The Question Let's try this again. Again. One concise question: "What significant and regular calendar-worthy events would either nomadic or stationary humans perceive on a distant future Earth that (long ago) stopped spinning about its axis (but is otherwise identical to our current Earth)?"
I cannot stress this enough but the following is not asking a different question, only providing examples of helpful answers: I am specifically interested in understanding how astronomy events would be changed because of Earth's lack of axial-spin (moon, stars, other planets, etc) and how significant and regular weather patterns would form on the planet (seasons, season length, temperature, precipitation, storms, etc).
Assumptions Please assume the following
- The lack of Earth's spin eliminated our equatorial bulge, flooding the oceans to North and South, creating a large North Ocean and a large South Ocean and one planet-spanning mega-continent along the equator.
- The lack of spin created 6 (current) months of "day" and 6 (current) months of "night". There will be two twilight periods in between: dawn and dusk. I do not know how long they will be (but would like to <-- mods, not asking a new question). This is NOT a tidally-locked scenario, so please don't direct me to those sources or talk about the planet's "day" side and "night" side.
- Assume humans have found ways to survive the temperature, storms, radiation, and agricultural difficulties. I'm not asking how they survive but what they will experience by surviving in this situation.
- Assume there are 3 human populations experiencing this situation: (1) those that stay at a fixed location somewhere along the equatorial mega-continent, (2) those that travel along the dawn twilight band, (3) those that travel along the dusk twilight band.
Relevance to others The guys says to add this. These answers will help anyone working in the same no-axial spin scenario I am or anyone working in a scenario that has disturbed the Earth's axial rotation speed or anyone working on a scenario that requires an understanding of the climate or astronomical effects of Earth's axial spin.
Conclusions so far Feel free to correct any of the below if you think otherwise.
- Stars. For the fixed-location humans, they would always see the same stars. For the nomadic-humans, they would see new stars as they travelled around the Earht.
- Sun. The sun will be above the horizon 50% of the time, but sunlight will appear more than 50% of the time (atmospheric diffraction). . Moon. With no axial spin we will see the moon less often. Rather than seeing it once every 24 hours (due to our spin) we will see it based on its orbital period of 27 days. As it will be out of view for approx half that, we would see it for 13.5 days at a time. During that period, it would go through its normal phases because our axial tilt hasn't changed. (Really unsure about the moon, but this is what I got so far).
- Wind. There will be a very strong wind going night side to day side (at both sunrise and sunset) on the planet's surface. At some elevation (don't know where) the opposite would be true; i.e., a very strong wind going day to night side (at both sunrise and sunset).
- Flooding. Sunrise/dawn will create significant flooding. Small creeks will thaw before big rivers/oceans, so water will flood all over.
- Mega-Storm. At noon (and some degrees to either side), there will be a mega thunderstorm.