1 [caption]: Dawn, somewhere in the Caribbean.
2 Mate: {looking through a sextant's telescope at the horizon} No sign of the pirates, captain.
3 Ponsonby: What's our position?
4 Mate: I'd say: Pretty hopeless.

The mate is holding a sextant, a navigation instrument typically used to measure the height of the sun above the horizon at noon, which gives a measurement of one's latitude. At dawn, he might just be using it for the small telescope that is typically part of the instrument. This isn't the normal use of a sextant, but you could do it if you needed to.

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Several people have written to inform me that there are plenty of practical uses for a sextant at dawn too. You can sight the height of stars above the horizon. You need to do this at dawn because at night you can't see the horizon, and once the sun is up you can't see the stars. The heights of various stars give you the latitude - even more directly than the sun in fact, since the sun moves on a more complicated path across the sky than the stars, dependent on the season.

You can also sight - horizontally - the angle between the dawn sun and a landmark, which will give you an absolute bearing from the landmark.

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2017-09-09 Rerun commentary: It's called a sextant, by the way, because the sector of a circle made up by the curved part and the two radial arms is one-sixth of a full circle (at least approximately, if not exactly). So no, it has nothing to do with sex. Although I suppose if you were creative enough...

Ahem.

Sextants aren't the only such devices, either. There are also quadrants and octants, which, as you might guess, have sectors equal to one quarter and one eighth of a circle, respectively. The general collective term for such devices is reflecting instrument, and the linked article mentions other more exotic examples such as quintants, too.