Free sextant simulator
How a sextant works, from sight to latitude
See how a sextant doubles angles, align the Sun with the horizon, and work a simplified noon-sight latitude calculation. It is an independent revision aid, not official RYA training or assessment.
Direct answer
A sextant measures the angle between a celestial body and the horizon by double reflection. After applying index, dip, and altitude corrections, a noon Sun sight can be reduced to observed altitude, zenith distance, and latitude.
- Best for
- Index error, dip, observed altitude, noon sight
- Includes
- Sextant instrument, telescope view, calculation ladder
- Practice mode
- Alignment, guided steps, latitude quiz
- Cost
- Free, no login required
Altitude, corrections, noon latitude
Sextant simulator
Move a simplified sextant, align the Sun with the horizon, then work a noon-sight calculation without hiding the correction chain.
Index arm
23.5 degrees
Arc reading Hs
47.0 degrees
The mirror moves through the arm angle; double reflection makes the sextant arc read twice that angle.
Sight target
47.0 degrees
Alignment
Lower limb on horizon