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An Interesting Case Study - Asteroid Cacus
#1
The large asteroid Cacus (161989) will make a close approach (22.38LD) on Sept 1, 2022. Suspected of being ~1Km in size and listed as a Possible Hazardous Asteroid, I thought I might consider observing its close approach as it may reach a magnitude of 13.5 and be within reach of my 13" scope visually.

I did a bit of research and discovered it has been known since early 1978 and was provisionally designated 1978 CA when discovered by the German astronomer Hans-Emil Schuster at the European Southern Observatory, La Silla. Its orbital uncertainty is 0!

This rock has a high inclination of 26° so passage near our home planet is somewhat rare as they can only happen when near ascending or descending node. It's descending node is close to the Earth's orbit, but it's ascending node is quite distant, which is why the close approaches appear to be all in the first week of September, with none in the first week of March. I went looking for future passes under 22LD and only found 7 in the next 300 years.

I created a stereographic chart using the ecliptical coordinate system and plotted those passes positions in the sky. Pretty interesting stuff.
 
Turns out of the 2,275 PHAs, 350 have inclinations higher than 25°. So not as rare as I thought with about 15% having high inclinations. Only a few recent discoveries of PHAs have similar high inclinations (2022 CN1, 2022 EX, 2022 BA, 2022 BJ3 with fairly good orbital uncertainties). BJ3 has the highest (28.8°) of 2022 PHA discoveries.

   

Forgot to mention, all the ephemeris data is for my home location in SE Texas. Should maybe have used geocentric instead.
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#2
Hi BMD,

Very interesting. Unless these events are very close, parallax shouldn't be too bad. In any event something for the grandkids & beyond to be concerned about without some unexpected medical breakthroughs  Big Grin.

Phil S.
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#3
(2022-06-19, 04:46 PM)PMSchu Wrote: Hi BMD,

Very interesting. Unless these events are very close, parallax shouldn't be too bad. In any event something for the grandkids & beyond to be concerned about without some unexpected medical breakthroughs  Big Grin.

Phil S.

Don't forget to try for the giant (1Km), slow moving rock from space, Cacus (161989), aka 1978 CA anytime over the next week or so.

Our weather is predicted to remain very cloudy over that time period. For me, closest approach comes at 3:52CDT on September 1 at a distance of 8,603,015Km (22.38025LD, 0.057508AU) and an estimated magnitude of 13.7. If I could wait 24 hours, it may brighten to 13.6 due to Phase % change.

It should be best tracked down in the early morning hours just b4 astronomical twilight when it is high in the south. Should be moving 18-20 seconds per minute and be in the bright 14s to mid 13s.
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#4
CNEOS predicts that the close approach for (161989) Cacus will occur on 2022 Sep 1 06:54±<00:01 UT at a distance of 0.05754 AU. H=17.4, 'Rarity'=2, Condition Code=0. The diameter is 1.9 km, a big one.

Using MPC's elements for 2022 Aug 29 0000 UT, ST4v predicts that Cacus will reach a peak brightness of 13.6 magnitude on the mornings of Sep 2-4. Here's an Interactive Atlas chart showing the predicted path as seen from Columbus, Ohio:     

It covers quite a distance across the sky. It's in Cetus near the celestial equator around max brightness, so it should be visible from both the northern & southern hemispheres then. Plenty of opportunities for everyone  Big Grin.

Good hunting,

Phil S.
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#5
What I have found interesting is that this huge rock has been well placed (for me) and "bright" and will remain so for days. Only beginning to loose altitude as we approach the 8th & 9th of September. Bisecting Perseus, the Aries-Taurus border, then skimming Cetus-Eridanus and then continuing south bisecting Fornax. Hope others have good weather, as it looks like SE Texas is socked in for the next 10 days. Hard to believe! Although not a fast mover, this would have been and interesting rock to track just inside the limit of my skies and 13 incher.

   
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#6
Wow, BMD, that's some ugly weather. It looks like you might get a break on September 2 when it's only partly cloudy.

Bummer.  Sad

Perhaps Dennis can get a picture of it from Brisbane for you  Big Grin.

Phil S.
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#7
Phil, very funny....>>>

   
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#8
(2022-08-29, 10:42 PM)PMSchu Wrote: Wow, BMD, that's some ugly weather. It looks like you might get a break on September 2 when it's only partly cloudy.

Bummer.  Sad

Perhaps Dennis can get a picture of it from Brisbane for you  Big Grin.

Phil S.

Sorry Phil and BMD - we are screwed with a week of clouds and rain again, we are having an unusually wet period once more.... Dodgy
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#9
Sad

Phil S.
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#10
Hi Dennis,

Here's the .jpg image of (161989) Cacus that I recorded with iTelescope T69 at Siding Spring on 2022 Sep 12. Sure enough there were high clouds & moonlight interfering with this 120 sec exposure. Some of the other exposures were really terrible.

   

I don't have much luck imaging MPs.

Phil S.
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