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astronomy-mcp-server

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astronomy-mcp-server: find sky events

astronomy_find_events
Read-onlyIdempotent

Search forward from a start time for the next occurrences of one sky-event class, selected by the event enum: solar_eclipse, lunar_eclipse, equinox, solstice, moon_quarter, opposition, conjunction, max_elongation, or perigee_apogee. Both eclipse classes take an optional observer (latitude and longitude together). solar_eclipse without one returns global eclipses — kind, peak time, obscuration, and for a total or annular eclipse the latitude/longitude where it is greatest; with one it returns only eclipses visible from that point, with local contact times, local_visible, and the Sun's altitude at each contact. lunar_eclipse returns geocentric contact times, the same instants everywhere on Earth; an observer adds local_visible and the Moon's altitude at each contact. Every other class is geocentric and ignores a location. The body-relative events (opposition, conjunction, max_elongation, perigee_apogee) require a body: opposition applies to the superior planets (mars through pluto), conjunction to any planet, max_elongation to mercury and venus, and perigee_apogee to the moon (perigee/apogee), earth, or a planet (perihelion/aphelion). Returns the next count occurrences (default 1). Searches stop at the end of 2100, the close of the supported span; when that leaves fewer than count, a notice says so. Start defaults to now; pass an IANA timezone for observer-local timestamps.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
bodyNoTarget body — required for opposition, conjunction, max_elongation, and perigee_apogee; ignored otherwise. "earth" is accepted only for perigee_apogee, which returns its perihelion and aphelion.
countNoNumber of forward occurrences to return. Default 1, max 20.
eventYesWhich class of event to search for.
startNoSearch start as an ISO 8601 UTC string, e.g. "2024-01-01T00:00:00Z". Defaults to now. A value with no zone designator is read as UTC, not the local zone of the server process.
latitudeNoObserver latitude in decimal degrees, supplied together with longitude. Optional for solar_eclipse and lunar_eclipse, where it adds local circumstances; omit both for a global solar search. Ignored by every other event.
timezoneNoIANA timezone for localized output, e.g. "America/Los_Angeles". When omitted, output is UTC-only.
elevationNoObserver elevation in meters above sea level. Default 0.
longitudeNoObserver longitude in decimal degrees, supplied together with latitude. Optional for solar_eclipse and lunar_eclipse; ignored by every other event.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
errorNoPresent when the call failed. Absent on success.
eventsNoThe next occurrences of the requested event class, in chronological order.
noticeNoWhy the list is shorter than the requested count: the search reached the end of the supported span (2100). Absent when every requested occurrence came back.
totalCountNoNumber of event occurrences returned.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed10 schema fields changed
    • changedInput schema / properties / latitude / description
      Previous value: -"Observer latitude in decimal degrees — required for solar_eclipse to get local circumstances, ignored by every other event."New value: +"Observer latitude in decimal degrees, supplied together with longitude. Optional for solar_eclipse and lunar_eclipse, where it adds local circumstances; omit both for a global solar search. Ignored by every other event."
    • changedInput schema / properties / longitude / description
      Previous value: -"Observer longitude in decimal degrees — required for solar_eclipse, ignored by every other event."New value: +"Observer longitude in decimal degrees, supplied together with latitude. Optional for solar_eclipse and lunar_eclipse; ignored by every other event."
    • changedOutput schema / properties / error / properties / data / properties / reason / description
      Previous value: -"Machine-readable failure mode. Declared by this tool: `observer_required`: A solar_eclipse event was requested without observer latitude/longitude. `body_required`: A body-relative event was requested without a target body. `body_not_supported`: The body has no such event — opposition for the Sun, Moon, Earth, or an inner planet; conjunction for the Sun, Moon, or Earth; max_elongation for anything but mercury or venus; perigee_apogee for the Sun. `invalid_time`: The `start` value is not a parseable ISO 8601 instant, or names a calendar date that does not exist (e.g. 2026-02-30). `time_out_of_range`: The requested start instant is outside the engine's high-accuracy span (≈1900–2100). `invalid_timezone`: The `timezone` value is not an IANA zone this runtime knows. Other values are possible when a failure originates below the handler."New value: +"Machine-readable failure mode. Declared by this tool: `incomplete_observer`: A solar_eclipse or lunar_eclipse was requested with only one of latitude and longitude. `body_required`: A body-relative event was requested without a target body. `body_not_supported`: The body has no such event — opposition for the Sun, Moon, Earth, or an inner planet; conjunction for the Sun, Moon, or Earth; max_elongation for anything but mercury or venus; perigee_apogee for the Sun. `invalid_time`: The `start` value is not a parseable ISO 8601 instant, or names a calendar date that does not exist (e.g. 2026-02-30). `time_out_of_range`: The requested start instant is outside the engine's high-accuracy span (≈1900–2100). `invalid_timezone`: The `timezone` value is not an IANA zone this runtime knows. Other values are possible when a failure originates below the handler."
    • changedOutput schema / properties / error / properties / data / properties / reason / examples
      Previous value: -[
-  "observer_required",
-  "body_required",
-  "body_not_supported",
-  "invalid_time",
-  "time_out_of_range",
-  "invalid_timezone"
-]New value: +[
+  "incomplete_observer",
+  "body_required",
+  "body_not_supported",
+  "invalid_time",
+  "time_out_of_range",
+  "invalid_timezone"
+]
    • addedOutput schema / properties / events / items / properties / contact_altitudes_degrees
      Added value: +{
+  "additionalProperties": {
+    "type": [
+      "number",
+      "null"
+    ]
+  },
