diff --git a/lib/catalog.mjs b/lib/catalog.mjs
index ebb6c9e..6e2af90 100644
--- a/lib/catalog.mjs
+++ b/lib/catalog.mjs
@@ -8,27 +8,27 @@
 export const CATALOG = [
   {
     noradId: 25544, name: 'ISS (ZARYA)', aliases: ['iss', 'zarya', 'space station'],
-    tier: 'free', inclinationDeg: 51.6, viewingHint: null, defaultMode: 'visual',
+    tier: 'free', inclinationDeg: 51.6, standardMag: -1.8, viewingHint: null, defaultMode: 'visual',
   },
   {
     noradId: 48274, name: 'Tiangong (CSS)', aliases: ['tiangong', 'css', 'chinese space station'],
-    tier: 'free', inclinationDeg: 41.5, viewingHint: null, defaultMode: 'visual',
+    tier: 'free', inclinationDeg: 41.5, standardMag: -1.0, viewingHint: null, defaultMode: 'visual',
   },
   {
     noradId: 53807, name: 'BlueWalker 3', aliases: ['bluewalker', 'bluewalker 3', 'bw3'],
-    tier: 'free', inclinationDeg: 53.0,
+    tier: 'free', inclinationDeg: 53.0, standardMag: 0.5,
     viewingHint: 'One of the brightest satellites — easy naked-eye target.',
     defaultMode: 'visual',
   },
   {
     noradId: 20580, name: 'Hubble Space Telescope', aliases: ['hubble', 'hst'],
-    tier: 'free', inclinationDeg: 28.5,
+    tier: 'free', inclinationDeg: 28.5, standardMag: 2.0,
     viewingHint: 'Low inclination — best seen from lower latitudes.',
     defaultMode: 'visual',
   },
   {
     noradId: 33591, name: 'NOAA-19', aliases: ['noaa', 'noaa-19', 'noaa19'],
-    tier: 'free', inclinationDeg: 99.0,
+    tier: 'free', inclinationDeg: 99.0, standardMag: 3.5,
     viewingHint: 'Polar weather satellite — too dim to see; use radio passes.',
     defaultMode: 'radio',
   },
diff --git a/lib/mcp/passes.mjs b/lib/mcp/passes.mjs
index 4c9b4a5..ea190f7 100644
--- a/lib/mcp/passes.mjs
+++ b/lib/mcp/passes.mjs
@@ -27,7 +27,7 @@ export function getPosition(line1, line2, jsDate) {
   };
 }
 
-function summarizePass(win, observer, sampler, mode, minElevDeg) {
+function summarizePass(win, observer, sampler, mode, minElevDeg, stdMag = -1.8) {
   const STEP = 1000;
   let peakAlt = -Infinity;
   let peakMs = win.startMs;
@@ -54,13 +54,13 @@ function summarizePass(win, observer, sampler, mode, minElevDeg) {
     peakElevationDeg: round(peakAlt, 1),
     azimuthDeg: { rise: azAt(win.startMs), peak: azAt(peakMs), set: azAt(win.endMs) },
     durationSec: Math.round((win.endMs - win.startMs) / 1000),
-    peakMagnitude: round(peakMagnitudeInWindow(win, [observer], sampler), 1),
+    peakMagnitude: round(peakMagnitudeInWindow(win, [observer], sampler, stdMag), 1),
     sunlit,
     quality: round(quality, 3),
   };
 }
 
-export function findPasses({ line1, line2, observer, startMs, windowHours = 48, minElevationDeg = 10, mode = 'visual' }) {
+export function findPasses({ line1, line2, observer, startMs, windowHours = 48, minElevationDeg = 10, mode = 'visual', standardMag = -1.8 }) {
   const obs = { id: 'observer', latDeg: observer.latDeg, lonDeg: observer.lonDeg };
   const sampler = makeEcefSampler(line1, line2);
   const endMs = startMs + windowHours * 3_600_000;
@@ -71,6 +71,6 @@ export function findPasses({ line1, line2, observer, startMs, windowHours = 48,
   };
   const windows = findWindowsFromPredicate(predicate, startMs, endMs, 60_000);
   return windows
-    .map(w => summarizePass(w, obs, sampler, mode, minElevationDeg))
+    .map(w => summarizePass(w, obs, sampler, mode, minElevationDeg, standardMag))
     .filter(Boolean);
 }
diff --git a/lib/mcp/tools.mjs b/lib/mcp/tools.mjs
index 8b3e7c6..9e7ee0d 100644
--- a/lib/mcp/tools.mjs
+++ b/lib/mcp/tools.mjs
@@ -74,10 +74,11 @@ export async function getPositionTool(input, deps, tier = 'free') {
 }
 
