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.


The latest Observations:   Recordings      Swiss Occultation Numbers
July 04, 2024:   What an impressive observation: Andreas Schweizer took the opportunity to observe the Dwarf Planet (50000) Quaoar (diam. 1121 x 1020 km) using the 85cm-telescope of the Observatory Buelach. According Andreas, it was quite difficult to identify the Dwarf Planet between the numerous stars shown in the field of view. The occultation of the star (17.2 mag) by Quaoar (18.7 mag) took 45.70 sec. See the latest (preliminary) Chords (credits to IOTA/ES).
Congratulations! Find here more information.
May 04, 2024:   The 3. SOTAS-Meeting was held at the observatory Bülach. After the new IOTA/ES rules concerning the reporting of stellar occultations came into force, the meeting was planned as a workshop. During the 6 parts of the workshop, the participants learned the procedure of recording and reporting step by step. The protocol (see below) includes all necessary information and some impressions of this successful day.
Invitation,   Protocol,   SAG Blog
April 28, 2024:   Continued: The archive of our asteroidal Occultation Observations is now available at NASA’s Planetary Data System – Small Bodies node. The archive shall be updated on an annual basis. This is an official recognition of the value of the observations we make. The archive is located here.
March 20, 2024:   Now it's official: The Minor Planet Center confirms the discovery of a satellite of (5457) Queen's. The discovery bases on two stellar occultations, made within 15 days. The first occultation resulted in three positive chords. Two of them were made by .... Stefan Meister and Andreas Schweizer !!! Congratulations, well done boys!
For further information, please read the Minor Planet Bulletin MPB.
See also the News entry of November 16, 2023.
Feb. 24, 2024:   New rules: The observation of star occultations by asteroids is useful scientific work and is becoming increasingly important. At the same time, the requirements for accuracy in recording and evaluation are increasing. For this reason, new rules apply for reporting in the SODIS portal. In particular, there are some mandatory files that must be uploaded for both positive and negative observations. The new rules are effective immediately and showed here (see point 1) for positive and point 2) for negative observations).

Standardized naming: Beside of the SODIS portal, our working group maintains an archieve, containing all observations of the members. It is important that each individual file can be clearly assigned to an event, an observer and a location. It should also be possible to search the archive specifically, e.g. by date, observer, asteroid, location, content, etc. For this reason, all files have so far been (re)named accordingly. It would be desirable if all files were named according to the same scheme (see point 3).
Feb. 05, 2024:   Great success for the "Alagasta-Team": Stefano Sposetti organized an observing campaign along the shadow path, which was generated by (738) Alagasta during its occultation of a 11.6 mag star. The observing team consisted of experienced observers as well as of students (summarized in the station BEL). See the detailed recordings here.

Thanks to an excellent preparation and good weather conditions, the result is very impressive:
    Chords:      Video from Andrea Manna:       Congratulations to this great teamwork!
Dec. 12, 2023:   Once in a lifetime: The small asteroid (319) Leona passed in front of the red giant star Betelgeuse (alpha Orionis) on December 12, 2023 between approx. 01:10 and 01.16 UT (depending on the observing location). Dozens of amateurs traveled with their mobile equipment as close as possible to the center of the shadow path, which stretched from Greece through the southern parts of Italy, Sardinia, Spain, Portugal and on to Florida. Most of the observers were lucky with the weather. Many light curves were recorded and are now waiting to be analyzed.
As already suspected, the relatively small asteroid (approx. 80 x 55 km) was not able to occult the red giant completely. This is because the star has a small but already significant angular extent (approx. 50 milliarcseconds) due to its size (760 times the size of the sun) and proximity (550 light years). As a result, the star's drop in brightness during the occultation by (319) Leona (relative speed approx. 10 km/s, duration about 12 s) was not abrupt, but gradual. The otherwise 0.5 mag bright Betelgeuse became fainter by about 2 magnitudes, but was still clearly visible to the naked eye.
