Courtesy of EarthSky
A Clear Voice for Science
If you like to sleep late but don’t want to miss the sunrise, this time of year should be your favorite. The latest sunrises of the year for mid-latitudes in the northern hemisphere are happening around now and will continue for another week. For those in Wichita, Kansas for example, the sunrise time for the next 8 mornings is at 7:44 a.m. Sleep on!
The December solstice always brings the shortest day. But the latest sunrises do not coincide with the day of least sunlight.
The main reason is that the Earth’s rotational axis is tilted to the plane of our orbit around the sun. A secondary reason is that the Earth’s orbit is not a perfect circle. Due to our eccentric orbit, Earth is traveling a little faster in orbit right now than it does in summer. Clock time gets a bit out of synch with sun time – by about the tune of 1/2 minute per day for several weeks around the winter solstice.
If you’re a skywatcher, you might know that this sequence of earliest sunset, shortest day, and latest sunrise never varies from year to year. For us at middle latitudes in the northern hemisphere, the earliest sunsets come in early December. The shortest day comes on the solstice around December 21. And the latest sunrises come in early January.
Written by Kelley Knight HeinsPrint This Post