🔍 Key Concepts

• Parts of a sextant and what each one does (index mirror, horizon glass, shade glasses, frame, index arm) • The purpose of the horizon glass in taking a sight • Which sextant components are fixed to the frame and which are movable (like the index arm)

💭 Think About

• Picture the light path: how does light from the horizon and from the celestial body travel through the sextant? Where must the horizon glass be for this to work? • Ask yourself: which part of the horizon glass must reflect the image and which part must let you see straight through to the real horizon? • Decide which pieces on a sextant must stay aligned permanently (fixed to the frame) versus which must move when you swing the index arm.

✅ Before You Answer

• Verify which sextant glass is partially silvered and which side of that glass is treated (nearer the frame or nearer the observer?) • Confirm whether the horizon glass is a fixed mirror on the frame or a movable part attached to the index arm • Make sure you can distinguish between shade glasses (for reducing brightness) and the horizon glass (for combining images) before choosing.