diff --git a/CLAUDE.md b/CLAUDE.md
index 89042df..e9d641a 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -37,6 +37,8 @@ SceneryStack **first-person planetarium** for the night sky. Observer location,
 **Gotchas**
 
 - **Ctrl-drag** and **Ctrl+arrow keys** advance **sidereal time** (stars move 1:1 with gesture); civil time advances ~1/1.0027 as fast.
+- Civil time is bounded by `CIVIL_TIME_MS_RANGE` (derived from `CIVIL_YEAR_RANGE`, 1900–2100). Route every write that could leave that span through `setCivilTimeMs()`; the `date` query parameter rejects out-of-range epochs rather than clamping them.
+- `epochPresetProperty` only flips to `CUSTOM` once civil time is a full minute off the preset — the timer starts playing, so a tighter test would mark it CUSTOM on the first frame and the combo could never show a preset.
 - Reset All restores model Properties but **not** preference-backed overlays (`showStarLabels`, `showConstellations`, `showPlanetLabels`, `deepStarCatalog`).
 - Planet positions use `astronomy-engine` only through `PlanetEphemeris.ts`; equatorial↔horizontal transforms are intentionally hand-rolled (see [doc/astronomy-engine.md](doc/astronomy-engine.md)).
 - Default sky: Boulder (40° N, 105° W), 2024-06-21 18:00 UTC, look south 30° alt, 140° FOV.
@@ -48,7 +50,9 @@ Follows the shared [OpenPhysics accessibility convention](https://github.com/Ope
 
 ## Compliance carve-outs
 
-- **Hardcoded colors:** `#ffffff` pin stroke in `ObserverLocationNode.ts` — fixed white ring for map legibility on both land and ocean fills; not a profile theme token.
+- **Hardcoded colors:** `#ffffff` pin stroke in `ObserverLocationNode.ts` — fixed white ring for map legibility on both land and ocean fills; not a profile theme token. Invisible hit targets use `Color.TRANSPARENT`, not a literal `rgba(0,0,0,0)`.
+
+**Color pairing gotcha:** `LIGHT_SURFACE_TEXT_FILL` (`controlSurfaceText`, near-black) is only for text on the *white* control surfaces — combo items, flat-button labels, editable field values. Anything drawn on the dark `panelBackground` fill takes `ZenithColors.textColorProperty`. Mixing these up yields ~1:1 contrast and is invisible rather than merely ugly (see the `ObjectNameSearch` result rows).
 
 ## Testing
 
diff --git a/README.md b/README.md
index 42f60d3..6ce05c5 100644
--- a/README.md
+++ b/README.md
@@ -18,7 +18,11 @@ Vite 8, TypeScript 7, and Biome 2.
 - Sun, Moon, and Mercury–Neptune via `astronomy-engine` ephemerides (angularly correct Sun/Moon discs; optional true-scale planets)
 - Observer latitude/longitude, civil UTC time, and derived local sidereal time with play / pause / speed
 - English, Spanish, and French localization via `StringManager`
-- Deep-link startup via query params (`lat`, `lon`, `date`, `fov`, `magLimit`)
+- Deep-link startup via query params (`lat`, `lon`, `date` — 1900–2100, `fov`, `magLimit`)
+- Optional "Use my location": browser geolocation, falling back to a third-party IP lookup
+  (`get.geojs.io`, then `ipapi.co`) when the browser cannot answer. An explicit permission
+  denial is honoured with no fallback, and the button is the only thing that makes either
+  request — nothing is sent at startup, and the rest of the sim runs fully offline.
 - Default (night-sky) and projector color profiles
 - Progressive Web App (installable, offline-capable)
 - Git hooks for Biome pre-commit checks
diff --git a/doc/model.md b/doc/model.md
index 1b624b4..adfd8db 100644
--- a/doc/model.md
+++ b/doc/model.md
@@ -68,7 +68,9 @@ works across many longitudes):
 - June / December solstices
 
 Year / month / day / hour controls jump to any UTC civil moment in range
-(1900–2100).
+(1900–2100). That range bounds civil time everywhere: playback stops at either
+end rather than running past it, and a `date` deep link outside it falls back to
+the default epoch instead of being silently clamped to the boundary.
 
 ### Default sky (reset / first load)
 
@@ -101,7 +103,10 @@ south at a modest altitude — a natural outdoor “looking up” pose.
 
 - **Object name search** (top-center) — type-ahead over **47 named entries** (38 curated bright stars +
   9 solar-system bodies). Enter selects and enables tracking.
-- **"Use my location"** — browser geolocation with IP fallback.
+- **"Use my location"** — browser geolocation, with a coarse third-party IP-address
+  lookup as a fallback when the browser cannot answer. Pressing the button is what
+  triggers the request; declining the browser permission prompt stops there, with no
+  IP fallback. Worth knowing before using it on a classroom machine.
 - **N / P** — cycle only among named stars and planets currently in the field of view.
 
 ### Coordinate systems (overlays)
@@ -192,7 +197,7 @@ You can open the sim with a prepared observer and epoch in the URL, for example:
 
 `?lat=-33.9&lon=151.2&date=2024-12-21T10:00:00Z&fov=60&magLimit=4`
 
-Useful parameters: `lat`, `lon`, `date` (ISO-8601 UTC), `fov`, `magLimit`, plus
+Useful parameters: `lat`, `lon`, `date` (ISO-8601 UTC, 1900–2100), `fov`, `magLimit`, plus
 optional toggles for star names, constellation lines, planet names, and the
 deeper star catalog. Full list:
 [implementation-notes.md](./implementation-notes.md#deep-link-query-parameters).
diff --git a/src/ZenithConstants.ts b/src/ZenithConstants.ts
index a80f543..c8d495f 100644
--- a/src/ZenithConstants.ts
+++ b/src/ZenithConstants.ts
@@ -71,12 +71,6 @@ export const LONGITUDE_RANGE = new Range(-180, 180);
 /** Arrow-key nudge (degrees) when dragging the observer pin on the location map. */
 export const LOCATION_STEP_DEGREES = 5;
 