+  "description": "Apparent altitude in degrees of the eclipsed body (the Sun for solar_eclipse, the Moon for lunar_eclipse) above the observer's horizon at each contact, keyed by bare phase name: partial_begin, total_begin, peak, total_end, partial_end, plus penumbral_begin and penumbral_end for a lunar eclipse. Negative means below the horizon; null marks a phase this eclipse does not reach. Present only when latitude/longitude are supplied.",
+  "propertyNames": {
+    "type": "string"
+  },
+  "type": "object"
+}
    • changedOutput schema / properties / events / items / properties / contacts / description
      Previous value: -"Eclipse contact times in ISO 8601 UTC keyed by phase (e.g. partial_begin_utc, peak_utc); a phase that does not occur is null."New value: +"Eclipse contact times in ISO 8601 UTC keyed by phase (e.g. partial_begin_utc, peak_utc); a phase that does not occur is null. A global solar eclipse carries peak_utc only."
    • changedOutput schema / properties / events / items / properties / local_visible / description
      Previous value: -"True when the eclipsed Sun is above the observer's horizon at peak. Present for solar eclipses only — lunar eclipses are geocentric and report no local visibility."New value: +"True when the eclipsed body — the Sun for solar_eclipse, the Moon for lunar_eclipse — is above the observer's horizon at any contact. Present only when latitude/longitude are supplied. A solar result with an observer is always true, because the local search returns only eclipses with the Sun up at first or last contact; contact_altitudes_degrees tells an eclipse at sunrise or sunset from one at midday."
    • addedOutput schema / properties / events / items / properties / peak_latitude_degrees
      Added value: +{
+  "description": "Geographic latitude in degrees where a total or annular solar eclipse is greatest. Present for a solar_eclipse searched without an observer; absent for a partial eclipse, whose shadow axis misses Earth.",
+  "type": "number"
+}
    • addedOutput schema / properties / events / items / properties / peak_longitude_degrees
      Added value: +{
+  "description": "Geographic longitude in degrees where a total or annular solar eclipse is greatest. Present for a solar_eclipse searched without an observer; absent for a partial eclipse.",
+  "type": "number"
+}
    • addedOutput schema / properties / notice
      Added value: +{
+  "description": "Why the list is shorter than the requested count: the search reached the end of the supported span (2100). Absent when every requested occurrence came back.",
+  "type": "string"
+}
  2. Changed4 schema fields changed
    • removedOutput schema / properties / events / items / properties / contacts / additionalProperties / anyOf
      Removed value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]
    • addedOutput schema / properties / events / items / properties / contacts / additionalProperties / type
      Added value: +[
+  "string",
+  "null"
+]
    • removedOutput schema / properties / events / items / properties / obscuration / anyOf
      Removed value: -[
-  {
-    "type": "number"
-  },
-  {
-    "type": "null"
-  }
-]
    • addedOutput schema / properties / events / items / properties / obscuration / type
      Added value: +[
+  "number",
+  "null"
+]
  3. Changed6 schema fields changed
    • changedInput schema / $schema
      Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"
    • addedInput schema / additionalProperties
      Added value: +false
    • changedOutput schema / $schema
      Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"
    • addedOutput schema / anyOf
      Added value: +[
+  {
+    "not": {
+      "required": [
+        "error"
+      ]
+    },
+    "required": [
+      "events",
+      "totalCount"
+    ]
+  },
+  {
+    "required": [
+      "error"
+    ]
+  }
+]
    • addedOutput schema / properties / error
      Added value: +{
+  "additionalProperties": {},
+  "description": "Present when the call failed. Absent on success.",
+  "properties": {
+    "code": {
+      "description": "JSON-RPC error code for this failure.",
+      "maximum": 9007199254740991,
+      "minimum": -9007199254740991,
+      "type": "integer"
+    },
+    "data": {
+      "additionalProperties": {},
+      "properties": {
+        "reason": {
+          "description": "Machine-readable failure mode. Declared by this tool: `observer_required`: A solar_eclipse event was requested without observer latitude/longitude. `body_required`: A body-relative event was requested without a target body. `body_not_supported`: The body has no such event — opposition for the Sun, Moon, Earth, or an inner planet; conjunction for the Sun, Moon, or Earth; max_elongation for anything but mercury or venus; perigee_apogee for the Sun. `invalid_time`: The `start` value is not a parseable ISO 8601 instant, or names a calendar date that does not exist (e.g. 2026-02-30). `time_out_of_range`: The requested start instant is outside the engine's high-accuracy span (≈1900–2100). `invalid_timezone`: The `timezone` value is not an IANA zone this runtime knows. Other values are possible when a failure originates below the handler.",
+          "examples": [
+            "observer_required",
+            "body_required",
+            "body_not_supported",
+            "invalid_time",
+            "time_out_of_range",
+            "invalid_timezone"
+          ],
+          "type": "string"
+        },
+        "recovery": {
+          "additionalProperties": {},
+          "description": "Actionable next step for the caller.",
+          "properties": {
+            "hint": {
+              "type": "string"
+            }
+          },
+          "required": [
+            "hint"
+          ],
+          "type": "object"
+        },
+        "retryable": {
+          "description": "Whether retrying may succeed.",
+          "type": "boolean"
+        }
+      },
+      "type": "object"
+    },
+    "message": {
+      "description": "Human-readable description of what went wrong.",
+      "type": "string"
+    }
+  },
+  "required": [
+    "code",
+    "message"
+  ],
+  "type": "object"
+}
    • removedOutput schema / required
      Removed value: -[
-  "events",
-  "totalCount"
-]
  4. Changed1 schema field changed
    • changedInput schema / properties / start / description
      Previous value: -"Search start as an ISO 8601 UTC string, e.g. \"2024-01-01T00:00:00Z\". Defaults to now."New value: +"Search start as an ISO 8601 UTC string, e.g. \"2024-01-01T00:00:00Z\". Defaults to now. A value with no zone designator is read as UTC, not the local zone of the server process."
  5. First observed

