to calculate one's nativity

Webster's Dictionary (GCIDE)

Nativity \Na*tiv"i*ty\, n.; pl. Nativies. [F. nativit['e], L. nativitas. See Native, and cf. Na["i]vet['e].]

1.The coming into life or into the world; birth; also, the circumstances attending birth, as time, place, manner, etc. --Chaucer. [1913 Webster]

I have served him from the hour of my nativity.— Shak.[1913 Webster]

Thou hast left . . . the land of thy nativity.— Ruth ii. 11.[1913 Webster]

These in their dark nativity the deep Shall yield us, pregnant with infernal flame.— Milton.[1913 Webster]

2.(Fine Arts) (capitalized) A picture representing or symbolizing the early infancy of Christ. The simplest form is the babe in a rude cradle, and the heads of an ox and an ass to express the stable in which he was born. [1913 Webster]

3.(Astrol.) A representation of the positions of the heavenly bodies as the moment of one's birth, supposed to indicate one's future destinies; a horoscope. [1913 Webster]

The Nativity, the birth or birthday of Christ; Christmas day.

To cast one's nativity or To calculate one's nativity (Astrol.), to find out and represent the position of the heavenly bodies at the time of one's birth. [1913 Webster]