Place a naked-eye star by SIMBAD's name only within a magnitude of its source, and hold HD 45951 to it

e7c420b placed two naked-eye HYG rows along the Gaia source SIMBAD names them as. One of them,
θ¹ Ori A (HD 37020, HYG 26155), came with HYG's V 4.98 and O7, which are Hipparcos's for it and a
companion together: SIMBAD has θ¹ Ori A at V 6.73 and B0V, and its source at G 6.63. At 378 pc the
map drew it at 2.7e4 L and 37 100 K, brighter than θ¹ Ori C beside it, and counted it naked-eye.
The lookup by position already refuses a source more than a magnitude off HYG's V (it refused
this one); the lookup by name now does too. At its own magnitude and 378 pc the map does not keep
the star, as it keeps none that faint past 250 pc: 455 519 -> 455 518 stars, naked-eye 8 899 ->
8 898, of them past 250 pc 1 664 -> 1 663. HD 45951 (V 6.20 against G 5.90) is placed as before.

Nothing checked where HD 45951 was placed, only that its name was there. Along HYG's direction,
31.7' out, every check passed with the star drawn twice: under its name, and as its bare Gaia
designation. validateStars now requires the star named HD 45951 to carry that source's
designation, and requires HYG 26155 to be absent. The MIN_NAKED_EYE_STARS comment gives the new
counts and says why θ¹ Ori A is left out.

ETL mutants, each in a throwaway worktree with a copy of the cache, reached validation and failed
with the expected message:
- HD 45951 placed along HYG's x/y/z: "HD 45951 is not on Gaia DR3 3369454521490604416, the source
  SIMBAD names it as"
- the magnitude check dropped from the lookup by name: "θ¹ Ori A is drawn in the V and type of
  Hipparcos's blend of it with a companion."

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

tools/etl/build.ts

@@ -74,23 +74,30 @@ const MIN_COLOURS_FROM_TEMPERATURE = 40;
  */
 const MAX_ARCHIVE_IDS_OFF_THEIR_NAME = 5;
 /**
- * Every star the naked eye sees, kept at any distance (c64eea0): measured 8 899 of V 6.5 or
- * brighter, 1 664 of them past 250 pc. With no magnitude handed to placementDistancePc, 7 379 are
+ * Every star the naked eye sees, kept at any distance (c64eea0): measured 8 898 of V 6.5 or
+ * brighter, 1 663 of them past 250 pc. With no magnitude handed to placementDistancePc, 7 379 are
  * left and Rigel, Deneb and Alnilam are gone — and every other check passed, the HYG survivors
  * going down rather than up. HD 197770 and HD 45291 are two of the twelve only Gaia's bright
  * sources place, by position; without that lookup they are gone and the count drops by twelve,
- * which the floor alone would not see. HD 45951 is one of the two only SIMBAD's name for its Gaia
- * source places, HYG's declination for it being 31.7′ out; θ¹ Ori A (HD 37020) is the other.
+ * which the floor alone would not see.
+ *
+ * HD 45951 is the one only SIMBAD's name for its Gaia source places, HYG's declination for it being
+ * 31.7′ out. Placed along HYG's direction instead, every check here passed, with the star drawn
+ * twice: there, and as its bare source 31.7′ away. So it is held to that source by designation.
  *
  * Twenty HYG rows of V 6.5 or brighter are still left out, for want of a distance: neither HYG nor
  * Hipparcos gives one, and Gaia DR3 has no source brighter than G 7.5 with a parallax five times
  * its error within a minute of arc, nor under the name SIMBAD gives. They are β Phe, φ Cas, χ Aur,
  * ο¹ Cen, Polis, 16 Sgr, ρ Cas, η Car, and HD 47240, 50820, 90772, 97534, 100198, 101205, 101947,
- * 129092, 151804, 185936, 202214 and 212466.
+ * 129092, 151804, 185936, 202214 and 212466. A 21st, θ¹ Ori A (HYG 26155), is left out on purpose:
+ * its V 4.98 and O7 are Hipparcos's for it and a companion together, and SIMBAD names it a source
+ * of G 6.63 at 378 pc, which the map does not keep; placed, it was drawn brighter than θ¹ Ori C.
  */
 const MIN_NAKED_EYE_STARS = 8_800;
 const NAKED_EYE_MAGNITUDE_V = 6.5;
 const REQUIRED_NAKED_EYE_STARS = ['Rigel', 'Deneb', 'Alnilam', 'HD 197770', 'HD 45291', 'HD 45951'];
+const IDENTIFIED_NAKED_EYE_STARS = [{ name: 'HD 45951', gaiaDesignation: 'Gaia DR3 3369454521490604416' }];
+const BLENDED_NAKED_EYE_ROWS = [{ id: 26155, name: 'θ¹ Ori A' }];
 
