2023 Occultations by Near-Earth Asteroids - Updated 2023 January 19

Occultations by Didymos, target of NASA's 1st planetary protection DART Mission, have the highest priority

Some important last chances to observe Didymos occultations in 2023


These occultations are described and illustrated (with maps and tables) 
in this .pdf document. IOTA will have campaigns 
for some of the early 2023 Didymos events. 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 below. And see at the end, links to 
papers and presentations about NEA occultations that give important 
background information. Especially for those less familiar with occultations, 
some good links are in the short "Basic Information" section after the Goal 
paragraph below. See farther down this page for maps and other UPDATED 
information about the good bright occultations by Didymos in January.

THE GOAL

On 2022 Oct. 15, the first ccultation by Didymos was observed by Roger Venable
in Oklahoma, in spite of hitting a deer on his way to his observation sites. 
IOTA and the ACROSS project are now trying to secure additional observations.
The ACROSS and JPL predictions are currently in close agreement, but more 
occultations by both Didymos and its battered moon, Dimorphos, are needed to 
better determine the orbits of both objects, to help ESA'a Hera mission that 
will launch in Oct. 2024 and rendezvous with the Didymos system in Dec. 2026.
On 2022 Oct. 19 and Nov. 12, occultations by both Didymos and Dimorphos were 
recorded in Florida and southern California, respectively. We are trying to 
get observations of a few more occultations by Dimorphos; please help us with 
these efforts. By about March, the apparent motion of Didymos will increase, 
making the Dimorphos events too short to record with common video systems; 
also, Didymos will recede from Earth so far that diffraction smearing will 
also likely prevent observation of their occultations. Success before that will 
allow a more accurate determination of Dimorphos' post-DART-impact orbit than 
can be obtained by other means; the asteroid is already too far from Earth to 
be observed by currently operational radar systems. The errors of the orbit of 
Dimorphos, determined from rotational light-curve (transit) observations, are 
growing, so we hope to obtain a few Dimorphos occultation detections to reduce
those errors.

BASIC INFORMATION ON HOW TO RECORD OCCULTATIONS

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.

WEATHER FORECASTS

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.
_ _ _

GOOGLE EARTH FILES FOR DIDYMOS OCCULTATIONS

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.

Recently, Dave Herald has 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. 

More about some of the upcoming Didymos events is below. For them, more 
observers are always welcome, to occupy more of John Irwin's Google Earth 
observer lines described above. If you are interested in participating in 
any of these events, contact me, dunham@starpower.net or 301-526-5590, 
to get a line assignment. For some events, Roger Venable, 
rjvmd@progressivetel.com, will be assigning the lines.
_ _ _

2023 JANUARY 1 DIDYMOS OCCULTATION

1h UT, Southwestern USA
1h UT, eastern North America
1h UT, southeastern Canada
1h UT, southwestern Europe
1h UT, n. Africa and Middle East

This good occultation has already occurred. Unfortunately, cloudy skies 
plagued all of the path from which observers planned to try it. The cloud 
cover was so extensive in most areas that all observers except for Vadim 
Nikitin did not leave home to try the occultation. Vadim travelled to 
south-central Colorado, where he was able to acquire the target star and 
record it through the time of the occultation. But the observation was 
through rather thick and variable cloud at the expected event, and his 
recording is still being analyzed, to see if a real event might be 
detected in the very noisy recording. Under the circumstances, there was 
no chance to try for the Dimorphos occultation. 
_ _ _

ACROSSs Damya Souami noted a faint event, an occultation of a 15.1-mag.	
star by Didymos around 7:05 UT (2:05am EST) of Tues. morning, Jan 17th,
visible from the northeastern USA with zoomable Aladin charts and other
event details on Occult Watcher Cloud; for the zoomable Google map there, 
select the 2nd line (using the JPL#201 orbit) or directly, click here.
The path crosses North America from coast to coast, but the current 
NWS cloud forecast shows that it will be very cloudy along most of the 
path, with the only predominantly clear area being the Hudson Valley and Conn.
The path over the Hudson Valley and Conn. is shown in this map.
I think only an 18-in. or larger scope might detect the 1/3rd-sec. occultation
of this faint star by Didymos, and larger scopes would be needed for Dimorphos.
The Occult input file, using the latest JPL201 orbit, for the event is here.
Also showing clear sky in the Hudson Valley/Conn. area are the cloud forecasts 
of GFS and the Canadian weather forecast for astronomy.
Probably this event was not observed; I have not heard from possible 
observers since the occultation occurred 2 nights ago.
_ _ _

2023 JANUARY 18 DIDYMOS OCCULTATION

This is our next chance to record an occultation by Dimorphos with video 
but a large telescope, probably 12-in. or larger, will be needed to
record the short Dimorphos occultation of this 13.1-mag. star. The path 
crosses the southernmost part to Arizona and southern Florida; it also 
crosses Texas and other south-central US areas, but the cloud cover forecast
is poor for them. It looks good for Florida, and partly cloudy in aouthern 
Arizona, but maybe OK there with the high event altitude, nearly in the 
Zenith there.

Occult map, Florida to Houston
Occult map, Houston to southern Arizona
cloud cover forecast

Path across Florida
Zoomed in map, South Palm Beach area

Roger Venable, rjvmd@progressivetel.com, is coordinating observations
for this event using this Path across Google Earth file from John Irwin, who 
writes about it here. Half a dozen observers have signed up for the 
event, and Roger plans to deploy a few stations. Email Roger if you 
might be interested in helping for this event. I have added the OWC links and 
some other information to Rogers Jan. 14th message here. 
Also, see this explanation of Irwins Google Earth file.

Sky Plane diagrams of the Didymos-Dimorphos system for this event by John Irwin:
Florida
Arizona

So far, I have not heard if this occultation was observed.
_ _ _

2023 JANUARY 21/22 DIDYMOS OCCULTATION

This is our last really good chance to record an occultation by 
Dimorphos with video with relatively small telescopes; please join 
our effort to observe this occultation in Florida if you can. 
But the cloud forecast for Florida is poor, so we may 
cancel the effort there for this outstanding event. The European 
ECMWF, US GFS, and Canadian cloud forecasts are all similar to 
the NWS one, so it is very unlikely that any observations will 
be possible from Florida.  We will need to depend on observations 
from Europe and possibly farther east.

ACROSS is coordinating the observations in Europe with a special 
Web page they have set up using parallel "fence" lines that take 
into account elevation above sea level, like John Irwin's Google 
Earth files. this message about it by me and Paolo Tanga;
it includes the OW cloud link, that can be used for Aladin star 
charts and other event details, but of course, use Paolo Tangas
link for the path, and to select a line for your observation.

Occult maps
Florida, Jan. 22, 0h UT or 7pm EST
s. Europe, Jan. 21, 23h UT
s. Europe to India, Jan. 21, 22h-23h UT

ECMWF cloud cover forecast maps for Europe and Asia; note these maps
are from a US Web site that uses CST (Central Standard Time), which 
is UT - 6h:
n. Italy to s.w. France 
w. Bulgaria to Croatia 
Middle East 
India 

Sky plane diagrams of Didymos and Dimorphos by Steve Chesley, JPL
Florida
France
These use the recently-updated orbit of Dimorphos but they are 
essentially no different than the earlier sky plane diagrams.

John Irwin has supplied this this Google Earth file; it is not completely 
redundant with Tangas interactive path since Irwins includes the 
predicted path for Dimorphos that Tanga does not have. 
Also, Irwins file extends the path east across India which Tangas 
does not reach. This document describes Irwins Google Earth file 
and its use, while this message is what John says about this event.
_ _ _

2023 JANUARY 23 DIDYMOS OCCULTATION

This is mmostly a southern Canadian event; in the USA, only 
Washington state is crossed by the path, over the Seattle area,  
at 5:05 UT (or Sun., Jan. 22, at 9:05 pm PST).

