Hey, everyone! Today’s International Women’s Day. A single day hardly seems like enough to thank all the women in my life, but… thanks to all of them, and to all women.
The other night, I was out with one of the women in my life, not doing anything in particular, just out and about. It was a warmish night, especially for February, and the stars were doing what they do all around of us. I always like that sensation of seeing stars twinkling in front of you, while new ones pop into view as your eyes adjust to the dark. Off in our peripheral vision, other stars twinkled. It sort of feels like being in a glass of champagne.
In front of us as we walked were the familiar W-shaped asterism in Cassiopeia, and the Big Dipper in Ursa Major. Between them, Polaris, understated as always, showed us the way northward. For such an unimposing star in a difficult-to-see constellation, Polaris holds a lot of weight, doesn’t it? One of the first things I do at night when I visit a new place is find it. It helps me get a feel for where I am.
Believe it or not, this brings us to this week’s word of the week!
Imagine the whole sky as a big sphere. I mean, the whole sky, all of it, even the parts below the ground. So, Earth is a ball within this bigger sky ball. The meridian is an imaginary line that runs from the due north horizon straight up overhead, through the zenith (highest point), to due south where it disappears below the horizon. Then it runs through the nadir (lowest point), and continues until it meets back up with itself at the northern horizon. This cuts the whole sky into an eastern and a western half.
As the things in the sky go about their nights, they reach their highest point in the sky as they cross the meridian. Maybe that point is at the zenith. Maybe it’s just a couple of degrees above th horizon. Usually it’s somewhere between but, whatever it is, the culmination is the the spot where an object crosses the meridian for a given night. It’s where that thing goes from rising to setting and is its highest point in the sky for that night.
Everything culminates twice each day. Generally, the one nearer the zenith is called the upper culmination; the one nearer the nadir, the lower culmination. Usually culmination by itself is used to mean upper culmination, as I did in the paragraph above.
Back to Polaris and those stars in the far northern sky for a second. Polaris is almost exactly due north, and it looks from Earth to be revolved around by Ursa Minor, Ursa Major, Cassiopeia, and a couple of other circumpolar objects and constellations. These things are so far north that they reach their lower culmination above the horizon and never set, as opposed to… I don’t know… Sirius or Vega, which rise and set just like the sun and moon do.
This culmination point is great. Since it’s the time when an object is at its highest, it’s easiest to get a good look at. If things culminate at a convenient time, drop what you’re doing and take out the trash. Tonight, March 8, Betelgeuse crosses the southern meridian, has its upper culmination at about 6:45 PM, just after sunset, where I am. Sirius follows a little less than an hour later. I hope the clouds stay away.
Clear skies, everyone!