Comets, Occultations, Meteors and Asteroids (COMA)
Comets, Occultations, Meteors and Asteroids (COMA)
Several members of the Astronomical Society of South Australia have an interest in observing dynamic solar system objects and events.
This includes the apparition of comets, meteor showers, asteroids and occultation events when a body such as the Moon, a planet, or an asteroid passes in front of a star.
Local observers · International result
A brief blink of starlight reveals something unexpected
Congratulations to ASSA members Blair Lade, Andrew Wendelborn and Paul Martinaitis. By watching the same star from three locations around Adelaide, they helped uncover evidence that asteroid (1757) Porvoo may have a small companion.
What is an occultation?
An occultation happens when an object such as an asteroid passes in front of a distant star. For a few moments the star appears to dim or disappear. Careful timing from different locations lets observers trace the asteroid’s size and shape — a little like measuring a silhouette from its shadow.
On 7 July 2026, the three observers watched Porvoo pass in front of the star UCAC4 312-094580. Blair recorded an extra, very short dip in the star’s light. When the observations were brought together and analysed, that unexpected signal pointed to a second, much smaller object travelling near the asteroid.
The result was officially reported on 22 September in Central Bureau Electronic Telegram 5742. Scientists describe the object as an apparent satellite because further observations will help confirm its nature.
Three observers, one result
No single observation told the whole story. Combining recordings from three suburbs allowed the team to compare different paths across the asteroid and test other explanations for the extra dip.
Blair Lade · Mawson Lakes
Recorded Porvoo’s main shadow and the unexpected second dip using a 20-cm telescope and astronomy camera.
Andrew Wendelborn · Largs North
Captured the event with an 11.4-cm Unistellar eVscope, adding a second view of the asteroid’s silhouette.
Paul Martinaitis · Salisbury
Recorded a third path with a 20-cm telescope and astronomy camera, helping complete the picture.
This is why coordinated observing is so valuable. A small group of people, watching from their own locations, can combine their results to make a meaningful contribution to astronomy.
Technical details from CBET 5742
The observations
The occultation occurred at 0.487 UT. Blair’s ZWO 533MM Pro recorded two drops lasting 0.30 and 2.73 seconds, separated by 3.30 seconds. These produced paths, known as chords, of 1.71 and 15.54 km, separated by 18.83 km. Andrew’s IMX224 sensor recorded 1.20 seconds, or a 6.83 km chord. Paul’s ZWO 462MM recorded 1.85 seconds, or a 10.53 km chord.
What the analysis found
The main asteroid fits an ellipse measuring 15.9 × 10.8 km, with a mean diameter of 13.1 km, consistent with earlier NEOWISE and Akari AcuA measurements. Modelling of the apparent satellite gives a minimum ellipse of about 1.5 × 0.8 km and a maximum circular diameter of about 2.6 km. Its projected separation was 27.5 km at position angle 274 ± 2 degrees.
A double-star explanation was considered, but rejected because Andrew or Paul should then have recorded a matching second event. Dave Herald, David Gault and Christian Weber supported the analysis. Bob Anderson supplied the Fresnel diffraction software used to model the short secondary event.
Curious about occultations?
COMA — the Comets, Occultations, Meteors and Asteroids special interest group — brings together ASSA members who enjoy observing these changing and sometimes surprising objects. If this story has sparked your interest, the group is a friendly place to learn how observations are planned, recorded and shared. Contact details and more about the group appear below.
A more detailed technical account of the observations, discovery and analysis will follow in a forthcoming issue of The Bulletin.
Meet the special interest group
Occultations
With Andrew Wendelborn
Discover the fleeting events that occur when a solar system object passes in front of a star.
Watch on YouTube ↗Group Focus
The Comets, Occultations, Meteors and Asteroids group (COMA) was formed in 2021 and provides a focus for these activities in the ASSA.
The group supports the exchange of local information for this very dynamic area of astronomy.
Activities
The group plans regular communications, including Zoom meetings, comet and meteor observing sessions, and encourages members to participate in asteroid occultation events.
Objects and Events
- Comet apparitions
- Meteor showers
- Asteroids
- Lunar, planetary and asteroid occultations
- Time-sensitive solar system observing opportunities
Member observations in practice
COMA observations can contribute useful timing and light-curve data for fast-changing solar system events.
Light curves from an observation showing the discovery of a previously unknown double star system.
Asteroid shape fit using timing information from member observations.
Point of contact
| Name | Andrew Wendelborn |
|---|---|
| coma@assa.org.au | |
| Phone | Not currently listed |