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2021 RG19
#21
Hi BMD,

Last millenium a friend, Dan Grieser for whom (10482) Dangrieser) is named, wanted to predict the positions of comets shortly after discovery to see if they would occult bright stars. I wrote a FORTRAN 77 program that ran on an Atari 520ST to calculate an initial set of elements assuming parabolic motion, then refine the orbit to elliptical elements by refinement with additional positions. We took data from the Minor Planet Circulars to get the positions to input into the program. Our predicted positions usually agreed with the MPC positions within a few arcseconds, so we were pretty happy with the results.

It looks like 2014 TM has gone the same way as 2010 CA261 - lost.

razvan, your paragraph is too small to read  Big Grin.

Phil S.
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#22
Interesting as 2014 Tm just popped up on CNEOS with an uncertainty of 7! Running the Horizon ephemeris, it's ~33' SW of the position Horizons gave a few days ago.
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#23
(2021-10-03, 04:33 PM)PMSchu Wrote: razvan, your paragraph is too small to read  Big Grin.

Phil S.

Odd. It's a copy/paste from the Horizons documentation and on a desktop it appears just one point smaller than the default font, but looking at the stylesheet, there is a "font-size: 1pt;" and a "font-size13px;" declaration, I guess the former took precedence on your system. Anyway, the paragraph read: "Output for asteroids and comets can include formal +/- 3-standard-deviation statistical orbit uncertainty quantities. There is a 99.7% chance the actual value is within given bounds. These statistical calculations assume observational data errors are random. If there are systematic biases (such as measurement timing, reduction, or star-catalog errors), results can be optimistic. Because the epoch covariance is mapped using linearized variational partial derivatives, results can also be optimistic for times far from the solution epoch, particularly for objects having close planetary encounters."

Other than that, it was great to hear the story with the F77 program.
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#24
Thanks, razvan. I've seen similar font problems when I copy/paste from Discord too. Usually I paste into a notepad file, then copy/paste from there & the funny font problem doesn't occur.

Those errors in the elements can really add up + you don't know how the errors interact.

Glad you liked the story about the F77 program. I wish I had a FORTRAN compiler for this computer, but I don't have the notes that I used to write that orbit program anymore. It used a method that Dan found called Dubyago's method I believe. He'd made a Xerox copy of the whole book.

Phil S.
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#25
You may find this paper interesting (you may know it already): A Method for the Determination of an Intermediate Orbit from Three Positions of the Small Body on the Celestial Sphere, it uses Icarus as an example. The author has published a number of papers about this topic. 

Astrometry is fun, I hope to find more time to study it in depth one day.
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#26
Phil, I'm mostly bad about retaining old notes. That can, but not often come back and bite us in the axx. I've been an observer of the skies since 1983 and the best notes I've got are books of observations of young and old crescent moons since 1988 and comet stuff. Most of the other stuff, deep sky drawings & notes, are a hogpog of pages and penciled into atlases.

I've got a friend that just spent the better part of an evening looking thru 70 disks going back 20 years hunting for a conversion program I had asked for to no avail.
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#27
Wow, razvan, that brings back memories! I see that he references Dubyago too. It's funny that the search came from a Medicine topic under Opthamology>Orbit. It looks like a good method. He ran it on a 350 MHz PentiumII.

BMD, I don't see 2014 TM at CNEOS, but do see 2021 TM. It reached 17.6 mag on Oct 2.

Phil S.
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#28
My mistake. Got excited when I saw "TM"!

From my location, 2021 TM is best on Oct 5 00:00CDT based on Horizons output....
alt 74.3° azi 110.8° mag 17.629 Could be as bright as 16.2 Illum 96%, distance 0.006168AU, moving ~2'/min
Although I find that the Horizons position differs with that of both a JPL and MPC element import by 2.32° while the JPL & MPC differ by 10.5".

Another rock to not get excited about. Crazy stuff.
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#29
Hi BMD,

How do you decide which positions are the correct one to use to find these MPs? It seems that the epoch of the elements is key. If I'm checking the CNEOS website & clock on one of the MPs in the list, the elements are frequently for July 1 or July 5. Way off the mark for a close approach. Just downloaded the MPC's NEAs at Today's Epoch file & 2021 TZ is the last one on the list. I'll run the DBPS in ST4v next & see if anything turns up.

Check out 2015 TQ21. I had it reaching 22.6 mag & Re 0.04 AU on Oct 9 using elements for 2021 Oct 4, but today CNEOS shows it at close approach of 0.002 AU on Oct 7. Time to repeat the calculations & report back.

Good hunting,

Phil S.

I see that I've been misinterpreting the CNEOS table. I should use the 'Nominal' distance for the approach instead of the 'Minimum' distance. The 'Minimum' distance seems to be the distance that's calculated using the element values within the uncertainties that yields the closest approach distance. The elements for 2015 TQ21 weren't even updated from the 2021 Oct 4 values today, so no change in the estimated trajectory. It's still predicted to be 22.6 mag.

Clicking it in the CNEOS table yields the elements for 2015, too.

The DBPS for MPs <0.05 AU on Oct 7 found 29 objects, a new record! Most were on the list for Oct 3 & 5 of course.

Phil S.
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#30
Phil, it gets crazy when working with the new finds. I go to https://minorplanetcenter.net/db_search and put in the object to see what is listed for the arc number of observations and then look at the uncertainty. TZ is 8 so that would be a stretch to find no matter what. It has a one day arc and only 14 observations!! I like to use the elements from the MPC but often find that the JPL elements are more up to date. That's their job, to keep track of dangerous rocks from space. Use CNEOS minimum distance table as a guide only. Just a tool to begin a hunt.

When I do hunting for 2021 TZ, I find close approach to my house (always use that and with Horizons also), to be September 21 2021, 11:22:11TDB at 58LD mag 20.5 using JPL elements epoch Oct 3, 2021. Positions agree with those at Horizons. And it's in daylight or moon interference. Closest approach on the Horizons ephem page is found easily by looking for the deldot closest to zero.

So looking at 2015 TQ21. On the CNEOS page the uncertainty is 5days 23hours 8minutes!! Close approach data 2021-Oct-07 13:37 ± 5_23:08. So good luck hunting that lost rock.

Again, looking on the Minor Planet Search page the uncertainty is 7 but at least there are 21 observations over 4 days.

So I find it just takes a lot of research b4 plugging things into ST4. And then you'll need elements (JPL) within one day of your plotting and searching. Let horizons make you a set near when you want to observe the field.

Look at 1998 SD9 on the MPC search page. It has 115 observations over a 3668 day arc. Uncertainty zero!

It appears we missed, due to late find, 2021 TX. A very close pass small rock that was about 1 mag out of reach. On Oct 1 16:27CDT (daylight), it came whipping by my yard, moving 1.5°/min. As dark arrived, it quickly dropped below my horizon then back up but slammed on the brakes down to 86"/min and dropping another 2 mags.

Also missed 2021 TV1 close pass.
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