Observe means to look or see When studying in a scientific field, it usually means to look carefully.
I saw nothing. This question can be handled better by someone who was there and actually saw it.
The Cichen Itza culture had two different calendars. One has three hundred five days the other had two hundred and sixty days and when a day on both calendars came together they consider that a season.
Use of unmanned space craft eliminates the years of training needed for astronauts. It allows for missions of much longer durations, as well as increased distances beyond where humans can safely travel.