 function validateStars(stars: StarRecord[]): void {
   assertCondition(stars.length > 0, 'No stars were produced.');
@@ -179,6 +186,15 @@ function validateStars(stars: StarRecord[]): void {
   for (const name of REQUIRED_NAKED_EYE_STARS) {
     assertCondition(stars.some((star) => star.name === name), `${name} is missing — naked-eye stars are no longer kept wherever a survey places them.`);
   }
+  for (const expected of IDENTIFIED_NAKED_EYE_STARS) {
+    assertCondition(
+      stars.some((star) => star.name === expected.name && star.gaiaDesignation === expected.gaiaDesignation),
+      `${expected.name} is not on ${expected.gaiaDesignation}, the source SIMBAD names it as — it is drawn where HYG has it, beside that source.`
+    );
+  }
+  for (const blended of BLENDED_NAKED_EYE_ROWS) {
+    assertCondition(!stars.some((star) => star.id === blended.id), `${blended.name} is drawn in the V and type of Hipparcos's blend of it with a companion.`);
+  }
   console.log(`  ${nakedEye} naked-eye stars.`);
 
   const gaiaAtHipparcosDistance = stars.filter((star) => star.source === 'gaia' && star.magnitudeBand === 'V' && !star.distanceFromGaia).length;

tools/etl/fetchStars.ts

@@ -113,8 +113,12 @@ export async function fetchStars(): Promise<StarRecord[]> {
     const crossMatched = row['hip'] ? gaiaByHip.get(Number(row['hip'])) : undefined;
     const positional = crossMatched === undefined && unplaced ? brightCounterpart(row, magnitude, brightGaia) : undefined;
     // Where HYG's position leads to no bright source, the one SIMBAD names it as: HD 45951, whose
-    // declination HYG has 31.7′ out, and θ¹ Ori A (HD 37020), whose V it has 1.65 brighter than G.
-    const byIdentity = crossMatched === undefined && positional === undefined && unplaced ? brightByDesignation.get(nakedEyeDesignations.get(`HD ${row['hd']}`) ?? '') : undefined;
+    // declination HYG has 31.7′ out. Within a magnitude of HYG's V, as by position: θ¹ Ori A
+    // (HD 37020) has V 4.98 and O7 in HYG, Hipparcos's entry for it and a companion together, and
+    // its own source G 6.63 (SIMBAD: V 6.73, B0V). Placed, it was drawn brighter than θ¹ Ori C and
+    // counted as naked-eye; at 378 pc and its own magnitude the map does not keep it.
+    const named = crossMatched === undefined && positional === undefined && unplaced ? brightByDesignation.get(nakedEyeDesignations.get(`HD ${row['hd']}`) ?? '') : undefined;
+    const byIdentity = named && Math.abs(named.magnitudeG - magnitude) <= BRIGHT_COUNTERPART_MAGNITUDES ? named : undefined;
     const gaia = crossMatched ?? positional ?? byIdentity;
     const gaiaPc = gaia?.distancePc;
     const hipparcosError = hipparcos?.relativeError;