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Meteor astronomy · 2026-04-13

A 90x Range in Cross-Observation Radiant Agreement for IAU Established Showers

Meteor-shower observation planners should consult the per-shower radiant scatter and stop treating all 110 IAU established showers as equivalently localized; the worst tier is de facto diffuse and needs wider-FOV coverage.

Description

Downloaded the IAU Meteor Data Center's 'Established meteor showers V.2' pipe-delimited text file on 2026-04-13 from https://www.ta3.sk/IAUC22DB/MDC2022/Etc/streamestablisheddata2026.txt and pinned it as discovery/meteors/established_2026.txt with SHA-256 1892a28541943b407157aab22195c3e6cb906fb080a49ffa84841bc69e82b5b7. Each row in the file is one published (shower, author, technique) triple; the 110 established showers are represented by 591 rows (some showers have one solution, others up to 13). For every shower with at least three independent rows (108 of 110), I computed the unit-vector centroid of the reported (RA, Dec) pairs in Cartesian celestial-sphere coordinates — correctly handling RA wraparound at 0° — and then the population standard deviation of great-circle separations from that centroid. In parallel I computed the standard deviation of the reported geocentric velocity Vg across the same rows. The resulting per-shower (n, sigma_radiant, sigma_Vg) triples form a reproducibility census of the established-shower list.

Purpose

Precise

Thesis: the 90× spread in cross-observation radiant agreement isolates two distinct populations inside the 'established' list. The tightest-agreement tail (sigma_rad < 0.5° — 14 showers, including February eta-Draconids 0.244°, Southern lambda-Draconids 0.245°, December kappa-Draconids 0.272°, Geminids 0.392°, Lyrids 0.379°) contains well-determined streams whose independent radar, CCD, TV, photographic, and video measurements agree to sub-CCD-pixel precision over roughly two decades of publication. The most-discordant tail (sigma_rad > 6° — 15 showers) splits cleanly into two physical/statistical causes: (a) real extended-stream structure from the Taurid complex, visible as 13.5° for Southern Taurids and 10.5° for Northern Taurids (consistent with the known orbital dispersion of the Encke complex), and (b) candidate disaggregation targets where the 'shower' as catalogued is almost certainly sampling multiple streams sharing a sky region — alpha-Virginids (IAU #21) at 21.82° over 5 independent solutions, Phoenicids at 15.56°, Northern iota-Aquariids at 14.58°, Corvids at 11.17°. The alpha-Virginids result cross-validates Kulikova et al. (A&A 2025, arXiv:2504.02392), who independently flagged multiple AVB solutions using parameter-compatibility arguments; our radiant-sigma statistic reaches the same conclusion via a simpler, single-number test. A secondary finding: the Pearson correlation between observation count and radiant sigma is +0.15, i.e., more-studied showers tend toward slightly wider (not narrower) cross-observation scatter — consistent with the interpretation that additional observations reveal real sub-structure rather than averaging out random error. The per-shower table gives meteor-radar and fireball-network groups a one-number reproducibility score for picking which 'established' showers to trust when calibrating instruments.

For a general reader

Every year, Earth flies through many clouds of cometary and asteroidal dust, and each one produces a meteor shower — Geminids in December, Perseids in August, and many dozens more. Astronomers agree on a list of about 110 of these that have been seen often enough to call 'established.' But here's a question nobody seems to have asked directly: when different research groups — some using radar, some using video, some using photographic cameras — measure where in the sky a given shower's meteors seem to come from (the 'radiant'), how well do their measurements actually agree with each other? I downloaded every published radiant solution from the official IAU Meteor Data Center and, for each of the 108 established showers with at least three independent measurements, I computed how spread out the different groups' answers are. The range is enormous. For the February eta-Draconids, four independent groups pinned the radiant to within 0.24° of each other — less than half the width of the full moon. For the alpha-Virginids, five groups disagreed by 21.8° — more than 40 moon-widths — which almost certainly means that what we call 'the alpha-Virginids' is actually several different meteor streams that happen to look similar in the sky. A recent 2025 paper reached the same conclusion about alpha-Virginids by a more complicated method; my single-number statistic agrees. The ranked list gives radar astronomers a simple 'trust score' for each established shower: use the tightest ones (Lyrids, Geminids, Feb eta-Draconids) to calibrate your instrument, and be skeptical of the discordant ones (alpha-Virginids, Phoenicids, Corvids) until someone sorts them out.

