On Tuesday, December 19, 2017 at 1:53:11 PM UTC-7, Gutless Umbrella Carrying Sissy wrote:
What the hell is wrong with you?

Although I certainly can't speak for him, I should note for your benefit as I
have before that he *has* a point (of sorts, even if he's taken it much too
far).

When I was in junior high school, astronomers still believed that one side of
Mercury always faced the Sun, the same way that one side of the Moon always
faces the Earth.

My science textbook had a little table in it of Solar System facts. For each of
the planets in the Solar System, it included things like the diameter of the
planet and the radius of its orbit.

One of the facts included was the length of day for each planet.

Bizarrely enough, though, it gave the length of the day for the planet Earth
as...

23 hours and 56 minutes.

Not 24 hours. What?

I remember working it out. At four minutes a day, in 15 days all our clocks and
watches would be out of sync with the day by a whole hour.

Oh, and the length of day for Mercury was 88 days, not "infinity" or "forever".

So the row was *mislabeled*. It wasn't the *length of the day* for the different
planets, it was their... sidereal rotational period. Sometimes it's called the
"sidereal day", because that's a simple, friendly term.

But it isn't "the length of the day". It isn't how long the cycle of daytime,
when the sun is up and everything is bright, and nighttime, when things are
dark, takes.

So I found this annoying. I think it's important that we keep straight the
difference between the day and night cycle, which is important in our normal
lives, and the physical rotational period of the planet we live on.

The way I see it, Oriel36 has perhaps reacted to the same thing - *but*, in his
case, he fails to realize, perhaps because of a lack of mathematical
sophistication, that the "sidereal day", however remote it may be from our daily
lives, is still significant. If you're going to work with the Earth's rotation
mathematically, you need to disentangle it from the Earth's orbital motion
(which isn't a perfect circle, and furthermore is in a plane inclined to the
equator).

He doesn't care about this kind of stuff, and furthermore goes around claiming
that Newton's notion that the planets are kept in their orbits by gravity -
obeying the same laws of inertia and angular momentum as a child's top or a
tennis ball - is a myth.

He's just not into science.

John Savard