2024 Occultations by Near-Earth Asteroids - New 2024 January 3

In early January, there are important good occultations by the Hayabusa-2 extended mission target (98943) 2001 CC21

In 2022 October, a large expedition in Japan observed a significant shift during an occultation by (3200) Phaethon, so 4 occultations in North America this year are now of great interest, to better understand the evolution of the orbit of this important object

The Asteroids, Comets, Meteors Conference (ACM 2023) in Flagstaff, Arizona brought major asteroid scientists and occultation workers from around the world together in June 2023.

One paper there, about the 20 most dangerous km-sized asteroids during the next 1000 years, gives us important new targets for occultations

These occultations are described and illustrated (with maps and tables) 
in this .pdf document. There are hot links to external 
Web pages, but links to internal files, especially the .xml input files 
used by the Occult program, are given at the bottom of this page. At the 
bottom is a link to another Web page that has links to papers and presentations 
about NEA occultations that gives useful background information. Especially for 
those less familiar with occultations, some good links are in the short 
"Basic Information" section below. Important is a description of the Google 
Earth files set up to follow terrain with parallel "fence" lines to coordinate 
site selection to optimize coverage for NEA occultations (since this currently 
can not be done with Occult Watcher), and the links for Occult input data for 
generating your own local predictions, are all given after the sections 
_ _ _

Early January occultations by (98943) 2001 CC21

Here are the OW cloud links for the events on Jan. 4, 6, and 7:

Jan. 4
Jan. 6
Jan. 7

Occult maps are in the .pdf document, but also given below:

Jan. 4
Jan. 6
Jan. 7

The Google Earth files with parallel fence lines that correct for 
elevation above sea level are linked to below:

Jan. 4
Jan. 6
Jan. 7

for an explanation of using the Google Earth files.

If you might be able to try one of these events (or later ones), 
please send me (David) an email at dunham@starpower.net so we 
can coordinate coverage with unique line assignments.
_ _ _

THE GOAL FOR (98943) 2001 CC21

This estimated 600m NEA is a flyby target of the Hayabusa2 extended mission 
(the flyby will occur in July 2026). The Japanese space agency JAXA is interested 
in characterizing 2001 CC21 that is currently occulting many stars. The goal now
is to obtain a FIRST GOOD detection of the asteroid via an occultation, in a situation 
like we were with Didymos before radar and DART tracking refined its orbit in 2022 
September. The current 1-sigma uncertainty is over 6 path-widths, with typical 
event rank of 8 on Occult Watcher. We are trying to cover the sky plane around 
the current best orbit in a semi-organized fashion, but the changing direction of 
the object's motion complicates this. Six large expeditions were mounted in Japan 
in early 2023; 2 were clouded out and the others had 10 and 12 stations that had no 
occultation, except for an event on 2023 Mar. 5 that had one positive that was used 
to update the orbit. Unfortunately, that star had a high Gaia RUWE, and a larger-than-
expected error, which caused the new orbit to be wrong, with all observers having no 
occultation for the subsequent events that were attempted. Now in early 2024, we
have more opportunities, although the durations are quite short; those will improve 
later this year. Once anyone records an occultation of a Gaia star with a good 
astrometric solution (RUWE <1.4) by the object, the orbit can be determined well 
enough that subsequent efforts will be successful with only a few observers. For now, 
we need to cover the predicted paths as best we can out to 12 or more path-widths 
(to 2-sigma or better) when possible. 
_ _ _


Besides Didymos and Phaethon, other events considered were from a new list of
asteroids that are potentially hazardous during the next 1000 years, according 
to a presentation from the Asteroids, Comets, Meteors (ACM) meeting; the 
abstract for the talk lists 20 objects 1km across or larger whose 
mean orbit intersection distance (MOID) with Earth will pass through zero during 
the next 1000 years, and whose current orbit is indeterminant (error in the mean 
anomaly becomes greater than 180 deg.) within the next few hundred years due to 
accumulation of the current uncertainty in the mean motion of the object's orbit. 
So these objects are most important to observe with high-precision observations 
(occultations and radar) to reduce the current errors in their orbital elements, 
to enable more accurate propagation of their orbits to see if there might be any 
possible collisions when the MOID for them becomes very small. Early efforts 
concentrated on 9 objects, including (4179) Toutatis, (4183) Cuno, (5011) Ptah, 
(7092) Cadmus, (7482) 1994 PC1, (66391) Moshup, (143404) 2003 BD44, 
(143651) 2003 QO104, and (314082) Dryope. But in our 2024 NEA prediction files, 
we consider all 20 objects in the list.
_ _ _


For those less familiar with recording occultations, you can learn about 
the main techniques, equipment, and software currently used in a 
good primer by George Viscome. Some more detailed information can be 
found in the observing tab of IOTA's main Web site.


Usually, we will provide little, if any, cloud cover forecast information 
on the event Web pages, like we did for some previous events. Mobile 
observers are encouraged to get their own cloud cover forecasts for 
their target areas, using Web sites and advice that I give on 
this cloud-cover forecast Web page.
_ _ _


Since the paths for these events are all very narrow, one must travel to the 
paths with mobile equipment to observe them, rather like grazing occultations 
of stars by the Moon. And like lunar grazes, it is necessary to adjust the 
location for elevation above sea level. John Irwin in the UK has helped IOTA 
with this by supplying special Google Earth files that take elevation into 
account. Consequently, we can not use Occult Watcher (OW) for these events, 
since OW does not take elevation into account. Instead, we use the Google 
Earth (GE) files by J. Irwin that he describes in this .pdf document.

In Dec. 2022, Dave Herald updated his Occult4 program to generate GE files 
similar to John Irwins, but Dave uses the same color scheme used in other 
parts of the program, so unlike Irwin, Heralds central line is green, the 
limits are dark blue, and the 1-sigma limits are red. The parallel fence 
lines for observers are light yellow and can be set up with a specified 
spacing on the sky plane and a specified number from either side of center. 
But unlike Irwins GE file, the Occult one does not include lines for the 
occultation by Dimorphos, so Irwins file is preferred for Didymos events. 
However, they are fine for NEAs with no known moons, such as for 
(98943) 2001 CC21.
_ _ _ _ _ _


IOTAs Occult4 program is a free comprehensive occultation prediction program 
for Windows systems. You can use it with the input files below to 
generate your own predictions for your observatory or region, as 
described in this .pdf document. It describes a prediction input file 
for planetary and asteroidal files called All2023.xml. You can use that 
file to generate local predictions for many mainly main-belt occultations, 
but you can replace it with the other files listed below to generate 
predictions for more occultations, mainly of fainter stars than shown on 
the maps, or for other parts of the world:

When you open these files with your Web browser,
you should get a display that looks like this.
The larger files may take a couple of minutes to show this appearance, 
showing a messed-up display before then. Once the proper view appears, 
right-click anywhere on the display, then "Save as" to a directory
on your computer; the best directory is the \Asteroid\ subdirectory 
in your Occult\ directory. Always, to get the latest orbit update, you 
should view the event with Occult Watcher (OW) , or its OW cloud page.

For the 23 NEA events mapped and tabulated in the main .pdf document
  But these all use orbits from August 2023; better orbits are 
  now available for most of them via Occult Watcher.
About 137 NEA events for N. America
  of stars brighter than mag. 13.
4242 Worldwide selected NEA occultations to mag. 14,
  including occultations by the NEA's listed in the .pdf document and 2005 UD 
  (a Phaethon-like small extended mission target of DESTINY+) but NOT any of the 
  20 most threatening NEAs described above.
Worldwide main belt (and many NEA) events from Steve Preston
 - for them, prediction maps and data are available at https://www.asteroidoccultation.com/.
Worldwide NEA events from Steve Preston
 - when unzipped, there are 12 files with monthly NEA occultation events worldwide.
   They include most NEA events, including by the 20 "most hazardous" ones.


Bright Main-Belt Asteroids, has links to the others
  and see it for corrections to the printed RASC Observers Handbook for 2024;
  several pages about occultations are affected.
Trojan Asteroids (Lucy targets are emphasized) 
Selected Special Main-Belt Asteroids
IOTA main asteroidal occultations predictions


is given with many links and discussion on this Web page.

David and Joan Dunham, 2024 January 3
e-mail:  dunham@starpower.net
cell phone:  301-526-5590