🔍 Key Concepts

• Dip correction is related to your height of eye above the sea surface • Difference between visible horizon, sensible horizon, and celestial (true) horizon • What hs (sextant altitude) and Ho (observed altitude) each represent in sight reduction

💭 Think About

• Ask yourself: From where are you actually observing – at sea level or some height above it – and how does that affect where you see the horizon? • Think about whether dip is moving your measured altitude toward an ideal, geometrical horizon or toward what you actually see from the bridge wing. • Consider at what step in the sight reduction process dip is applied: directly to hs, or later when forming Ho?

✅ Before You Answer

• Verify which horizon is defined by a plane through the observer’s eye parallel to the celestial horizon. • Confirm that dip is always a negative correction and comes from height of eye above the sea, not from instrument error. • Check whether Ho already includes dip, index error, and other corrections, or if dip is applied before Ho is computed.