4 ms·

Solar time doesn't involve different lengths of seconds. The length of day and all the pieces doesn't change. Local solar time is effectively time zone on longi

Solar time doesn't involve different lengths of seconds. The length of day and all the pieces doesn't change. Local solar time is effectively time zone on longitude. It is mean solar time. The downside of solar time is that 1 minute of time is 15 arc minutes which is roughly 17 mi east west. Which means need to deal with time zones in same metro area. The railroads invented time zones because dealing with local solar time was a pain. Minute accuracy is needed for time tables. We might be able to do it with computers, but it would require knowing the location of everything.

zzo38computer 1y ago
When the minute accuracy is needed between different places, that is when UTC would be used. It is helpful for travel, and for many other purposes. For local stuff that does not involve precise measurement of timing, you can use solar time (and you can use a sundial), and you can do by the sun light (even, in summer it is more light and in winter it is dark early, you can use that, e.g. to go outside when it is light and don't need to turn on light inside, and in night time is dark you can sleep), and by the moon light (less commonly, but sometimes it is also meaningful and useful). Even for things that do use precise measurement of timing, UTC is not always appropriate; for some uses you will use TAI, or SI seconds instead of UTC seconds.
- layer8 1y ago
  UTC seconds are the same as SI seconds. Or rather, there is no defined term "UTC second". You may be thinking of seconds-since-epoch counts that don’t include leap seconds, like in POSIX timestamps. That's not UTC though. UTC is a naming scheme for points in time, not a prescription for how to count seconds. What's true is that the exact number of seconds between future UTC times isn't known, because leap seconds aren't known arbitrarily in advance. But that doesn’t usually affect measurements of time. It does affect adding (large) SI-second counts to the current time to compute a future time. The exact UTC designation of that future time may not be known in advance.
layer8 1y ago
Okay, that's mean solar time then, not actual (apparent) solar time.

zzo38computer 1y ago

When the minute accuracy is needed between different places, that is when UTC would be used. It is helpful for travel, and for many other purposes. For local stuff that does not involve precise measurement of timing, you can use solar time (and you can use a sundial), and you can do by the sun light (even, in summer it is more light and in winter it is dark early, you can use that, e.g. to go outside when it is light and don't need to turn on light inside, and in night time is dark you can sleep), and by the moon light (less commonly, but sometimes it is also meaningful and useful). Even for things that do use precise measurement of timing, UTC is not always appropriate; for some uses you will use TAI, or SI seconds instead of UTC seconds.

layer8 1y ago
UTC seconds are the same as SI seconds. Or rather, there is no defined term "UTC second". You may be thinking of seconds-since-epoch counts that don’t include leap seconds, like in POSIX timestamps. That's not UTC though. UTC is a naming scheme for points in time, not a prescription for how to count seconds. What's true is that the exact number of seconds between future UTC times isn't known, because leap seconds aren't known arbitrarily in advance. But that doesn’t usually affect measurements of time. It does affect adding (large) SI-second counts to the current time to compute a future time. The exact UTC designation of that future time may not be known in advance.

layer8 1y ago

Okay, that's mean solar time then, not actual (apparent) solar time.