Astro-Databank:Handbook chapter 14
14. Time Changes
The standard reference work of the AstroDatabank is the ACS full electronic atlas, along with the ACS American Atlas and the International Atlas books. When a location and time signature are not found in the full electronic atlas they are researched with the Rand Mc-Nally Atlas or other sources. We are constantly digging up more information about date and time changes in history around the world. We urge you to not rely on anything but the latest printing of reference books or the information may not be the most accurate. The electronic atlas is the most up-to-date.
There are, nonetheless, deviations from the Atlas: The ACS Atlas lists all of England as going on GMT in 1848. However, prior to 1855, the following communities were still observing LMT: Cambridge, Colchester, Harwich, Ipswich, Norwich and Yarmouth to the east and Bath, Bristol, Dorchester, Exeter, Falmouth, Launceston, Oxford and Portsmouth to the west.
During the reign of George V, from 1910-1936, the clocks at Sandringham were always kept half an hour fast to keep his majesty on time for functions. During this period, Sandringham time was a time standard used in that location (not given in the ACS Atlas). George V's son, Edward VIII, abolished this practice when he took the throne in 1936.
Astronomical Time counts from noon of one day to noon of the next.
Civil Time counts from midnight of one day to midnight of the next.
LAT (Local Apparent Time /or Sundial time) is the apparent time of day indicated by the hour angle of the Sun or by a Sundial.
LMT (Local Mean Time) is mean solar time reckoned from mean noon on a local meridian time based on the motion of the Sun were it to move uniformly along the celestial equator at a constant rate of motion.
GMT Greenwich Mean Time is mean solar time reckoned from mean noon on the meridian of Greenwich. Astrologers uniformly refer to GMT as our reference point at Greenwich even though ephemeredes have been calculated on U.T. (Civil time) since 1930. In 1884, at the International Meridian Conference held in Washington, DC, representatives from 26 countries voted to make the common practice official. They declared the Greenwich meridian the prime meridian of the world. (The French, however, continued to recognize their Paris Observatory meridian as the starting point for another 27 years, until 1911.)
U.T. (Universal Time, the same as Civil Time) is always reckoned from Greenwich midnight. There are four types of UT: first UTO (UTZero), which is UT as determined by actual astronomical observations at a particular observatory and thus affected by the tilt of the earth's rotational axis in relation to the surface of the earth. UTO corrected for this effect gives UTI. UTI is a measure of the true angular orientation of the earth in space. But, since the earth does not spin at an even rate, UTI is not constant. So, in order to derive a more uniform time scale, UT2 was established. UT2 adjusts for the uneven spin of the earth, but is still subject to tidal friction and inner core momentum, so it still is not a constant unit of measure.
UTC (Coordinated Universal Time) is the end result, at present; the use of Atomic Time which is based upon the constant frequency of radio emission from cesium atoms when they move from one energy state to another. Atomic Time is expressed by the unit of time known as the Atomic Second, which is kept within 0.9 seconds of UTI. From 1972, U.S. Geological Survey monitored earth changes by the atomic clock.
WET Western European Time is another term for GMT. It may be misleading when the location of the data is east of Greenwich. Standard Time is the mean solar time of a longitudinal meridian that is a multiple of 15, one for each of the 24 hours around the earth.
The Equation of Time is the difference between mean time and sundial time; the difference between clocks set according to Local Mean Time and according to Local Apparent Time (sundial). Prior to the invention of the telegraph in 1844, mean time was hard to come by, so most clocks were adjusted to keep Local Apparent Time. Go into the yard and get the time off the sundial, then set the clock to the same time. When there was no radio and no telegraph, people used sundials. Mean time came into use sometime between 1780 and 1845 in most places. The Equation of Time Table facilitates the conversion the LAT to LMT.
