CycleCalcs Astronomy

Planet events: apparitions, oppositions, constellation entries

astro_planet_events

Read-onlyIdempotent

Dated planet events. For Mercury and Venus, the apparition cycle: inferior and superior conjunctions, greatest eastern and western elongations, peak brightness (a Venus-only event: Mercury's brightness peaks behind the Sun where it cannot be seen), and the rare transits across the Sun; with no dates it also reports where each is in its cycle right now: morning star or evening star, the conjunctions bounding the current apparition, and the live elongation, phase, magnitude and apparent size. For Mars, Jupiter, Saturn, Uranus and Neptune: conjunction with the Sun, western quadrature, opposition and eastern quadrature, the instants the planet's apparent geocentric ecliptic longitude minus the Sun's reaches 0, 270, 180 and 90 deg, each with the planet's constellation, distance, magnitude and elongation. For any of the seven, constellation_entry, returned only when listed in kinds: each crossing of an IAU constellation boundary, with the two constellations and the direction of motion. The right tool for "when does Venus become the morning star", "when is Mars at opposition", or "when does Uranus cross from Taurus into Gemini". For tonight's visibility of all eight planets use astro_planet_board. Mercury and Venus conjunction instants use the classical heliocentric convention, named on each event.

Input Schema

TableJSON Schema

Name	Required	Description
`tz`	No	IANA timezone like "Europe/Lisbon" to render event times in local time. Optional; a resolved place supplies its own timezone.
`end`	No	Last day of an explicit window, exclusive. ISO 8601 UTC date or datetime, e.g. "2026-08-06" or "2026-08-06T21:00:00Z". Or jd: followed by a Julian Day on the UT scale, e.g. "jd:2461000.5". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there.
`lat`	No	Latitude in decimal degrees, north positive. Send lat and lon together.
`lon`	No	Longitude in decimal degrees, east positive (Lisbon is about -9.14). Send lat and lon together.
`date`	No	Anchor instant; with no start/end the response covers the next full synodic cycle from here. ISO 8601 UTC date or datetime, e.g. "2026-08-06" or "2026-08-06T21:00:00Z". Or jd: followed by a Julian Day on the UT scale, e.g. "jd:2461000.5". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there.
`kinds`	No	Optional filter of event kinds. Omit for each planet's own family: the seven apparition kinds for mercury and venus, the four Sun-relative kinds for mars to neptune. peak_magnitude only ever fires for venus; the transit kinds are body-specific and genuinely rare. constellation_entry applies to all seven and must be listed.
`place`	No	Place name instead of lat/lon, as "City" or "City,CC" with an ISO country code, e.g. "Lisbon,PT". Resolved server-side; the response then carries a required GeoNames CC BY 4.0 credit in its attribution field, which must be preserved when shown.
`start`	No	First day of an explicit window (use with end). ISO 8601 UTC date or datetime, e.g. "2026-08-06" or "2026-08-06T21:00:00Z". Or jd: followed by a Julian Day on the UT scale, e.g. "jd:2461000.5". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there.
`bodies`	No	Which planets to report. Default mercury and venus.
`cursor`	No	Opaque pagination cursor from a previous result's next_cursor. Send it with the same start/end arguments as the first page.

Output Schema

TableJSON Schema

Name	Required	Description
`data`	Yes	Planet events in a date range: the Mercury and Venus apparition events (conjunctions, greatest elongations, Venus's peak brightness, transits across the Sun), the Sun-relative events of Mars to Neptune (conjunction with the Sun, quadratures, opposition) and, when asked for, constellation entries. Stations (retrograde turning points) are not among them: astro_planet_board gives each planet's next station, and the full station list is served by the REST route /v2/retrogrades.
`rights`	No	Either unrestricted, or attribution_required when third-party place data was used. When attribution_required, the attribution line must be shown.
`warnings`	No	Machine-readable notices about this answer. Present only when non-empty. Never changes whether the call succeeded.
`attribution`	No	The credit line to display verbatim when rights is attribution_required.
`next_cursor`	No	Present only when more rows exist. Send it back with the SAME start/end arguments as the first call to get the next page.
`not_computed`	No	Data this API deliberately does not serve, and why. Present only when the question touched such a field. An absence named here is information: treat it as "withheld", never as "none exists".

Schema Changelog

Changes observed during successful MCP inspections.

Changed9 schema fields changedSep 27, 2026

changedInput schema / properties / bodies / description

Previous value: -"Which inferior planets to report. Default both."New value: +"Which planets to report. Default mercury and venus."

changedInput schema / properties / bodies / items / enum

Previous value: -[
-  "mercury",
-  "venus"
-]New value: +[
+  "mercury",
+  "venus",
+  "mars",
+  "jupiter",
+  "saturn",
+  "uranus",
+  "neptune"
+]

changedInput schema / properties / bodies / maxItems
```
Previous value: -2New value: +7
```

changedInput schema / properties / date / description

Previous value: -"Anchor instant; with no start/end the response covers the next full synodic cycle from here. ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."New value: +"Anchor instant; with no start/end the response covers the next full synodic cycle from here. ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Or jd: followed by a Julian Day on the UT scale, e.g. \"jd:2461000.5\". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."

changedInput schema / properties / end / description

Previous value: -"Last day of an explicit window, exclusive. ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."New value: +"Last day of an explicit window, exclusive. ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Or jd: followed by a Julian Day on the UT scale, e.g. \"jd:2461000.5\". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."

