I know the days get shorter every winter. That’s not my question.
My question is this:
My father has been keeping track of when the sun sets each evening for many years. And the last couple of years the sun sets earlier than it used to.
In the past, the earliest time of the year when the sun would go down behind the mountains was around 1 PM in the afternoon. This would happen around Christmas.
But at some point in recent years, this changed. Now the sun already sets behind the mountains at 1 PM at the end of November. Which means that around Christmas, the sun sets noticeably earlier than it used to.
I don’t keep track of this, but I think he’s right.
So how is that possible?
I am not an astronomer by any means but I am a curious person. Can we do a thought experiment here?
Let’s assume that OP’s father has been making observations for several decades from a fixed location and height each time. He also faces due west at the same time of day and even has accounted for daylight savings time. The mountain peaks have always been rocky without any trees or vegetation and there have been no changes to the geology of the land at the point of observation or the land between and including the mountain.
If all of the above is true (and anything that I may have overlooked) what astrological change(s) would have to take place in order for the sun to set earlier than in previous years? Would it be a change in the tilt of the earth, the distance from the sun, or something entirely different?
Easy answer? The fact that a solar day isn’t actually 24 full hours, it’s 23.9 hours. Leap years account for this, but imperfectly - so much so that centenary years not divisible by 400 are non-leap years to adjust in the opposite direction of a leap year. Theoretically (unmedicated, top-of-my-head math) over the course of 20 years the 1pm sunset could shift forward by a month, since human timekeeping is our static perception of time rather than the actual solar day starting and ending; night and day aren’t actually flipping, the clock and calendar are because they’re not perfect, so because we adhere to those and not sunrise/sunset it seems like the sunset is “wandering.”