For an arbitrary date of when time standards were changed from LAT to LMT, we may choose 1834, as this is when the planetary computations in the Nautical Almanac were switched from GAT (Greenwich Apparent Time) to GMT (Greenwich Mean Time). This is when time zones were instituted world wide, and this is when Greenwich was established as the world prime meridian. However it was as difficult then to educate the nations and convince them to agreement as it is today.
Inasmuch as there is no standard date or location, the transition is extremely vague. For example, a New Jersey newspaper clipping in 1838 mentions that most people in Bridgeton still use LAT. There is some evidence that Philadelphia went onto LMT in 1834. LMT replaced LAT in London as of 1792. When King George III installed good clocks on post roads in 1797 and 1798, it probably furthered the spread of LMT. In Great Britain, LMT continued to be the legal time until December 6, 1848, when it was replaced by GMT. Most sources say that GMT became legal in 1880 but this appears to have been merely an extension of the law to cover all acts of parliament. Whenever time standards changed, the rural areas always adopted slowly, trailing behind for years or even decades.
The transition from Sun Time to Mean Time occurred in Geneva in 1780; England, 1792; Berlin, 1810; and Paris, 1816. It was not until 1918 did an act of Congress legalize Standard Time throughout the U.S., although 85% of locations with a population over 10,000 had adopted Railroad Time by 1884. When trains began to travel across the country, uniform schedules were needed so time zones were established.
There were exceptions: Detroit, on the border between Eastern and Central time zones, continued to keep local time until 1900. That year, the city council began a debate that lasted until 1905 when Central replaced the different time systems used in different districts. In May, 1915, an ordinance changed this to Eastern time zone.
During World War I, the first Daylight Savings time was implemented for the purpose of power conservation, to provide more daylight hours for the working man to use less electricity. Since then, state and world changes from standard to daylight have been a morass of confusion for astrologers with standards that were poorly observed and in cases, not even recorded. In 1996 the whole European Union changed Daylight time to begin in October, but inasmuch as observation is not uniform, it only leaves us with another unstable reference.
Clocks. Predecessors of the clock were the sundial, the hourglass, and the clepsydra. The first heavy and bulky weight-driven clocks may have been built in the 9th century. Therefore, in the charts of royalty during the middle ages, it is quite possible that they had time keeping devices that were more sophisticated than the sundial and even capable of giving time to the minute. The introduction of the coiled spring, circa 1500, made possible the construction of smaller, lighter-weight clocks. The Dutch scientist Christiaan Huygens invented a pendulum clock, probably the first, in 1656 or 1657. However the pendulum clock would not work on a ship so a gearing system needed to be devised that was mechanically uniform. Good clocks were widespread in the late 1600s and 1700s, good enough for navigation at sea. Electric clocks were first made in the late 19th century, quartz clocks were invented c. 1929, and an atomic clock was constructed in 1948.
LAT (Local Actual Time) to LMT (Local Mean Time) Corrections LMT was not used before the late 1700s, when mechanical clocks became accurate enough for precision. Any time before then would have been LAT, requiring an equation of time adjustment to produce LMT. The oversimplification of labeling all times as LMT before zones were designated is a known shortcoming of the PC atlas. (Mark Pottenger, mid-1999)
All LAT data in the AstroDatabank has been converted to LMT for ease in chart casting. When the reference (secondary source, not birth records) gives LMT, it is often not clear if the source document was recorded in LMT or the reference document had been converted to LMT. If there is no designation of LAT or LMT, and the reference has a general time (such as "afternoon," "four hours into the day," "after vespers," "before noune," we assume that the reference time has already been converted to an LMT time and leave it as such. It would not improve the accuracy of a general time at any event. Whenever LAT (sundial time) is given to the minute, it has obviously been rectified, so it would further alter the data to add another correction.
Note on Russian Data Farida Assadullina of Russia has confirmed that the USSR went on Daylight Savings time in 1930 and did not leave Daylight standard until Perestroika (1986), when the time standards became extremely complicated from one region to the next. From then, Daylight Savings began at different times each year.