Mayo, Jeff - The different ways of measuring time
Type of Spiritual Experience
You think you know what time is? Read on ...............
A description of the experience
Jeff Mayo Astrology
Raphael’s Ephemeris was based on GMT until 1959. Since 1960, it has been calculated in Ephemeris Time [ET]. It is the theoretical uniform time system employed in gravitational theories of the Sun, Moon and planets, used side by side with Universal Time, especially for making predictions. ET was identical with GMT early in 1903, but the two have slowly diverged and in 1962 was 35 seconds in advance of GMT.................
Time, so far as we on Earth are concerned, exists because of and therefore depends upon, the rotations of the Earth on its axis and its revolution about the Sun. This period of the Earth’s revolution we call a year. It is a measurement between two successive vernal equinoxes, equal to 365 days 5 hours 48 minutes, 46 seconds of mean solar time. We see it as the time the Sun takes to perform a complete revolution to the First Pont of Aries. It is a natural, basic unit of time for man, who for thousands of years has recorded the recurrence of the seasons corresponding to this Earth-Sun cycle. This cycle is usually called the tropical year, or the year of the seasons [Greek TROPE = turning] ………………..
There is another kind of year. The sidereal year [Latin sidus: star] which refers to the period of a complete (apparent) revolution by the Sun, measured from its passage across a secondary to the ecliptic through some fixed star until its return to that same star. This equals 365 days, 6 hours, 9 minutes, 9.5 seconds. The sidereal year exceeds the tropical year by just over 20 minutes and this difference, expressed in degrees of celestial longitude, gives us the figure of 50.26 seconds which … is the annual displacement resulting in the Procession of the Equinoctial Pont.............
The synodic month is the period between consecutive conjunctions of the Sun-Moon as seen from the Earth, thus it combines, in fact, the Earth-Sun-Moon cycle. The more commonly used name for this period is lination. These points of conjunction are called New Moons, when the Sun and the Moon have the same longitude. When they also have the same declination (i.e. the Moon is exactly on the ecliptic and between the Earth and the Sun), there is a solar eclipse. The mean average synodic month is 29 days, 12 hours, 44 minutes, 2.7 seconds.
The sidereal month is the Moon’s period of revolution relative to the stars. The mean length of this period is 27 days, 7 hours, 43 minutes, 11.5 seconds. This is the average time the Moon takes from one star back to the same star as seen from the Earth.
The calendar month is of course the month we use in our calendar, January, February and so on.....................
The next unit of time is the week, which with its 7 days comes to us from ancient Babylonia, even the names of the days can be traced back to the planetary gods. The length of the week corresponds roughly to one of the four phases of the Sun Moon cycle or lunation..........
The fourth basic unit of time is the day. This is the period of the Earth’s rotation on its axis. It may be measured with respect to the stars (sidereal day), the true Sun (apparent Solar day) or the mean Sun (mean Solar day).
Sidereal day – is the time period of the Earth’s rotation; the interval between two successive transits of a fixed star over the meridian of any place. In actual practise, the First point of Aries is used to define the sidereal day, and the instant this Point crosses the meridian, corresponding to 0h 0m sidereal time, the sidereal day begins. Although the hours are reckoned from 0 to 24 these do not quite correspond to the length of the 24 mean solar hours. The sidereal day in mean solar units = 23 hours 56 minutes and 4.09 seconds. Thus each successive day the stars rise and set about 3 minutes 56 seconds earlier due to the difference between sidereal and mean solar days.
Greenwich mean time – was legally defined to be the mean time to which clocks throughout the world are now synchronised
Apparent solar time - When it is noon for any place on Earth, the Sun is at that moment crossing or transiting the upper meridian of that place. The sun transits a meridian twice in 24 hours. At midnight it transits the lower meridian. As our day begins at midnight, this apparent solar day is the interval between two successive passages of the Sun across the lower meridian … Because the orbit of the Earth about the sun is an ellipse, this causes the Earth to move round the sun with variable speed. The closer to the sun the faster it gets, the further from the sun the more its speed decreases. So the apparent speed of the sun as seen from the Earth varies similarly. Around 23rd December the solar day is 51 seconds longer than it is around 23rd September
Mean solar time – As there would be no sense in making clocks which kept pace with the apparent solar time, a fictitious Sun was invented and was called the ‘mean’ sun. It moves uniformly, its rate of motion is the average, throughout the year of the true Sun’s angular motion in the eliptic and this is known as the mean solar time.
The addition or subtraction to be made daily to convert apparent solar time into mean solar time is called the Equation of Time. The Equation of Time is nil on only 4 occasions in the year – about 16th April, 14th June, 1st September and 25th December.
In addition to these times we also measure time using local time, zone time and standard time, but these would not necessarily correspond to any of the times above. Zone time is used at sea, standard time on land. Not only this but we have Summer time or Daylight saving time.