What to observe

To return to the Section home page. Select here

Occultation studies

Welcome to the Occultation group of the Asteroids and Remote Planets Section. (ARPS)

From Tim Haymes …

Introduction
The occultation of stars by asteroids and remote planets, are contributing to the determination of their sizes, shapes and positions.  In the last few years we have been fortunate to add two binary asteroid discoveries; a relatively new class of object.  Despite the “English weather”  we are in the top five European regions in terms of the number of observations reported.   There is much to discover out there.

More observers are encouraged to take part.

The “minor planets” we in-directly observe via occultations are:  Main Belt, NEOs, Trojans, Trans-Neptunian objects (TNOs), Centaurs and planetary satellites;  and some comets.  Sizes range from 100+ km down to 1 km.  The ease of observing these events depends on the magnitude of the star being occulted, but also on the telescope and camera sensitivity.  More on the technical aspects can be read <here>

Techniques
We time (UT) the disappearance (D) and reappearance (R) of a star when occulted by these bodies.  The star is often brighter than the asteroid, but not always.  Sometimes the asteroid and star can be of similar magnitudes.  The occultation provides us with important scientific information not easily obtained by other means.  IR Photometry  (IRAS) has produced most of the size data now being checked by occultations, and Gaia (ESA) has improved the orbits.

Our main technique uses video recordings from USB3 CMOS and analogue cameras.  These recordings are time-stamped by the software used (E.g Sharpcap), so that the observer can report the UTC to 0.1 sec accuracy. (Typically).  During the video analysis, we produce a light curve (using TANGRA) which may contain hidden information.    Section members are guided through the techniques used and how to make a preliminary report.

Results from our observations

Above:  D/R Chords from four observers fitted to an asteroid profile model. The observer (blue dashed line) recorded no occultation. (Produced by D.Herald’s Occult4 software, and results in the IOTA-ES  SODIS database.)

Timing data produces an accurate position (ca 10 mas accuracy).  Several observers might observe the same occultation from their home based telescope to form a shape-profile.  We use OccultWatcher software to plan our observations, and to assist collaboration between observers, often widely separated across countries and sometimes oceans ! (US-EU)

Occasionally, an observer might operate a mobile telescope to get timings from widely separated locations (10-20km apart). This is more valuable than a single observation. Suitably equipped observers are encouraged to do this team work.

We don’t always get an occultation, because of remaining uncertainties such as shape and dimensions but its always worth a try.  Negative observations can be used to restrain asteroid profiles.

There are international and Pro/Am projects that ask for observations of particular importance.  When successful,  amateur data is requested for upload to the Pro/Am results portal where observations are fully acknowledge via astrophysical publications.

Transient events like occultations are challenged by the weather, so positive results are always greeted with glee.

Movie from the Assistant Director’s web page: (External link) (8581) Johnen on 2026 Mar 11.9   (Diameter 6 km)
QHY174m-GPS (2×2 bin)  Exp 0.02s,   C11 F5.8,     Star magnitude 10, asteroid mag 18

The asteroid occultation observer’s information “tool-kit”.

UKoccultations group.io                                                                                https://ukoccultations.groups.io/g/main

Occultwatcher (OW) software.  Predictions, and “who is observing”.   https://www.occultwatcher.net/

Occultwatcher Cloud (OWC)                                                                        https://cloud.occultwatcher.net/

OW and OWC are linked with the same password. An account is need for the full functionality.

IOTA-ES  Call-4-Observations                                                                    https://call4obs.iota-es.de/

TANGRA:  Video analysis and reports. (Windows users).                         http://www.hristopavlov.net/Tangra3/

Recording software (e.g. SharpCap,  IOTA Video Capture 2.3,  or other possibilities ).

Computer time synchronisation software:    NTP/Meinberg  (With assistance from the Section).

GOTO the Section web page on techniques <here>

Photometry of asteroids

Text goes here …