The star finder

A star finder answers the planning question for every navigational star at once: which stars will be up at twilight, how high, and in what direction. The American one is the 2102-D Star Finder and Identifier; the British Admiralty's is NP 323. Both are plastic, both last for decades, and many boats have one in the chart table.

It has two parts:

• The star base: a disc with the navigational stars printed on it, the pole at the center. A star's distance out from the center is its declination; its place around the disc comes from its SHA. The rim is marked in LHA ♈︎. One side is for north latitudes, the other for south.
• The templates: clear sheets, one for each band of latitude, printed with your horizon, curves of equal altitude and lines of equal bearing, and an arrow along your meridian.

Lay the template for your latitude on the base and turn its arrow to the LHA of Aries for the time of your sights. Every star inside the horizon curve is up, at the altitude and bearing the grid shows.

Here is one to try. Turn the template by dragging the rim, or with the controls beside it, and tap a star to read its altitude and bearing. The curves are altitude every 10°, the lines out from the zenith bearing every 30°, and the bold curve is your horizon.

Turn it slowly through an hour or two of LHA ♈︎ and watch stars come up over the eastern horizon and go down in the west. Try a southern template too: the base turns over, and the Southern Cross comes into view.