September equinox around the corner

The September equinox is just around the corner. This year it happens at 11:09 PM EDT on September 22. I wrote about the problem of equating “equal day and night” with the date of the equinox last year, and rather than repeat myself, I just link to that article. Suffice to say here that, because our Sun, unlike all the other stars in the universe, is not a point source of light, not many places on Earth experience equal lengths of day and night precisely on the date that the geometric center of the Sun’s disk is above the horizon for 12 hours everywhere on earth.

Why is our Sun so different from all the other stars in the universe? Simple geometry. (You don’t even need trigonometry for this one.) We are close enough to it that we can see it as a disk (but please don’t look directly at it without taking the proper precautions!); all the other stars are trillions and trillions of miles away. (By the way, don’t buy a telescope that tells you it can show you objects “billions” of miles away; you won’t even make it outside our solar system with that thing!)