-/**
- * Default local sidereal time is derived from civil time + longitude at reset;
- * this constant is only used as a fallback before the first sync.
- */
-export const DEFAULT_LOCAL_SIDEREAL_TIME_HOURS = 0;
-
 /**
  * Hours of civil (and roughly sidereal) time advanced per second of simulation
  * clock at the base `1×` rate. Real-time: one wall-clock second advances civil
@@ -114,6 +108,18 @@ export const CIVIL_DAY_RANGE = new Range(1, 31);
 /** UTC hour-of-day range for the civil date jump UI. */
 export const CIVIL_HOUR_RANGE = new Range(0, 23);
 
+/**
+ * Supported span of civil time in UTC milliseconds, derived from
+ * {@link CIVIL_YEAR_RANGE}. This is the authoritative bound: the date-jump
+ * spinners, the `date` deep-link parameter, and clock playback are all held
+ * inside it, so the Year spinner can never display a value outside its own
+ * range and a shared link can never resolve to an epoch the UI cannot express.
+ */
+export const CIVIL_TIME_MS_RANGE = new Range(
+  Date.UTC(CIVIL_YEAR_RANGE.min, 0, 1, 0, 0, 0),
+  Date.UTC(CIVIL_YEAR_RANGE.max, 11, 31, 23, 0, 0),
+);
+
 /**
  * Discrete time-rate ladder: each value multiplies the base educational rate
  * {@link CIVIL_HOURS_PER_SIM_SECOND}. Symmetric with no zero, so stepping the
@@ -306,11 +312,11 @@ ZenithNamespace.register("ZenithConstants", {
   CONTROL_PANEL_WIDTH,
   DEFAULT_LATITUDE_DEG,
   DEFAULT_LONGITUDE_DEG,
-  DEFAULT_LOCAL_SIDEREAL_TIME_HOURS,
   CIVIL_HOURS_PER_SIM_SECOND,
   HOURS_PER_SIDEREAL_DAY,
   DEFAULT_CIVIL_TIME_MS,
   CIVIL_YEAR_RANGE,
+  CIVIL_TIME_MS_RANGE,
   CIVIL_MONTH_RANGE,
   CIVIL_DAY_RANGE,
   CIVIL_HOUR_RANGE,
diff --git a/src/i18n/StringManager.ts b/src/i18n/StringManager.ts
index e1a12a7..cd4c05c 100644
--- a/src/i18n/StringManager.ts
+++ b/src/i18n/StringManager.ts
@@ -10,10 +10,17 @@ import stringsEn from "./strings_en.json";
 import stringsEs from "./strings_es.json";
 import stringsFr from "./strings_fr.json";
 
+// Compile-time locale parity: every locale must carry exactly the same key set.
+// Both directions are asserted for each pair, so a key missing from — or added to —
+// any one locale is a build error (`npm run check`), not a runtime fallback.
 // biome-ignore lint/complexity/noVoid: intentional compile-time type assertion
 void (stringsEn satisfies typeof stringsFr);
 // biome-ignore lint/complexity/noVoid: intentional compile-time type assertion
 void (stringsFr satisfies typeof stringsEn);
+// biome-ignore lint/complexity/noVoid: intentional compile-time type assertion
+void (stringsEn satisfies typeof stringsEs);
+// biome-ignore lint/complexity/noVoid: intentional compile-time type assertion
+void (stringsEs satisfies typeof stringsEn);
 
 const stringProperties = LocalizedString.getNestedStringProperties({
   en: stringsEn,
diff --git a/src/main.ts b/src/main.ts
index 774a42e..60759e9 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -64,13 +64,9 @@ onReadyToLaunch(() => {
       },
     }),
 
-    // Optional: fill in credits shown in Help → About
-    credits: {
-      leadDesign: "",
-      softwareDevelopment: "",
-      team: "",
-      qualityAssurance: "",
-    },
+    // `credits` is deliberately omitted: joist renders a row for every key it is
+    // given, so empty strings produce blank labelled rows in Help → About. Add
+    // the keys back only with real names. Project attribution lives in CREDITS.md.
   });
 
   sim.start();
diff --git a/src/preferences/ZenithPreferencesModel.ts b/src/preferences/ZenithPreferencesModel.ts
index c3c2cc9..cce7b89 100644
--- a/src/preferences/ZenithPreferencesModel.ts
+++ b/src/preferences/ZenithPreferencesModel.ts
@@ -42,12 +42,9 @@ export class ZenithPreferencesModel {
     });
   }
 
-  public reset(): void {
-    this.showStarLabelsProperty.reset();
-    this.showConstellationsProperty.reset();
-    this.showPlanetLabelsProperty.reset();
-    this.deepStarCatalogProperty.reset();
-  }
+  // Deliberately no reset(): these overlay toggles are preference-backed and
+  // outlive Reset All (see ZenithModel.reset). An unused reset() here would
+  // invite wiring it into Reset All and silently breaking that contract.
 }
 
 ZenithNamespace.register("ZenithPreferencesModel", ZenithPreferencesModel);
diff --git a/src/preferences/zenithQueryParameters.ts b/src/preferences/zenithQueryParameters.ts
index dcfb479..12210fe 100644
--- a/src/preferences/zenithQueryParameters.ts
+++ b/src/preferences/zenithQueryParameters.ts
@@ -17,6 +17,7 @@
 import { logGlobal } from "scenerystack/phet-core";
 import { QueryStringMachine } from "scenerystack/query-string-machine";
 import {
+  CIVIL_TIME_MS_RANGE,
   DEFAULT_CIVIL_TIME_MS,
   DEFAULT_DEEP_STAR_CATALOG,
   DEFAULT_FIELD_OF_VIEW_DEG,
@@ -34,7 +35,14 @@ import {
 import ZenithNamespace from "../ZenithNamespace.js";
 
