AAVSO: American Association of Variable Star Observers

Proposal #283

Proposer (45793) Arushi Nath (astroarushi@gmail.com) obscode: NARC
Assigned To(3663) Dirk Terrell
Date SubmittedSept. 17, 2022

On September 26, 2022, NASA's Double Asteroid Redirection Test (DART) led by NASA Johns Hopkins University Applied Physics Laboratory.will impact the satellite (Dimorphos) in the 65803 Didymos system, a binary near-Earth asteroid. The impact will modify Dimorphos' orbit through momentum transfer, with a predicted orbit period change of at least 73 seconds.

I aim to measure changes in the Didymos asteroid system after the kinetic impact on Dimorphos, in terms of the rotational period of Didymos. To do so, I need precise measurements of the system before and after the collision and to analyze changes that could be explained by a successful kinetic impact on Dimorphos.

I request high precision lightcurve (S/N>100) of the Didymos system in order to confirm the orbital position. The lightcurve photometry will provide me with data for the precise timing of mutual events (occultations and eclipses of Didymos by Dimorphos and vice versa). I would need consecutive data for at least 2 half-nights so that the the measurements can be accepted by the DART mission too.

Target RA (H.HH) Dec (D.DD) Magnitude Telescope Observation Frequency Expiration Date Proprietary Term
Didymos 1.723122 -35.39606 14.825–14.925 OC61 March 22, 2023 6 Months


(4726) Kenneth Menzies — Sept. 19, 2022, 4:41 p.m.


Since this is moving, it poses a significant issue with respect to pointing to it on a small FOV (15 arcmin) scope such as in OC61 on different nights. We would need RA/Dec for each night (hour) from say Sep 20 to Oct 2. Can you provide that? How far (arcminutes) will it move in 4 hours?

I wonder if ACP has access to an asteroid plotting catalog?


(3663) Dirk Terrell — Sept. 19, 2022, 5:16 p.m.

If we give it the current orbital elements, ACP can compute the current position when observing. We do this a lot with our 0.6m systems. The other question that will need to be answered is whether the tracking should be sidereal or on the asteroid.

(45793) Arushi Nath — Sept. 21, 2022, 4:07 a.m.

Hi Ken

Thanks. Yes. I could provide hourly Ephemeris data from NASA Horizon Database for Didymos.

It should now be moving across around 5 arcmins per hour. or 20 arcmins for 4 hours.

Hi Dirk,

Thanks. The tracking should be sidereal only so that we can keep the same comparison stars in the frame. If FOV is small then we can do tracking of asteroids but at half the rate to keep the same reference stars in the frame for twice as long.

Best, Arushi

(4726) Kenneth Menzies — Sept. 21, 2022, 7:07 p.m.

If there is any hope of imaging this in the desired time frame, I need approval and the data soon!


(4726) Kenneth Menzies — Sept. 21, 2022, 7:13 p.m.


Please send in a spreadsheet with RA/Dec in sexigesimal format and UTC time used.

RA - HH MM SS.ss and Dec- DD MM SS.s each in six cells.

And hourly reporting.


What is needed for ACP and how should it be entered in ACP/Scheduler??

Ken (kenmenstar@gmail.com)

(3663) Dirk Terrell — Sept. 22, 2022, 4:17 p.m.

See my email to the TAC on 9/20, but here is the text:

On 9/20/2022 12:58 PM, Dirk Terrell wrote:
> Here are the elements in the 1-line format:
> 65803 18.27 0.15 K2289 325.51990 319.31887 73.19329 3.40788 0.3839233 0.46743685 1.6443241 0 MPO711140 2888 15 1996-2022 0.82 M-v 3El MPC 0000 (65803) Didymos 20220907
> You can get these from the MPC ephemeris service at
> https://www.minorplanetcenter.net/iau/MPEph/MPEph.html
> In the Scheduler Browser application, on the Observation page, select the Ephemeris button, then Enter/Edit. Paste in the above. Some consideration should be given to whether you want to track on the orbital motion or sidereal tracking (also selected on that page in the Browser). See attached.

(45793) Arushi Nath — Sept. 22, 2022, 10:37 p.m.

Hi Ken and Dirk,

Thanks. I have prepared the excel file with the following cells:

RA - HH MM SS.ss and Dec- DD MM SS.s

I am unable to attach it online so is there any email Id I could send it to?


(4726) Kenneth Menzies — Sept. 22, 2022, 11:08 p.m.


If I select sidereal rate, do you know how often ACP re-centers the FOV to keep the target near the center of the images?

I'm hesitant to select target rate since I'm not sure how the ACP scope driver modifies the gear rotation of this Optical Craftsman mount??


(4726) Kenneth Menzies — Sept. 23, 2022, 12:56 a.m.

Committed to OC61 using asteroid orbital elements for pointing.

Dirk: Learned something new. Thanks. However, I did not see where to select either sidereal or orbital rate?

(3663) Dirk Terrell — Sept. 23, 2022, 1:45 a.m.

Selection of orbital tracking is on that same page just under the Enter/Edit button. As for re-centering the FOV, I think it does so for each Observation (in ACP lingo). You might need to create multiple Observations that have the right number of Image Sets to trigger the re-centering.

(45793) Arushi Nath — Sept. 25, 2022, 2:41 a.m.

Thanks for acceptance of the proposal. Let me know if you need more information to schedule the observations.


(4726) Kenneth Menzies — Sept. 25, 2022, 2:07 p.m.


I think the trick then is to take some images in a series (e.g., time = 1/2 hour) that will not move the asteroid completely off the field BUT then use Repeat to collect the final desired total number (e.g., time = 4 hours) of images to be collected. I think each Repeat will force a re-alignment.


(4726) Kenneth Menzies — Oct. 2, 2022, 9:17 p.m.


Having any luck analyzing the images? You have received a lot!


(45793) Arushi Nath — Oct. 5, 2022, 4:59 p.m.

Hi Ken,

Thank you for sending those images. I am currently analyzing some of the pre-impact images from other telescopes. Post-impact images from AAVSO would be wonderful to compare them with. I will keep you posted on the results. Preliminary pre-impact observation results will get posted at: https://hotpoprobot.com/2022/10/03/presentation-on-didymos-asteroid-system-photometric-observations-pre-impact-royal-astronomical-society-of-canada-toronto/


Comments on this proposal are closed.