Southern hemisphere equinox

A few days ago was the equinox - vernal or autumnal, depending on where you are on the globe. Day and night are pretty much equal in length.

My parents have some friends living in Boston in the US. These friends noticed thiscartoon in the Boston Sunday Globe on the 22nd.

It's about right. Because sunshine just grazes both the North Pole and the South Pole at the time of an equinox, everyone on the Earth's surface gets a bit of sunshine on that day (barring those tucked behind mountains, in holes, wearing sunglasses, and so on). Please don't troll me.

Of course, all these things are "more or less", because of any number of factors.

Probably the most important one is the precession (yes, that's spelled right) of the equinoxes. This happens because the Earth's axis of rotation also rotates - imagine a spinning top slowing down. It starts to wobble, but the direction it droops towards rotates around slowly - much slower than the top itself is spinning. The Earth's axis takes about 26,000 years to complete this rotation. More or less.

And, there are other factors that cause all these calendar events to not be quite "as advertised". The Moon wobbles as well, and the Earth doesn't exactly follow its orbit around the Sun. Instead, the centre of gravity of the Earth and the Moon does, and both the Earth and the Moon dance around this point (called the barycentre). And this doesn't take other planets or the Sun itself into account.

My brain hurts.

Which reminds me - do people living on the equator call the 21st of September the vernal or autumnal equinox? For them, every single day is an equinox.

More or less.