 /**
- * Returns true when `value` is empty/null (use sim default) or a parseable civil date.
+ * Returns true when `value` is empty/null (use sim default), or a parseable
+ * civil date that falls inside the span the simulation can actually represent
+ * ({@link CIVIL_TIME_MS_RANGE}, i.e. the `CIVIL_YEAR_RANGE` the date-jump
+ * spinners cover). Parseability alone is not enough: an out-of-range epoch would
+ * be silently clamped to the range boundary further down, so a shared link would
+ * quietly render a different sky than the one it names. Rejecting it here makes
+ * QueryStringMachine warn and fall back to the documented default instead.
+ *
  * Used by QueryStringMachine `isValidValue` for the `date` parameter.
  * `StringType` from QueryStringMachine includes `null`, so accept that here.
  */
@@ -42,18 +50,20 @@ export function isValidCivilDateQueryParam(value: string | null): boolean {
   if (value === null || value === "") {
     return true;
   }
-  return !Number.isNaN(Date.parse(value));
+  const ms = Date.parse(value);
+  return !Number.isNaN(ms) && CIVIL_TIME_MS_RANGE.contains(ms);
 }
 
 /**
- * Parses a civil-date query string to UTC ms, or null when empty / invalid.
+ * Parses a civil-date query string to UTC ms, or null when empty, unparseable,
+ * or outside {@link CIVIL_TIME_MS_RANGE}.
  */
 export function parseCivilDateQueryParam(value: string | null): number | null {
   if (value === null || value === "") {
     return null;
   }
   const ms = Date.parse(value);
-  return Number.isNaN(ms) ? null : ms;
+  return Number.isNaN(ms) || !CIVIL_TIME_MS_RANGE.contains(ms) ? null : ms;
 }
 
 /**
@@ -86,8 +96,9 @@ const zenithQueryParameters = QueryStringMachine.getAll({
   },
 
   /**
-   * Civil UTC timestamp (`Date.parse` / ISO-8601). Empty string uses the sim default.
-   * Example: `?date=2024-12-21T10:00:00Z`.
+   * Civil UTC timestamp (`Date.parse` / ISO-8601), within the supported civil
+   * year range (1900–2100). Empty string — or a date outside that range — uses
+   * the sim default. Example: `?date=2024-12-21T10:00:00Z`.
    */
   date: {
     type: "string",
diff --git a/src/zenith-screen/model/ZenithModel.ts b/src/zenith-screen/model/ZenithModel.ts
index 38a4129..2a9186d 100644
--- a/src/zenith-screen/model/ZenithModel.ts
+++ b/src/zenith-screen/model/ZenithModel.ts
@@ -34,6 +34,7 @@ import type { ZenithPreferencesModel } from "../../preferences/ZenithPreferences
 import zenithQueryParameters, { resolveCivilTimeMsFromQuery } from "../../preferences/zenithQueryParameters.js";
 import {
   CIVIL_HOURS_PER_SIM_SECOND,
+  CIVIL_TIME_MS_RANGE,
   DEFAULT_CIVIL_TIME_MS,
   DEFAULT_LATITUDE_DEG,
   DEFAULT_LONGITUDE_DEG,
@@ -65,6 +66,7 @@ import { DEFAULT_LOCATION_PRESET, LOCATION_PRESET_COORDS, LocationPreset } from
 import type { SelectedSkyObject } from "./SelectedSkyObject.js";
 
 const MS_PER_HOUR = 3600 * 1000;
+const MS_PER_MINUTE = 60 * 1000;
 
 /**
  * Single instantaneous ephemeris for the whole solar system at one civil time /
@@ -269,7 +271,7 @@ export class ZenithModel implements TModel {
     this.longitudeProperty = new NumberProperty(startLon, {
       range: LONGITUDE_RANGE,
     });
-    this.civilTimeMsProperty = new NumberProperty(startCivilMs);
+    this.civilTimeMsProperty = new NumberProperty(CIVIL_TIME_MS_RANGE.constrainValue(startCivilMs));
     this.localSiderealTimeHoursProperty = new NumberProperty(localSiderealTimeHours(startCivilMs, startLon));
     this.lookAzimuthDegProperty = new NumberProperty(DEFAULT_LOOK_AZIMUTH_DEG);
     this.lookAltitudeDegProperty = new NumberProperty(DEFAULT_LOOK_ALTITUDE_DEG, {
@@ -391,10 +393,24 @@ export class ZenithModel implements TModel {
     this.disposers.push(() => this.latitudeProperty.unlink(markLocationCustom));
     this.disposers.push(() => this.longitudeProperty.unlink(markLocationCustom));
 
-    const markEpochCustom = (): void => {
-      if (!this.applyingPreset) {
-        this.epochPresetProperty.value = EpochPreset.CUSTOM;
+    // Leaving a named epoch marks it CUSTOM — but only once the clock has moved
+    // far enough for the UTC readout (minute precision) to disagree with the
+    // preset. Without that tolerance the timer, which starts playing, advances
+    // civil time by a few milliseconds on the very first step and flips the combo
+    // to "Custom time" while the readout still shows the preset epoch — so the
+    // selector could never display a preset, not even right after one is chosen.
+    const markEpochCustom = (civilMs: number): void => {
+      if (this.applyingPreset) {
+        return;
+      }
+      const preset = this.epochPresetProperty.value;
+      if (preset !== EpochPreset.CUSTOM) {
+        const presetMs = EPOCH_PRESET_CIVIL_MS.get(preset);
+        if (presetMs !== undefined && Math.abs(civilMs - presetMs) < MS_PER_MINUTE) {
+          return;
+        }
       }
+      this.epochPresetProperty.value = EpochPreset.CUSTOM;
     };
     this.civilTimeMsProperty.lazyLink(markEpochCustom);
     this.disposers.push(() => this.civilTimeMsProperty.unlink(markEpochCustom));
@@ -456,7 +472,17 @@ export class ZenithModel implements TModel {
 
