For an explanation, see the main splats page
SPLATS about time measurement
The principles of time measurement
- A sundial can be accurate, within limits such as fuzziness of the shadow, variations in day length, and the annual 'equation of time' which must be allowed for.
- Slow-burning candles, protected from draughts, can be used as clocks at night and on cloudy days, and have been used since the days of the Anglo-Saxons.
- The Julian calendar was used until the Gregorian calendar was adopted: the Julian calendar was well out of synchronization with the seasons by that time.
- Christiaan Huygens invented the pendulum clock around 1655, and patented it in June 1657, introducing a new standard and opening the way to chronometers.
- Pendulum clocks use the uniform motion of a pendulum to produce an accurate timekeeper, although the rate varies with small variations in gravity.
- An accurate mechanical clock needs a good escapement, a device which converts the rhythmic movement of something such as a pendulum to equal steps.
- Clocks such as pendulum clocks which can be affected by expansion in warm weather often have Invar parts, or other compensation systems to allow for expansion.
- Water clocks can be calibrated: the earliest form of water clock was the klepsydra of the ancient Greeks, but many cultures have used water clocks.
- An effective water clock was used in Indonesia, in the 19th century, made by sitting a half of a coconut shell with a small hole in it, in a bucket of water.
- The Julian date is a day-numbering system used in astronomy, and it is entirely unrelated to the Julian calendar. It counts days from January 1, 4713 BC.
- Time around the world is based on Greenwich Mean Time, and time zones are defined by their time relative to that time zone, usually in one-hour jumps.
- Accurate time zones and consistent times within zones were not essential until the world began to be linked by railways and telegraphs and needed standards.
- Occasional leap seconds are used to align planetary time with clock time, as these are not always precisely the same. These are applied when they are needed.
- The solar day differs from lunar and sidereal days which are defined by the time taken for the Sun, the Moon and a star to reach the same position again.
- Our understanding of the Earth's history comes from the science of geological dating, which has allowed us to place geological events in a rough order.
- Tree growth rings are useful for measuring time over a few hundred to a few thousand years, relying on patterns of thickness that reflect good and bad seasons.
- Most living things have internal 'clocks' that operate on a cycle of approximately 24 hours, and kept in alignment with real days by exposure to light.
- Humans suffer 'jet lag' when they travel too far east or west, if the extent of the travel is too great for the internal clock to realign itself immediately.
- Jet lag shows up in human beings as wakefulness in the night and sleepiness in the daylight hours that correspond with night time at the point of origin.
- Studies of the Earth have led to a consistent geological time scale that reflects a wide variety of measures from many different branches of science.
This file is http://members.ozemail.com.au/~macinnis/scifun/splatstime.htm, first created on February 19, 2008. Last recorded revision (well I get lazy and forget sometimes!) was on February 19, 2008.
©The author of this work is Peter Macinnis, who asserts his sole right to the product as it is packaged here, recognising that many of the ideas are common. You are free to use this as a model to do your own version. Copies of this whole file or site may be made and stored or printed for personal or educational use. You can contact me at email@example.com, but only if you add my first name to the front of that email address -- this is a low-tech way of making it harder to harvest the e-mail address I actually read.
This site had 219,000 hits on the index page from 1999 to January 2007 and an unknown number on other pages. In January 2007, a combined counter was placed on all of the pages, counting page hits which now total