Universal Time/GMT & Birth Time

byjove

Account Closed
Hi all,

I have a question about how UT/GMT work, as I suspect the natal chart I've been using for some time may be inaccurate.

I noticed on my Astro print-out that I've entered my birth time of 12.04 noon correctly, but under Universal Time, it says 11.04am. Why? I live in Dublin, Ireland. We use the very same time as Grenwich, though we are clearly a couple of degrees west of there so that may be relevant. But surely it wouldn't merit a full 1-hour alteration?

I just discovered that there is the option upon chart creation to manually enter time settings, including UT/GMT, so why have they altered it in my chart? I just checked timeanddate.com and checked daylight savings for the year of my birth. It says that DST was not used and there was no change to UT. So should I manually override chart calculation with GMT/UT rather than automatic settings, which seems to be assuming DST?

Can anyone help me understand, or does anyone have the same problem?

Thanks for any feedback!
 
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wilsontc

Staff member
contact astro.com, to jove

jove,

You said:
byjove said:
I have a question about how UT/GMT work, as I suspect the natal chart I've been using for some time may be inaccurate.

You didn't mention the website, but if it is astro.com, send your comment to the web master. Astro.com is VERY responsive to issues such as possible time errors and will respond to your question, either explaining why the time is correct as is, or how they plan to resolve the error. If it's some other website, it's probably just their error and you should ignore it and use astro.com. You also didn't mention the date you are talking about, so there is no way for me to verify what you are saying.

Timely,

Tim
 

aquarius7000

Well-known member
I have a question about how UT/GMT work, as I suspect the natal chart I've been using for some time may be inaccurate.

I noticed on my Astro print-out that I've entered my birth time of 12.04 noon correctly, but under Universal Time, it says 11.04am. Why? I live in Dublin, Ireland. We use the very same time as Grenwich, though we are clearly a couple of degrees west of there so that may be relevant. But surely it wouldn't merit a full 1-hour alteration?
Jove,

UT or UTC (Coordinated Universal Time) = GMT (Greenwich Mean Time) = BST = British Standard Time, BUT only in Winter (between Oct and Mar).

UTC = GMT = BST + 01.00 h in Summer (due to daylight saving time).

Were you born between March and Oct?

:)AQ7
 

byjove

Account Closed
Yes, I was using Astro, but wasn't sure about naming it, in case I was wrong,
after criticizing it. And thanks for replying. I'll email them, thanks for suggesting. I was born on April 11th 1987. Just an asto-nipper, me!
 

aquarius7000

Well-known member
byjove said:
I was born on April 11th 1987.
Well, your birth month then corresponds with:
aquarius7000 said:
UTC = GMT = BST + 01.00 h in Summer (due to daylight saving time).
Were you born between March and Oct?
which thus explains:
byjove said:
I noticed on my Astro print-out that I've entered my birth time of 12.04 noon correctly, but under Universal Time, it says 11.04am.
..so you might not need to contact astro.com after all.

:)AQ7
 

wilsontc

Staff member
time is correct, to jove

jove,

aquarius said:
aquarius7000 said:
UT or UTC (Coordinated Universal Time) = GMT (Greenwich Mean Time) = BST = British Standard Time

I am also getting very confused on this, so I looked it up on the Time and Date website to check on the facts:
http://www.timeanddate.com/worldclock/timezone.html?n=78&syear=1980

It turns out "BST" does NOT = British STANDARD Time but instead BST = British SUMMER Time. GMT DOES = UTC, but GMT (and UTC) do NOT correct for any Daylight Savings Time (e.g., "summer time"). So BST = GMT (or UTC) + 1 hour. In the same way, Ireland has IST (Irish Summer Time) where IST = GMT (or UTC) + 1 hour.

So this time is correct, since you were born on IST, which equals UTC (11:04 AM) + 1 hour = 12:04 PM IST.

