- #1
Dandy Candy
- 10
- 0
Hi all,
I am a new member in your forum and I am very pleased to join it. This my first theard in this great forum.
My Q.:
The unit of time was originally defined as 1/86400 of the mean solar day. Because of irregularities in the Earth roatation, the definition was changed to the '' emphemeris second '', i.e., 1/31556925.9747 of the tropical year 1900. In 1967 , this definition was replaced.
the second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine of the ground state of the cesius-133 atom.
The defintion is based on the atomic clock. One of the best atomic clocks ( NIST-F1) is precise to within about 1 second in 60 million years, or 5 parts in 10^16. Commercially available atomic clocks are precise to within 3 parts in 10^12.
I didn't understand this paragraph .. it's from my textbook !
Concepts in Engineering
Second Edition
Mark Holtzapple and W. Reece
McGraw-Hill
2008Would you mind explaining it, please?
I am a new member in your forum and I am very pleased to join it. This my first theard in this great forum.
My Q.:
The unit of time was originally defined as 1/86400 of the mean solar day. Because of irregularities in the Earth roatation, the definition was changed to the '' emphemeris second '', i.e., 1/31556925.9747 of the tropical year 1900. In 1967 , this definition was replaced.
the second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine of the ground state of the cesius-133 atom.
The defintion is based on the atomic clock. One of the best atomic clocks ( NIST-F1) is precise to within about 1 second in 60 million years, or 5 parts in 10^16. Commercially available atomic clocks are precise to within 3 parts in 10^12.
I didn't understand this paragraph .. it's from my textbook !
Concepts in Engineering
Second Edition
Mark Holtzapple and W. Reece
McGraw-Hill
2008Would you mind explaining it, please?
Last edited by a moderator: