The Stellar Occultation Timing Association Switzerland (SOTAS) is a working group of the Swiss Astronomical Society. The members are engaged in the observation and the recording of occultations of stars, caused by astronomical bodies such as asteroids, moons and planets.


March 05, 2019:   Dave Herald presented the latest statistic of asteroidal occultation observations - by regions. While the growth was relatively small (in numbers) for many decades, there has been a doubling in the number of observed events in the 3 years since 2015.
SOTAS says: Let's go on!
March 04, 2019:   What a nice gift: The Journal for Occultation Astronomy (JOA) is free now! IOTA/ES (Oliver Klös) informed us as follows: "In coordination with the sister organisation IOTA and RASNZ, we would like to give more people worldwide fast access to the information in our “Journal for Occultation Astronomy” (JOA). So we cancel the function to hide the last 2 issues. It would be possible to download the JOA for the whole occultation community and all interested professionals and amateurs from now on."
SOTAS says: Thank you very much!
Stefan Meister and Oliver Klös offer the following index for easy search:
Index of JOA (.xlsx)         Index of JOA (.pdf)         Index of ON (.pdf)
February 05, 2019:   The occultation of the bright star named Rasalasad borealis (my Leonis, 3.4 mag) by the small 15 km asteroid (34339) 2000 QH218 should be very impressive: the expected magnitude drop was 14.0 mag! The shadow of the star was crossing Switzerland from East to the West. Unfortunately, several participating observatories were blocked by snow or stucked in the fog! That's why Stefan Meister moved the mobile equipment to the Hulftegg (950 m/msl) for observing the event. Although the observing place was located only 2.6 km north off the center line, the event was observed as a missed event.
More information and impressive pictures taken during this cold night you will find on the VdS forum or here:
February 01, 2019:   The analysis of the star occultation by (476) Hedwig of November 13, 2018, reveals the double star nature of the occulted star. To record the light curve, Stefan Meister (member of the SOTAS section) used a ZWO ASI 120MM camera (modified for digital time stamp). Three further independent observations provided the proof: The occulted star UCAC4-593-004965 is a binary star system. Congratulations on the discovery!
January 27, 2019:   Predictions of stellar occultations by the moon can be made with the software GRAZPREP. Stefan Meister prepared some predictions of grazing star occultations for Switzerland for the first quarter of the year. Please follow to the agenda. Before using the prediction files GG0 and GG1, you have to install the software GRAZPREP.
January 01, 2019:   The spacecraft New Horizons just passed the asteroid 2014 MU69 "Ultima Thule" in a distance of about 3500 km. According the latest pictures, the shape of the body matches very well with the predicted model, which was calculated from a stellar occultation on July 17, 2017 by Ultima Thule. See the profile in comparison.
December 20, 2018:   A new tool for the calculation of the combined brightness of two astronomical objects, standing close to each other, was created. If the apparent brightness of the two bodies are known, the excel sheet calculates the combined brightness and, more important, the drop of the brightness during the occultational event. The tool can be downloaded from here.
December 2, 2018:   In addition to stellar data, Gaia Data Release 2 (DR2) also contains accurate astrometry and photometry of about 14000 asteroids covering 22 months of observations. From these data, the Gaia team is able to derive shape models from numerous asteroids. The great thing about this is that we will be able to combine our occultation results with all these shape models to get accurate measurements of the diameter – provided we have at least two well-timed and spaced chords to fit to the shape model.
October 27, 2018:   The first meeting of the working group SOTAS was held in the Liceo cantonale in Bellinzona. Totally 16 "Occultazionisti" exchanged their experiences and discussed the coming projects. The successful event was very motivating for all participants.
Protocol,   Digital VTI,   Prepointing,   History,   1st observation in CH,   ESOP37-Review,   ESOP37-Lectures
September 8, 2018:   The astronomical exhibition AME2018 was successfully held in D-Villingen. The Swiss Astronomical Society and the magazine ORION participated to this event too. The topic of this year was dedicated to the useful observations of stellar occultations by asteroids. The observing campaigns are coordinated by IOTA-ES, the European Section of the International Occultation Timing Association. Please enjoy some impressions:
Picture 1: Helen Oertli (orionmedien), Christian Wernli (president of SAG), Thomas Baer (editor of ORION)
Picture 2: Helen Oertli (orionmedien)
Picture 3: Sven Melchert (president of VdS).
