Comment by graemep
3 days ago
We have GMT for standardised solar time. I assume there were good reasons for moving to UTC? Either is fine for many purposes.
3 days ago
We have GMT for standardised solar time. I assume there were good reasons for moving to UTC? Either is fine for many purposes.
So, the thing you probably want for "standardized solar time" is named UT1, there are a bunch of complicated technical details here, which do not matter, but ultimately UT0 and UT2 are not relevant to normal people, UT1 is a hypothetical solar time, estimated by observatories, and UTC is the world's civil time, now fixed to TAI plus 37 seconds.
GMT (Grenwich Mean Time) is a legacy from when Britain (and thus Grenwich, an observatory in London, England) was more important. These days GMT, even in British legislation, just means UTC. When we say "In the winter we use GMT not BST" we're not switching to or from some archaic time system, GMT is just defined as UTC+0 and BST is defined as UTC+1 the same way summer time zones work in several others places which have them.
GP wanted solar time, so that would be old style GMT, which would be now UT1, right?
UT1 is what you'd actually use if you specifically want solar time today, yes.
I'm just highlighting that in most places when it says "GMT" it does not mean solar time, just like how "New Street Station" in Birmingham is not in fact a New Station, or on a New Street, it's a station which was close enough to the road in Birmingham named "New Street" that it's forever associated.
When actual Grenwich Mean Time was "still a thing" astronomers would use it for solar time because we had no better approximations. Today the IERS looks at very distant objects in the sky. We know that in some sense (relative to us) these are not moving because they're incredibly far away, and so we can use them to measure rotation. And then we adjust for where the Sun is from that data.