Why is ensuring precise local time or UTC crucial when using location-based charts?

Answer

The calculated longitude might place the Sun across a boundary several hours before or after your local time if the chart defaults to Universal Time (UT).

When utilizing online star charts or celestial simulators, the exact time reference is vital for accurate boundary crossing determination. Many location-based charts default to displaying positions based on Universal Time (UT) or Coordinated Universal Time (UTC). If a user checks the chart while observing from a time zone significantly ahead of or behind UT, the calculated longitude for the Sun might appear to place it within the next constellation boundary based on UT, even though, according to the user’s local time frame, the Sun will not officially cross that boundary until several hours later. Therefore, verifying whether the tool uses local time or clearly labels its UTC reference is necessary for absolute precision.

Why is ensuring precise local time or UTC crucial when using location-based charts?

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