"The alternations of night and day grew slower and slower, and so did the passage of the sun across the sky, until they seemed to stretch through centuries. At last a steady twilight brooded over the earth, a twilight only broken now and then when a comet glared across the darkling sky. The band of light that had indicated the sun had long since disappeared; for the sun had ceased to set—it simply rose and fell in the west, and grew ever broader and more red. All trace of the moon had vanished. The circling of the stars, growing slower and slower, had given place to creeping points of light. At last, some time before I stopped, the sun, red and very large, halted motionless upon the horizon, a vast dome glowing with a dull heat, and now and then suffering a momentary extinction. At one time it had for a little while glowed more brilliantly again, but it speedily reverted to its sullen red-heat. I perceived by this slowing down of its rising and setting that the work of the tidal drag was done. The earth had come to rest with one face to the sun, even as in our own time the moon faces the earth."
It would eventually become tidally locked with the moon, with the day becoming equal in length to the lunar month. But the sun is going to turn into a red giant before that can happen.
Venus still rotates. It rotates on it's axis very slowly, every 243 earth days, and goes around the sun every 224 earth days. Its direction of rotation is opposite ours, so when combined with the orbit you get a sunrise every 117 earth days.
Mercury is weird. It is tidally locked, but not like our moon. Mercury rotates around its axis three times for every two orbits. (Which I just learned while writing this comment because as a child my books told me it had a permanent sunward side.)
The discovery of Mercury’s 3:2 orbital resonance is apparently quite recent, coming from the 60s or so. Apparently this was because of a coincidence in Mercury’s synodic period with Earth being twice its rotation period, making it look like it had the same face towards the Sun all the time.
Once rotation gets slow enough, the orbital period becomes an important factor in further change.
On its face, it is surprising that rotational direction can change, but rotational momentum is conserved not by individual bodies, but by the whole, interacting system, subject also to conservation of energy. So, momentum and energy trade around between bodies in complicated ways.
I think you have it backwards. Days are getting longer. So assuming tidal lock with Sun in the future which means 1 year = 1 day (1 revolution per year). So how long until 1 day becomes 365 days long. Assuming the 30min per 70M years is linear, this would take 1.2 Trillion years.
Somebody double check this please. ;) Also, the Sun will only last for another 4B years.