   /** Jumps civil time to the observer's real-world current instant ("Now"). */
   public setToNow(): void {
-    this.civilTimeMsProperty.value = Date.now();
+    this.setCivilTimeMs(Date.now());
+  }
+
+  /**
+   * Sets civil time, held inside {@link CIVIL_TIME_MS_RANGE}. Every write that
+   * can leave the supported span (playback, scrubbing, "Now") goes through here,
+   * so the clock stops at the range edge rather than drifting to an epoch the
+   * date-jump spinners cannot represent.
+   */
+  public setCivilTimeMs(civilTimeMs: number): void {
+    this.civilTimeMsProperty.value = CIVIL_TIME_MS_RANGE.constrainValue(civilTimeMs);
   }
 
   /**
@@ -503,7 +529,7 @@ export class ZenithModel implements TModel {
 
   /** Advances civil time by `hours` (educational scrub / Ctrl-drag). */
   public advanceCivilTimeHours(hours: number): void {
-    this.civilTimeMsProperty.value += hours * MS_PER_HOUR;
+    this.setCivilTimeMs(this.civilTimeMsProperty.value + hours * MS_PER_HOUR);
     this.syncLocalSiderealTime();
   }
 
diff --git a/src/zenith-screen/view/ObjectNameSearch.ts b/src/zenith-screen/view/ObjectNameSearch.ts
index c732bb4..36fd6c5 100644
--- a/src/zenith-screen/view/ObjectNameSearch.ts
+++ b/src/zenith-screen/view/ObjectNameSearch.ts
@@ -14,7 +14,7 @@
 
 import { DerivedProperty, Multilink, PatternStringProperty, Property, type TReadOnlyProperty } from "scenerystack/axon";
 import type { OneKeyStroke } from "scenerystack/scenery";
-import { KeyboardListener, Node, Rectangle, Text, VBox } from "scenerystack/scenery";
+import { Color, KeyboardListener, Node, Rectangle, Text, VBox } from "scenerystack/scenery";
 import { PhetFont } from "scenerystack/scenery-phet";
 import { LIGHT_SURFACE_TEXT_FILL } from "../../common/ZenithButtonOptions.js";
 import { ZenithPanel } from "../../common/ZenithPanel.js";
@@ -151,14 +151,19 @@ export class ObjectNameSearch extends Node {
 
     // ── Result rows ─────────────────────────────────────────────────────────────
     const rowFont = new PhetFont(CONTROL_FONT_SIZE);
+    // Result rows sit directly on the dark panel fill, not on the white field
+    // surface, so they take the panel text color. Using LIGHT_SURFACE_TEXT_FILL
+    // here (near-black on deep indigo) renders them at ~1:1 contrast. The
+    // highlighted row inverts: dark text on the light accent fill.
     const createRow = (entry: Entry, active: boolean): Node => {
       const background = new Rectangle(0, 0, ROW_WIDTH, ROW_HEIGHT, {
         cornerRadius: 3,
-        fill: active ? ZenithColors.accentColorProperty : "rgba(0,0,0,0)",
+        // Transparent (not null) so the whole row stays a pointer hit target.
+        fill: active ? ZenithColors.accentColorProperty : Color.TRANSPARENT,
       });
       const label = new Text(entry.nameProperty, {
         font: rowFont,
-        fill: active ? ZenithColors.controlSurfaceColorProperty : LIGHT_SURFACE_TEXT_FILL,
+        fill: active ? LIGHT_SURFACE_TEXT_FILL : ZenithColors.textColorProperty,
         maxWidth: ROW_WIDTH - 12,
       });
       label.left = 6;
@@ -174,9 +179,10 @@ export class ObjectNameSearch extends Node {
     );
 
     // ── "No matches" line + list visibility ────────────────────────────────────
+    // Also on the dark panel fill, not the white field — panel text color.
     const statusText = new Text(controls.searchNoMatchesStringProperty, {
       font: rowFont,
-      fill: LIGHT_SURFACE_TEXT_FILL,
+      fill: ZenithColors.textColorProperty,
       maxWidth: FIELD_WIDTH,
     });
     Multilink.multilink([focusedProperty, queryProperty, matchesProperty], (isFocused, q, matches) => {
diff --git a/src/zenith-screen/view/ObserverLocationNode.ts b/src/zenith-screen/view/ObserverLocationNode.ts
index 08a09df..842ee3e 100644
--- a/src/zenith-screen/view/ObserverLocationNode.ts
+++ b/src/zenith-screen/view/ObserverLocationNode.ts
@@ -20,6 +20,7 @@ import { Shape } from "scenerystack/kite";
 import { ModelViewTransform2 } from "scenerystack/phetcommon";
 import {
   Circle,
+  Color,
   DragListener,
   KeyboardListener,
   Line,
@@ -215,7 +216,8 @@ export class ObserverLocationNode extends Node {
     const pin = new Node({
       cursor: "grab",
       children: [
-        new Circle(12, { fill: "rgba(0,0,0,0)" }),
+        // Transparent (not null) so the disk still hit-tests as a grab target.
+        new Circle(12, { fill: Color.TRANSPARENT }),
         new Line(-9, 0, 9, 0, { stroke: ZenithColors.locationPinColorProperty, lineWidth: 1.5 }),
         new Line(0, -9, 0, 9, { stroke: ZenithColors.locationPinColorProperty, lineWidth: 1.5 }),
         new Circle(3.5, { fill: ZenithColors.locationPinColorProperty, stroke: "#ffffff", lineWidth: 0.75 }),
diff --git a/src/zenith-screen/view/SelectedObjectReadout.ts b/src/zenith-screen/view/SelectedObjectReadout.ts
index de95243..5783193 100644
--- a/src/zenith-screen/view/SelectedObjectReadout.ts
+++ b/src/zenith-screen/view/SelectedObjectReadout.ts
@@ -163,6 +163,15 @@ const buildVisibility = (
 };
 
