here it comes, here it goes. Today I will write about the strange shape of Moon which is actually pretty normal and you probably saw it some day, of course I mean that the strange thing is that it is “turned” by 90° degrees. I saw it yesterday/today during flight from Rio de Janeiro to London. It was very difficult for me to imagine the position of Moon, Earth and Sun to create this. But today I have downloaded Stellarium which seems to be pretty awesome and now it is clear to me so I will try to explain it.
Fine, the problem is the rotational axis of Earth. It is tilted by over 20°. This means that when you are standing on equator you are moving by a huge distance up and down like on rail coaster during day and night (this changes your point of view on the Moon so the lighted part seems to change). When you are far away from equator you are not moving that much. Parallel are not so long, the difference is less and less and when you get on pole it is not moving at ALL! By this move I mean rotating of the part of lighted Moon through its journey since from our point of view Moon seems to be lighted from different sides throughout the day.
Well it was kind of hard for me to find the right words but you can always ask in the comments.
Source of 1st picture: https://10minuteastronomy.wordpress.com/category/sky-motions/