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Close Approach of 2024 ON
#1
CNEOS predicts that the newly discovered Apollo class NEO, 2024 ON, will make a close approach on 2024-Sep-17 18:52±1_12:17 UT at  a distance of 0.00704 AU. This is another 'Rarity'=3 event this summer. Currently the Condition Code=9, so the orbit isn't well defined yet, but I thought that this event was worth a heads-up for any minor planet observers out there.

Using MPC's elements for the epoch 2024 Jul 30 0000 UT, ST4.1.11.10 Visual predicts that 2024 ON will reach a peak brightness of 11.9 on 2024 Sep 17 at 1700 EDT at a distance of 1072.88k km traveling through Indus at 103"/minute. This is also the time (to the nearest hour) of the predicted close approach. This object will be best observed from the southern hemisphere, weather permitting, but it should be bright enough to be visible to northern hemisphere observers before and after close approach when the declination will be further north.

I'll post an update  when the orbit is better defined, as the uncertainty of the time of close approach is a day and a half at present. Usually the final value for the close approach time is very close to the predicted time; however, so don't expect too much difference.

Phil S.
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#2
As of 2024 August 21, CNEOS predicts the close approach of 2024 ON on 2024-Sep-17 10:07±00:31 UT at a distance of 0.00668 AU. The Condition Code=7  with a 24 day arc length. The close approach time has changed by >8 hours from the prediction of July 30.

Phil S.
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#3
As pf August 25, CNEOS predicts the close approach of 2024 ON on  2024-Sep-17 10:15±00:19 UT. The Condition Code is still 7 with a 28 day arc length.

Phil S.
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#4
As of August 30, CNEOS has the close approach on 2024-Sep-17 10:18±00:08 UT at a distance of 0.00668 AU. There is a 33 day observation arc, the Condition Code=6 and the Earth MOID=0.00311411 AU. The solution date was 2024-Aug-30 05:47:57 PDT.

Using MPC's elements for 2024 Aug 30 0000 UT, ST4.1.11.10 Visual predicts that this object is currently 17.6 magnitude and 0.09 AU distant in Ophiuchus traveling at 39"/hour.

Phil S.
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#5
As of September 9, CNEOS has the close approach of 2024 ON on 2024-Sep-17 10:19±<00:01 UT at a distance of 0.00668 AU moving with V Relative=8.87 km/sec, H=20.5 magnitude, diameter 210 m - 470 m and 'Rarity'=3. As of 2024 Sep 9 there is a 44 day observation arc, the Condition Code=6 and Earth MOID=0.00311429 AU. The solution date was 2024-Sep-09 06:21:56 PDT. The initial reported observation was by ATLAS-MLO, Mauna Loa on 2024-07-27. This NEO is on the MPC's list of Potentially Hazardous Asteroids (PHA).

Using MPC's elements for 2024 Sep 9 0000 UT, ST4.1.11.10 Visual Pro predicts that this NEO will reach a peak brightness of 12.0 magnitude on 2024 Sep 17 at 0600 EDT when the MP will be traveling through Indus at 107"/minute, but below the horizon in Columbus, Ohio. Close approach is predicted (to the nearest hour) on 2024 Sep 17 at 0600 EDT as well. This NEO is predicted to be brighter than 16 magnitude from Sep 10 (15.8 magnitude in Ophiuchus, 4.25"/minute, 0.03 AU distant) to Sep 23 (15.8 magnitude in Lepus 4.71"/minute, 0.03 AU distant). The close approach is best observed from the southern hemisphere, but the NEO should be visible from the northern hemisphere before and after close approach.

Here's the Object Info dialog for this NEO:     

Since the close approach distance is only 0.00668 AU, perturbations will be an issue. Orbital elements should be downloaded near the day of observation for best results.

Good hunting,

Phil S.

Edit: Just noticed that on 2024 Sep 15 ~1800 Brisbane time, 2024 ON will pass through the open cluster M25 in Sagittarius then on Sep 16 ~0300 it will pass within 1° of the globular cluster M22.
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#6
The NEO 2024 ON has made its close approach, but it's returning to the morning northern sky. 

Here's an article about this object:

Stadium-sized asteroid will pass relatively close to Earth, NASA says | Fox News

The 'Rarity'=3 events are happening much more frequently than every 5-10 years, however. This is the 3rd one since late June and there's another one coming on November 5.

Phil S.
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