Occult map, Labrador to Lake Winnipeg
Occult map, Ontario to s.e. B.C. and n.w. Washington

The OW Cloud link; for the path, be sure to use JPL#201.
In her message of Jan. 13, for this event, Damya Souami copied the OW Cloud link 
from the Jan. 21/22 event, so it is wrong, going to the earlier event instead.

We have requested a sky-plane plot and Google Earth file for this event, 
in case there are some observers willing to try it; let me know if you 
might try it, to coordinate observations. 
_ _ _

2023 JANUARY 26 DIDYMOS OCCULTATION

I only found this good 10.6-mag. event on Jan. 15 with a new Occult search 
using JPL#201, now considered the best orbit for Didymos fitted to the 
2022 Oct. – Dec. observations. The #201 orbit shifted by less than a km from 
the previous 200 orbit, so I do not know why this event was not found during 
my late Dec. search using #200. For this relatively bright star, the central 
duration is a nice 0.57s, so a central Dimorphos event should be more than 0.10s. 
The event altitude is >15 in Wyoming & higher westward. 

Occult map, Nebraska to British Columbia

Here is the OW Cloud link; but for the path, be sure to use the JPL#201 map,
but just for preliminary planning since it does not take into account 
elevation above sea level.

Here is the Occult input file for the event.

We have requested a sky-plane plot and Google Earth file for this event, 
in case there are some observers willing to try it; let me know if you 
might try it, to coordinate observations. 
_ _ _

2023 JANUARY 28 DIDYMOS OCCULTATION

Here is a last eastern US occultation, although rather faint at mag.. 13.4, 
so it requires a rather large telescope. However, with a central duration 
of 0.71s, integration can be used, with a central Dimorphos event about 0.14s
so integration might be used to detect it with 10-in. scopes, if sky conditions
permit. Unfortunately, the event occurs too soon after sunset to give enough 
dark time to deploy multiple telescopes. Nevertheless, I will let Roger Venable 
coordinate observation of this event; contact him at rjvmd@progressivetel.com 
if you might be interested in trying it. The event has a very high RUWE of 10.5, 
so the accuracy of the star position may be too poor to really predict this event.
We are asking the Gaia team to look into this star; since the EDR3 release, 
hopefully there are enough new observations that a new solution for the star might 
be computed that would reduce the RUWE.

Occult map, Newfoundland and s.e. Nova Scotia
Occult map, Delmarva to s. Alabama

Here is the OW Cloud link; but for the path, be sure to use the JPL#201 map,
but just for preliminary planning since it does not take into account 
elevation above sea level.

Here is the Occult input file for the event.

We have requested a sky-plane plot and Google Earth file for this event.
_ _ _

2023 JANUARY 29 DIDYMOS OCCULTATION

Like the Jan. 26th occultation, this 12.20mag. event was only found on 
Jan. 15. The occultation has a whopping 0.76s central duration, so a 
Dimorphos occultation could last 4 NTSC frames. The path actually passes 
over Washington, DC, but with an altitude of only 4 deg. In s.e. Michigan, 
the altitude is 10 deg., and increases farther west along the path. 

Here is the OW Cloud link; but for the path, be sure to use the JPL#201 map,
but just for preliminary planning since it does not take into account 
elevation above sea level.

Occult map, Nebraska to British Columbia

Here is the Occult input file for the event.

We have requested a sky-plane plot and Google Earth file for this event, 
in case there are some observers willing to try it; let me know if you 
might try it, to coordinate observations. 
_ _ _

The later Didymos occultations will e quite difficult to observe, most being 
too brief to record reliably with video. If anyone is interested in any of
them, we can provide more information.
_ _ _

OCCULT INPUT .XML FILES FOR 2023

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.

