alt Hacker NewsTime is a mess. Always. The author only scratched the surface on all the issues. Even if we exclude the time dilation of relativity which affects GPS/GNSS satellites - independent of if it is due to difference in gravitational pull or their relative speed over ground, it's still a mess.
Timezones; sure. But what about before timezones got into use? Or even halfway through - which timezone, considering Königsberg used CET when it was part of Germany, but switched to EET after it became Russian. There's even countries that have timezones differenting by 15 minutes.
And dont get me started on daylight savings time. There's been at least one instance where DST was - and was not - in use in Lebanon - at the same time! Good luck booking an appointment...
Not to mention the transition from Julian calendar to Gregorian, which took place over many, many years - different by different countries - as defined by the country borders at that time...
We've even had countries that forgot to insert a leap day in certain years, causing March 1 to occur on different days altogether for a couple of years.
Time is a mess. Is, and aways have been, and always will be.
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It is, there are a couple of timezones where not only there is a hour difference, but even a 30 and 45 minutes difference. India is UTC +5:30, and Lord Howe Island is UTC +10:30 / +11:00 and New Zealand, Chatham Islands is UTC +12:45 / +13:45, Iran is UTC +3:30 / +4:30 and so on. Where the format is X / Y, that means X is Standard Time, and Y is Daylight time.
Messy.
I think the full list can be found here: https://www.timeanddate.com/time/time-zones-interesting.html
You can use a Bash script that can give you an exhaustive list based on files from /usr/share/zoneinfo/, i.e. find timezones with non-whole hour offsets.
Author covers how IANA handles Königsberg, it is logically its own timezone.
An IANA timezone uniquely refers to the set of regions that not only share the same current rules and projected future rules for civil time, but also share the same history of civil time since 1970-01-01 00:00+0. In other words, this definition is more restrictive about which regions can be grouped under a single IANA timezone, because if a given region changed its civil time rules at any point since 1970 in a a way that deviates from the history of civil time for other regions, then that region can't be grouped with the others
Even worse, there are some areas where the timezone depends on your religion. Lebanon had "Muslim time" and "Christian time" at one point (Unsure if that's still a thing)
Yep. Fortunately, a lot of apps can get by with just local civil time and an OS-set timezone. It’s much less common that they need to worry about leap seconds, etc. And many also don’t care about millisecond granularity, etc. If your app does care about all that, however, things become a mess quite quickly.
The worst is probably Marocco DST
https://en.wikipedia.org/wiki/Daylight_saving_time_in_Morocc...
Calculating Ramadan is something software packages most likely won't do. To get the visibility of the moon correct, I think you have to know the exact location - and maybe check, if there is a mountain obstructing the view.