How do I install the Eclipse Time skill?

Run npx skillmds@latest add ashfordeou/eclipse-time in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

Is Eclipse Time safe to use?

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Which AI agents work with Eclipse Time?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Eclipse Time free to use?

Yes. Installing skills from SkillMD is free. This skill is licensed under Apache-2.

Who published Eclipse Time?

ashfordeOU (@ashfordeou) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Eclipse Time by ashfordeou — Agent Skill

Name: Eclipse Time
Author: ashfordeOU

Eclipse Time

Use when you must compute the time a spacecraft spends inside the earth shadow during each orbit: derive the beta angle of the orbit plane relative to the sun vector from the inclination, the right ascension of the ascending node, and the sun position, then evaluate the shadow fraction from the beta angle and the orbit radius and multiply by the orbital period to produce the eclipse time and the daylight fraction. Produces the beta angle in degrees, the shadow fraction, and the eclipse time in seconds that gate eclipse duration inputs for spacecraft power and thermal sizing. Trigger: eclipse time, earth shadow, beta angle, shadow fraction, orbit plane, sun vector, eclipse duration.

ashfordeOU e9e8aa7 3 files · 12.6 KB Updated Sep 17, 2026

File contents

Eclipse Time (space-systems/orbit-mechanics/eclipse-time)

Use when the task is eclipse geometry for a circular Earth orbit: the beta angle of the orbit plane relative to the sun vector, the shadow fraction, and the eclipse time that feeds power and thermal sizing.

Domain quick reference

Units: altitude in km in, meters internally; angles in radians, degrees for display; period and eclipse time in seconds; fractions dimensionless in [0, 1].
Gravitational parameter mu = 3.986004418e14 m^3/s^2, mean Earth radius Re = 6371000 m.
Orbital period: T = 2 pi sqrt(a^3 / mu) with a = Re + altitude. At 500 km altitude T = 5668 s (94.5 min); at GEO (35786 km) T = 86142 s (23.93 h).
Beta angle from orbit and sun geometry: sin(beta) = sin(i) cos(delta) sin(RAAN - alpha) + cos(i) sin(delta), with i the inclination, delta the sun declination, alpha the sun right ascension. Range [-90, 90] deg.
Shadow fraction (spherical Earth, umbra only): f = arccos( sqrt(r^2 - Re^2) / (r cos(beta))) / pi while |beta| < beta_max = arcsin(Re / r); f = 0 otherwise. beta_max is about 68 deg at 500 km and about 8.7 deg at GEO.
Eclipse time = shadow fraction times orbital period. At 500 km with beta = 0 the eclipse is about 2142 s (35.7 min); the GEO maximum is about 4160 s (69 min).
Daylight fraction = 1 - shadow fraction.

Workflow

Take the circular orbit altitude in km and the orbit and sun angles: inclination, RAAN, sun declination, sun right ascension.
Compute the orbital period with orbital_period.
Compute the beta angle with beta_angle (radians) or beta_angle_deg (degrees).
Evaluate the shadow fraction with shadow_fraction and the eclipse time with eclipse_time.
Pack the full solution with eclipse_properties for the power and thermal sizing handoff.
Gate on the eclipse duration band: a beta angle above beta_max means a fully sunlit orbit with zero eclipse time.

Pitfalls

Feeding degrees into radian-based functions; beta_angle_deg exists for degree input.
Using a negative altitude or an orbit radius at or below Re, which raise ValueError.
Forgetting the beta_max cutoff: beyond about 68 deg at 500 km the orbit is fully sunlit and the shadow fraction is exactly zero.
Confusing the beta angle with the sun elevation above the local horizon; the beta angle is an orbit-plane-to-sun-vector angle.
Treating the geometric umbra estimate as exact; real eclipse durations shift slightly with penumbra, Earth oblateness, and the finite sun radius.

