Calculating True Local Time

Now that you understand what local time is, we're going to walk you through what the computer is going to calculate for Spielberg's local time. First of all, it's going to determine if he was born during daylight saving, war, or standard time. If he had been born during either daylight saving or war time, the computer would have subtracted one hour from his birth time. But since it was an Eastern Standard Time birth, no changes were made at this step.

Next, his birth location is Cincinnati, Ohio, which has a longitude of 84W31. This is 9 degrees, 31 minutes west of the 75W00 primary meridian. The clock time when he was born was 6:16 PM EST, but that was accurate only at the 75W00. In Cincinnati, the solar time was a little bit earlier. So the computer multiplies the difference in longitude by four minutes and gets 36 minutes and 124 seconds, which converts to 38 minutes and 4 seconds.

Since Cincinnati is west of the 75W00 meridian and it's earlier there, the computer subtracts this amount from the time of 6:16 p.m. to get 5 hours, 37 minutes, and 56 seconds as his true local time. But to keep this in a 24-hour clock system, so we don't confuse a.m. and p.m., 12 hours are added and his true local time is shown as 17 hours, 37 minutes, and 56 seconds (17:37:56). This is what the computer adds to the sidereal time shown in the midnight ephemeris, as this is the real difference in time between the start, or reference time, shown there.

If Spielberg had been born in Europe, though, calculating the true local time would be a slightly different process from what we've used, because the time there is later than in Greenwich.

So far, we have the sidereal time and the true local time, which will be added together as follows (in a 24-hour system):

Sidereal time shown in ephemeris: 5 hours

+ True local time (past midnight): 17 hours

But there are still a few minor corrections to make before the computer has the final calculated sidereal time.

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    How to find astralogical local time?
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