diff --git a/src/app/shared/astro/spectral.spec.ts b/src/app/shared/astro/spectral.spec.ts
index daa67ec..6e63e9b 100644
--- a/src/app/shared/astro/spectral.spec.ts
+++ b/src/app/shared/astro/spectral.spec.ts
@@ -47,8 +47,8 @@ describe('parseSpectralClass', () => {
 });
 
 describe('isGiant', () => {
-  it('reads luminosity classes I to III off the primary, and the giant and supergiant prefixes', () => {
-    for (const type of ['M1Ib + B2.5V', 'K5III', 'M2II-IIIvar', 'C7Iab', 'K0IIIb', 'gK0', 'cM2']) {
+  it('reads luminosity classes I to III off the primary, the giant and supergiant prefixes, and carbon and S stars', () => {
+    for (const type of ['M1Ib + B2.5V', 'K5III', 'M2II-IIIvar', 'C7Iab', 'K0IIIb', 'gK0', 'cM2', 'N5', 'Ce+', 'S57:']) {
       expect(isGiant(type), type).toBe(true);
     }
   });
@@ -166,4 +166,10 @@ describe('dwarfSequenceAtColor', () => {
     expect(dwarfSequenceAtColor(null)).toBeNull();
     expect(dwarfSequenceAtColor(-0.29, 'B-V')!.gMinusV).toBeNull();
   });
+
+  it('reads the row at the end a colour is past, when asked to', () => {
+    expect(dwarfSequenceAtColor(2.2, 'B-V', true)).toEqual({ temperatureK: 2420, bolometricCorrectionV: -5.78, gMinusV: -3.09 });
+    expect(dwarfSequenceAtColor(-0.15, 'BP-RP', true)).toEqual({ temperatureK: 10700, bolometricCorrectionV: -0.42, gMinusV: 0.018 });
+    expect(dwarfSequenceAtColor(null, 'B-V', true)).toBeNull();
+  });
 });
diff --git a/src/app/shared/astro/spectral.ts b/src/app/shared/astro/spectral.ts
index 3169075..e1f7728 100644
--- a/src/app/shared/astro/spectral.ts
+++ b/src/app/shared/astro/spectral.ts
@@ -73,12 +73,14 @@ export function parseSpectralClass(
 const GIANT_LUMINOSITY_CLASS = /(?<![IV])(?:III|II|I)(?![IV])/;
 
 /**
- * Whether a spectral type says its star is a giant or supergiant: luminosity class I to III, or
- * HYG's `g` or `c` prefix. Read off the primary only — Antares is `M1Ib + B2.5V`.
+ * Whether a spectral type says its star is a giant or supergiant: luminosity class I to III,
+ * HYG's `g` or `c` prefix, or a carbon or S star (C, N, R, S), which are all giants on the
+ * asymptotic branch whether or not a class is given. Read off the primary only — Antares is
+ * `M1Ib + B2.5V`.
  */
 export function isGiant(spectralType: string | null | undefined): boolean {
   const primary = (spectralType ?? '').split('+')[0].trim();
-  return /^[gc][OBAFGKM]/.test(primary) || GIANT_LUMINOSITY_CLASS.test(primary);
+  return /^(?:[gc][OBAFGKM]|[CNRS])/.test(primary) || GIANT_LUMINOSITY_CLASS.test(primary);
 }
 
