system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why some sunny days are hotter than others?

Why 2 consecutive days can be with great temperature differences,  given that the sun is at the same angle and botth days are sunny, clear sky, no wind? 
By great temperature differences I mean from 21 degrees Celsius onde day to 32 the next, to 39 the next next.
gpt
There are many variables that can cause temperature and weather to change (and ‘feel like’ a different temperature), much of which is interconnected, but essentially the density of the air that the sun’s heat must travel through will make it feel cooler (colder, denser air) or hotter (warmer, thinner air).