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In Pathfinder, one of the effects of the 20th-level capstone ability of the Heavens spirit Shaman is that if you ever die, you are reborn/reincarnated as a "star child".

If she dies, she’s reborn 3 days later in the form of a star child, maturing over the course of 7 days (as reincarnate).

(Not to be confused with the starchild trait, which gives you +4 to survival checks to avoid getting lost.)

What is a star child in the context of this ability?

A "star child" is not defined by the game

This term first appeared on the Advanced Players Guide, under the oracle mysteries, then getting repeated on the Advanced Class Guides for the shaman class.

There is speculation that it is simply a "child born under the stars", with no mother and father, but still a normal person. This is inspired on the tale of the goddess Desna, which is said to have been born from star dust. Others say that it is inspired by the fetus at the end of 2001 Space Odyssey movie (video spoiler).

James Jacobs (Creative Director) has said that this is merely flavor:

Correct. "Star child" is merely a flavorful way of saying "A reincarnated oracle." And an easter egg to 2001, I suppose.

The ability does exactly what the text of Reincarnate says it does, with the exceptions noted on the ability.