 /**
@@ -191,17 +193,19 @@ export interface DwarfSequencePoint {
  * same table the spectral estimate reads, so a star's temperature and its estimated type agree.
  * Linear rather than nearest, because the red end is steep: B−V runs 1.495 to 1.53 from M1.5 to
  * M3, over which the temperature drops 190 K and the correction 0.4 magnitudes. `null` outside
- * the table, as for the estimate.
+ * the table, as for the estimate — or, with `clampToTable`, the row at the end the colour is past.
  */
-export function dwarfSequenceAtColor(colorIndex: number | null, system: 'B-V' | 'BP-RP' = 'B-V'): DwarfSequencePoint | null {
+export function dwarfSequenceAtColor(colorIndex: number | null, system: 'B-V' | 'BP-RP' = 'B-V', clampToTable = false): DwarfSequencePoint | null {
   const column = system === 'B-V' ? 1 : 2;
   const rows = DWARF_SEQUENCE.filter((row) => row[column] !== null);
-  if (colorIndex === null || !(colorIndex >= rows[0][column]! && colorIndex <= rows[rows.length - 1][column]!)) {
+  const [bluest, reddest] = [rows[0][column]!, rows[rows.length - 1][column]!];
+  if (colorIndex === null || !Number.isFinite(colorIndex) || (!clampToTable && !(colorIndex >= bluest && colorIndex <= reddest))) {
     return null;
   }
-  const above = Math.max(1, rows.findIndex((row) => row[column]! >= colorIndex));
+  const colour = Math.min(Math.max(colorIndex, bluest), reddest);
+  const above = Math.max(1, rows.findIndex((row) => row[column]! >= colour));
   const [blue, red] = [rows[above - 1], rows[above]];
-  const t = (colorIndex - blue[column]!) / (red[column]! - blue[column]!);
+  const t = (colour - blue[column]!) / (red[column]! - blue[column]!);
   const lerp = (from: number, to: number): number => from + (to - from) * t;
   return {
     temperatureK: lerp(blue[3], red[3]),
diff --git a/src/app/shared/astro/stellar.spec.ts b/src/app/shared/astro/stellar.spec.ts
index b1dec4c..8a30ca5 100644
--- a/src/app/shared/astro/stellar.spec.ts
+++ b/src/app/shared/astro/stellar.spec.ts
@@ -158,6 +158,17 @@ describe('effectiveTemperatureK', () => {
     expect(effectiveTemperatureK({ magnitude: 11, distancePc: 5, spectralType: 'M5Ve', colorIndex: null })).toBeCloseTo(3106, 0);
     expect(effectiveTemperatureK({ magnitude: 11, distancePc: 5, spectralType: 'Unknown', colorIndex: null })).toBeNull();
   });
+
+  it('reads a colour past the table at its end where there is no type, and the type where there is', () => {
+    // An ultracool dwarf redder than M8.5, a white dwarf bluer than B9, and an O star B−V puts at B0.
+    expect(effectiveTemperatureK({ magnitude: 14.005, distancePc: 4.005, spectralType: 'Unknown', magnitudeBand: 'G', colorIndex: 5.113, colorSystem: 'BP-RP' })).toBe(2420);
+    expect(effectiveTemperatureK({ magnitude: 14, distancePc: 25, spectralType: 'Unknown', magnitudeBand: 'G', colorIndex: -0.25, colorSystem: 'BP-RP' })).toBe(10700);
+    expect(effectiveTemperatureK({ magnitude: 7, distancePc: 121, spectralType: 'O8', colorIndex: -0.31, colorSystem: 'B-V' })).toBe(31400);
+    // HD 49748, G5 V at B−V −0.32: the colour is the one that is wrong.
+    const g5 = effectiveTemperatureK({ magnitude: 9, distancePc: 184, spectralType: 'G5V', colorIndex: null })!;
+    expect(effectiveTemperatureK({ magnitude: 9, distancePc: 184, spectralType: 'G5V', colorIndex: -0.319, colorSystem: 'B-V' })).toBe(g5);
+    expect(g5).toBeGreaterThan(5500);
+  });
 });
 
 describe('radiusFromLuminositySolar', () => {
@@ -165,6 +176,14 @@ describe('radiusFromLuminositySolar', () => {
     expect(radiusFromLuminositySolar(1, SOLAR_EFFECTIVE_TEMPERATURE_K)).toBeCloseTo(1, 12);
   });
 
