The shortest day of the year in our northern hemisphere, the winter solstice, arrives on Thursday, Dec. 21. It marks the calendar beginning of winter, though these past frosty mornings already tell of seasonal change. This year, the solstice coincides with the peak of the Ursid meteor shower. It produces just five to 10 per hour but is perhaps easier to watch, as it radiates from the constellation Ursa Minor, the Little Dipper. The full…