Reference Frames

<aside> ⏩ ChatGPT wrote all of this! There may be mistakes especially with the numbers, but the information generally looks right.

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Definitions

Definition: ECEF is a coordinate system that rotates with the Earth. The origin is at the Earth's center of mass.
Axes:
- X-axis: Points from the center of the Earth towards the intersection of the Equator and the Prime Meridian (Greenwich).
- Y-axis: Points from the center of the Earth towards the intersection of the Equator and 90° East longitude.
- Z-axis: Points from the center of the Earth towards the North Pole.
Use Cases: Used for GPS, satellite tracking, and any system where coordinates tied to the Earth's surface are needed.

Definition: ECI is a non-rotating coordinate system with its origin at the Earth's center of mass.
Axes:
- X-axis: Points towards the vernal equinox.
- Y-axis: Points 90° to the east of the X-axis in the equatorial plane.
- Z-axis: Points towards the North Pole.
Use Cases: Used for satellite orbit calculations and space missions, where an inertial frame is needed.

Definition: The ICRF is a fixed celestial reference frame based on the positions of distant quasars and other extragalactic objects. It is used to provide a stable and precise reference for celestial coordinates.
Axes:
- X-axis: Points towards the vernal equinox (mean equinox of J2000.0).
- Y-axis: Points 90° to the east of the X-axis in the equatorial plane.
- Z-axis: Points towards the North Celestial Pole.
Characteristics:
- Barycentric: Centered on the solar system's barycenter.
- Fixed and Inertial: Does not rotate with the Earth or any other body, providing a stable reference frame relative to the distant universe.
- Reference Objects: Defined by the positions of extragalactic radio sources, such as quasars, which are extremely distant and provide fixed points.
Use Cases: Used in high-precision astrometry, fundamental astronomy, and for defining celestial coordinates and motions.