Astronomy MCP Server

What astronomy-mcp-server does

The astronomy-mcp-server MCP server exposes observational astronomy calculations to MCP clients. It can determine where a planet, the Sun, the Moon, or a cataloged bright star appears; calculate rise, set, and transit times; report solar twilight; describe the Moon’s current phase; and find upcoming astronomical events.

The core calculations cover any supplied time and observer location where the operation requires coordinates. Results include coordinate systems, visibility-related values, event times, and additional metadata such as constellation, apparent magnitude, illuminated fraction, or transit altitude. The server also provides a body resource with reference information for solar-system objects and a stargazing prompt that chains astronomy operations with geocoding and weather steps.

How it works

Most calculations run locally through the astronomy-engine library, so the primary astronomy tools do not depend on a remote astronomy API. The server communicates through MCP using either STDIO or Streamable HTTP. A public hosted endpoint is also listed at https://astronomy.caseyjhand.com/mcp.

Optional capabilities use external data sources. JPL Horizons supplies ephemerides for small bodies and spacecraft, while CelesTrak element sets are propagated with SGP4 to identify visible satellite passes. These features are disabled unless their corresponding configuration flags are enabled.

Tools and capabilities

The astronomy-mcp-server MCP server includes seven tools:

• astronomy_get_sky_position returns equatorial, horizontal, and ecliptic coordinates, along with magnitude, phase, elongation, constellation, and object metadata where applicable. Named stars resolve from a bundled 32-star catalog.
• astronomy_get_rise_set reports rise, set, and transit data. For the Sun, it also returns civil, nautical, and astronomical dawn and dusk.
• astronomy_get_moon_phase gives the illuminated fraction, phase name, synodic age, phase longitude, and next four quarter phases.
• astronomy_find_events searches for eclipses, equinoxes, solstices, lunar quarters, oppositions, conjunctions, elongations, and apsides.
• astronomy_list_visible ranks above-horizon naked-eye bodies and can include bright stars, with a sky-condition classification.
• astronomy_get_ephemeris queries JPL Horizons for small bodies or spacecraft when enabled.
• astronomy_get_satellite_passes finds visible passes from CelesTrak data when enabled.

Setup and configuration

Install or run the package through an MCP client using the repository’s published installation options. The listing provides client installation links for Claude Desktop, Cursor, and VS Code. The server can also be operated through its STDIO or Streamable HTTP interfaces, including the published hosted endpoint.

Core tools need no optional data-source flag. Set ASTRONOMY_ENABLE_HORIZONS=true to register the JPL Horizons ephemeris tool, or ASTRONOMY_ENABLE_SATELLITES=true to register satellite-pass queries. These are opt-in features rather than requirements for local planet, Moon, event, and visibility calculations.

Limitations and notes

Rise and set can be null for circumpolar or never-rising objects, with an explanatory note instead of an error. Visibility is evaluated at one instant rather than across a time window, and the tool accounts for daylight, twilight, and nearby solar glare. Satellite searches are limited to recent element data and a bounded search period. Horizons requests can fail for ambiguous, unsupported, or invalid designations, and event searches stop at the end of 2100. The astronomy-mcp-server MCP server is therefore best suited to observational calculations and planning, not as a replacement for a full astronomical data archive.