A the frequency of light emitted by Kr86
B none of these
C the daily rotation of the earth
D a precision pendulum clock
E the yearly revolution of the earth about the sun
2007-04-21 18:38:13 · 6 answers · asked by parvati710 1 in Science & Mathematics ➔ Earth Sciences & Geology
If one has to pick one of the choices given, B is most likely.
Historically it would have been C, but modern clocks have shown that the rotation of the earth is not quite constant, it is gradually slowing .
A is a possibility, but I found conflicting information, while Kr86 is used as a standard, it seems caesium-133 is more common for a standard of time..
2007-04-21 21:11:35 · answer #1 · answered by tinkertailorcandlestickmaker 7 · 1⤊ 0⤋
C and E, initially. The earth revolves about the sun once each year, placing the sun in the same position with the same times of rise and set on the same date, year to year. The ancients gradually came to recognize this. Ditto for the 24-hour daily cycles.
Time zones, and the evolution of what is called "Standard Time" evolved in the United States in the 1880's, based on the need to schedule trains with accuracy so as to avoid collisions. The story makes an interesting read. The link is below.
2007-04-21 23:20:56 · answer #2 · answered by boss_alwi 2 · 0⤊ 0⤋
The current standard of time is UTC1, french for Universal Coordinated Time, the 1 meaning it is based on one earth rotation, measured by astronomical observation. The reference is a cesium based clock which allows an exact determination of time down to the nanosecond between rotations. This is known as UTC and time measured this way has to be corrected occassionally to compensate for irregularities in the Earth rotation. so the answer is C, if the rotation changes, we change our clocks to match.
2007-04-22 09:11:53 · answer #3 · answered by lare 7 · 0⤊ 0⤋
Answer C, originally it took 24 hrs. for one revolution, from there we just divided by 60`s apparently. How they came up with these particular divisions is a mystery to me. As someone else pointed out, it now takes a little longer than it used to for one revolution. Also, a report I heard says that the moon is very slowly drifting away from earth, which in itself could be bad news.
2007-04-21 21:33:11 · answer #4 · answered by Dan N 3 · 0⤊ 0⤋
the idea that the day begins with the sun rising on japan.
C
calender is based on the E
2007-04-21 18:42:48 · answer #5 · answered by gonavy271 2 · 0⤊ 0⤋
A..!
2014-09-14 05:25:40 · answer #6 · answered by Anonymous · 0⤊ 1⤋