Behavior contract (gate 3)

The period, beta angle, shadow fraction, and eclipse time logic is exercised by the gate 3 contract test: scripts/test_eclipse_time.py against scripts/eclipse_time_logic.py (stdlib unittest, offline). Run: python3 scripts/test_eclipse_time.py

Compliance

Standards referenced, not reproduced: ECSS series text is copyright ESA; the beta angle and shadow fraction geometry are common astrodynamics, summary-only per standards-map.yaml (ecss is a free ESA download).
compliance: STANDARDS-REF, gated: false.

---name: eclipse-timedescription: Use when you must compute the time a spacecraft spends inside the earth shadow during each orbit: derive the beta angle of the orbit plane relative to the sun vector from the inclination, the right ascension of the ascending node, and the sun position, then evaluate the shadow fraction from the beta angle and the orbit radius and multiply by the orbital period to produce the eclipse time and the daylight fraction. Produces the beta angle in degrees, the shadow fraction, and the eclipse time in seconds that gate eclipse duration inputs for spacecraft power and thermal sizing. Trigger: eclipse time, earth shadow, beta angle, shadow fraction, orbit plane, sun vector, eclipse duration.license: Apache-2.0---# Eclipse Time (space-systems/orbit-mechanics/eclipse-time)Use when the task is eclipse geometry for a circular Earth orbit:the beta angle of the orbit plane relative to the sun vector, theshadow fraction, and the eclipse time that feeds power and thermalsizing.## Domain quick reference- Units: altitude in km in, meters internally; angles in radians, degrees for display; period and eclipse time in seconds; fractions dimensionless in [0, 1].- Gravitational parameter mu = 3.986004418e14 m^3/s^2, mean Earth radius Re = 6371000 m.- Orbital period: T = 2 pi sqrt(a^3 / mu) with a = Re + altitude. At 500 km altitude T = 5668 s (94.5 min); at GEO (35786 km) T = 86142 s (23.93 h).- Beta angle from orbit and sun geometry: sin(beta) = sin(i) cos(delta) sin(RAAN - alpha) + cos(i) sin(delta), with i the inclination, delta the sun declination, alpha the sun right ascension. Range [-90, 90] deg.- Shadow fraction (spherical Earth, umbra only): f = arccos( sqrt(r^2 - Re^2) / (r cos(beta))) / pi while |beta| < beta_max = arcsin(Re / r); f = 0 otherwise. beta_max is about 68 deg at 500 km and about 8.7 deg at GEO.- Eclipse time = shadow fraction times orbital period. At 500 km with beta = 0 the eclipse is about 2142 s (35.7 min); the GEO maximum is about 4160 s (69 min).- Daylight fraction = 1 - shadow fraction.## Workflow1. Take the circular orbit altitude in km and the orbit and sun angles: inclination, RAAN, sun declination, sun right ascension.2. Compute the orbital period with orbital_period.3. Compute the beta angle with beta_angle (radians) or beta_angle_deg (degrees).4. Evaluate the shadow fraction with shadow_fraction and the eclipse time with eclipse_time.5. Pack the full solution with eclipse_properties for the power and thermal sizing handoff.6. Gate on the eclipse duration band: a beta angle above beta_max means a fully sunlit orbit with zero eclipse time.## Pitfalls- Feeding degrees into radian-based functions; beta_angle_deg exists for degree input.- Using a negative altitude or an orbit radius at or below Re, which raise ValueError.- Forgetting the beta_max cutoff: beyond about 68 deg at 500 km the orbit is fully sunlit and the shadow fraction is exactly zero.- Confusing the beta angle with the sun elevation above the local horizon; the beta angle is an orbit-plane-to-sun-vector angle.- Treating the geometric umbra estimate as exact; real eclipse durations shift slightly with penumbra, Earth oblateness, and the finite sun radius.## Behavior contract (gate 3)The period, beta angle, shadow fraction, and eclipse time logic isexercised by the gate 3 contract test: scripts/test_eclipse_time.pyagainst scripts/eclipse_time_logic.py (stdlib unittest, offline). Run:python3 scripts/test_eclipse_time.py## Compliance- Standards referenced, not reproduced: ECSS series text is copyright ESA; the beta angle and shadow fraction geometry are common astrodynamics, summary-only per standards-map.yaml (ecss is a free ESA download).- compliance: STANDARDS-REF, gated: false.

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