Three amateurs (Stefano Sposetti, Stefan Meister and Andreas Schweizer) from the SAG specialist group SOTAS (Stellar Occultation Timing Association Switzerland) traveled to the shadow path. The recorded light curves are shown below. Congratulations on their great success! The chords of all existing recordings are currently being calculated, which will make it possible to determine the shape and size of the asteroid as well as the position and size of Beteigeuze. We can look forward to it!
See all recordings here.
Read the story to the following pictures:
See the preliminary results.
Nov. 30, 2023:   On Dec. 12, 2023, the bright and giant star Beteigeuze will be occulted by (319) Leona. For precise predictions, the orbital parameter of Leona should be known as precise as possible. Great: Just a few days before the big event, Stefan Meister and Peter Englmaier observed successfully a previous occultation of (319) Leona! On Nov. 30, 2023 and in parallel to Karl-Ludwig Bath (IOTA/ES), they used a telescope of the VdS Remote Observatory located at the Hakos farm in Namibia. This important observation allowed to actualize the orbital parameters of the small asteroid just in time. Well done!
See Recordings
Nov. 16, 2023:   Great News: CBET reports the discovery of the probable binary nature of the minor planet (5457) Queen's. On Sept. 04, 2023, Stefan Meister (EGL) and Andreas Schweizer (BUE) recorded the light drop during a stellar occultation caused by the asteroid. Further observations by IOTA/ES members (about 15 days later) showed a double drop during the same occultation. The analysis of all available observations suggests that (5457) has a satellite.
Please read the corresponding CBET, the IOTA/ES Press Release the Sky & Telescope contribution and the Minor Planet Bulletin MPB.
Sep. 16.-17, 2023:   The 42th ESOP will take place at the Armagh Observatory and Planetarium (AOP) in the historic City of Armagh, Northern Ireland.
Invitation   Registration
September 04, 2023:   Congratulations again! Stefan Meister and Andreas Schweizer recorded for the first time an occultation caused by the asteroid (5457) Queen's! The small asteroid (about 20 km diameter) occulted the star, viewed from both locations EGL and BUE.
Video,  Chord
December 10, 2022:   Congratulations! The Uranus Moon (P7M03) Titania (III) occulted the Star UCAC4 531-004984.
During 73.0 sec (!!!) this occultation was observed by Stefano Sposetti. Have a look to the Lightcurve.
October 29, 2022:   The 2. SOTAS-Meeting was held at the observatory Mirasteilas in Falera, Switzerland. Totally 12 participants listened to the lecturers, exchanged their experiences and discussed important points.
Invitation,   Protocol,   DVTI+CAM,   mobile Observations with telescopes
September 10/11, 2022:   This year, the 41th European Symposium on Occultation Projects (ESOP) took place at Granada, Spain.
Follow the YouTube videos to see the sessions:
- Saturday morning
- Saturday afternoon
- Sunday morning
     => The contribution of Andreas Schweizer about the DVTI camera project status starts at 2:25:00
- Sunday afternoon
February 08, 2022:   What a great sensation! For the first time, a stellar occultation caused by a nucleus of a comet was recorded! We congratulate warmly to our SOTAS members Stefano Sposetti, Alberto Ossola and Luca Buzzi! Well done guys!

The facts: Observed from Monte Ceneri and Muzzano, the nucleus of the comet 28/P Neujmin (18.3 mag, diam. about 21 km) occulted the star UCAC4 638-016921 (11.9 mag) and extincted its light for 1.76 resp. 1.28 sec.
Have a look to the report,  lightcurve,  target star,  video,  chord and the contribution in the Journal JOA (see page 10).
August 27/29, 2021:   This year, the 40th European Symposium on Occultation Projects (ESOP) took place at Białystok, Poland.
Follow to the Lectures.
For the Swiss contribution of Andreas Schweizer/Stefan Meister about the progress of the DVTI Cam Project, please forward to the time 00:28:30.
