Sextant simulator

Measure the altitude of the sun the way a navigator does: bring the sun's reflection down until its lower edge just touches the horizon, then read the angle.

Through the telescope

The sextant

Reading = arc degrees + drum minutes

How to take a sight

  1. Start with the arm at 0°. The sun appears high above the horizon in the center of the view.
  2. Raise the index arm in whole degrees until the sun comes close to the horizon line.
  3. Use the micrometer drum to fine-tune until the bottom edge of the sun just touches the horizon.
  4. Select Check my reading. You are graded to the nearest arc-minute.

Simplified: this sim has no index error, dip, or refraction, and takes the sun's lower limb. Far from the horizon the sun's distance is compressed so it always stays in view; near the horizon the scale is true. The real sextant's arc is marked in half-angles so it reads the altitude directly.