 export async function findPassesTool(input, deps, tier = 'free') {
-  const { record } = await requireRecord(input.satellite, deps, tier);
+  const { entry, record } = await requireRecord(input.satellite, deps, tier);
   const loc = await resolveLocation(input, deps);
   const passes = findPasses({
     line1: record.line1, line2: record.line2,
+    standardMag: entry.standardMag,
     observer: { latDeg: loc.latDeg, lonDeg: loc.lonDeg },
     startMs: deps.now(),
     windowHours: input.windowHours ?? 48,
diff --git a/lib/pass-finder-scene.js b/lib/pass-finder-scene.js
index 188d50c..a306152 100644
--- a/lib/pass-finder-scene.js
+++ b/lib/pass-finder-scene.js
@@ -502,7 +502,7 @@ function updateObserverLabelText(wrapper, obs, d, ms) {
   if (issEcef && observerSeesIss(obs, issEcef, d)) {
     const { alt, az } = issAltAzDeg(obs, issEcef);
     const azStr = String(Math.round(az) % 360).padStart(3, "0");
-    const m = magnitudeAt(obs, issEcef, sunPositionEcef(d));
+    const m = magnitudeAt(obs, issEcef, sunPositionEcef(d), selectedSatStdMag());
     const magStr = m == null ? "" : `  m ${m.toFixed(1)}`;
     lines.push(`alt ${alt.toFixed(1)}°  az ${azStr}°${magStr}`);
   }
@@ -608,7 +608,7 @@ const POLAR_ARC_COLOR = "#aab8d4";
 //  is a thin wrapper that hands the pure version our scene-local
 //  issEcefAt callback so the module stays satrec-free.)
 function computeArcSamples(obs, win, cx, cy, R, SAMPLES) {
-  return _computeArcSamplesPure(obs, win, cx, cy, R, SAMPLES, issEcefAt);
+  return _computeArcSamplesPure(obs, win, cx, cy, R, SAMPLES, issEcefAt, selectedSatStdMag());
 }
 
 function paintPolarModalArc(svg, obs, win) {
@@ -836,6 +836,13 @@ function selectedSatName() {
   const entry = CATALOG.find((s) => s.noradId === id);
   return entry?.name || state.tle?.name || "Satellite";
 }
+// Intrinsic (standard) magnitude of the selected satellite, for the
+// brightness model. Defaults to the ISS's -1.8 when unknown.
+function selectedSatStdMag() {
+  const id = usePassFinderStore.getState().selectedNoradId;
+  const entry = CATALOG.find((s) => s.noradId === id);
+  return entry?.standardMag ?? -1.8;
+}
 // Compact form for the globe dot label — strips a trailing "(...)" so
 // "ISS (ZARYA)" → "ISS", "Tiangong (CSS)" → "Tiangong".
 function selectedSatShortName() {
@@ -1275,7 +1282,7 @@ function radioPassSuccessProbability(win, observers, minElevDeg) {
   return _radioPassSuccessProbabilityPure(win, observers, minElevDeg, issEcefAt);
 }
 function peakMagnitudeInWindow(win, observers) {
-  return _peakMagnitudeInWindowPure(win, observers, issEcefAt);
+  return _peakMagnitudeInWindowPure(win, observers, issEcefAt, selectedSatStdMag());
 }
 