For the 23 NEA events mapped and tabulated in the main .pdf document
  But these all use orbits from August 2022; for Didymos, better orbits are 
  now available.
Worldwide Didymos events to mag. 14 for 2023 (but using Aug. 2022 orbit).
  A new version using the current JPL orbit will be posted soon.
Worldwide Didymos events to mag. 14 for 2023 Jan. 15 - Dec. 31, 
  using the JPL#201 orbit, currently the best available.
North American Didymos events to mag. 14 for 2023 Jan. 15 - Dec. 31,
  using the JPL#201 orbit, currently the best available.
Worldwide 2023 events for our selected NEAs (except Phaethon) to Mag. 14
Worldwide 2023 events for Phaethon to mag. 14
_ _ _ _ _ _

BACKGROUND INFORMATION ABOUT NEA OCCULTATIONS

Comprehensive PDC2021 paper on NEA occultations, .pdf
Didymos occultations presentation for SBAG mtg., 2022 Jan., .pdf by D. Dunham

SBAG27, 2022 June 7-9
Didymos occultations presentation for SBAG mtg., 2022 June, .pdf by D. Dunham
ACROSS presentation for SBAG mtg., 2022 June, .pdf by Damya Souami
_ _ _ _ _ _

ACROSS (Asteroid Collaborative Research via Occultation Systematic Survey)

On 2022 March 1, the ACROSS team announced their project and Web site:

It is our pleasure to introduce a new project for occultation campaigns:

ACROSS (Asteroid Collaborative Research via Occultation Systematic Survey)
https://lagrange.oca.eu/fr/home-across

This campaign is led by the Nice Observatory (OCA) and the Aristotle  
University of Thessaloniki (AUTh), and funded by the European 
Space Agency (ESA).

The goal is to support observations of occultations by NEAs,  
specifically the asteroid system composed by (65803) Didymos and its  
satellite Dimorphos. The focus is to obtain positive chords before and  
right after the impact date of the DART mission satellite, expected to  
impact Dimorphos on September 26th, the main objective being improving  
our knowledge on the orbit of Didymos such that we can track the  
change caused by the impact. A secondary group of objects being  
campaigned for is a potential set of fly-by targets of the Hera  
mission that will follow-up DART. Other promising NEAs are in our  
"training" list.

We share through our web site two different sets of events: involving  
bright stars (V < 10), and a general prediction file (XML by  
WinOccult) for large telescopes (V<16), that can be checked for  
specific regions. You may also find there details on our project, news  
and results of ongoing campaigns and tutorials on how to attempt  
observations of NEA events.

For priority events, updates are provided through the Occult Watcher  
Cloud (OWC) web site, under the "ACROSS" campaign tag. Specific campaigns  
will be advertised.

It must be pointed out that, due to the nature of NEAs, these are fast  
events, both because they move fast in the sky, and because a good  
portion of the NEA database is comprised of small objects. Therefore,  
only those who can track fast events should consider attempting these  
events. It is also preferable that you have a mobile station, as these  
are events with very small shadow paths. The trade-off is that, if  
positive, they will allow us to greatly improve the orbit of a NEA.

Two Didymos events already being worked on are a mag 10 event in Abu  
Dhabi on September 20th and a mag 13 event in Spain on August 25th,  
which are addressed in greater detail on our website, and we want to  
cover as much ground as possible.

On behalf of every member part of this mission, we thank you in  
advance for your interest and your contributions, and we look forward  
to working with you.

Best regards,

ACROSS Team

Coordinators: Paolo Tanga and Kleomenis Tsiganis

Core Team: Damya Souami, Joao Ferreira, Alex Siakas, Lyu Abe, 
Rodrigo Leiva, Luana Liberto, Pascal Oberti
______

David and Joan Dunham, 2023 January 5; updated Jan. 6, 6pm EST, Jan. 16, and Jan. 19
e-mail:  dunham@starpower.net
cell phone:  301-526-5590