changedInput schema / properties / kinds / description

Previous value: -"Optional filter of event kinds. Omit for all. peak_magnitude only ever fires for venus; the transit kinds are body-specific and genuinely rare."New value: +"Optional filter of event kinds. Omit for each planet's own family: the seven apparition kinds for mercury and venus, the four Sun-relative kinds for mars to neptune. peak_magnitude only ever fires for venus; the transit kinds are body-specific and genuinely rare. constellation_entry applies to all seven and must be listed."

changedInput schema / properties / kinds / items / enum

Previous value: -[
-  "inferior_conjunction",
-  "superior_conjunction",
-  "greatest_elongation_east",
-  "greatest_elongation_west",
-  "peak_magnitude",
-  "transit_of_mercury",
-  "transit_of_venus"
-]New value: +[
+  "inferior_conjunction",
+  "superior_conjunction",
+  "greatest_elongation_east",
+  "greatest_elongation_west",
+  "peak_magnitude",
+  "transit_of_mercury",
+  "transit_of_venus",
+  "conjunction_with_sun",
+  "quadrature_west",
+  "opposition",
+  "quadrature_east",
+  "constellation_entry"
+]

changedInput schema / properties / start / description

Previous value: -"First day of an explicit window (use with end). ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."New value: +"First day of an explicit window (use with end). ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Or jd: followed by a Julian Day on the UT scale, e.g. \"jd:2461000.5\". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."

changedOutput schema / properties / data / description

Previous value: -"Apparition events per planet in a date range: conjunctions, elongations, stations."New value: +"Planet events in a date range: the Mercury and Venus apparition events (conjunctions, greatest elongations, Venus's peak brightness, transits across the Sun), the Sun-relative events of Mars to Neptune (conjunction with the Sun, quadratures, opposition) and, when asked for, constellation entries. Stations (retrograde turning points) are not among them: astro_planet_board gives each planet's next station, and the full station list is served by the REST route /v2/retrogrades."

Changed1 schema field changedAug 9, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "additionalProperties": true,
+  "description": "The MCP projection of a CycleCalcs v2 response: the answer, plus the provenance a caller needs to use it honestly.",
+  "properties": {
+    "attribution": {
+      "description": "The credit line to display verbatim when rights is attribution_required.",
+      "type": "string"
+    },
+    "data": {
+      "additionalProperties": true,
+      "description": "Apparition events per planet in a date range: conjunctions, elongations, stations.",
+      "properties": {
+        "bodies": {
+          "description": "One entry per body, each holding its events in time order.",
+          "type": "array"
+        },
+        "body_count": {
+          "description": "How many bodies are covered.",
+          "type": "integer"
+        },
+        "definition": {
+          "description": "How each event kind is defined.",
+          "type": "string"
+        },
+        "event_count": {
+          "description": "How many events matched in total.",
+          "type": "integer"
+        },
+        "kinds_selected": {
+          "description": "The event kinds included.",
+          "type": "array"
+        },
+        "window": {
+          "description": "The range actually evaluated.",
+          "type": "object"
+        }
+      },
+      "type": "object"
+    },
+    "next_cursor": {
+      "description": "Present only when more rows exist. Send it back with the SAME start/end arguments as the first call to get the next page.",
+      "type": "string"
+    },
+    "not_computed": {
+      "description": "Data this API deliberately does not serve, and why. Present only when the question touched such a field. An absence named here is information: treat it as \"withheld\", never as \"none exists\".",
+      "type": "array"
+    },
+    "rights": {
+      "description": "Either unrestricted, or attribution_required when third-party place data was used. When attribution_required, the attribution line must be shown.",
+      "type": "string"
+    },
+    "warnings": {
+      "description": "Machine-readable notices about this answer. Present only when non-empty. Never changes whether the call succeeded.",
+      "type": "array"
+    }
+  },
+  "required": [
+    "data"
+  ],
+  "type": "object"
+}

First observedAug 9, 2026

TDQS

A4.6/5.0

Behavior4/5

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), but the description adds real behavioral context: constellation_entry fires only when listed in kinds, peak_magnitude only ever occurs for Venus, transits are rare and body-specific, and conjunction instants for Mercury/Venus use the classical heliocentric convention named on each event. It does not mention pagination limits or the response envelope, which keeps it short of a 5.

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?

Front-loaded with the core purpose, then organized by body family in one dense paragraph with no filler sentences. It is on the long side and some per-event field detail (constellation, distance, magnitude, elongation) borders on restating likely output, but every clause carries information.

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

Completeness5/5

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

For a zero-required-parameter, 10-param tool with an output schema, the description covers body families, default kinds, the special-case events, time-window semantics, and the sibling alternative. Nothing an agent needs to select or invoke it correctly is missing, and return-value shape is handled by the output schema.

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

Parameters4/5

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

Schema description coverage is 100%, so baseline is 3, but the description contributes semantics the schema does not: without dates the tool augments output with the current cycle position (morning/evening star, bounding conjunctions, live elongation/phase/magnitude), the default kinds family per planet, and the fact that constellation_entry is never returned implicitly. That is genuine added meaning over the enum list.

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?

Opens with a specific verb+resource ('Dated planet events') and precisely scopes it by body family: Mercury/Venus apparition cycles, Mars–Neptune Sun-relative events, and constellation crossings. It explicitly names the sibling to use for the adjacent need ('For tonight's visibility of all eight planets use astro_planet_board'), so the agent can separate the two without opening either schema.

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?

Gives concrete triggering questions ('when does Venus become the morning star', 'when is Mars at opposition', 'when does Uranus cross from Taurus into Gemini') and an explicit alternative with its own condition (astro_planet_board for tonight's visibility). It also states the no-dates fallback behavior, so the agent knows what happens if it omits the window.

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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