May 14, 2021:   Successful observation: Thomas Erzinger (station ID: SNG) recorded the magnitude drop of Io during the eclipse caused by Jupiter's moon Ganymed.
August 29/30, 2020:   This year, the 39th European Symposium on Occultation Projects (ESOP) took place online as a video conference. On average, over 100 participants were online. Besides participants from the EU, participants from Japan, Australia, Thailand, Turkey, Switzerland, UK, USA, Argentina and Brazil were registered. Many presentations and all live recordings including discussion can be viewed here.
July 31, 2020:   The 2020 IOTA Annual Meeting was held as a virtual session on July 25/26. During these two days, about 27 lectures were presented. Also the DVTI Camera Project of Andreas Schweizer and Stefan Meister was mentioned in a honorable manner.
Please follow the links for the agenda, protocol and video lectures.
July 07, 2020:   New issue of JOA - the Journal for Occultation Astronomy: Starting with page 8, the new Astronomical Digital Video (ADV) data format is presented. ADV can now be used with the DVTI (Digital Video Time Inserter) system and it will be available in the upcoming releases of several capture softwares, like SharpCap, DVTI Cam Control (by Andreas Schweizer and Stefan Meister), PyMovie or PyOTE, etc. Don't miss the future and inform yourself by reading the article.
June 22, 2020:   Successful observation of (2) Pallas: Thanks to good weather conditions, the occultation of a 11.5 mag star by (2) Pallas (9.6 mag) was recorded by numerous stations all around Europe. Totally 6 (from 41) recordings were taken from Switzerland (members of SOTAS). The magnitude drop during the occultation was only 0.2 mag. Many thanks to Eric Frappa (IOTA/ES) for the appreciated tricky analysis of the data. For the detailed reports and the resulting chords please visit the following link.
June 19, 2020:   Gerhard Dangl just informed: "I would like to draw your attention to a very interesting project by two Swiss amateur astronomers. It is about the development of a digital USB camera with GPS time stamps for occultation observation. In the meantime I have tested two different development stages of this DVTI camera with EXTA. The Swiss development team continuously developed the camera hardware and firmware as well as the PC control and recording software. The camera version DVTIv2b already delivers very good and usable results. Therefore I would like to share this with all interested observers. For this I have created an extra page on my website. Details of the measurements and the results are presented there."
Gratulations to the SOTAS members Andreas Schweizer and Stefan Meister! Well done, guys!
August 29/30, 2020:   Update: The 39th European Symposium on Occultation Projects (ESOP) in D-Freiburg i. Breisgau will only take place online due to the impact of Covid-19. A participation to this virtual meeting is highly recommended!
Dezember 20, 2019:   New archieve initiated: This website includes all reports, lightcurves and videos of stellar occultations, observed by SOTAS members. The observed events are sorted by year, then by date.
September 10, 2019:   New available in agenda: Occultation Calendar, especially for Switzerland, by Stefan Meister/SOTAS.
30/8 - 01/9 2019:   38th European Symposium on Occultation Projects (ESOP) at the famous Paris Observatory. From Switzerland, five SOTAS members participated to this highly interesting event. In the historic Cassini Hall, Andreas Schweizer and Stefan Meister presented the Digital Video Time Inserter (DVTI) Camera Project.
May 30, 2019:   Recently, Eric Frappa (Euraster) informed that, in future, he will only publish occultation events, which include at least one positive observation. He has taken this measure because of the large work related to it, which is understandable.
At the same time, I noticed that in April and May, our section had only a few observations, this in contrast to the previous months. Since our website should reflect the activity of the SOTAS members, I would like to invite you to report ALL observations to me, including where the observation was negative or "missed".
At this point I thank all active observers for their highly valuable data.
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 02, 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 08, 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 05, 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. 09, 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. 06, 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. 05, 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 01, 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 07, 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 02, 2017:   "3 - 2 - 1 - lift off" for the new working group! Let's occult!