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At noon now in midwinter, the Sun stands a bit higher each day. Most of us do not notice the slow changes in the sky, like daylight increasing by just seconds a day, and what that does to us. Let鈥檚 explore these often unseen natural wonders.
1. Note the Sun鈥檚 position rising鈥攐ver five times its width every week.
Each day, the Sun moves eastward against the stars. Being in Aquarius, it simultaneously has a northern component that yields this elevation rise. Sky watchers perceive this, and welcome the heightened rays, especially because the loftier angle increases sunlight鈥檚 skin-warming infrared component.
Yet for most, the change is too slow to be noticed. You can鈥檛 blame anyone. Our culture prizes speed. Many can recite the cheetah鈥檚 70-mile-per-hour capability while far fewer know that sloths, those dawdling archetypes, lope along at 0.07 mph, a thousand times slower. We tend to ignore sluggish things.
Backyard telescope owners see this when entertaining visitors. They鈥檙e impressed if we explain that the hum they hear is the telescope tracking the Moon as it crosses the sky. Interest flags when they realize that following any celestial object merely requires that the motor perform a one-revolution-per-day.
2. Yes, we can see Earth鈥檚 spin with the naked eye.
Award yourself an acre on the Moon if you said yes. Because of course, you can perceive Earth鈥檚 rotation.
When watching the setting Sun, you鈥檝e certainly observed it slowly bury itself into the ocean horizon. And the Sun鈥檚 red final upper pinpoint, which some of us always hope will briefly turn emerald and gift us with a 鈥済reen flash,鈥 visibly vanishes all too quickly.
So happens, the setting Sun and Moon pretty much match the apparent visual speed of a minute hand鈥檚 pointy tip on a wall clock. It鈥檚 right on the edge of appearing stationary, but if you鈥檙e patient you鈥檒l definitely detect its motion. That our planet spins at such a rate is fascinating, even if we鈥檝e grown used to it.
Mars almost exactly matches our rotation speed, while Jupiter鈥檚 equator zooms 25 times faster than ours. On the other hand, our nearest planet neighbor Venus has a spin speed of just ten miles an hour, so you鈥檇 never visibly detect a sunset from there, even if it wasn鈥檛 always overcast.
3. We can visibly detect the Moon鈥檚 orbit.
Such slow speeds can actually manage to be exciting.
The Moon in its orbit lopes along at one kilometer per second, which makes its entire disk fully shift position in space in one hour, making it the only known celestial body that moves exactly one of its widths per hour.
We鈥檒l see this very phenomenon if we observe April鈥檚 solar eclipse since the Moon will require one hour to fully cover the Sun, from start to finish. Or, for that matter, for the Moon to wholly enter Earth鈥檚 shadow during any lunar eclipse. So, yes, we鈥檝e already derived excitement from the Moon鈥檚 leisurely orbit.
4. Even dust bunnies and flower blossoms are moving
It鈥檚 all around us on Earth too.
Bedroom dust hanging in the air, illuminated by shafts of sunlight, settles at the rate of an inch an hour.
The continental plate we鈥檙e on typically moves an inch a year. The fastest, carrying Hawaii northwest, zooms at four inches a year.
The quickest bacteria sprint the width of a human hair in a mere second, which lets them cross a damp kitchen counter in an hour. (No wonder diseases spread.)
And during the next month or two, springtime鈥檚 awakening of blossoms moves poleward at 0.6 mph, or one kilometer per hour, about the rate of a parent pushing a stroller.
That鈥檚 a wonderful image鈥攖hat tree buds opening into leaves is a process that creeps northward at the rate of a slow walk.
5. Watch the stars above which reveal Earth鈥檚 shifting poles
But if your focus is the absolutely most leisurely celestial phenomena that have managed to grab human attention, you could start with the ancient Greek Hipparchos back in 129 BC, who realized that star positions had slightly changed since the charts of the earlier Babylonians.
This precession of the poles makes spring equinoxes move slowly westward against the fixed stars. The rate is extremely slow in Earth time; the poles slowly shift in a 27,780-year cycle. But precession explains why people sang about the dawning of the age of Aquarius when the spring equinox鈥攚hen the Sun annually stands momentarily over the equator鈥攏owadays happens against the stars of Taurus the Bull.
6. But what about you and me?
Do we ever focus on minuscule motion? Rarely. The only plant that grows fast enough to be seen to visibly change is bamboo.
Got two hours? Planet Jupiter is the brightest 鈥渟tar鈥 out early these nights. You鈥檒l see its moon Io, and its shadow slide across Jupiter鈥檚 cloud-covered disk. In reality, they鈥檙e moving at a rate of 25 arcseconds per hour, a motion 2,000 times slower than the setting Sun.
Of course, it wouldn鈥檛 have been detectable without a telescope. Still, it reveals that despite our hurry-up culture, some of us have let astronomy help us 鈥渃hill out.鈥
7. Enjoy the increasing daylight鈥攐nly a minute per day (soon two)
Speaking of chill, the most obvious and life-affecting winter change these days is in the length of daylight. We had our earliest sunset (darkest afternoon) on December 7, and then saw our darkest morning (latest sunrise) during the first week of January.
How it all fits together to deliver hours and minutes of daylight boils down to the very darkest day being the recent solstice on December 21.
The increase in sunlight was just a few seconds per day at first. In late January, the gain in daylight reached more than a minute per day.
But it鈥檚 now changing quickly. In just a few weeks, we鈥檒l be gaining over two minutes of daylight each and every day!
When it reaches three minutes per day by the end of February, it鈥檒l remain glued to that same rapid sunshine-growth right through April.
And that鈥檚 the visible change the greatest number of us will be aware of. We won鈥檛 even care when June and July glue that darkness/daylight ratio in place so that, until late in summer, there鈥檚 barely any further change to observe.
Bob Berman, astronomer editor for The Old Farmer鈥檚 蜜桃恋人, covers everything under the Sun (and Moon)! Bob is the world鈥檚 most widely read astronomer and has written ten popular books. Read More from Bob Berman
This morning I waited at an open window pre-dawn with my camera poised to capture the morning star in a particular spot among the branches of my neighbor's tree as the sky steadily grew lighter and I had to keep changing my settings. Later, on a cloudless morning, I stood and waited until the sun moved into place from between those branches and my neighbor's house to illuminate a cascading stepped tree fungus at the bottom of a tree trunk I'd cut several years ago defining the edges of each layer. Patience. Observe each moment and the change happens like a steady breeze.
Hi, Bob! You can actually see and hear corn growing during its time of most rapid growth. The catch is, you have to be up in the middle of a hot, humid breathless August night to experience it. At least, that's the way it was when I was a kid - who know what these new frankencorns do...