Say which band each star was measured in, whose catalogue it is, and how sure its distance is

The readout named Hipparcos, Yale and Gliese while 378 775 of the 455 608 stars are described by
Gaia DR3, printed one "Magnitude" for G and V alike, and gave every distance to the parsec. The
band cannot be read off the star's source, which records whose position it has: 62 002 stars Gaia
places keep HYG's V and B-V, and the 575 hosts renamed after their planets are Gaia's, in G.

stars-meta.bin gains two byte columns, 14 to 16 bytes a star (6 378 512 to 7 289 728 bytes; gzip
-9 2 804 049 to 3 110 991). One holds the magnitude's band (V 76 555 stars, G 378 744, none 309,
whose magnitude is a stand-in), which colour the colour index is (B-V 75 203, BP-RP 376 703), and
whether the distance is Gaia's parallax. The other holds the distance's relative error as its
square root in 255ths: a step is 0.08 % of distance at 1 %, 0.35 % at 20 %, and 100 % is the top.
encode, decode, BYTES_PER_STAR_META and the build.ts round trip cover both; no workflow reads the
format.

Where the errors come from:
- Gaia rows keep the parallax_error their query already fetched: median 0.3 %, 90th percentile
  1.2 %, at most 20 %, the query's own cut.
- A HYG star at Gaia's distance takes the cross-match's parallax_over_error, and a star merged
  into a Gaia entry keeps that entry's error with its position.
- The 3 067 Hipparcos stars that keep their Hipparcos distance, Rigel, Deneb and Alnilam among
  them, take e_plx from van Leeuwen's 2007 reduction: a new cached query of
  public.hipparcos_newreduction on the ESA archive, whose 117 955 rows HYG's distances invert.
- The archive's stars take sy_disterr1/2 from pscomppars, in a query and cache file of their own
  so the composite rows already cached were not refetched.
- 439 distances have no published error: 357 Gliese rows and 82 archive hosts.

Of the errors, 392 786 are 1 % or less and are not printed; 61 156 print as "117 ± 12 pc" to the
distance's own digits; 1 196 between 20 and 100 %, and 30 past it, print as the range the
parallax gives, since a symmetric error in parallax is a lopsided one in distance.

The star card (measured on the dev server) now reads, for example:
- Rigel: 265 ± 23 pc, V 0.18, B-V -0.03, source HYG.
- Deneb: 433 ± 60 pc.
- Alnilam: "476 pc to 833 pc" (Hipparcos 1.65 ± 0.45 mas).
- Gaia DR3 5612323414549657984: 111 ± 2 pc, G 4.63, BP-RP -0.15, source Gaia DR3.
- Proxima Centauri: 1.30 pc, V 11.01, source "HYG, Gaia DR3 distance".
- TRAPPIST-1: G 15.62, BP-RP 4.90, source Gaia DR3.
- Kepler-186: V 15.14, source NASA Exoplanet Archive.
The neighbourhood's subtitle reads "Gaia DR3 378,775 · HYG 73,556 · NASA Exoplanet Archive
3,277", counted by the catalogue describing each star.

build.ts validateStars now fails a catalogue with more than 1 000 stars without a band (309
today) or without a distance error (439). Dropping G from the Gaia rows gave 379 040 without a
band, and dropping their parallax_error gave 441 216 without an error; both runs failed.

Decoding the catalogue in Node took a median 29 ms before and 24 ms after (nine runs each, within
noise). In the app, five cold boots gave a 654-786 ms long task after the data landed and the
HUD at 1.83-2.07 s.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tools/etl/fetchExoplanets.ts