August, 2018:   Meeting of the Stellar Occultation Timing Association Switzerland (SOTAS), Bellinzona
Invitation,   Registration
May 13, 2018:   New: The Swiss Occultation Numbers, a monthly statistic about the observing activities of SOTAS members, was launched.
April 21, 2018:   Great success for SOTAS members: At 00:31 UT, the shadow of (130) Elektra, a 180 km asteroid, crossed Europe with center line directly along Switzerland. After good preparation works (workshop) and thanks to brillant weather conditions along the whole path, totally 9 (nine!) SOTAS stations recorded the disappearance and reappearance of the light of a 11.6 mag star. Eric Frappa (Euraster) arranged the chords and simulated the suitable model of the asteroid. Well done guys!
See the observations in detail...
April 5, 2018:   Announcement: On August 24 - 26, 2018, the 37th European Symposium on Occultation Projects (ESOP) will be held in CZ-Rokycany (near Pilsen).
March 30, 2018:   Dave Herald published the Summary Report of asteroidal occultations. It includes the observations during the year 2017. The publication is expected in the coming Minor Planet Circular.
More reports...
Dec. 30, 2017:   Oliver Klös (IOTA-ES) updated the list of Asteroid Occultations in Europe with target stars brighter than 9 mag. Call for observation: (788) Hohensteina (Feb. 22) and (129) Antigone (Feb. 23). Thanks to Oliver for the information.
Nov. 9, 2017:   Four times a year, the Journal for Occultation Astronomy (JOA) will be published by IOTA-ES. The magazine contains helpful information, reports and predictions concerning occultations. The journal is free, except the latest two issues (available with membership).
Wanted: Writers for the magazine. Who can imagine to write for the magazine? Please contact me.
Nov. 6, 2017:   Grazing occultation of Aldebaran by the moon: Between 03:14 and 03:18 UT, the star Aldebaran (alpha Tauri) was occulted in a grazing pattern caused by the limb profile of the moon. The observing path of this spectacular event passed Eglisau, a small town North of Switzerland. Stefan Meister prepared and organized an excellent observing campaign. Unfortunately, and once more, sky was clouded out during the interesting moments.
Oct. 5, 2017:   Star occultation by Triton: After an extra workshop and numerous previous successful tests, we all felt ready for the rare occultation event. Unfortunately, the weather was clouded out, stormy and/or rainy all over Switzerland exactly during the occultation event. Only one station reported an observation!
Summary and what we expected to see! Results
Sept. 18, 2017:   SOTAS has got a forum! Discuss your projects and stay informed. Register for automatic messages.
Special thanks to SAG for hosting the forum.
Sept. 16, 2017:   Meeting with workshop at the observatory Bülach, considering the technics of recording and video time inserter. Goal: The participants are ready to record the occultation by Triton on Oct. 5, 2017.
Tips and recording schedule.
Sept. 15-19, 2017:   The 36th European Symposium on Occultation Projects (ESOP) was held in D-Freiberg. There were no participants from Switzerland. Program with Lectures and Abstracts.
Aug. 19, 2017:   A new Website referring to the occultation by Triton was launched: Therein the MIT Planetary Astronomy Lab and the Deutsches SOFIA Institut will actualize the relevant information for planning and observation of the stellar occultation by Triton.
July 1, 2017:   A Map of the Triton Occultation shows the path of the shadow and further information about the occultation circumstances on October 5, 2017.
June 30, 2017:   Steve Preston and Oliver Klös published the Calls for Observations of asteroidal occultations in Europe (target star brighter than 9 mag).
June 7, 2017:   Dave Herald published the Summary Report of asteroidal occultations. It includes the observations from 2015/08/07 to 2017/02/10. The publication is expected in Minor Planet Circular no. 104988.
More reports...
June 2, 2017:   "3 - 2 - 1 - lift off" for the new working group! Let's occult!