🔍 Key Concepts

• Construction and parts of a sextant – especially which mirror is fixed to the frame and which moves with the index arm • Horizon glass vs. index mirror – what is silvered, and on what portion of each glass • Location of horizon glass in the light path – relative to the frame, index arm, and shade glasses

💭 Think About

• First, picture a standard marine sextant and trace the light path from the horizon to your eye. Where does the horizon glass sit in that path? • Which part of the sextant actually moves when you slide the index arm, and which mirror/glass stays attached to the frame? • Of the listed statements, could any be obviously wrong based on how a sextant is held and used? Are any options mutually exclusive?

✅ Before You Answer

• Verify which glass (horizon glass or index mirror) is fixed to the frame and which is mounted on the index arm • Recall whether the horizon glass is partially silvered (only part of its surface reflecting) or fully silvered • Confirm the physical position of the horizon glass: is it between the horizon and shade glasses, or do the shade glasses sit in front of it on the frame?