Birth charts and time zones
A local clock reading is not an absolute instant until its time zone and date are known. Historical offset and daylight-saving rules can affect the convers
A local clock reading is not an absolute instant until its time zone and date are known. Historical offset and daylight-saving rules can affect the conversion.
Understand the method
Use a named time zone appropriate to the place and date rather than assuming today's offset. At some clock changes, a local time occurs twice or does not occur at all. Those cases need an explicit choice or an error message.
Use the information carefully
Check the recorded location, local date, time and whether the source already converted to UTC. Applying a time-zone conversion twice creates a different instant.
Does the visitor's current time zone describe the birthplace?
No. A phone's current zone can be useful for today's local display but is not evidence of the zone at a historical birth location.