Dear Tom,

I notice that the sunset time is getting later, even though the winter solstice is not for another week. And yet the sunrise time keeps getting later until a week or so after the solstice. Can you explain why? I would expect the latest sunrise and earliest sunset to both occur on the solstice date.
Thanks, Carl Wagner

Dear Carl,

Chicago experiences its earliest sunset of 4:20 p.m. from Dec. 2-14. Beyond that date, sunset slowly increases to 4:30 p.m. by Dec. 31. Despite the later sunsets, the city’s least amount of daylight still occurs around the Dec. 21-22 winter solstice because of later sunrises. Chicago sunrises finally reach their latest time of 7:18 a.m. from Dec. 28-Jan. 10. Chicago area astronomer Dan Joyce attributes these discrepancies to the eccentricity of the Earth’s orbit and the proximity of the winter solstice to the Jan. 4 perihelion when the Earth is closest to the sun.