Celestial Navigation · Celestial Sphere — First Point of Aries
The First Point of Aries (vernal equinox) is used in navigation as:
- AThe brightest star in the sky
- BThe zero reference from which sidereal hour angle (SHA) and GHA Aries are measured✓ Correct
- CThe observer's assumed position
- DA point on the visible horizon
Explanation
The First Point of Aries is the position of the sun at the vernal equinox; it is the origin for sidereal hour angle. The almanac tabulates GHA Aries, and a star's GHA is GHA Aries plus its SHA.
Authority: Bowditch (Pub. No. 9), Celestial Coordinates
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