Lost in time,

Tim
 
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aquarius7000

Well-known member
Re: time is correct, to jove

You will still find BOTH full forms in use. The explanation is below.
BST stands for British Standard Time and British Summer Time, though now the latter is more in use, as British Standard Time ≠ GMT always (so not standard all yr round). I should have mentioned this earlier, but was more concentrated on the maths of it. However, read below.

British Standard Time as the clocks in Britain were earlier set at GMT + 01.00 h all year round (so standard all yr round).

However, when in Britain for the period between late Oct and Mar, the clocks were set back by one hour in Winter (so no + 01.00 on the GMT), so Britain's time = GMT in Winter or BST = GMT = UTC.

But, in Summer, between late Mar and Oct, Britain's time + 01.00 = GMT = UTC, as *Britain* (not UTC or GMT, as mentioned earlier) has the daylight saving time system, so the BST was automatically affected.

Thus, in order to distinguish between this period of summer when the 1 hour is added to GMT in Britain, the BST was called by many in Britain as British Summer Time (as then not standard anymore).


:)AQ7
 

byjove

Account Closed
Yikes...well I got an email reply. Two comments were made; the first was that DST was in operation, the second was that their online calculator is always correct. Why would two credible websites suggest contrary info? There could be a misunderstanding and the dialogue here is definitely useful to us all...
 

aquarius7000

Well-known member
Yes, Jove, this dialogue will certainly help at least some around. Re DST, I guessed as much the moment I read your dilemma (about that extra hr) that it has to be DST creating the confusion.

I have actually always found astro.com to be most reliable besides my own Astrology software.

Btw, I forgot to mention earlier that IST = BST.
As Wiki says:
Officially the Republic of Ireland is on UTC+1, but goes to UTC in winter, and for all practical purposes uses the same time as the United Kingdom.

So clocks in Eire move the same as in the Kingdom next door;). Thus the BST explanation is valid for you in Dublin, too.

:)AQ7
 
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RishiRahul

Well-known member
Jove,

UT or UTC (Coordinated Universal Time) = GMT (Greenwich Mean Time) = BST = British Standard Time, BUT only in Winter (between Oct and Mar).

UTC = GMT = BST + 01.00 h in Summer (due to daylight saving time).

Were you born between March and Oct?

:)AQ7

Hello Aquarius 7000,

Would you say the Universal time gets affected/changed due to changes of Summer time?

Thanks,

RishiRahul
 

JUPITERASC

Well-known member
Hello Aquarius 7000,

Would you say the Universal time gets affected/changed due to changes of Summer time?

Thanks,

RishiRahul
Sundials tell "sun time".
Clocks and watches tell "clock time".
Neither kind of time is intrinsically "better" than the other
- they are both useful and interesting for their separate purposes.

"Sun time" is anchored around the idea that when the sun reaches its highest point
(when it crosses the meridian), it is noon
and, next day, when the sun again crosses the meridian, it will be noon again.
The time which has elapsed between successive noons is sometimes more
and sometimes less than 24 hours of clock time.
In the middle months of the year, the length of the day is quite close to 24 hours
but around 1 September the days are only some 23 hours, 59 minutes and 41 seconds long
while around Christmas, the days are 24 hours and 31 seconds long.
"Clock time" is anchored around the idea that each day is exactly 24 hours long.
This is not actually true :smile:
but it is obviously much more convenient to have a "mean sun"
which takes exactly 24 hours for each day
since it means that mechanical clocks and watches, and, more recently, electronic ones
can be made to measure these exactly equal time intervals.
Obviously, these small differences in the lengths of "sun days" and "mean days"
build up to produce larger differences between "sun time" and "clock time".
These differences reach a peak of just over 14 minutes in mid-February
(when "sun time" is slow relative to "clock time")
and just over 16 minutes at the beginning of November
(when "sun time" is fast relative to "clock time").
There are also two minor peaks in mid-May
(when "sun time" is nearly 4 minutes fast)
and in late July
(when sun time is just over 6 minutes slow)
(These minor peaks have the fortunate effect, in the Northern hemisphere,
that the differences are relatively minor during most of the months
when there is a reasonable amount of sunshine).
The differences do not cumulate across the years, because "clock time" has been arranged
so that, over the course of a four year cycle including a leap year
the two kinds of time very nearly come back to the same time they started.
(The "very nearly" is because "clock time" still has to be adjusted
by not having a leap year at the turn of each century
except when the year is exactly divisible by 400
so 1900 was not a leap year, but 2000 will be).
Even with this correction, we had an extra second added to "clock time" recently.
If you want to see the actual values of sun time and clock time for your (or any other) location
Time Zone Master is free and also has plenty of astronomical data as well
http://www.sundials.co.uk/equation.htm