@@ -77,6 +77,13 @@ const COMPOSITE_COLUMNS = [
 // pl_name is unique here too, one row per planet.
 const COMPOSITE_URL = `${TAP_BASE_URL}?query=select+${COMPOSITE_COLUMNS}+from+pscomppars+order+by+pl_name&format=csv`;
 const COMPOSITE_CACHE_FILE = `exoplanet-archive-pscomppars-${createHash('sha1').update(COMPOSITE_URL).digest('hex').slice(0, 8)}.csv`;
+/**
+ * The same table's distance errors, for the stars placed from the archive. A query of its own,
+ * cached apart, so that asking for them did not refetch the columns above: the archive changes
+ * daily, and a new answer would have moved every figure the catalogue was checked against.
+ */
+const DISTANCE_ERRORS_URL = `${TAP_BASE_URL}?query=select+pl_name,sy_disterr1,sy_disterr2+from+pscomppars+order+by+pl_name&format=csv`;
+const DISTANCE_ERRORS_CACHE_FILE = `exoplanet-archive-disterr-${createHash('sha1').update(DISTANCE_ERRORS_URL).digest('hex').slice(0, 8)}.csv`;
 
 /**
  * Where the ids of the stars only the archive places begin: past Gaia's two ranges, and under
@@ -109,6 +116,7 @@ export async function fetchExoplanets(stars?: StarRecord[]): Promise<{ exoplanet
   const csv = await fetchTextCached(TAP_URL, CACHE_FILE);
   const rows = parseCsvObjects(csv);
   const composite = new Map(parseCsvObjects(await fetchTextCached(COMPOSITE_URL, COMPOSITE_CACHE_FILE)).map((row) => [row['pl_name'], row]));
+  const distanceErrors = new Map(parseCsvObjects(await fetchTextCached(DISTANCE_ERRORS_URL, DISTANCE_ERRORS_CACHE_FILE)).map((row) => [row['pl_name'], row]));
 
   let matched = 0;
   // Catalogue stars known only by their Gaia designation, which take the archive's host name —
@@ -144,21 +152,29 @@ export async function fetchExoplanets(stars?: StarRecord[]): Promise<{ exoplanet
         // Carried back from the archive's epoch like any Gaia row, and placed at `sy_dist`.
         const j2000 = propagateProperMotion(raDeg, decDeg, pmRaMasPerYear ?? 0, pmDecMasPerYear ?? 0, ARCHIVE_TO_CATALOGUE_YEARS);
         // V where the archive has it, as HYG's stars are; else Gaia's G, the band the catalogue's
-        // Gaia stars are already in. The assets carry no band, so it is counted below instead.
+        // Gaia stars are already in.
         const v = host('sy_vmag');
         const g = host('sy_gaiamag');
         const b = host('sy_bmag');
         const temperatureK = host('st_teff');
-        bands[v !== undefined ? 'V' : g !== undefined ? 'G' : 'none']++;
+        const band = v !== undefined ? 'V' : g !== undefined ? 'G' : undefined;
+        bands[band ?? 'none']++;
+        // B-V where the archive has both magnitudes, else the effective temperature's; with
+        // neither, null leaves the colour to the spectral type, as for any other star.
+        const colorIndex = b !== undefined && v !== undefined ? b - v : temperatureK !== undefined ? temperatureToColorIndex(temperatureK) : null;
+        // The archive gives the distance's error as two one-sided ones; their mean, relative.
+        const errors = distanceErrors.get(row['pl_name']);
+        const [above, below] = [parseOptionalNumber(errors?.['sy_disterr1']), parseOptionalNumber(errors?.['sy_disterr2'])];
         archiveStar = {
           id: ARCHIVE_ID_BASE + archiveStars.size,
           name: row['hostname'],
           ...raDegDecDistanceToXyz(j2000.raDeg, j2000.decDeg, distancePc),
           magnitude: v ?? g ?? UNKNOWN_MAGNITUDE,
+          ...(band === undefined ? {} : { magnitudeBand: band }),
           spectralType: compositeRow?.['st_spectype'] || 'Unknown',
-          // B-V where the archive has both magnitudes, else the effective temperature's; with
-          // neither, null leaves the colour to the spectral type, as for any other star.
-          colorIndex: b !== undefined && v !== undefined ? b - v : temperatureK !== undefined ? temperatureToColorIndex(temperatureK) : null,
+          colorIndex,
+          ...(colorIndex === null ? {} : { colorSystem: 'B-V' as const }),
+          ...(above === undefined || below === undefined ? {} : { distanceError: (Math.abs(above) + Math.abs(below)) / 2 / distancePc }),
           source: ARCHIVE_SOURCE
         };
         archiveStars.set(row['hostname'], archiveStar);