OK, spacefans, I just got some schooling from a real astronomer about the title of Program 897 "Perigee." I'm a little embarrassed, but a lot better educated. (For the record, what I meant was "low energy point" which is called the "ground state" in physics. Not very poetic, though. "Nadir" would have been better...)
:: SH
From: Larry Krumenaker
Date: January 2, 2010
Subject: astronomical misconception in this week's playlist
Hello, Pair of Steves.
My name is Dr. Larry Krumenaker, I'm an astronomer and educator in Atlanta. I get your programming list every week.
This week I noticed your use of "perigee" for the 'low point' of the year. Unfortunately, you have used the word in a completely wrong context. "Perigee" refers to the closest point of a satellite or the Moon in its orbit around Earth. The northern hemisphere's view of the Sun is truly at its lowest points for the year in our skies but it isn't due to perigee, the Moon and its orbit has nothing to do with it.
I believe you were really meaning to use the word "perihelion," which is the Earth's closest distance in _its_ orbit around the Sun. But even that isn't the cause of the Sun's 'low point' in our skies. That's due entirely to the Earth's tilt. The Earth's tilted axis points away from the Sun for Northern Hemisphere listeners of Hearts of Space.Thus the sun appears low because we're kind of looking way down toward the Sun shining high over the southern continental and oceanic areas, Australia, South Africa, etc. At perihelion, we are actually closest to the Sun and, logically, that should mean we'd be warmer here in the US than we are, therefore, you can deduce that the solar distance has little, if anything, to do with our cold weather. Unfortunately, this is an all too common misconception, that we are cold in January because we must be farther from the Sun. That is quite far...from the truth.
It's the fewer hours of sunshine we have, and the more spread out and less concentrated sunshine that causes our low point of weather, and the tilted earth's axis that causes the low altitude of the Sun. It has nothing to do with either the moon's distance from us, or our distance from the Sun.
If you want to astronomically distinguish between highest and lowest, the highest you can get is "zenith" or "zenithal". The lowest point is the "nadir." Using "perigee" for lowest is completely wrong, as the prefix "peri-" doesn't mean lowest, it means closest. "gee" refers to earth, as
in "geology". The opposite of "peri-" is "ap-" as in aphelion, the farthest distance from the Sun the earth gets (in July), or "apogee", the moon's farthest distance from the earth. While one could perhaps conceive of perigee and apogee as highest and lowest distances of the moon from us, that would be linguistically wrong, and has nothing to do with the highness or lowness of our solstitial sun.
You can read more about my work in Atlanta teaching astronomy, and about my magazine The Classroom Astronomer, at my business website http://www.toteachthestars.net .
Sincerely,
Dr. Larry Krumenaker
Thanks for clearing that up, Dr. Krumenaker!
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