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Greenwich Mean Time
 
"Universal Time" is the current term for what was commonly referred to as Greenwich Mean Time (GMT). Zero (0) hours UTC is midnight in Greenwich England, which lies on the zero longitudinal meridian. (The standard of UT replaced GMT in 1926 because too many different definitions of GMT were in use.)
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Thanks. We're planning for the Mercury transit on Monday...

Alicante is 1 hour ahead of London, so Alicante is UT? IOW the times I see as UT on the transit diagrams e.g. this one, are Alicante local time?

Sorry, plain English to the rescue. I'm being yelled at in several different languages!

Edited by alacant

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UT, of course, is not UTC - UT1 is an Earth rotation based time standard, UTC is a coordinated standard based on atomic clocks. GMT generally refers to UTC.

Your timing for the purposes of the transit, though, could use any or either and be close enough 🙂 there have only been 27 leap seconds so at worst you'd be 30 seconds out.

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54 minutes ago, alacant said:

Thanks. We're planning for the Mercury transit on Monday...

Alicante is 1 hour ahead of London, so Alicante is UT? IOW the times I see as UT on the transit diagrams e.g. this one, are Alicante local time?

Sorry, plain English to the rescue. I'm being yelled at in several different languages!

London is currently on GMT (or UT), Summer Time or Daylight Saving Time having finished on 27 October, so Alicante is 1 hour ahead of UT, when on Daylight Saving Time, Alicante would be 2 hours ahead of UT. 

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&title=Is%20UT%20the%20same%20as%20GMT?%

So in this diagram, for Alicante, I must add 1 hour to the times shown?

TIA

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2 minutes ago, alacant said:

So in this diagram, for Alicante, I must add 1 hour to the times shown?

 

Yes, that's correct.

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Almost on topic. My observatory computer with Win10 operating system is left on GMT with summertime (daylight saving time) disabled.
It saves a lot of confusion 😕 about the timing of astro events!

David.

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