 export class SelectedObjectReadout extends Node {
+  /**
+   * Teardown steps for the axon graph this node builds, in the order they must
+   * run: internal links first, then the Text/Checkbox subtree, then the pattern
+   * Properties they read, then the DerivedProperties those patterns depend on.
+   * `DerivedProperty.dispose()` throws while it still has listeners, so the order
+   * matters — each stage releases the subscribers of the next.
+   */
+  private readonly disposers: (() => void)[] = [];
+
   public constructor(model: ZenithModel) {
     super();
 
@@ -176,9 +185,12 @@ export class SelectedObjectReadout extends Node {
     const nameProperty = new Property(
       objectName(model.selectedObjectProperty.value, stars, controls.selectedNoneStringProperty.value),
     );
-    Multilink.multilink([model.selectedObjectProperty, controls.selectedNoneStringProperty], (selected, noneLabel) => {
-      nameProperty.value = objectName(selected, stars, noneLabel);
-    });
+    const nameMultilink = Multilink.multilink(
+      [model.selectedObjectProperty, controls.selectedNoneStringProperty],
+      (selected, noneLabel) => {
+        nameProperty.value = objectName(selected, stars, noneLabel);
+      },
+    );
 
     const coordsProperty = new DerivedProperty(
       [
@@ -258,8 +270,16 @@ export class SelectedObjectReadout extends Node {
     const elongDegProperty = new DerivedProperty([elongationProperty], (e) => (e ? e.deg : "—"));
     const elongDirProperty = new DerivedProperty([elongationProperty], (e) => (e ? e.dir : ""));
 
+    // Pattern Properties are hoisted (rather than built inline in each Text) so
+    // dispose() can release them after the Texts that read them are torn down.
+    const patterns: { dispose: () => void }[] = [];
+    const pattern = <T extends { dispose: () => void }>(property: T): T => {
+      patterns.push(property);
+      return property;
+    };
+
     const nameText = new Text(
-      new PatternStringProperty(controls.selectedObjectStringProperty, { name: nameProperty }),
+      pattern(new PatternStringProperty(controls.selectedObjectStringProperty, { name: nameProperty })),
       { font: labelFont, fill: ZenithColors.accentColorProperty, maxWidth },
     );
     const noneText = new Text(controls.selectedNoneStringProperty, {
@@ -267,27 +287,34 @@ export class SelectedObjectReadout extends Node {
       fill: ZenithColors.textColorProperty,
       maxWidth,
     });
-    const magText = new Text(new PatternStringProperty(controls.selectedMagStringProperty, { mag: magProperty }), {
-      font: labelFont,
-      fill: ZenithColors.textColorProperty,
-      maxWidth,
-    });
+    const magText = new Text(
+      pattern(new PatternStringProperty(controls.selectedMagStringProperty, { mag: magProperty })),
+      {
+        font: labelFont,
+        fill: ZenithColors.textColorProperty,
+        maxWidth,
+      },
+    );
     const eqText = new Text(
-      new PatternStringProperty(controls.selectedEquatorialStringProperty, {
-        ra: raProperty,
-        dec: decProperty,
-      }),
+      pattern(
+        new PatternStringProperty(controls.selectedEquatorialStringProperty, {
+          ra: raProperty,
+          dec: decProperty,
+        }),
+      ),
       { font: labelFont, fill: ZenithColors.textColorProperty, maxWidth },
     );
     const hzText = new Text(
-      new PatternStringProperty(controls.selectedHorizontalStringProperty, {
-        alt: altProperty,
-        az: azProperty,
-      }),
+      pattern(
+        new PatternStringProperty(controls.selectedHorizontalStringProperty, {
+          alt: altProperty,
+          az: azProperty,
+        }),
+      ),
       { font: labelFont, fill: ZenithColors.textColorProperty, maxWidth },
     );
     const typeText = new Text(
-      new PatternStringProperty(controls.selectedTypeStringProperty, { type: typeNameProperty }),
+      pattern(new PatternStringProperty(controls.selectedTypeStringProperty, { type: typeNameProperty })),
       {
         font: labelFont,
         fill: ZenithColors.textColorProperty,
@@ -295,16 +322,20 @@ export class SelectedObjectReadout extends Node {
       },
     );
     const constellationText = new Text(
-      new PatternStringProperty(controls.selectedConstellationStringProperty, {
-        constellation: constellationNameProperty,
-      }),
+      pattern(
+        new PatternStringProperty(controls.selectedConstellationStringProperty, {
+          constellation: constellationNameProperty,
+        }),
+      ),
       { font: labelFont, fill: ZenithColors.textColorProperty, maxWidth },
     );
     const elongationText = new Text(
-      new PatternStringProperty(controls.selectedElongationStringProperty, {
-        deg: elongDegProperty,
-        dir: elongDirProperty,
-      }),
+      pattern(
+        new PatternStringProperty(controls.selectedElongationStringProperty, {
+          deg: elongDegProperty,
+          dir: elongDirProperty,
+        }),
+      ),
       { font: labelFont, fill: ZenithColors.textColorProperty, maxWidth },
     );
 
