In medieval alchemy sometimes sappeared as a time sign for day. The ideogram means
astronomy and astrology, i.e. two celestial bodies lie on the same
longitude as seen from the earth. Compare with
With the circle filled, , it can be used as an astronomical sign for an eclipse of the sun, which makes sense when one realizes that such an eclipse is a conjunction of the sun and the moon, that is the new moon, which is symbolized by in almanacs.
When drawn with a very small, filled circle (i.e. a point), , it has been used as a meteorological sign to indicate coating of ice or ice needles.