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Close Approach of 2020 MP1
So, 24 hours from now a rock from space will pass just outside the orbit of the Moon. I downloaded the MPC NEA Today rocks and searched and excepted the 2020 MP1 data. I set the starting date for 24 hours in the future 2020 June 24 21h00m to run the position ephemeris over a period of 6 hours in one hour steps. I got the output in the image. There is a small green filled circle at the bottom left corner that blinks red???  I was going to print a finder chart but the positions are well off from those produced by Horizons -- 2020-Jun-25 04:00UT  RA 19 43 52.54 DEC -06 22 39.1  Mag. 14.507 Horizons will not print finder charts. See my attached field chart where I hand plotted the positions given by SkyTools 4g (S), Horizons (H) and plotted by another popular program with the local CDT of all the positions. Taking Horizons as the gold standard, I find the SkyTools position 52 arc minutes WNW and the other software well over a degree too far NW. What can I do to improve the plotting on the Interactive Atlas if the position ephemeris is not correct? Should I create an IA with a Skymark at the several Horizons positions?

[Image: yKYsJzH.jpg]

[Image: Kl6r1I4.jpg]

The green/red is the indicator that one of your subscriptions has been undated. Click on it to see which one. I update the novae/supernovae regularly.

Regarding the asteroids, I am sorry, but don't have your answers. I am confident that SkyTools is plotting orbits accurately, given an accurate orbit. Under normal circumstances, the NEA Today orbital elements reflect the most recent observations, and are also calculated for an epoch at the current date. But the MPC is having trouble right now because of the pandemic. The telescopes on Mount Lemon have been evacuated because of a wild fire. It is important to understand that most close approaching asteroids need constant monitoring in order to continuously refine the orbit.

I see no reason to assume that HORIZONS is more accurate. The normal advantage of HORIZONS is that it does the orbital calculations necessary to produce a position independent from the limitations of osculating orbital elements, which lose accuracy over time. But keep in mind that the special NEA Today elements are supposed to accomplish the exact same thing. The discrepancy means that either the data from the MPC or JPL has not been updated to reflect the latest observations. For all we know, neither of them have been. Consider that the MPC is where everyone sends their observations for analysis and the MPC is specifically tasked with tracking near earth asteroids. So as far as I know, HORIZONS is actually dependent on the MPC for updated data. It is possible that they have direct data pipelines from some of the big surveys, but I doubt it.

Previous experience does not seem to apply in the current situation. If you really want to know which one is generating the correct positions, your best bet is to compare to actual observations, or to ask the MPC or JPL. Another possibility is to get on the MMPL listserv and ask the knowledgeable people there, many of whom are part of the professional asteroid community.
Clear skies,
Head Dude at Skyhound
Thanks for the reply. I was hoping to make a verification observation tonight but weather will stall that attempt. It was going to be really dubious due to altitude and being near my limiting magnitude reach. I'm friends with one of the astronomers at Lowell so I might contact him.
The MPC used to post the observed positions for comets. Do they do that for the MPs as well. You could try to compare the observed positions from MPC Circulars with the calculated positions from ST4v & HORIZONS to see how they compare.

Just a thought,

Phil S.
Sounds like a good idea. I might need to know where the rock is observed from. I think I ran across an observatory code list somewhere that has that info.

One thing that I did try was to edit the elements of 2020 MP1 to precisely match those being used by Horizons. They were only slightly off to begin with. This put the ST position about 1.3' farther away from the Horizons position.

Best I can tell from a little digging 2020 MP1 was detected by NASA’s automated asteroid tracking system, Center for Near-Earth Object Studies (CNEOS).
Yes, you are correct. You will need to calculate the ephemeris  for the location of the observatory that provided the position observations. The parallax on an asteroid at close approach would be significant otherwise.

Phil S.
I'm still struggling to paste the elements from the HORIZONS Web Interface as a complete package like
2459028.375000000 = A.D. 2020-Jun-27 21:00:00.0000 TDB
EC= 5.238841053944705E-01 QR= 9.242164835514164E-01 IN= 1.188510931962212E+00
OM= 1.041546627877560E+02 W = 2.145497618343036E+02 Tp= 2459061.407473874278
N = 3.644286642321961E-01 MA= 3.479620196697919E+02 TA= 3.175887842275441E+02
A = 1.941158642303144E+00 AD= 2.958100801054871E+00 PR= 9.878476512226976E+02

into the editor. I get this when I click paste.

[Image: VH27mBs.jpg]

Yes, there is a known bug in the pasting of JPL elements. I am sorry that the update isn't ready yet that will fix it. The deeper I dug into the Scheduler, the more there was to fix. Until today, meridian flips were completely broken, so there was no way to release the update with the other fixes. Thankfully, my deep dive into that abyss seems to be about over. Fingers crossed.

In the meantime, if you tell what date/time you want a HORIZONS orbit for, I can copy/paste it and then post it here as a single-object observing list. All you have to do is read it into ST4 and you will have the orbit in your database.
Clear skies,
Head Dude at Skyhound

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