@@ -333,41 +364,48 @@ export class SelectedObjectReadout extends Node {
 
     const eventTextOptions = { font: labelFont, fill: ZenithColors.textColorProperty, maxWidth };
     const riseText = new Text(
-      new PatternStringProperty(controls.selectedRiseStringProperty, {
-        time: riseTimeProperty,
-        clock: riseClockProperty,
-        az: riseAzProperty,
-      }),
+      pattern(
+        new PatternStringProperty(controls.selectedRiseStringProperty, {
+          time: riseTimeProperty,
+          clock: riseClockProperty,
+          az: riseAzProperty,
+        }),
+      ),
       eventTextOptions,
     );
     const setText = new Text(
-      new PatternStringProperty(controls.selectedSetStringProperty, {
-        time: setTimeProperty,
-        clock: setClockProperty,
-        az: setAzProperty,
-      }),
+      pattern(
+        new PatternStringProperty(controls.selectedSetStringProperty, {
+          time: setTimeProperty,
+          clock: setClockProperty,
+          az: setAzProperty,
+        }),
+      ),
       eventTextOptions,
     );
     const transitText = new Text(
-      new PatternStringProperty(controls.selectedTransitStringProperty, {
-        time: transitTimeProperty,
-        clock: transitClockProperty,
-        alt: transitAltProperty,
-      }),
+      pattern(
+        new PatternStringProperty(controls.selectedTransitStringProperty, {
+          time: transitTimeProperty,
+          clock: transitClockProperty,
+          alt: transitAltProperty,
+        }),
+      ),
       eventTextOptions,
     );
     const circumpolarText = new Text(controls.selectedCircumpolarStringProperty, eventTextOptions);
     const neverRisesText = new Text(controls.selectedNeverRisesStringProperty, eventTextOptions);
 
-    visibilityProperty.link((v) => {
+    const onVisibility = (v: Visibility): void => {
       riseText.visible = v.kind === "risesSets";
       setText.visible = v.kind === "risesSets";
       transitText.visible = v.kind === "risesSets" || v.kind === "circumpolar";
       circumpolarText.visible = v.kind === "circumpolar";
       neverRisesText.visible = v.kind === "neverRises";
-    });
+    };
+    visibilityProperty.link(onVisibility);
 
-    coordsProperty.link((coords) => {
+    const onCoords = (coords: SelectionCoords): void => {
       const hasSelection = coords.kind !== "none";
       noneText.visible = !hasSelection;
       nameText.visible = hasSelection;
@@ -376,14 +414,17 @@ export class SelectedObjectReadout extends Node {
       magText.visible = hasSelection;
       eqText.visible = hasSelection;
       hzText.visible = hasSelection;
-    });
+    };
+    coordsProperty.link(onCoords);
 
     // Elongation only applies to planets (and the Moon), never a bare star or the Sun.
-    elongationProperty.link((elong) => {
+    const onElongation = (elong: { deg: string; dir: string } | null): void => {
       elongationText.visible = elong !== null;
-    });
+    };
+    elongationProperty.link(onElongation);
 
     // ── Track toggle (enabled only when an object is selected) ────────────────
+    const trackEnabledProperty = new DerivedProperty([model.selectedObjectProperty], (s) => s !== null);
     const trackCheckbox = new Checkbox(
       model.trackSelectedObjectProperty,
       new Text(controls.trackSelectedStringProperty, {
@@ -393,7 +434,9 @@ export class SelectedObjectReadout extends Node {
       }),
       {
         ...ZENITH_CHECKBOX_OPTIONS,
-        enabledProperty: new DerivedProperty([model.selectedObjectProperty], (s) => s !== null),
+        // Not owned by the Checkbox (EnabledComponent only disposes an
+        // enabledProperty it created), so dispose() below releases it.
+        enabledProperty: trackEnabledProperty,
         accessibleName: a11y.controls.trackSelectedStringProperty,
       },
     );
@@ -420,5 +463,78 @@ export class SelectedObjectReadout extends Node {
         ],
       }),
     );
+
+    // ── Teardown, in dependency order ─────────────────────────────────────────
+    // 1. Internal listeners on Properties we are about to dispose.
+    this.disposers.push(() => {
+      visibilityProperty.unlink(onVisibility);
+      coordsProperty.unlink(onCoords);
+      elongationProperty.unlink(onElongation);
+      nameMultilink.dispose();
+    });
+    // 2. Pattern Properties (their Text readers are disposed by dispose() first).
+    this.disposers.push(() => {
+      for (const patternProperty of patterns) {
+        patternProperty.dispose();
+      }
+    });
+    // 3. Derived Properties that fed those patterns, leaf-most first…
+    this.disposers.push(() => {
+      for (const property of [
+        magProperty,
+        raProperty,
+        decProperty,
+        altProperty,
+        azProperty,
+        typeNameProperty,
+        constellationNameProperty,
+        constellationSourceProperty,
+        elongDegProperty,
+        elongDirProperty,
+        riseTimeProperty,
+        riseAzProperty,
+        riseClockProperty,
+        setTimeProperty,
+        setAzProperty,
+        setClockProperty,
+        transitTimeProperty,
+        transitAltProperty,
+        transitClockProperty,
+      ]) {
+        property.dispose();
+      }
+    });
+    // 4. …then the bases they derived from, and the standalone Properties.
+    this.disposers.push(() => {
+      coordsProperty.dispose();
+      visibilityProperty.dispose();
+      elongationProperty.dispose();
+      trackEnabledProperty.dispose();
+      nameProperty.dispose();
+    });
+  }
+
+  /**
+   * Releases this panel's axon graph. `Node.dispose()` only detaches children, so
+   * the readout's Texts, its pattern Properties, and the ~20 DerivedProperties
+   * behind them would otherwise stay subscribed to the model and the shared
+   * StringManager after the screen is torn down. Children are disposed between
+   * stages 1 and 2 so no Text is still reading a pattern when it is released.
+   * Idempotent — the disposer list is drained on the first call.
+   */
+  public override dispose(): void {
+    const [detachListeners, disposePatterns, ...rest] = this.disposers.splice(0);
+    detachListeners?.();
+
+    const children = this.children;
+    super.dispose();
+    for (const child of children) {
+      child.disposeSubtree();
+    }
+
+    disposePatterns?.();
+    for (const disposeStage of rest) {
+      disposeStage();
+    }
   }
 }
diff --git a/src/zenith-screen/view/ZenithScreenView.ts b/src/zenith-screen/view/ZenithScreenView.ts
index afd68b9..48006b6 100644
--- a/src/zenith-screen/view/ZenithScreenView.ts
+++ b/src/zenith-screen/view/ZenithScreenView.ts
@@ -62,6 +62,7 @@ const SELECTION_PANEL_BOTTOM_CLEARANCE = 52;
 