TDQS

A4.6/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is covered. The description adds valuable behavioral context beyond the schema: the 2100 end-of-span cutoff, the notice when fewer than `count` are found, observer-local timestamp semantics, and the fact that some event classes ignore the observer parameters. It does not contradict the annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is dense but every clause contributes a distinct fact about behavior or parameter usage, and it is front-loaded with the core purpose. It could be tightened by splitting into shorter sentences, but the density is justified for a tool with nine event classes and branching behavior.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's complexity and the rich output schema, the description covers the major behavioral branches (global vs. local eclipses, geocentric vs. observer-based events, body constraints, count cutoff, timezone defaults). The only notable gap is that elevation is not mentioned in the description narrative, though it is documented in the schema; since schema coverage is 100%, this is a minor omission.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3, but the description substantially enriches parameter understanding: it explains that latitude/longitude are required together, that they are only meaningful for the two eclipse classes, that `body` is required only for four event classes and is accepted for `earth` only in perigee_apogee, and how `timezone` changes output. This is genuine semantic guidance beyond the schema field descriptions.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb ('Search forward from a start time') and a specific resource ('one sky-event class, selected by the `event` enum'), and it enumerates the exact event classes. It clearly distinguishes the tool from the sibling tools, which cover ephemerides, moon phase, rise/set, satellite passes, and sky position.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides explicit when-to-use guidance for each event class: it explains which events accept an observer, which events require a `body`, which bodies apply to which event, and the special behavior of solar vs. lunar eclipses. It also covers the 'every other class is geocentric and ignores a location' rule, leaving little ambiguity about how to choose parameters for a call.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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