 function clearActivePassGradient() {
diff --git a/lib/pass-finder/polar-arc.js b/lib/pass-finder/polar-arc.js
index 2b31949..0b6c1e8 100644
--- a/lib/pass-finder/polar-arc.js
+++ b/lib/pass-finder/polar-arc.js
@@ -31,7 +31,7 @@ export function issAlphaForMag(m) {
 // diagnostically useful on a dark-sky radio pass where the ISS dips
 // into Earth's shadow mid-arc and the operator wants to know "where
 // would I be looking if it were lit?"
-export function arcSampleStyle(obs, issEcef, jsDate) {
+export function arcSampleStyle(obs, issEcef, jsDate, stdMag = -1.8) {
   const sunDir = sunPositionEcef(jsDate);
   const sunAlt = sunAltitudeDeg(obs, jsDate);
   // Unified rule: dashed whenever the ISS isn't naked-eye visible at
@@ -43,7 +43,7 @@ export function arcSampleStyle(obs, issEcef, jsDate) {
   if (!issIlluminated(issEcef, sunDir)) {
     return { alpha: ARC_DASH_ALPHA, dashed: true };
   }
-  const m = magnitudeAt(obs, issEcef, sunDir);
+  const m = magnitudeAt(obs, issEcef, sunDir, stdMag);
   if (m == null || m > naturalSkyLimMag(sunAlt)) {
     return { alpha: ARC_DASH_ALPHA, dashed: true };
   }
@@ -58,7 +58,7 @@ export function arcSampleStyle(obs, issEcef, jsDate) {
 //
 // `issEcefAtFn(jsDate) → [x, y, z] | null` is threaded in by the
 // scene so this module doesn't need a satrec dependency.
-export function computeArcSamples(obs, win, cx, cy, R, SAMPLES, issEcefAtFn) {
+export function computeArcSamples(obs, win, cx, cy, R, SAMPLES, issEcefAtFn, stdMag = -1.8) {
   const dt = (win.endMs - win.startMs) / SAMPLES;
   const samples = [];
   for (let i = 0; i <= SAMPLES; i++) {
@@ -68,7 +68,7 @@ export function computeArcSamples(obs, win, cx, cy, R, SAMPLES, issEcefAtFn) {
     const { alt, az } = issAltAzDeg(obs, issEcef);
     if (alt < 0) continue;
     const [x, y] = altAzToSvg(alt, az, cx, cy, R);
-    samples.push({ x, y, ...arcSampleStyle(obs, issEcef, d) });
+    samples.push({ x, y, ...arcSampleStyle(obs, issEcef, d, stdMag) });
   }
   return samples;
 }
diff --git a/lib/pass-finder/ratings.js b/lib/pass-finder/ratings.js
index c1aec80..8c7b6ce 100644
--- a/lib/pass-finder/ratings.js
+++ b/lib/pass-finder/ratings.js
@@ -133,15 +133,16 @@ export function radioDurationFactor(sec) {
   return Math.min(1, 1 - Math.exp(-sec / 90));
 }
 
-// Visual magnitude of the (sunlit) ISS from one observer at one instant.
+// Visual magnitude of a (sunlit) satellite from one observer at one instant.
 // Standard satellite-magnitude formula:
-//   m = m_std + 5·log10(range / 1000 km)  −  2.5·log10(F(α))
-// where m_std = −1.8 is the intrinsic magnitude at 1000 km / full phase,
-// α is the phase angle (satellite→sun vs satellite→observer), and
-// F(α) = (1 + cos α) / 2 is the Lambertian-sphere phase function.
+//   m = stdMag + 5·log10(range / 1000 km)  −  2.5·log10(F(α))
+// where stdMag is the satellite's intrinsic magnitude at 1000 km / full
+// phase (per-satellite, from the catalog; defaults to the ISS's −1.8 for
+// back-compat), α is the phase angle (satellite→sun vs satellite→observer),
+// and F(α) = (1 + cos α) / 2 is the Lambertian-sphere phase function.
 // Returns null when the observer is looking at the unlit hemisphere
 // (F ≤ 0) — in that case the satellite isn't visible at all.
-export function magnitudeAt(obs, issEcef, sunDir) {
+export function magnitudeAt(obs, issEcef, sunDir, stdMag = -1.8) {
   const obsEcef = geodeticToEcef(obs.latDeg, obs.lonDeg, 0);
   const dx = obsEcef[0] - issEcef[0];
   const dy = obsEcef[1] - issEcef[1];
@@ -152,7 +153,7 @@ export function magnitudeAt(obs, issEcef, sunDir) {
   const cosAlpha = (dx * sunDir[0] + dy * sunDir[1] + dz * sunDir[2]) * inv;
   const F = (1 + cosAlpha) / 2;
   if (F <= 0) return null;
-  return -1.8 + 5 * Math.log10(range / 1_000_000) - 2.5 * Math.log10(F);
+  return stdMag + 5 * Math.log10(range / 1_000_000) - 2.5 * Math.log10(F);
 }
 