 export class ZenithScreenView extends ScreenView {
   private readonly skyNode: PlanetariumSkyNode;
+  private readonly selectedReadout: SelectedObjectReadout;
   private readonly searchNode: ObjectNameSearch;
   private readonly controlPanel: AccordionBox;
   private readonly timePanel: TimeControlPanel;
@@ -184,7 +185,7 @@ export class ZenithScreenView extends ScreenView {
       },
     );
 
-    const selectedReadout = new SelectedObjectReadout(model);
+    this.selectedReadout = new SelectedObjectReadout(model);
 
     const checkbox = (
       property: typeof model.showGridProperty,
@@ -419,7 +420,7 @@ export class ZenithScreenView extends ScreenView {
     this.addChild(this.skyNode);
 
     // Selection readout sits over the sky (bottom-left).
-    const selectionPanel = new ZenithPanel(selectedReadout, {
+    const selectionPanel = new ZenithPanel(this.selectedReadout, {
       xMargin: 8,
       yMargin: 6,
     });
@@ -500,8 +501,24 @@ export class ZenithScreenView extends ScreenView {
       this.searchNode.centerX = visibleBounds.centerX;
       this.searchNode.top = visibleBounds.minY + SCREEN_VIEW_MARGIN;
 
-      selectionPanel.left = visibleBounds.minX + SELECTION_PANEL_INSET;
+      // Selection readout: bottom-left over the sky. The left column (Location +
+      // Time) can reach the bottom of the window at common sizes, which would
+      // leave the readout painted over by the Time panel — so when they would
+      // overlap, slide it clear to the right of that column instead.
+      //
+      // `left` is computed once and assigned once: this runs re-entrantly from
+      // selectionPanel.boundsProperty, so writing it twice (default, then the
+      // shifted value) would notify back into here forever. Anchoring `bottom`
+      // first is safe — the overlap test reads `top`, which depends on `bottom`
+      // and the panel height, never on `left`.
       selectionPanel.bottom = safeBottom - SELECTION_PANEL_BOTTOM_CLEARANCE;
+      const selectionClearsLeftColumn = selectionPanel.top >= this.timePanel.bottom + RESET_ALL_PANEL_GAP;
+      selectionPanel.left = selectionClearsLeftColumn
+        ? visibleBounds.minX + SELECTION_PANEL_INSET
+        : Math.min(
+            this.timePanel.right + RESET_ALL_PANEL_GAP,
+            visibleBounds.maxX - SELECTION_PANEL_INSET - selectionPanel.width,
+          );
 
       resetAllButton.right = visibleBounds.maxX - SCREEN_VIEW_MARGIN;
       resetAllButton.bottom = safeBottom - SCREEN_VIEW_MARGIN;
@@ -577,6 +594,7 @@ export class ZenithScreenView extends ScreenView {
       dispose();
     }
     this.skyNode.dispose();
+    this.selectedReadout.dispose();
   }
 
   public override step(_dt: number): void {
diff --git a/tests/ZenithModel.test.ts b/tests/ZenithModel.test.ts
index 3ed0e96..468fce6 100644
--- a/tests/ZenithModel.test.ts
+++ b/tests/ZenithModel.test.ts
@@ -10,6 +10,7 @@ import { equatorialToHorizontal } from "../src/common/sky/SkyCoordinates.js";
 import { ZenithPreferencesModel } from "../src/preferences/ZenithPreferencesModel.js";
 import {
   CIVIL_HOURS_PER_SIM_SECOND,
+  CIVIL_TIME_MS_RANGE,
   DEFAULT_CIVIL_TIME_MS,
   DEFAULT_FIELD_OF_VIEW_DEG,
   DEFAULT_LATITUDE_DEG,
@@ -287,4 +288,33 @@ describe("ZenithModel", () => {
     expect(model.epochPresetProperty.value).toBe(EpochPreset.CUSTOM);
     expect(model.civilTimeMsProperty.value).toBe(Date.UTC(2020, 0, 1, 3, 0, 0));
   });
+
+  it("keeps the epoch preset selected while the clock ticks within the readout's precision", () => {
+    // The timer starts playing, so the first step advances civil time by a few
+    // milliseconds. That must not flip the combo to CUSTOM while the UTC readout
+    // (minute precision) still shows the preset epoch.
+    model.epochPresetProperty.value = EpochPreset.DECEMBER_SOLSTICE;
+    model.step(1 / 60);
+    expect(model.epochPresetProperty.value).toBe(EpochPreset.DECEMBER_SOLSTICE);
+  });
+
+  it("marks epoch CUSTOM once the clock has moved a full minute off the preset", () => {
+    model.epochPresetProperty.value = EpochPreset.DECEMBER_SOLSTICE;
+    model.advanceCivilTimeHours(1 / 60);
+    expect(model.epochPresetProperty.value).toBe(EpochPreset.CUSTOM);
+  });
+
+  it("holds civil time inside the supported year range", () => {
+    model.setCivilTimeMs(CIVIL_TIME_MS_RANGE.max + 5 * 365 * 24 * 3600 * 1000);
+    expect(model.civilTimeMsProperty.value).toBe(CIVIL_TIME_MS_RANGE.max);
+
+    model.setCivilTimeMs(CIVIL_TIME_MS_RANGE.min - 5 * 365 * 24 * 3600 * 1000);
+    expect(model.civilTimeMsProperty.value).toBe(CIVIL_TIME_MS_RANGE.min);
+  });
+
+  it("stops the clock at the range edge instead of playing past it", () => {
+    model.setCivilTimeMs(CIVIL_TIME_MS_RANGE.max);
+    model.advanceCivilTimeHours(48);
+    expect(model.civilTimeMsProperty.value).toBe(CIVIL_TIME_MS_RANGE.max);
+  });
 });
diff --git a/tests/memory-leak.test.ts b/tests/memory-leak.test.ts
index b4214da..5aa4a53 100644
--- a/tests/memory-leak.test.ts
+++ b/tests/memory-leak.test.ts
@@ -9,6 +9,7 @@ import { TimeModel } from "../src/common/TimeModel.js";
 import { ZenithPreferencesModel } from "../src/preferences/ZenithPreferencesModel.js";
 import { ZenithModel } from "../src/zenith-screen/model/ZenithModel.js";
 import { PlanetariumSkyNode } from "../src/zenith-screen/view/PlanetariumSkyNode.js";
+import { SelectedObjectReadout } from "../src/zenith-screen/view/SelectedObjectReadout.js";
 import { ZenithScreenView } from "../src/zenith-screen/view/ZenithScreenView.js";
 
