It moves
A relative of mine recently had a birthday and this is a version of the note I sent her.
This is a composite image I made from two photographs that are part of a project I've been doing for a while now. I'm tracking the apparent movement of the Sun in the sky throughout the year. These are pictures of the sunrise taken by flying my drone above my house. The most recent photo I've made was yesterday, and it is paired in this image with a similar photograph from three months ago on December 20, 2018. You can see how the Sun has tracked north since the time of the winter solstice until now.
Of course, the Sun is not moving. The Earth is moving around the Sun. Something that makes our annual trip around the Sun more interesting is that the Earth is simultaneously rotating on an axis that is tilted at 23.5 degrees relative to its orbital plane around the Sun. Our tilted axis points in the same direction at all times during Earth’s orbit, which causes any one place on the surface of Earth to have a constantly changing relationship to the position of the Sun in the sky. This effect is less at the equator and increases toward the poles. We experience seasons as a consequence of all this. When the northern hemisphere is maximally tilted toward the Sun, we have summer. When it is tilted away from the Sun, we have winter.
A phenomenon called the “Vernal equinox” occurs each year around the date of your birthday. The exact day of the equinox varies by a day or two from year-to-year. This year it is on March 20. The equinox is a moment when the plane of Earth’s equator is lined up with the center of the Sun and at this time of year the length of day and night are just about equal. The Vernal equinox marks the first day of spring.
Earth's rhythmic relationship to its star is only one of many unique physical characteristics that makes life possible here. But unlike other planets, or moons, or asteroids where there may also be simple forms of single-celled life, Earth has an astonishing coincidence of many special physical features that make intelligent life possible – the kind of creatures that can do things like play the cello.
So, happy birthday. I hope you have a great day on this fragile but beautiful planet that might be the only place in the universe where you could happen.
Monte