Editing Astronomical clock (section)

=== "Dragon" hand: eclipse prediction and lunar nodes ===
The Moon's orbit is not in the same plane as the Earth's orbit around the Sun but crosses it in two places. The Moon crosses the ecliptic plane twice a month, once when it goes up above the plane, and again 15 or so days later when it goes back down below the ecliptic. These two locations are the ascending and descending [[lunar nodes]]. Solar and lunar eclipses will occur only when the Moon is positioned near one of these nodes because at other times the Moon is either too high or too low for an eclipse to be seen on the Earth.

Some astronomical clocks keep track of the position of the lunar nodes with a long pointer that crosses the dial, with its length extended out to both sides of the dial to pointing at two opposite points on the solar or lunar dial. This so-called "dragon" hand makes one complete rotation around the ecliptic dial every 19&nbsp;years. It is sometimes decorated with the figure of a serpent or lizard (''{{langx|el|drakon}}'') with its snout and tail-tip touching the outer dial, traditionally labelled ''{{langx|la|"caput draconam"}}'' and ''{{langx|la|"cauda draconam"}}'' even if the decorative dragon is omitted (not to be confused with the similar-seeming names of the two sections of the constellation [[Serpens]]).

During the two yearly [[eclipse season]]s the Sun pointer coincides with either the dragon's snout or tail. When the dragon hand and the full Moon coincide, the Moon is on the same plane as the Earth and Sun, and so there is a good chance that a [[lunar eclipse]] will be visible on one side of the Earth. When the new Moon is aligned with the dragon hand there is a moderate possibility that a [[solar eclipse]] might be visible somewhere on the Earth.