THE ASTRONOMICAL CLOCK: HANDS AND FACE OF THE CLOCK.
The next description concerns the computer program Astroclock, which you can download via the Out Basket on page 1. Around the outside of the clock face we see a 24 hours-division with a subdivision of 4 quarters in an hour. The points of the compass are showed according to the old custom on sun dials. The sun- and moon symbols give the truth position of the sun and moon at the sky. On the ring with the white star symbol are the 12 constellations of the zodiac turning corresponding the time and datum showed. The line to the white star symbol gives the stellar time on the place where the lengthening of this line cuts the outside of the clock face. On the inner circle we see the division of the day in light, darkness and twilight. Where the imaginary lines of the center of the clock to the border of light and twilight cut the outside of the clock face, we find the points of sunset and sundown. The blue hand gives the normal time in summer- or wintertime. Wintertime is called daylight saving time in some countries. The common time deviates in general from the true solar time due to the division of the earth in 24 time zones. At your choice, there can be showed also for the common time a ring of light, dark and twilight in blue colors. Also there is the possibility to set on or off the letters for the constellations. The division of the months of the year in accordance with the symbols of the zodiac is given according to the age-long tradition in astronomical clocks and horoscopes. The hand for the sun gives the position of the sun in the zodiac according to the data of the Saison's.
THE SUMMERTIME AND WINTERTIME.
Before the import of the summertime we had in the Netherlands the Middle European Time (MET). This time accords to our recent wintertime. Our summertime is now named the 'Midden Europese Zomertijd' (MEZT).
In the de aviation and navigation people uses the Worldtime or Universal Time (UT), this is the mean solar time for Greenwich.
Before Worldwar II we had in the Netherlands the Amsterdam Time (AT), that is the mean solar time for Amsterdam. This is the time on a sundial in Amsterdam, corrected for the equation of time.
Worldtime = Universal Time = UT = MET - 1 hour
Middle European Time = MET = UT + 1 hour
Middle European SummerTime = MEZT = UT + 2 hour
Amsterdam's Time = AT = UT + 20 minutes
At 12 o clock Amsterdam's time, the sun reaches in the Netherlands nearby his highest position in the south. Than we have :
12h AT = 11h 40m UT = 12h 40m MET = 13h 40m MEZT
BEGIN AND END OF THE SUMMERTIME.
Recently in 1997 cool and clear rules are made for the beginning and ending of the summertime for the 15 countries of the European Union, for the next coming four years. The summertime will begin at the last Sunday in march and will end at the last Sunday in October.
Internationally there are still many differences between the diverse countries.
Therefore this computerprogram starts the summertime at 1 April and ends it at 31 October. The computer clock must manually be set on the right time and datum with the DOS-commando's TIME en DATE.
THE 24-HOURS CLOCKS FOR SOLAR TIME AND STELLAR TIME.
The solar time is based on the position of the sun and the stellar time on the position of the stars at the sky.
In fact the local solar time is the time, who a local sundial should give. The sun is positioned in the south when it is twelve o'clock local solar time.
The local stellar time is derived from the position of the stars. The stars are moving faster four minutes a day compared with sun, because the sun is moving between the stars.
THE TIME ZONES AND INTERNATIONAL DATUM LINE.
The earth is global divided in 24 time zones around each 15the meridian. The Worldtime or Universal Time (UT) is in force around the zero meridian and around the whole world.
The West European Time (WET) is in force around 0 WL (Western Longitude). The Middle European Time (MET) is in force around -15 WL. The East European Time (EET) is in force around -30 WL, etc.
The zone time is going to the east always an hour later, because the sun is risen there earlier, and going to the west always an hour earlier.
In general: Zone time = UT - WL/15 , where WL is a positive number
West of Greenwich and a negative number East of Greenwich.
Then we have: MET = UT + 1 hour and EET = UT + 2 hour
N.B. The place of the international datum line is at -180 WL = +180 WL.
