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name: time-coordinates description: "Use Astropy Time and coordinates for timescales, formats, frames, transformations, separations, matching, observatory geometry, and solar-system helpers." metadata: disco-role: operating disable-model-invocation: true license: BSD 3-Clause

Time and Coordinates Router

Use this sub-skill when a task asks for time scales/formats or astronomy coordinate objects and transformations.

Load This When

• The task mentions Time, TimeDelta, UTC/TAI/TT/TDB, Julian dates, ISO formats, precision, leap seconds, or observatory location on a time object.
• The task uses SkyCoord, Angle, Longitude, Latitude, EarthLocation, ICRS/FK5/Galactic/AltAz/Galactocentric, or transform_to.
• The user needs angular separation, catalog matching, proper motion, radial velocity, or space-motion propagation.
• Observation planning requires AltAz transforms, local sidereal time, Sun/Moon positions, or no-network handling for IERS data.

Route Away When

• Pixel/world transformations from FITS WCS are central; use ../wcs-nddata/SKILL.md.
• Unit conversion itself is the obstacle; use ../units-constants/SKILL.md.
• Remote-data cache/config policy is the main question; use ../cli-config-data/SKILL.md.
• Table serialization of coordinates is central; use ../tables-io/SKILL.md.

First Actions

1. Identify input types: strings, numbers, arrays, Quantity, Time, SkyCoord, frame object, or table columns.
2. Make time scale and format explicit: Time(value, format=..., scale=...).
3. Attach location when needed for local or Earth-rotation dependent results.
4. Construct SkyCoord with units and a frame; do not assume degrees for raw numbers unless the user says so.
5. For transforms, use coord.transform_to(target_frame_or_name) and validate representative outputs.
6. For matching, keep returned index, separation, and 3D distance together.
7. For offline/reproducible tasks, set IERS/network policy before transforms that need Earth orientation data.

References

• references/api-reference.md lists constructors, methods, frame and matching APIs.
• references/workflows.md covers time conversion, coordinate transforms, matching, AltAz observation planning, proper motion, and offline-safe settings.
• references/troubleshooting.md covers units, frame attributes, IERS warnings, name-resolution/network traps, and array shape issues.

Safety and Validation

• Always state angle units and time scale.
• Avoid name resolution in unattended tasks unless network access is explicit; prefer literal coordinates.
• Validate transforms with sanity checks: finite angles, expected frames, round-trip where appropriate, and separations in angular units.
• Do not treat WCS pixel coordinates as SkyCoord without a verified WCS transformation.

Native-Backed Validation Ideas

• Convert a UTC Time to JD and assert the known result for J2000-like inputs.
• Build an ICRS SkyCoord, transform to Galactic, and assert finite longitude and latitude.
• Match a two-object catalog and assert the returned index and separation units.