This event is a high value NEO ("Near Earth Object") Earth grazing asteroid - the largest such asteroid to pass by Earth in decades. It's passing closest to Earth today June 27. It's rapid motion is making for many occultation possibilities and there's a concerted effort by Vince Sempronio to calculate and distribute predictions for these events. I expect there will be updates during today before tonight's event. The star is very bright, one of the brightest of the entire campaign, and it passes through a hotbed of asteroid occulters - us!
Weather has turned and it looks favorable to avoid fog tonight. But if not, there's an alternative spot at 2700 ft elevation which should be fine - on Summit Road near Ormsby Cutoff a few miles past where Summit has the offshoot north to Loma Prieta Peak.
We want to avoid our pixels being saturated by the asteroid itself at mag 10.1, but that should be easy. Just turn down the gain a couple of notches. Don't overdo it. We want good S/N and are not worried about the combined object being saturated for some pixels. 1x setting should handle most of the worry about saturation, but go a few notches down on Gain as well, is my ball-park estimate. Definitely go to 1x! 7.2 magnitude will still be saturated at 1x.
Alt=32, Az= 'south'
The target is only 12 degrees above the 97% moon, so that'll be a bit of a pain, but you'll be at 1x and moon glow will be no problem.
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We had 4 observers for this event. The fog ZoomEarth map was confusing, looking at decision time like there was fog right up to and not beyond the exact coastline. Was this just an IR artifact the water was colder than the ground? Not wanting to risk getting fogged out like I did in my drive to San Martin 2 days earlier for another 1997 NC1 event, I decided I should tell the team to meet at 2700 ft on Summit Rd near Mt Madonna Rd below/east of Loma Prieta. This was an easier drive for Karl as well, and so it seemed the right idea. But as decision time got closer, it just felt my outdoor weather sense, and my sense as I did my afternoon run through Fall Creek up to 2,000 ft elevation, that there was no real marine layer, and it felt safe to instead set up far easier at / around Aptos High School. That allowed Bernard to join, and I took Kirk in my RAV4. Sandy expressed early afternoon interest so I brought all the gear for him to use, from Jordan's OccBox4. But, he fell out of communication and never showed up. It was Karl, me, Bernard, and Kirk.
I set Kirk up at New Hope Church parking lot. He had the closest track to the centerline. Farther SE was me just east of Freedom Blvd as it entered Aptos High School. As Bernard showed up, I ported his 5" eq Newtonian 150 yard or so up the road into the high school. I got on-target easily and had enough time to try and take the unused 8SE/OccBox4 for another track, 70 yards up, halfway to Bernard. I madly tried to get it all put together, 2-star aligned, tried to ID the field (this, all after trying similarly to get on the Eryanthe event at 12:33am after getting Kirk off-loaded at New Hope Church and trying to find an acceptable site for myself, settling on the entrance to a mobile home? park on the road into the high school. I got 95% of the way to getting on-target with the OccBox4 rig, and had to abandon, run back to my own set up and start the recording. I was at Gain=41 (not enough time to fiddle with Gain) and 1x. Tracking was very good.
It looked like a miss. For Bernard, it also looked like a miss, he was at 40ms per frame cadence. Kirk was at 1x setting and lowered gain. Karl was the hero on this one - he had a positive, verified by play-back and single-field stepping (1x setting, Gain=35) his video, using the VTI 'position' setting to get the long/lat. His event lasted guesstimated at 0.08s.
I set up on the southern edge of the concrete driveway entrance to the mobile home? park just east of the intersection with Freedom Blvd. Use 1x setting, Gain=41, other settings standard. It was a miss, as it must be given Kirk's miss west of me, and Karl's positive much further west of me.
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A miss for 1997 NC1, 1x at New Hope Church, Aptos on June 28, 1:11:39am. No apparent event. There is a rise in the target curve around predicted time, presumably due to the combined light of the star and approaching asteroid. On playback, the asteroid and its motion are clearly visible. The target was not saturated, I reduced the gain to 29dB. In PyMovie I used static masks, size 3.2. In PyOTE I tried normalizing on a tracking star, but the smoothing metric did not minimize even after 1000 points, so I left the curve un-normalized. There was minimal variation in the tracking stars, the sky was clear, although the moon was almost full. PyOTE detectability tool reports an event as short as 0.017s would likely be detectable, max predicted was 0.09s.
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The hump in the light curve is when the 10th mag asteroid itself enters the mask of the target star in yellow. |
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Observed from about 100 yard up the road from me, on the opposite side (football field side) of the road's narrow sidewalk. His visual impress was of a miss.
Got a positive from his location on Summit Rd at a turnout. Static circular masks 3.2px. 5.1px square aperture.
NIE test: 3.0 sigma
DNR: 6.87
D time: [08:11:38.8906] D: 0.6800 containment intervals: {+/- 0.0020} seconds D: 0.9500 containment intervals: {+/- 0.0045} seconds D: 0.9973 containment intervals: {+/- 0.0086} seconds
R time: [08:11:38.9240] R: 0.6800 containment intervals: {+/- 0.0020} seconds R: 0.9500 containment intervals: {+/- 0.0045} seconds R: 0.9973 containment intervals: {+/- 0.0086} seconds
Duration (R - D): 0.0334 seconds Duration: 0.6800 containment intervals: {+/- 0.0028} seconds Duration: 0.9500 containment intervals: {+/- 0.0061} seconds Duration: 0.9973 containment intervals: {+/- 0.0107} seconds
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There was a disagreement in the predicted UT of the event depending on ephemeris. The JPL #103 on OWc shows the UT time at Karl's location to be 8:11:38 (OWc rounds to the nearest second), not 8:11:40 UT Karl placed on his light curve here and in later plots. |
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Histogram significance would probably be improved if all of the non-event interval had been used for the metric interval. |
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Bottom Line: Western shift, but it might be only small'ish. Kirk Bender might have only barely missed the asteroid. Karl may have only gotten a bit of the NW side of the asteroid. That's probably the most likely outcome. See the tracks for these two below. The other observers - me and Bernard, were east (to the right) of Kirk's miss, and so we had misses too.
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