THE SYMBOLS OF THE ZODIAC.
The annual orbit, who the sun describes around the skyglobe, is called the way of the sun. The constellations around this orbit are the twelve constellations of the zodiac. Each month the sun stays in an other constellation. The stars around the sun are only visible during a total darkening of the sun (eclipse). Hence the name ecliptic or way of eclipses as the official name for this way of the sun.
At each of the twelve constellations of the ecliptic (or zodiac) there belongs a sign of old. Thousands of years ago the ecliptic is divided in twelve equal parts and a symbol is given to each part. Each part occupies an arc of thirty degrees of the ecliptic. The sun enters at the beginning of the spring the symbol of Aries. In the same way the sun enters at the beginning of the autumn the symbol of Libra, now as well as five thousand years ago.
In this five thousand years the stars in the constellations of the ecliptic are moved because of the proceeding (precession) of the rotation axis of the earth.
The hand of the sun gives the position of the sun in the ecliptic according to the old symbols after the data of the Saison's and gives not the true position of the sun on the sky according to the stars of these constellations. The corresponding stars of the constellation with the same name are being found in a symbol farther away.
A way out of this confusing situation should be to assign at each symbol a next month, what should hold the breaking with a centuries old tradition and for that reason should not occur for the time being.
THE CHRISTIAN ERA.
Our calendar is based on the Julian calendar with three years of 365 days and a leap-year of 366 days. This calendar is introduced in the first century before Christ by Julius Caesar. The years were counted from the foundation of the city of Rome or from the first year of government of a certain emperor. Since the twelfth century people counts the years from the Year of the Lord or Anni Domini.
The Julian calendar is replaced in the sixteenth century by the Gregorian calendar with as extra addition, that the years of the turn of the century, not divisible by 400, disappear as leap-year. Moreover there was a moving up in the calendar with eleven days, so that the spring was beginning again on the right time.
For astronomical purposes people uses from 1582 AD the Julian Day, who begins on 1 January 4713 before Christ, and begins at midday in stead of midnight. Nowadays the Julian Day is still beloved by astronomers. Also in this computer program the data are converted to Julian Days. So at twelve o'clock Universal Time exact begins at 1 January 1996 the Julian Day number 2450084.
THE TIDES: LOW AND HIGH TIDE.
The gravitational pull of the moon causes a tidal wave on that side of the earth, where the moon is positioned and the pull is the largest. Also a sort like tidal wave originates at the opposite side of the earth, where the gravitational pull of the moon is the smallest.
Also there is a sort like gravitational pull of the sun on the water in the oceans, but much smaller than that of the moon, because the sun is positioned much farther away.
During the 24 hours turning of the earth there is always two times high tide, that is during the highest and lowest position of the moon and two times low tide in between that just named periods.
LIGHT, TWILIGHT AND DARKNESS
The period of sunlight begins by sunrise and ends by sunset.
When the sun is still under the horizon, there comes nevertheless light on the surface of the earth through breaking and diffraction of sunlight in the upper layers of the air. We call that indirect sunlight then daylight.
When the sun is less then 12 degrees beneath the horizon, we call this period of daylight officially the nautical twilight. This goes on early in the morning from nearly total darkness till full daylight by sunrise. Also early in the evening from sunset till nearly full darkness.
The computer program consists of several simulations and texts over clocks and time. The program is made for a modern MS DOS-computer with a color monitor and works also in Windows 3x, 95 and 98. The computerprogram Astroclock is a product from Drs. Jan Nentjes, The Netherlands. For remarks about the program and the texts or wishes for a next version you can turn to the author by E-mail.
This program is no shareware and may on no way be distributed without written permission of the maker. For free downloading of the Dutch or English version of this program go to the Out Basket of our Virtual Office. See, if needed, also instructions for downloading and installing.
NB. This older DOS program still works under Windows XP but not under Vista.
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