I was just wondering what units I could scale down to (or or shouldn't) for working out values like Local Solar Times, or Local Time etc...

From the papers I'm looking at, I can't see any mention of SI's or ISO's so I'm a little lost as to what to use as a reference.




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In a time, the word "standard" normally means the civil time, recognized by the government in the place of interest. I'm not sure about other countries, but in general conversation in the USA, "standard" also means that daylight saving time is not in effect. "Daylight" time (as in "Eastern Daylight Time") means the civil time, recognized by the government, and daylight saving time is in effect.

These can be expressed in the ISO 8601 format; the standard gives the example "15:27:46+01:00" meaning the time zone is one hour ahead of (east of) Greenwich.

In astronomy, time can also be the local time of the observer, ignoring the existence of time zones. This is local mean time, and is obtained from Universal Time by adjusting for the longitude of the observer. Usually the exact form of Universal Time that would be used would be UT1.

Local apparent solar time is based on the actual position of the sun; it is the time given by a sundial. It can be about 15 minutes ahead of or behind local mean time.

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    $\begingroup$ What degree of accuracy should I hone down to (the depth doesn't matter) but to the nearest hour, minute, second, ms? The reason I ask is that the LSTM equation I have is: LSTM = 15° * ΔGMT(Time).. Going by this, it appears to be the nearest hour, but 15 degrees is a huge chunk of space when you think of your position on the earth... $\endgroup$ Commented Mar 10, 2016 at 0:12
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    $\begingroup$ The equation LSTM = 15° * ΔGMT(Time) seems designed to answer the question "on what meridian is the local mean solar time the same as the legal civil time in my area?" So you take the difference between what is often called GMT, but is really UTC, and local legal civil time. This is usually an even number of hours, although sometimes it may be a multiple of 30 minutes or 15 minutes. You plug the time difference into the formula and get your meridian. If you time ls behind UTC, it is west longitude; if your time is ahead of UTC, it is east longitude. Accuracy 1 second of time. $\endgroup$ Commented Mar 10, 2016 at 12:51
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    $\begingroup$ Just to follow up, when I was looking at this, I came across the Time Correction Factor, 4(LSTM - Longitude) + EoT which plugged in nicely to my context e.g. Local Solar Time :) $\endgroup$ Commented Aug 30, 2016 at 16:45
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    $\begingroup$ For anyone else interested, I found the above from: pvcdrom.pveducation.org/SUNLIGHT/SOLART.HTM $\endgroup$ Commented Aug 30, 2016 at 16:45
  • $\begingroup$ The page cited above is now located at: pveducation.org/pvcdrom/2-properties-sunlight/solar-time $\endgroup$ Commented Feb 25, 2017 at 17:15

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