What is an Astronomical Clock?
955965
An astronomical clock is a clock with special mechanisms and dials to display astronomical information, such as the relative positions of the sun, moon, zodiacal constellations, and sometimes major planets.\n\nThe term is loosely used to refer to any clock that shows, in addition to the time of day, astronomical information. This could include the location of the sun and moon in the sky, the age and phase of the moon, the position of the sun on the ecliptic and the current zodiac sign, the sidereal time, and other astronomical data such as the moon's nodes (for indicating eclipses) or a rotating star map.\n\nAstronomical clocks usually represent the solar system using the geocentric model. The center of the dial is often marked with a disc or sphere representing the earth, located at the center of the solar system. The sun is often represented by a golden sphere, shown rotating around the earth once a day around a 24 hour analog dial. This view accords both with daily experience and with the philosophical world view of pre-Copernican Europe.\n\n- From http://en.wikipedia.org/wiki/Astronomical_clock
260221
They have clock kits that you can use to make a clock out of almost any thin item (CD, plate, metal sheet, etc.).  \n\nhttp://scientificsonline.com/search.asp?t=ss&ss=clock+kit&sid=yahoo&cm_mmc=yahoo-_-cpc-_-edmu-_-clockkits&OVRAW=clock%20kits&OVKEY=clock%20kit&OVMTC=standard&bhcd2=1142905545
435328
Wow.  Too many questions.\nThe first one is answered by an analemna - it's the figure 8 diagram printed on many globes that gives the amount of time that the sun is "fast" or "slow" (by a sundial) compared to a watch.
1153026
It is a means of measurement of events that are taking place around us.   Think  of the days when people have relied on shadows produced by sun to be a measure of time.  They only understood that day and night repeat.  When the earth rotation of sun was understood, what we now term as 24 hrs a day came into being.  The past also was surmised to be at this time as Roman, mayan civilisation etc.,   hence wthout time the relative intervals of events cannot be placed and with new scientific inventions we are able to pin point happenings to part of seconds also.\nThe various calendars that have been made at different parts of the world also have taken events that have taken place as the basis or zero.   When scientific inventions result in exact no of rotations of earth that have taken place or earth got formed from the Sun, then that can be a basis and a new unit can be had for a fourth dimension.\nRamachandran V.
731930
If you have a compass measure the angle between the position of the sun and south.  Divide this by 15 (from 180 deg divided by 12hrs) to get hours before/after midday.  If the measured angle is greater than 180 (e.g. after midday) then add your hours to 12, if the angle is lower than 180 (i.e. before midday) then subtract you angle from 12 to get the time. this time will be in GMT (or universal time) so if you are somewhere that is using +1hrs (eg BST) then add that on afterwards. Alternatively without a compass you can eyeball it have guess where the sun is relative to the south.   Sunrise and sunset positions change throughout the year and are still related to time. \nAt night time you have to know the stars and the correct rising and setting times for the particular time of the year.  They all revolve around the north star.  One way to do it is to pick a constellation that you know - like Orion - the website link at the end say that in the UK this is at it's highest point in the sky at about midnight at this time of year, and it travels from east to west, so you can estimate the time based on it's height.\n\nIf it's cloudy you're stuffed.
843015
Biological clock. Read the article linked below about a very interesting experiment in human chronobiology.\n\nWK
8760
None, the two are not related. Earth's rotation is a measure of time and light years are a measure of distance.
351868
Time Dilation: Time dilation is a consequence of Albert Einstein's theories of relativity. It occurs when one observer finds a clock which is measuring proper time ticking slow with respect to the relative time defined by his own clock (which is also measuring proper time). In special relativity, this occurs for clocks which are moving with respect to an inertial observer. In general relativity this occurs for clocks at lower potentials in a gravitational field, and is called gravitational time dilation.
299849
The 24 hour clock was originally devised by the ancient civilisations of Egypt, India and China. It has stuck ever since.\n\nIt actually takes the Earth 23 hours, 56 minutes and 4 seconds to rotate 360 degrees. The reason for the extra 4 minutes or so it that the earth has to rotate just that little bit more (361 degrees) because it has orbited the sun a little during that period.
470281
The History of Analog Clocks (SEE FIRST LINK BELOW) provides an explanation of the origin of the 24-hour day. The system dates back 4,000 years, to ancient Egypt and Babylon. \n\nEgyptian astronomers divided the night hours into 12 distinct sets of star patterns, which emerged over the horizon at roughly hour-long intervals. They divided the day into 12 hours to match, and because they lived near the equator, the days and nights were of roughly equal length throughout the year. \n\nThroughout the rest of the world, the 12 "hours" of the day and night were flexible depending upon the season. It wasn't until the 13th century A.D. that an Arab scientist named Abul-Hassan suggested the idea of clearly defined hours. \n\nIt's also worth noting that the number 12 is special in many cultures. For example, Egyptians counted in base 12. Dividing the day into two sets of 12 was a simple and elegant way of condensing the annual calendar into a day. \n\n*Repost*
100345
go to http://www.howstuffworks.com/clock.htm and it will tell you everything you need to know.
394821
what is this?  this is not a question about astronomy.\n\nhttp://en.wikipedia.org/wiki/Astronomy
913486
Actually a good many countries around the world use the 24 hour clock system. Then there isn't a need to say AM or PM, you know whether its day or night. Also the military begins attacks, movements and such on Greenwich mean time, its a town in Britain. And its used so everyone that aware of an operation knows what time it begins regardless of what part of the world they are in.
975517
Every time zone is 1 hour apart\nbecause the earth is round
1107632
There's Greenwich Mean Time, which was measured from the 0 degree meridian in Greenwich, UTC (Universal Time co-ordinate) which is measured from an atomic clock in france somewhere (UTC doesn't have summer time, GMT does) and there's standard time which works on the premise that 1 rotation of the earth is 24 hrs, so 360 degrees in 24 hrs = 15 degrees every hour, so every 15 degrees of longitude is 1 hr of time difference
504809
The astronomical unit (AU or au or a.u. or sometimes ua) is a unit of length. It is approximately equal to the mean distance between Earth and Sun. The currently accepted value of the AU is 149 597 870 691 ± 30 metres (about 150 million kilometres or 93 million miles).
147453
An essay? You have to write an essay for school and you want someone to write an essay for you? What on earth? \n\nWhy don't you look on the web and do your own research? What is wrong with you? \n\n\nI will give you a little bit to get you started. \n\n1. There is a HUGE amount of documentation for water clocks during the time of the Greeks and Romans. \n\n2. For millenia, the movement of the stars and other celestial bodies was used for time keeping. Look at stonehenge and the Mayan calendars for examples of ancient uses of astronomy for time keeping. \n \n\n3. Springs and gears are another mechanism that came later (I think the spring is called an escapement mechanism).\n\n4. You should check out the device called the antikythera  mechanism, which might have been some sort of clock.\n\n4. There were atomic clocks developed after atomic physics was discovered. \n\n6. Quart crystals made accurate and cheap wrist watches available. \n\n\n7. The pendulum of course was well-known. I think it was Galileo that timed it with his own pulse and realized that a pendulum was regular.\n \nThere is a lot more to this subject. Look on the internet. Go to wikipedia.