 // Cesium-flavored rating color (Cesium.Color, used by the orbit-arc
diff --git a/lib/pass-finder/scoring.js b/lib/pass-finder/scoring.js
index df3eb58..fe7aacd 100644
--- a/lib/pass-finder/scoring.js
+++ b/lib/pass-finder/scoring.js
@@ -151,7 +151,7 @@ export function radioCaptureAt(observers, issEcef, minElevDeg) {
 // BRIGHTEST (lowest m) of those floors. This is the minimax
 // magnitude: the moment where even the dimmest observer sees the
 // ISS at its best across the joint-visibility window.
-export function peakMagnitudeInWindow(win, observers, issEcefAtFn) {
+export function peakMagnitudeInWindow(win, observers, issEcefAtFn, stdMag = -1.8) {
   if (!win || !observers.length) return null;
   const totalMs = win.endMs - win.startMs;
   if (totalMs <= 0) return null;
@@ -165,7 +165,7 @@ export function peakMagnitudeInWindow(win, observers, issEcefAtFn) {
     let worstAtT = -Infinity;
     let anyValid = false;
     for (const obs of observers) {
-      const m = magnitudeAt(obs, issEcef, sunDir);
+      const m = magnitudeAt(obs, issEcef, sunDir, stdMag);
       if (m == null) continue;
       anyValid = true;
       if (m > worstAtT) worstAtT = m;
diff --git a/test/magnitude.test.mjs b/test/magnitude.test.mjs
new file mode 100644
index 0000000..c13d116
--- /dev/null
+++ b/test/magnitude.test.mjs
@@ -0,0 +1,36 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { magnitudeAt } from '../lib/pass-finder/ratings.js';
+import { CATALOG } from '../lib/catalog.mjs';
+
+// Fixed full-phase geometry: observer at (0,0), satellite ~500 km straight
+// up on the +x axis, sun direction along -x so the satellite→observer
+// vector is fully lit (F = 1). Only stdMag varies between calls, so the
+// range/phase terms cancel and the result shifts one-for-one with stdMag.
+const obs = { latDeg: 0, lonDeg: 0 };
+const satEcef = [6_878_137, 0, 0];
+const sunDir = [-1, 0, 0];
+
+test('magnitudeAt defaults to the ISS standard magnitude (-1.8)', () => {
+  assert.equal(magnitudeAt(obs, satEcef, sunDir), magnitudeAt(obs, satEcef, sunDir, -1.8));
+});
+
+test('result shifts one-for-one with the standard magnitude', () => {
+  const bright = magnitudeAt(obs, satEcef, sunDir, -1.8);
+  const dim = magnitudeAt(obs, satEcef, sunDir, 2.0);
+  assert.ok(bright != null && dim != null);
+  assert.ok(Math.abs((dim - bright) - 3.8) < 1e-9, `delta ${dim - bright}`);
+});
+
+test('every catalog satellite has a numeric standardMag', () => {
+  for (const s of CATALOG) {
+    assert.equal(typeof s.standardMag, 'number', `${s.name} standardMag`);
+  }
+});
+
+test('relative brightness is sane: ISS brighter than Hubble/NOAA; NOAA dimmest', () => {
+  const byId = Object.fromEntries(CATALOG.map((s) => [s.noradId, s.standardMag]));
+  assert.ok(byId[25544] < byId[20580], 'ISS brighter than Hubble');
+  assert.ok(byId[25544] < byId[33591], 'ISS brighter than NOAA-19');
+  assert.equal(byId[33591], Math.max(...CATALOG.map((s) => s.standardMag)), 'NOAA-19 dimmest');
+});