+  it("gives an ultracool dwarf redder than the table an M8.5 dwarf's radius, not none", () => {
+    // Gaia DR3 6439125097427143808, 4.0 pc away at BP−RP 5.11; M8.5 V is 0.104 R☉ (Mamajek).
+    const star = { magnitude: 14.005, distancePc: 4.005, spectralType: 'Unknown', magnitudeBand: 'G', colorIndex: 5.113, colorSystem: 'BP-RP' } as const;
+    const radius = radiusFromLuminositySolar(luminositySolar(star)!, effectiveTemperatureK(star)!);
+    expect(radius / 0.104).toBeGreaterThan(1 / 1.2);
+    expect(radius / 0.104).toBeLessThan(1.2);
+  });
+
   it('gives Sirius and TRAPPIST-1 their published radii from colour and brightness alone', () => {
     // 1.711 R☉ (Liebert et al. 2005) and 0.119 R☉ (Agol et al. 2021), each to within a fifth.
     for (const [star, published] of [
diff --git a/src/app/shared/astro/stellar.ts b/src/app/shared/astro/stellar.ts
index 963226a..37742c1 100644
--- a/src/app/shared/astro/stellar.ts
+++ b/src/app/shared/astro/stellar.ts
@@ -1,4 +1,4 @@
-import { dwarfSequenceAtColor, isGiant, parseSpectralClass, SpectralClass, spectralTypeToColorIndex } from './spectral';
+import { DwarfSequencePoint, dwarfSequenceAtColor, isGiant, parseSpectralClass, SpectralClass, spectralTypeToColorIndex } from './spectral';
 
 /**
  * Stellar luminosity, derived from the two things the star catalogue actually measures.
@@ -133,7 +133,7 @@ export function luminositySolar(star: StellarPhotometry): number | null {
   // dwarf, whose correction is larger. Antares, M1 Ib at B−V 1.87, read as an M5 dwarf's −3.26
   // came out 1 516 R☉ against the 680 Ohnaka et al. (2013) measure, and 119 Tau 2 838 against 587;
   // its type's −1.55 gives 690.
-  const sequence = star.colorIndex != null ? dwarfSequenceAtColor(star.colorIndex, star.colorSystem) : null;
+  const sequence = sequenceAtColour(star);
   const absoluteV = absolute - (star.magnitudeBand === 'G' ? (sequence?.gMinusV ?? 0) : 0);
   const bolometric =
     absoluteV + (sequence && !isGiant(star.spectralType) ? sequence.bolometricCorrectionV : bolometricCorrection(star.spectralType));
@@ -141,6 +141,22 @@ export function luminositySolar(star: StellarPhotometry): number | null {
   return Math.min(Math.max(luminosity, MIN_LUMINOSITY_SOLAR), MAX_LUMINOSITY_SOLAR);
 }
 
+/**
+ * The dwarf sequence at a star's colour — at the end of the table a colour is past, where the star
+ * has no type to go by instead. Past the red end are the ultracool dwarfs Gaia measures redder than
+ * BP−RP 5.1, M8.5; past the blue end, its white dwarfs and hot stars bluer than −0.12, B9, and
+ * B−V's O stars. Unclamped, they had no temperature and were drawn at the Sun's: Gaia DR3
+ * 6439125097427143808, an ultracool dwarf 4.0 pc away, and 110 white dwarfs within 50 pc, all at
+ * 1 R☉. Beside a type, an off-table colour is more often a bad one than an extreme star — HD
+ * 49748, G5 V, at B−V −0.32 — and the type is read instead.
+ */
+function sequenceAtColour(star: StellarPhotometry): DwarfSequencePoint | null {
+  if (star.colorIndex == null) {
+    return null;
+  }
+  return dwarfSequenceAtColor(star.colorIndex, star.colorSystem) ?? (parseSpectralClass(star.spectralType) ? null : dwarfSequenceAtColor(star.colorIndex, star.colorSystem, true));
+}
+
 /** The Sun's effective temperature, the IAU 2015 nominal value. */
 export const SOLAR_EFFECTIVE_TEMPERATURE_K = 5772;
 
@@ -154,8 +170,8 @@ export function effectiveTemperatureK(star: StellarPhotometry): number | null {
   if (star.distancePc === 0) {
     return SOLAR_EFFECTIVE_TEMPERATURE_K;
   }
-  const measured = star.colorIndex != null ? dwarfSequenceAtColor(star.colorIndex, star.colorSystem) : null;
-  return (measured ?? dwarfSequenceAtColor(spectralTypeToColorIndex(star.spectralType)))?.temperatureK ?? null;
+  // A type's colour past the table is an O star's, which B−V no longer tells apart from B0.
+  return (sequenceAtColour(star) ?? dwarfSequenceAtColor(spectralTypeToColorIndex(star.spectralType), 'B-V', true))?.temperatureK ?? null;
 }
 
 /**