Wednesday, 9 March 2016

112) “The Sun brings noon to every time-zone as it passes directly over-head every 15 degree demarcation point, 24 times per day in its circular path over and around the Earth. If time-zones were instead caused by the uniform spinning of the ball-Earth around the Sun, every 6 months as Earth found itself on the opposite side of the Sun, clocks all over Earth would have to flip 12 hours, day would be night and night would be day.”

So here, Dubay  seems to say that because the earth spins around the sun, so day/night have to flip every 6 months. I'm a bit confused about what he’s  trying to say; He knows the earth spins around its axis, right?

Incomprehension of the model
Ok: How long is a day? Obviously 24 hours. That is the time it takes for the sun to reach the same longitude after 1 rotation of the earth. The big problem begins with the orbit of the earth: 

When the earth has travelled a certain distance on its orbit after one day, would it have to rotate exactly 360° to complete one day, to look at the sun with the same angle?

Obviously no. Because it would have to rotate a little bit more to compensate for the distance it has travelled. Because one year is 365 days long and a circle has 360° it follows that the earth has to rotate roughly one extra degree to complete one day. That means, an exact 360° rotation of the earth doesn't take exactly 24 hours, but a little less.

In fact it takes 23 hours and 56 minutes. That's what's called a sidereal day:

So we're 4 minutes off a 360° rotation each day. Let's calculate how much that offset is after roughly half a year (182 days):

So, yes, after roughly half an orbit we are close to a half-day off in our rotation. And that is the reason why "noon" after exactly 6 months is still "noon" because we are now looking at the sun from the opposite side! But only because geometry implies that there is a difference between a "day" and 360° rotation.

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