Occultations by (99942) Apophis during 2021 January - New 2021 January 9
Apophis is small, but important as it will pass very close to the Earth in 2029 and 2036, with a very small chance of impact in 2068
Occultations by the 6-km asteroid (3200) Phaethon were successfully observed in July, September, and October, 2019, and in October 2020, enabling a substantial improvement of Phaethon's orbit and a determination of its small non-gravitational acceleration (apparently due to shedding of Geminids meteroids from its surface caused by the extreme thermal stress of its close perihelion passes) to an accuracy of 10 sigma, three times better than previous determinations. Here is a press release about the Phaethon occultations, the first observed occultations for a relatively small near-Earth object (NEO). Links to presentation and other files giving much more information about the Phaethon occultations, and results from observations of them, are given on this Web page. I have conducted a search for occultations by other NEO's. As luck would have it, three events by the threatening asteroid (99942) Apophis will occur over parts of North America during the next several days, including one over the eastern USA Monday morning, Jan. 11, around 9:50 UT (4:50am EST). Unfortunately, the cloud cover forecast is rather poor over the path area, but not hopeless; maybe an observer will be lucky with both the weather and the occultation. But Apophis is about 400m across, more than 10 times smaller than Phaethon, and the current JPL orbit errors are rather large. But the fact that the small Yarkovsky effect on Apophis' orbit has been detected, I believe shows that a more accurate ephemeris might be possible to reduce the large occultation path errors, but maybe not in time for these occultations, especially the one Monday morning. There are radar observations, but I don't know if Apophis was bright enough to be observed by Gaia for its asteroid observations for DR2. The stars for the Apophis occultations aren't bright enough to generate the large interest, or justify organizing a large campaign, like the one for the 7th-mag. occultation by Phaethon on 2019 July 29, but observers near the paths for these events with telescopes large enough to record the short possible events with a reasonable signal-to-noise (S/N) ratio are encouraged to try. Steve Messner has placed the events in Occult Watcher's (OW's) North American "low-mag." feed, but to see them there, note that the diameter is 1 km (and that' rounded up from 0.5 km; the actual maximum dimension is 370m), so you need to select the OW diameter limit to be 1 or 0. In the table below, clicking on the link for the date and time will bring up an Occult- generated map of region, as seen looking towards the Earth from the direction to the target star. Above the map is a header with some of the more important information about the occultation. Clicking on the location information for the event will bring up an interactive Google map for it. There are several events that were found in my Occult search, just to mag. 11 since the fainter stars can't give a good-enough S/N to reliably detect an occultation, that I've eliminated from the table below for various reasons, including the entire path only over the daytime hemisphere of Earth, or the event visible in too bright twilight and/or only from high-latitude Arctic or Antarctic regions with no known observers. You can use IOTA's free Occult4 software to generate details of all of the events I found, using this "occelmnt" .xml Occult4 input file. Keep in mind that the times in the table below are for the time of geocentric closest approach; the times for locations in the path on the Earth's surface can be many minutes earlier or later, due to the slow motion of Apophis as it's near a stationary point in R.A. _____________ Occultations by (99942) Apophis, 2021 January Date U.T. Diam. Dura- Star dMag Elon Star Moon R.A. (J2000) Dec. y m d h m " tion mag V o No. Dist ill Location h m s o ' " 2021 Jan 11 10 46.4 0.003 0.4s 10.9 7.6 107 TYC 6093-00809-1 85 4% Ont.,MI-nwFla. 11 44 3.957 -16 23 58.04 2021 Jan 16 11 31.6 0.003 0.4s 10.6 7.7 112 TYC 6086-00002-1 146 12% B.C.,wWA-nwCal. 11 43 46.759 -17 25 33.77 2021 Jan 18 17 15.5 0.003 0.4s 10.5 7.7 114 TYC 6089-00311-1 157 30% nwMont.-Oregon 11 43 1.387 -17 50 15.50 Besides Apophis, my searches also found 3 occultations by the 7-km NEO (1866) Sisyphus, another Earth-crossing asteroid (with a safe MOID of 0.104 AU) that can't be observed by radar until 2046. I'll provide Google map links for them later. I also searched for occultations by the 4-km potentially hazardous NEO (2102) Tantalus, but found no observable events involving it through the end of 2023. Occultations by (1866) Sisyphus, 2021-2022 Date U.T. Diam. Dura- Star dMag Elon Star Moon R.A. (J2000) Dec. y m d h m " tion mag V o No. Dist ill Location h m s o ' " 2021 Apr 30 21 25.4 0.005 0.3s 10.6 6.4 130 TYC 2547-00822-1 85 81 sTH,India,SA,GH 13 58 28.016 34 11 36.30 2022 Nov 21 7 9.3 0.004 0.3s 8.8 8.4 78 HIP 60156 52 9 s.Brazil (low) 12 20 10.423 41 24 24.71 2022 Nov 26 7 39.7 0.004 0.3s 11.5 5.7 80 TYC 3020-00440-1 108 8 wOnt.,MN-wTX 12 29 18.765 41 51 25.12 The astrometric data for all of the stars is from Gaia Data Release 2 (DR2), which normally have negligible errors of well under a milli-arc-second, or less than a km in the path location on the ground. _________________ David Dunham, 2021 January 9 e-mail: dunham@starpower.net; cell phone: 301-526-5590