Merged from:
Asteroid Occultations (Shape Modeling).md+STELLAR OCCULTATIONS BY SMALL BODIES.mdBoth originals preserved. This is the canonical reference.
Stellar Occultations by Small Bodies¶
Tier 1 science — irreplaceable. Geographic distribution IS the instrument. No single telescope, professional or otherwise, can replicate multi-chord occultation geometry.
What It Is¶
When an asteroid, TNO, or KBO passes in front of a star, the star blinks out. The duration and shape of the light curve reveals the object's size and shape with kilometer precision. [Source: Millis & Elliot (1979), in "Occultations for Probing Atmospheres and Surfaces" — foundational review of stellar occultation geometry]
Different sites across Earth's surface see different "chords" across the occulting body. Combine enough chords and you reconstruct the 2D silhouette. Get the right chords and you can detect atmospheres via the central flash.
Shadow speed: 10–30 km/s across Earth's surface. You need sites separated by hundreds of km to sample different chords.
Why It's Irreplaceable¶
| Single Telescope | Distributed Network |
|---|---|
| 1 chord = diameter guess only | 5+ chords = full 2D shape reconstruction |
| Can't be in two places at once | Geographic density = chord density |
| Professional queue scheduling can't respond to prediction windows | Network is always on, always positioned |
Why professional telescopes can't replace this: - Hubble: Can't do high-speed photometry; wrong field of view - VLT/Keck: Queue scheduled; can't respond to specific prediction windows - TESS: 21 arcsec pixels; can't resolve individual stars - Dedicated surveys (OASES): Need more geographic spread, not better telescopes
Real-world proof: The Unistellar Network (eVscope users) characterized the asteroid Eurybates (a NASA Lucy mission target) and tracked JWST during deployment. [Source: Marchis et al. (2022), PASP 134, 014509 — Unistellar citizen science network results]
Ring discoveries made this way: Chariklo, Haumea, Quaoar — all from distributed occultation networks. [Source: Braga-Ribas et al. (2014), Nature 508, 72 — Chariklo ring discovery; Morgado et al. (2022), Nature 614, 239 — Quaoar ring discovery]
Technical Requirements¶
| Parameter | Minimum | Ideal | Why |
|---|---|---|---|
| Time resolution | 1 second | 0.1 second | Events last 0.1–30 seconds |
| Photometric precision | 5% | 1% | Must detect complete dimming |
| GPS timing | ±0.1 sec | ±0.01 sec | Chord timing is everything |
| Limiting magnitude | V~12 | V~14 | Brighter stars = more predictions |
| FOV | 10 arcmin | 30+ arcmin | Finding/tracking target star |
Equipment Tiers¶
| Tier | Setup | Cost | Capability |
|---|---|---|---|
| Minimum | 8" SCT + ZWO ASI290MM + GPS | $3,000 | V~12, 0.1s timing |
| Good | 11" SCT + QHY174M + GPS | $6,000 | V~13, 0.05s timing |
| Optimal | 16" f/4 + CMOS + GPS | $15,000 | V~14, 0.02s timing |
GPS is non-negotiable. NTP timing drifts at the second scale; occultation chord precision requires ±0.01–0.1 second timing. A GPS-PPS module costs ~$30 and eliminates this problem entirely. [Source: IOTA (International Occultation Timing Association) standard observing guide; see also Dunham et al. (2016) for GPS-PPS timing standards in occultation work]
What Goes Wrong¶
| Failure Mode | Cause | Mitigation |
|---|---|---|
| Missed event | Wrong target star | Plate solving + finder charts pre-loaded |
| Timing drift | No GPS, NTP unreliable | Require GPS timestamping for all nodes |
| False positive | Cosmic ray, satellite | Require 2+ simultaneous detections |
| Cloud during event | Single site clouded | Network redundancy is the fix |
| Wrong prediction | Orbital uncertainty | Use multiple prediction sources (Occult4, Lucky Star, Steve Preston) |
Science Output¶
- Size + shape with km precision — better than spacecraft flyby in many cases
- Atmosphere detection via central flash (requires high time resolution and bright event)
- Binary detection — double dip in the light curve
- Ring systems — Chariklo and Quaoar found this way with small amateur networks
- TNO shape statistics — feeding into Kuiper Belt formation models
Connection to OpenAstro Pipeline¶
- Prediction ingestion: Pull occultation predictions from Occult4 / Lucky Star / Steve Preston's page; convert to time-critical high-priority targets
- Geographic assignment: Scheduler assigns sites along the predicted shadow path, maximizing chord separation
- Data upload: Each node uploads its light curve immediately post-event
- Chord reconstruction: Central pipeline combines chords → 2D shape fit [Source: Herald et al. (2020), AJ 159, 56 — occultation chord reduction and shape-fitting methodology]
- Publication: Multi-chord events → paper with all contributing observers as co-authors
[NOVEL] The OpenAstro pipeline step of automated geographic assignment of sites along the predicted shadow path — assigning specific nodes to specific cross-track positions to maximise chord separation and shape-reconstruction fidelity — is an original scheduling algorithm contribution. No existing citizen-science occultation network automates this assignment; observers self-select their positions.