#TruthBeTold #time #day #solstice #astronomy #sidereal #ISS #relativity
The truth is...
A day is 24 hours long, plus or minus about 20-30 seconds. However, during the winter the days get longer. At the winter solstice the days are the shortest.
But the southern hemisphere is different. In the southern hemisphere the days are nearly always 24 hours (+/- about half a minute).
And on the equator it gets really weird, because a sidereal day on the equator is only about 23 hours, 56 minutes year-round. And at the north and south poles, occasional the day is a second longer (leap second), due to climate change, among other reasons.
In space, astronauts experience time differently because they are in an area of lower gravity due to general relativity. For example, the International Space Station experiences 16 sunrises and sunsets per Earth day.
In areas where there is daylight saving time, on the day those areas enter daylight saving time the day is 23 hours, and when it switches back to standard time it’s 25 hours. These short and long days only occur in the areas where there is daylight saving time which you’d think would cause massive geological strain on the Earth’s crust and upper mantle, but for some reason it doesn’t.
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#TruthBeTold = A statement that is logically or literally true (or partly true), but seems to imply something that isn’t true or is just plain weird. (for rhetoric, logic or propaganda studies… or just for fun)
(public domain image from Mediawiki Commons)
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@Pat Truth be told, I saw a calculation of time dilation from the constant speed of the ISS relative to the surface of earth's equator vs. the time dilation from gravity at sea level. I can't do the math, however the calculations would show the effects nearly (but of course not completely) cancel one another out.
The upshot is that I would not want to pin too much of importance on the difference unless I had someone like @/planet4589@mastodon.social account for all relevance effects and handle the math.
The effects from gravity are usually more than the effects from Special Relativity for stuff in space, but the ISS is only about 250 miles up so the gravitational field is not much different at that height. The GPS satellites are in Medium Earth Orbit which is high enough so that the gravity component dominates -- their clocks advance 38us per day compared to Earth clocks.
@Pat Cool! And thank you for checking into that. The math is *WAY* beyond my toolkit, and the topic is WAY the hell out of my professional life. I certainly wouldn't dare dispute it, but I grasp conceptually that both forms of acceleration would have to be accounted for, and how much depends upon what orbit is used.
So *I* don't know, but I'm quite happy *YOU* do and have the mathematical grasp to put numbers to it. :D
No, I definitely don't have the math skills, I just know how to use google. 
I think special relativity is relatively easy (pun intended), it's just algebra and trig., but GR uses much more exotic math. Apparently Einstein had to consult with a mathematician to learn Riemannian geometry and differential geometry in order to figure out his field equations.
