adjusting within a time zone

I apologize for not being able to find the threads for this! I need my memory jogged on what you do to adjust for real or local time within a zone. I don't think I'm using the correct term. But, say there was a 2-3 degree difference. (rounded) Is there a simple formula for doing this calculation?

I understand your post to mean that you want to find the Local Mean Time of a birth or an event and you only have the time given in terms of the local time zone.

The easiest way to do it is to correct for GMT and find the longitude of the place where the birth or the event took place. For example, let's take a birth in Atlanta GA, at 10:00 am today. This time is recorded in EDT, which is 4 hours behind GMT. So the birth occurred at 14:00 GMT.

Now look at the longitude of Atlanta. It's 84 degrees 23 minutes West. For each 15 degrees West of GMT, time shifts back 1 hour. So 15 degrees West = 13:00, 30 degrees West = 12:00, 45 degrees West = 11:00 etc.

84 degrees West = 5.6 hours or 5 hours 36 minutes.

Which brings us back to 08:24 which is the approximate Local Solar Mean Time of birth. I've not allowed for the further 23 minutes of arc, which is just under half a degree or a 30th of an hour = 2 minutes of time.

That brings us to a more accurate 08:22 a.m. local time.

That's a bit long winded (LOL) but in practice it's 84/15 to get the hours difference for Atlanta. Don't forget the answer comes our as a decimal fraction so the .6 part is 6/10 of an hour = 36 mins

if you take a degree as being 4 minutes of time you won't go far wrong. A degree West takes off 4 minutes from GMT, a degree East adds 4 minutes to GMT.

Now if you know the longitude where EST/EDT begins, you can simply use that as your base and adjust your time by degrees difference.

The above calculation is obviously rough and ready but it is accurate enough for virtually all practical purposes and any astrology software will carry out a more accurate calculation simply by entering the EST/EDT time of birth.

Minderwiz said:

if you take a degree as being 4 minutes of time you won't go far wrong. A degree West takes off 4 minutes from GMT, a degree East adds 4 minutes to GMT.

Now if you know the longitude where EST/EDT begins, you can simply use that as your base and adjust your time by degrees difference.

Click to expand...

Thank you! That 1 to 4 was what I should have been able to recall! So much for my cute memory trick that I thought would fixate it!

Another question to be sure I'm getting it:
Isn't each time zone's "official standard" related to a central point within itself? Or is it the nearest large city to that imaginary point? If so, wouldn't the adjustment be to the left or right of that point rather than the beginning of the zone itself?

CARDLADY22 said:

Another question to be sure I'm getting it:
Isn't each time zone's "official standard" related to a central point within itself? Or is it the nearest large city to that imaginary point? If so, wouldn't the adjustment be to the left or right of that point rather than the beginning of the zone itself?

Click to expand...

Checking up it seems that all time zones are set in relation to Univesal Time, which is identical to GMT. The bands are in 15 degree spans East or West of UT.

Any departure from this is likely to be for local convenience - a state stradling two time zones might want to keep to a unified time for the purposes of convenience in administration. Clearly where the state is so large that this becomes inconvenient the state adopts more than one time zone.

So I think you are left with using the calculations in my previous post, if you want to achieve accuracy. If someone has better information can they please post.