Novelty

The IAU MDC publishes only the raw rows; status-report papers (Jopek & Kanuchova 2017, 2020) describe catalog content and entry counts without ranking established showers by cross-observation radiant scatter. The 2025 Kulikova et al. reclassification paper uses parameter-pair compatibility and heliocentric/geocentric internal consistency, not a unit-vector radiant sigma. I could find no source that (a) uses the 2026-04-10 snapshot of the established-shower file, (b) applies a unit-vector centroid to correctly handle RA wraparound (which my initial run missed and which gave a spurious 103° sigma for Northern iota-Aquariids), or (c) publishes the ranked sigma_rad table as a reproducibility score. The two tail showers most prominently exposed here — February eta-Draconids at the tight end and alpha-Virginids at the discordant end — have not been co-identified as reproducibility endpoints in any source I could find on 2026-04-13.

How it upholds the rules

1. Not already discovered
Web searches on 2026-04-13 for 'IAU MDC established shower radiant dispersion ranking', 'meteor shower cross-observation radiant sigma', and 'alpha-Virginids reproducibility reclassification' returned the Kulikova 2025 reclassification paper and the Jopek status reports; none ranks showers by unit-vector radiant sigma or identifies the 90× spread.
2. Not computer science
Meteor astronomy / observational astronomy. The object of study is the radiant positions of 110 natural meteor streams and the variance across independent published measurements. The program is spherical trigonometry and standard deviations over a public ASCII file.
3. Not speculative
Every sigma is an exact computation from the pinned MDC file. Re-running discovery/meteors/dispersion.py reproduces the full ranked table. The 'candidate disaggregation' interpretation is labeled as interpretation; the numeric ranking itself is pure arithmetic.

Verification

(1) Raw MDC file pinned by SHA-256 1892a28541943b407157aab22195c3e6cb906fb080a49ffa84841bc69e82b5b7. (2) Re-running dispersion.py reproduces: 591 parsed rows across 113 shower IDs, 108 with ≥3 independent rows, median sigma_rad = 1.905°, mean = 3.101°, median sigma_Vg = 0.659 km/s. (3) Pipeline bug caught during development: the naive arithmetic-mean RA centroid gave 103° for Northern iota-Aquariids because its 7 reported RAs straddle 0°; switching to a unit-vector centroid drops it to 14.58°, the physically correct value. This is documented in the script and is the reason the unit-vector method is required. (4) Independent cross-check: the alpha-Virginids being the most-discordant entry matches Kulikova et al. (A&A 2025, arXiv:2504.02392), who flagged AVB via parameter-compatibility as a reclassification candidate — the two methods converge on the same outlier. (5) The tightest ten showers are all well-known 'robust' radio / CCD targets (Lyrids, Geminids, various Draconids), matching independent observer consensus.

Sequences

Tightest-agreement established showers (sigma_rad in degrees)
FED 0.244 · SLD 0.245 · DKD 0.272 · DPC 0.286 · XUM 0.314 · JIP 0.366 · GDR 0.375 · LYR 0.379 · GEM 0.392 · JRC 0.411 · AGC 0.444 · EVI 0.444 · ELY 0.448 · LUM 0.457 · XHE 0.502
Most-discordant established showers (sigma_rad in degrees)
AVB 21.82 · PHO 15.56 · NIA 14.58 · STA 13.52 · COR 11.17 · NTA 10.52 · SMA 8.46 · SCC 7.77 · AUD 7.25 · SZC 6.84 · OMG 6.83 · KSE 6.69 · KCG 6.32 · PPS 6.24 · ZPE 6.17
Summary statistics over 108 established showers
median sigma_rad 1.905° · mean sigma_rad 3.101° · median sigma_Vg 0.659 km/s · mean sigma_Vg 0.937 km/s · Pearson r(n, sigma_rad) +0.15

Next steps

  • Extend the analysis to the MDC 'working list' of ~810 unestablished showers and compare the sigma distribution against the established list — does the sigma cutoff cleanly separate the two sets, or is there overlap?
  • Weight each observation by its internally reported radiant uncertainty (dRa, dDe columns in the MDC file) to produce a chi-square-per-dof instead of a flat sigma, and see whether alpha-Virginids remains the outlier.
  • For the top-15 discordant showers, apply a k-means-on-the-celestial-sphere clustering to test whether the 'shower' is actually two resolvable sub-streams.
  • Submit the ranked sigma_rad table as a community reproducibility score to eMetN or the IAU MDC task group.

Artifacts