I suppose there’s much more to Santa’s vehicular get-up than some reindeer and a sled. My guess is that he has some sort of spaceship equipped with a faster-than-light drive and a star navigation system that can take him safely from Earth to the outer rim of the universe. After all, who are we to assume that Earth is the only inhabited planet?
No, he’s got quite a cargo hold in that spaceship of his. Toys for children in the Sudan (and hopefully they’ll stop fighting there long enough to breathe and unpack a present), wrapped-up marvels for the little pod-creatures of Rigulus 5, holiday gifts for the bird children of the Pleaides system, sweet stainless steel macaroons for the tykes of the Horsehead Nebulae (they have very strong teeth).
Everywhere there is a today happening today, complete with strange sunlight and stranger horizons (though, such horizons are commonplace enough to those who live there; they would think ours quite odd). But, despite the alien peculiarities of each strange sun, they all share in common a single star that could be seen from their shores, no matter how many light years away from Earth. A single star that shown over a barn, many years ago. And so, with this commonly held among them all, this tiny pivot upon which all of existence teeters, Christmas comes to the universe.