June 21st is the Summer Solstice, or midsummers day as most of us call it. Have you ever wondered why one particular day is the longest? (and the opposite in winter). It's something we just grow up with and take for granted. The working out of this was probably mankind's first astronomical puzzle, and it happened a very long time ago.
Contrary to popular belief, ancient people, or at least those lucky enough to have an education, did not think the earth was flat, they knew it was spherical. Just observing the horizon from a mountain was enough of a clue, and they performed experiments and worked it out. There were several measurements done over 2,500 years ago that were remarkably accurate, most famously by Eratosthenes in Alexandria. He took measurements of when the sun was exactly overhead in two different places and did simple geometry to work out the size of the planet, very accurate he was too. Anyone interested can Google his name and find the whole story.
Getting back to the seasons, once it was understood that the earth was a sphere, and that the sunrises and sunsets were in different places along the horizon as we went through the year, it was obvious that the Earth must turn at an angle to the sun, so that any place would get more sunshine and longer days in the summer.
The inclination of the Earth's axis to the sun is one of the most basic facts of our planet, but a fact that so many seem unaware of, it controls our weather, seasons, and the lives of us and most of the animal kingdom. Where would we be without it?
Charles Oates. Vega Baja Astronomy Group.
For more information on the group and meetings please visit: https://sites.google.com/site/vegabajaastronomy/.