YEARS EARLIEST SUNSET IS NOT ON THE WINTER SOLSTICE
https://www.timeanddate.com/astronomy/equation-of-time.html




presentation-on-equation-of-time-10-638.jpg
 

IleneK

Premium Member
Hello Aquarius 7000,

Would you say the Universal time gets affected/changed due to changes of Summer time?

Thanks,

RishiRahul

Universal Time is universal and does not change with Summer time. It is constant throughout the year for ordinary timekeeping purposes.
 

RishiRahul

Well-known member
Sundials tell "sun time".
Clocks and watches tell "clock time".
Neither kind of time is intrinsically "better" than the other
- they are both useful and interesting for their separate purposes.

"Sun time" is anchored around the idea that when the sun reaches its highest point
(when it crosses the meridian), it is noon
and, next day, when the sun again crosses the meridian, it will be noon again.
The time which has elapsed between successive noons is sometimes more
and sometimes less than 24 hours of clock time.
In the middle months of the year, the length of the day is quite close to 24 hours
but around 1 September the days are only some 23 hours, 59 minutes and 41 seconds long
while around Christmas, the days are 24 hours and 31 seconds long.
"Clock time" is anchored around the idea that each day is exactly 24 hours long.
This is not actually true :smile:
but it is obviously much more convenient to have a "mean sun"
which takes exactly 24 hours for each day
since it means that mechanical clocks and watches, and, more recently, electronic ones
can be made to measure these exactly equal time intervals.
Obviously, these small differences in the lengths of "sun days" and "mean days"
build up to produce larger differences between "sun time" and "clock time".
These differences reach a peak of just over 14 minutes in mid-February
(when "sun time" is slow relative to "clock time")
and just over 16 minutes at the beginning of November
(when "sun time" is fast relative to "clock time").
There are also two minor peaks in mid-May
(when "sun time" is nearly 4 minutes fast)
and in late July
(when sun time is just over 6 minutes slow)
(These minor peaks have the fortunate effect, in the Northern hemisphere,
that the differences are relatively minor during most of the months
when there is a reasonable amount of sunshine).
The differences do not cumulate across the years, because "clock time" has been arranged
so that, over the course of a four year cycle including a leap year
the two kinds of time very nearly come back to the same time they started.
(The "very nearly" is because "clock time" still has to be adjusted
by not having a leap year at the turn of each century
except when the year is exactly divisible by 400
so 1900 was not a leap year, but 2000 will be).
Even with this correction, we had an extra second added to "clock time" recently.
If you want to see the actual values of sun time and clock time for your (or any other) location
Time Zone Master is free and also has plenty of astronomical data as well
http://www.sundials.co.uk/equation.htm


YEARS EARLIEST SUNSET IS NOT ON THE WINTER SOLSTICE
https://www.timeanddate.com/astronomy/equation-of-time.html




presentation-on-equation-of-time-10-638.jpg

Thanks!

RishiRahul
 

RishiRahul

Well-known member
Hello Aquarius 7000,

Would you say the Universal time gets affected/changed due to changes of Summer time?

Thanks,

RishiRahul


Thanks for the answer.

I have often noted that many seeking predictions, from countries adopting summer time, give their birth time to us for calculation..... while they are not aware if the given time is standard time or daylight saving time.

The above leads to calculations from an incorrect time.

UT would help to differentiate if it is summer time or standard time. Right?

RishiRahul
 
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