I hope you were fortunate enough to catch a few Geminids these past nights. Clouds threatened at my location all evening. I waited until midnight then set the alarm for 2 a.m. and turned off the light. Something gnawed at me as I tried to sleep, so I parted the curtains for a one last look... and saw the sky sparkling with stars. My clothes and winter gear went back on and 10 minutes later I was outside in the lounge chair. Single digit temperatures, howling winds and occasional clouds couldn't dampen the spectacle. When I finished my vigil at 4 mine eyes had seen the glory of 105 Geminids.
Many burned brightly! Fainter meteors are typically more numerous but not this shower. Better than half were close to fireball-brightness. My older daughter joined me for an hour which made watching the "Gems" that much more enjoyable.
I was impressed by how much the stars move in 3 1/2 hours. The Big Dipper hid in the trees at midnight but by 4 a.m. had climbed high enough to spill the contents of its bowl. I had the distinct sensation of living on a spinning planet, not something we're ordinarily are aware of.
Our next meteor shower, the Quadrantids, peaks in the small hours of Jan. 3. Unfortunately the 84 percent full moon will compromise the view. The Geminids will also have moon issues next year, but thankfully not the August Perseids. Expect a great show in 2021.
December can feel positively radiant on a sunny day; the sun is so low it's always shining in your face. But most people rightly consider it a dark month because nights are long and daylight frugal. The longest night of the year occurs on Dec. 21, the winter solstice. It's natural to expect the sun to set earliest and rise latest that day, but does it? Nope.
Each day, the sun rises in the east because the Earth spins on its axis in that direction. As the planet rotates, the day goes on and the sun arcs across the sky from east to west until it sets below the western horizon. Keep in mind the sun's daily arc is due entirely to the spin of the Earth. If we suddenly stopped spinning the sun would stand still.
Because the Earth keeps on turnin' sunshine greets us again the next morning. And the next — ad (almost) infinitum. The Earth also revolves around the sun, completing one revolution in 365 1/4 days. Its revolution makes the sun appear to travel about 1° to the east each day against the background of the stars. Of course, we can't see those stars because of solar glare, but the sun is currently in Ophiuchus and will cross into Sagittarius on Friday (Dec. 18).
This slow, eastward drift due to Earth's revolution is superimposed on the daily rise-set cycle caused by rotation. You can sense the drift by noting that constellations and planets invisible in the solar glow around sunrise become visible again once the sun has moved off a sufficient distance to the east.
Earth orbits the sun in an ellipse, a shape resembling a slightly squashed circle, with one end of the ellipse closer to the sun than the other. We're closest to our star in December and January and feel its gravitational tug more, which makes the planet move faster. This in turn accelerates the sun's apparent eastward motion, slightly delaying the time of sunrise. A later sunrise also means the sun arrives at the sunset point later. The sun continues to rise later each day during the entire month of December and into January. But later sunsets only resume around mid-month. What up?
That's where the tilt of the Earth's axis comes into this story. In a nutshell, the 23.5° tilt is writ large on the sky every year in the changing path of the sun — from its high point (farthest north) in the summer sky on the summer solstice to its lowest point (farthest south) six months later on the winter solstice.
In late November and early December, the sun is still sinking to its southernmost point in the sky, its daytime arc shrinking a little each day. This southward slide coincides with the sun's faster fight to the east and further delays sunrise times.
Through early December, the southward-sinking sun also causes the sun to set earlier with the earliest sunset around Dec. 6. After that date, the sun's speedier eastern motion compensates for its southern decline, and it begins to set later. By the solstice the sun sets several minutes later compared to earlier in the month. For example, in Chicago, the earliest sunset occurs at 4:19 p.m. around Dec. 6th. By the 14th it sets one minute later and three minutes later on the 21st. These dates will vary some depending upon your latitude.
Once the sun reaches its lowest point in the sky on the solstice, it immediately begins moving northward again. But that extra eastward kick from the speedy Earth continues to delay its rising time into early January. Adding to the delay, the sun lies at the flat bottom of its curve. Most of its daily motion is to the east with only a small component to the north. Soon however, its northward motion catches up to and surpasses its flight to the east, and the sun starts to rise earlier.
With later sunsets and earlier sunrises working in tandem in January, keen-eyed skywatchers will begin to notice a increase in the amount of daylight as soon as the third week of the month. In this way the dark days of December transform into the long, bright days of summer.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.