Just for fun, I will add clickable links to info on the modern scientific understanding of the phenomenon listed in the Letter to Pythocles.
Infinite worlds and how they come into being (?)
How the sun, moon, and stars came into being - three hypothesis on how the moon was formed
The size of the sun, moon, and other stars
The risings and settings of the sun, moon, and other heavenly bodies
The tropics of sun and moon [The farthest points from the equator where the Sun can appear directly overhead are referred to as the tropics?]
The wanings of the moon and its subsequent waxings, and the source of the moon's light
The impression of a face in the moon [why the same side faces Earth]
The regularity of the periods of the heavenly bodies
The successive changes in the length of nights and days [and seasons]
Signs of the weather - clouds, rain, thunder, lightening and thunderbolts, wind, cyclones, [tornado] / waterspouts, hail, snow, dew, ice, rainbows, a halo around the moon
Wandering stars [planets]