PORTLAND, Maine — During these dark days of winter, it can feel like the sun has barely risen before it’s time to set again.
Some roadsides stay in shadow for months, while our closest star struggles to rise above the treetops or even modest city buildings. Throw some winter overcast into these post-holly jolly days and your spirits can really take a nosedive.
But fear not.
We’re seeing the latest sunrises of the whole year this week, but starting Sunday the sun will begin getting out of its celestial bed a minute or two earlier each day, until the summer solstice.
You might think the sun has already been coming up earlier, since last month’s winter solstice — the shortest day of the year.
The latest sunrise and earliest sunset do not occur on the winter solstice. It’s all got to do with some complicated, astronomical realities concerning our planet’s tilt and elliptical orbit around the sun.
It’s hard to explain.
Look up the sunrise and sunset times for any city in the Northern Hemisphere around the winter solstice. You’ll see the earliest sunset always occurs several days before the shortest day and the latest sunrise always happens a handful days after it.
In other words, they’re staggered. The latest sunset happens in early December, a week or so later we see the shortest day of the year, followed by the latest sunrise sometime after that.
The exact solstice moment came at 10:59 a.m. on Dec. 21. That day, the city saw just eight hours, 42 minutes and 15 seconds of daylight. It was two seconds shorter than the day before. The next day, Portland’s sunshine lasted two seconds longer.
That day the sun rose at 7:14 a.m. and set at 3:56 p.m.
But Portland had already seen its earliest sunset, at 3:53 p.m., on Dec. 7 — a full 13 days earlier.
Likewise, the sun has now continued to rise later, every day since the solstice. That won’t change until Sunday.
This yearly phenomenon happens because the Earth’s orbit around the sun is not a circle. It’s actually an ellipse.
Winter and summer solstices occur when the Earth is furthest away from the sun in its lopsided, yearly journey.
Side note, the Earth’s own spinning axis is a little tilted. Thus, the Northern Hemisphere is angled away from the sun at the winter solstice and closer to the sun at the summer solstice.
Our terrestrial clocks run on a 24-hour cycle but an astronomical “solar day” lasts between each “solar noon,” when the sun appears highest in our sky.
Due to the Earth’s elongated orbit, solar days are really a little longer than 24 hours at the solstices when we’re furthest from the sun and a bit shorter than that at the equinoxes, when we’re closer.
Thus, most days of the year, solar noon doesn’t match your watch. It’s a little before, or after, noon depending on the time of year and how close we are to the sun.
Daylight saving time is another factor that affects sunrises.
Suffice it to say, true solar noon’s shifting point in our clock’s day is why the earliest sunsets are before the winter solstice and the latest sunrises are after it.
Think of it as your daily window of sunshine. It’s shortest around Dec. 21, because of the Earth’s tilt, and the daylight’s midpoint gets shifted as our planet swings around the relatively sharp corner at the end of its orbital ellipse.
This goes for the summer solstice, too. The longest day is always around June 21 but the earliest sunrise is sometime before that and the latest sunset is afterwards.
Cheer up! Sunnier days are coming.