The Earth’s orbit around the sun is elliptical. This means that its distance from the sun varies, meaning that the whole Earth - not just one hemisphere - gets hotter twice yearly at the same time. Then there is the tilted axis of the Earth causing each hemisphere to be more exposed to the sun and therefore hotter at diametrically alternating points in the year. The first of these effects doesn’t seem to talked about. I need someone to explain this to me! I don’t want to trawl through astronomy books.
The only two explanations I can think of is that the decrease in distance from the sun is too small to influence the Earth’s temperature, or that the Earth orbits so that the equinoxes or solstices occur at exactly the points at which the Earth is closest to the sun.
I love how the Earth doesn’t have years that are perfectly divisible by a whole number of days. It’s like one of many pieces of evidence against conscious design of the Universe. Or against “Intelligent Design“. I also love all the pieces of evidence that strongly suggest the Universe was created by an entity with a deep love of mathematics and a bad case of OCD. It’s as if humans have been put in a puzzle with deliberate contradictions that can never be resolved. Perhaps resolution isn’t important, but the way humans go about debating the contradictions is instead. Process, not purpose