With the keyword
rectascension, one rectascension circle gets tic
marks, analogously with
declination. The celestial position
at' denotes the starting point of the labelling, and
step is the step skip (in hours or degrees respectively) for the
subsequent tic mark labels.
The label should contain one of the following special expressions:
For further options see Arbitrary text. Tic mark labels can also be flexes, see Flexes.