 async function forceGC(earlyExitRef?: WeakRef<object>): Promise<void> {
@@ -156,6 +157,50 @@ describe("Memory leak regression", () => {
     });
   });
 
+  describe("SelectedObjectReadout", () => {
+    it("is collected after dispose", async () => {
+      const ref = (() => {
+        const preferences = new ZenithPreferencesModel();
+        const model = new ZenithModel(preferences);
+        model.timer.isPlayingProperty.value = false;
+        const readout = new SelectedObjectReadout(model);
+        const weak = new WeakRef<object>(readout);
+        readout.dispose();
+        model.dispose();
+        return weak;
+      })();
+      await forceGC(ref);
+      expect(ref.deref()).toBeUndefined();
+    });
+
+    it("stops observing the model after dispose", () => {
+      const preferences = new ZenithPreferencesModel();
+      const model = new ZenithModel(preferences);
+      model.timer.isPlayingProperty.value = false;
+      const readout = new SelectedObjectReadout(model);
+      readout.dispose();
+
+      // The readout derives coordinates, rise/set times and the constellation
+      // name from these; after dispose none of that may still be listening.
+      expect(() => {
+        model.civilTimeMsProperty.value += 3_600_000;
+        model.latitudeProperty.value = -33.9;
+        model.selectedObjectProperty.value = null;
+      }).not.toThrow();
+
+      model.dispose();
+    });
+
+    it("double dispose() does not throw", () => {
+      const preferences = new ZenithPreferencesModel();
+      const model = new ZenithModel(preferences);
+      const readout = new SelectedObjectReadout(model);
+      readout.dispose();
+      expect(() => readout.dispose()).not.toThrow();
+      model.dispose();
+    });
+  });
+
   describe("ZenithScreenView", () => {
     // Full ScreenView GC is not asserted here: joist `ScreenView` plus sun
     // ComboBox / NumberControl / localized string Properties retain a graph that
diff --git a/tests/zenithQueryParameters.test.ts b/tests/zenithQueryParameters.test.ts
index 622d1fc..12e42df 100644
--- a/tests/zenithQueryParameters.test.ts
+++ b/tests/zenithQueryParameters.test.ts
@@ -10,7 +10,7 @@ import {
   parseCivilDateQueryParam,
   resolveCivilTimeMsFromQuery,
 } from "../src/preferences/zenithQueryParameters.js";
-import { DEFAULT_CIVIL_TIME_MS } from "../src/ZenithConstants.js";
+import { CIVIL_TIME_MS_RANGE, DEFAULT_CIVIL_TIME_MS } from "../src/ZenithConstants.js";
 
 describe("zenithQueryParameters date helpers", () => {
   it("treats empty or null date as the sim default civil epoch", () => {
@@ -33,4 +33,22 @@ describe("zenithQueryParameters date helpers", () => {
     expect(isValidCivilDateQueryParam("not-a-date")).toBe(false);
     expect(parseCivilDateQueryParam("not-a-date")).toBeNull();
   });
+
+  it("rejects parseable dates outside the supported civil year range", () => {
+    // Accepting these would let the date-jump spinners clamp them to the range
+    // boundary, so a shared link would silently render a different sky.
+    for (const outOfRange of ["1850-01-01T00:00:00Z", "2150-06-01T00:00:00Z"]) {
+      expect(isValidCivilDateQueryParam(outOfRange)).toBe(false);
+      expect(parseCivilDateQueryParam(outOfRange)).toBeNull();
+      expect(resolveCivilTimeMsFromQuery(outOfRange)).toBe(DEFAULT_CIVIL_TIME_MS);
+    }
+  });
+
+  it("accepts dates at both ends of the supported range", () => {
+    for (const ms of [CIVIL_TIME_MS_RANGE.min, CIVIL_TIME_MS_RANGE.max]) {
+      const iso = new Date(ms).toISOString();
+      expect(isValidCivilDateQueryParam(iso)).toBe(true);
+      expect(resolveCivilTimeMsFromQuery(iso)).toBe(ms);
+    }
+  });
 });