containment intervals: {+/- 0.8964} seconds
R: 0.9973 containment intervals: {+/- 2.1690} seconds
Duration (R - D): 53.9996 seconds
Duration: 0.6800 containment intervals: {+/- 0.4273} seconds
Duration: 0.9500 containment intervals: {+/- 1.2537} seconds
Duration: 0.9973 containment intervals: {+/- 2.6204} seconds
|
Zoomed in on D solution |
Zoomed in on R solution |
Solution; 54 seconds duration is not possible given the known dimensions and albedo of the asteroid. Indeed, the D looks too early by eye, despite PyOTE decision. |
|
This is impossibly too large, as Vesta is a well studied and visited asteroid. The oblong asteroid could accomodate a duration of +-4s from the advertised 36.5s. I then looked more closely at the light curve and found edges that likely corresponded to the true events, set the D and R ranges as below, and it found the solution below. The very high FP test confidence shows not that the D and R times are accurate, but that an event did happen, is the interpretation. There is an edge at the earlier time above, true. But there's also a chunk of reading right after that which are back at the average of the earlier un-occulted level. Clearly the drop was on the ragged edge of detectability, but the sheer length of the duration was enough to verify a true event, even if the timings are more uncertain than I would believe below or above. I think the science result is that Vesta's on orbit, and about the right diameter. Tony George observed from a chord close to mine and got a 35s event, but I don't know how good his data looks, at this time.
Second Analysis: Set D and R intervals narrower, by eye judgement...
...for D, given the gradualness of the light curve near the D and the possibility of haze. This solution is in better agreement with the predictions for this very well observed asteroid. The center of the event is now right on prediction, and the duration of 40s is possible if Vesta was turned sideways such as it appears in the photo. The magnitude depth is deeper, but still not as high as the advertised 0.18 magnitude. Signal to noise is also better for this solution than for the "wideDR" shown above.
This will be my reported timings, below.
magDrop report: percentDrop: 11.0 magDrop: 0.126 +/- 0.010 (0.95 ci)
DNR: 0.87
D time: [06:51:17.0679]
D: 0.6800 containment intervals: {+/- 0.1996} seconds
D: 0.9500 containment intervals: {+/- 0.7607} seconds
D: 0.9973 containment intervals: {+/- 1.8898} seconds
R time: [06:51:57.2276]
R: 0.6800 containment intervals: {+/- 0.1996} seconds
R: 0.9500 containment intervals: {+/- 0.7607} seconds
R: 0.9973 containment intervals: {+/- 1.8898} seconds
Duration (R - D): 40.1597 seconds
Duration: 0.6800 containment intervals: {+/- 0.3615} seconds
Duration: 0.9500 containment intervals: {+/- 1.0457} seconds
Duration: 0.9973 containment intervals: {+/- 2.2728} seconds
These are my chosen D and R intervals. I first tried to give it a range of duration in points, from 800 to 1050, but it was taking hours and I gave up. I chose these intervals above by eye. |
The solution. A case could be made that even though not chosen by PyOTE, the actual D could have been at the vertical dark mark. This would then give a duration of 36s and in better agreement with Tony George's event from only a few miles farther from the centerline as mine (35s he reports). His event was much lower in the Phoenix sky and suffered from increasing extinction so he had to use PyMovie's de-trending option before it would give the realistic 35s duration. Otherwise, it was too long. For me, there was no trending so de-trending will not help.. |
False positive test again passes. Clearly there was an event, obvious by eye, but the high confidence in the FP test should not be interpretted as high accuracy for the D and R times |
Space mission photo of Vesta up close. Measuring from this photo, I get that the max duration times could be as much as 4s longer or shorter than the advertised 36.3 sec. My result here was 4s longer than 36.3s. |
The PyOTE file has 3 solution attempts. The R settled on in the second (middle) of the file, looked too far to the right of the by-eye estimate of the actual R edge, so I altered the R range and ran it again to produce the "tightDR" solution given above. This is the result I will report, as the 1st and 3rd analyses clearly give unrealistically long durations.
Third Analysis
I also tried doing a TME aperture in PyMovie. The "wide DR" generous D and R ranges resulted in an event of duration 52s, which is better than the 56s from the static circular apertures, but still is unrealistically long, and also poorly centered on the predicted time. I noticed that during the PyMovie run, the configuration of TME pixels did not change at all, despite the changing brightness patterns of the pixels. The Signal/Noise is poorer, mag drop slightly less. Very similar to the static circular aperture wideDR range 1st analysis results.
magDrop report: percentDrop: 10.3 magDrop: 0.118 +/- 0.009 (0.95 ci)
DNR: 0.81
D time: [06:51:08.5080]
D: 0.6800 containment intervals: {+/- 0.4066} seconds
D: 0.9500 containment intervals: {+/- 1.5960} seconds
D: 0.9973 containment intervals: {+/- 4.0798} seconds
R time: [06:52:00.8676]
R: 0.6800 containment intervals: {+/- 0.4066} seconds
R: 0.9500 containment intervals: {+/- 1.5960} seconds
R: 0.9973 containment intervals: {+/- 4.0798} seconds
Duration (R - D): 52.3596 seconds
Duration: 0.6800 containment intervals: {+/- 0.7472} seconds
Duration: 0.9500 containment intervals: {+/- 2.2614} seconds
Duration: 0.9973 containment intervals: {+/- 4.9589} seconds
 |
|
 |
52 second event, not well centered on predicted time, but by-eye it seems a clearer proper fit by PyOTE to the data. But 52s is just plain inconsistent with the 36s maximum and this asteroid is well photographed close-up in space. |
