Nocturnal star clock

There are many sundials that can be used to determine the time at one's own location. But what about when the sun has long since set? This is where the much less well-known sundial comes into play. With its help, local time (i.e. solar time) can also be determined at night. This is done with the help of Polaris - one of the brightest stars in the northern hemisphere - and the fixed star Kochab, which can be found in the same constellation (Ursa minor).

But the Nocturnal star clock can do even more. On its back is a tide calculator that can be used to determine the tides - which is not only interesting for sailors, but also for vacationers on coasts with pronounced tidal changes. For this purpose, the current moon phase is selected (new or full moon, half moon, waxing or waning). The tide calculator shows the approximate time of the next high water (high tide), with the second high water occurring about 12.5 hours after the first. The low tide (ebb) occurs about six hours after each high tide.

Note that both the star clock and the tide calculator must be converted to current local time. This requires applying the equation of time, correcting for daylight saving time if necessary, and making a longitude adjustment. The enclosed instructions tell in short words how this is done. By the way, the historical model of the Nocturnal star clock dates back to 1570 and can be found in the British Museum in London.