319 Leona will occult Betelgeuse on 2023 Dec 12

This event (already predicted in 2022 actually) could be defined the most interesting occurring during 2023, even though limited to a small portion of the Earth’s surface, as visible below. Certainly a weird experience seeing Betelgeuse disappear from the sky for several seconds.

I will use this occultation, choosing Potenza’s Observatory (IT, IAU code L28), where the event should occur at 01:13 UT, to show how orbital osculating elements of Asteroids downloadable from the available sources (MPC, Lowell Observatory, etc.) should be handled with care when used several months away from their epoch.

In the same time we are going to appreciate how accurate Horizons’ minor planets and IMCCE positions can be, clearly obtained by more sophisticated models.

The image below shows the position of Leona computed by means of the osculating elements referred to 2023 Feb 26:

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At 01:13 UT (319) Leona is 180 arcsec (3′) distant from Betelgeuse, and it is not at least distance reached 6 hours later, 48 arcsec, as visible below.

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Surely not a good prediction, but actually we are 10 months away from the epoch of the osculating elements and this behaviour is quite normal in this case. What if we decide to pick up the position from Horizons Ephemeris? Ok, let’s do it. The image below shows the query to the JPL System. I chose to ask for the apparent position for Potenza’s Observatory so no other corrections are necessary.

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That done we can input these coordinates (at 01:13 UT) via copy and paste directly into the UrukFSP’s User Object Window, giving an appropriate label to distinguish the two Leona’s positions. Note that I haven’t applied any correction to the JPL data, as they are already apparent.

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In this case an occultation has a huge chance of happening. The distance between the two objects is just 0.12 arcsec! An interesting exercise could be following the downloadable osculating elements trend as we get closer to December: theoretically the computed position should get better and better…..

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Of course you can do a query to the IMCCE Ephemeris Service as well. I used the IAU code L28 for Potenza’s Observatory and obtained the apparent position visible below. A little difference in Declination (0.2″) with respect to JPL and the least distance appears to be in this case 0.27″. Small differences though.

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In conclusion, if you need high precision with Asteroid positions don’t use downloadable osculating elements for periods longer than, say, a couple of months from their epoch. JPL and IMCCE Ephemeris Services can help in this case, using the User Object Window of course.