Talk:Second
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This page contains text taken from the public domain article at http://tycho.usno.navy.mil/leapsec.html
Gentlemen, Interesting article, will be useful to include a historical note about why exist 60 seconds in a minute?
Milton 22:03, 28 Jan 2004 (UTC)
Now, I'm pretty sure a second is actually defined as the time it takes light to travel a specific fraction of a meter in a vacuum, I'll google and add it Thunderbolt16 22:17, Mar 20, 2004 (UTC)
- No. However, a metre is defined as the length that light travels in a specific fraction of a second. Morwen 22:19, Mar 20, 2004 (UTC)
- Thanks, I misremembered. Thunderbolt16
Ambiguous definition of ground state
The article twice defines the ground state of the cesium atom. First, as the state when there is zero magnetic flux, and then as the state when there is zero magnetic field. I don't think these two statements are equivalent, and I'm curious if anyone knows which definition is more correct? --ABQCat 00:31, 30 Aug 2004 (UTC)
- Magnetic flux is not applicable here, whereas magnetic field is. Magnetic flux is the total magnetic field passing through some area measured in webers, thus is a distributed quantity, whereas a magnetic field is applicable to a point, like an atom. We need not be concerned with the distinction between B and H (both point quantities) because it only exists in the metric system, or rationalized mks units. In CGS electromagnetic units they are one and the same, because permeability is the dimensionless unit 1. However, zero magnetic field need not be stated twice in the article. — Joe Kress 16:10, Aug 31, 2004 (UTC)
- Thank you - I just didn't have sufficient technical knowledge to be able to correct the ambiguity. I agree with you that we don't need double definition of the second. The article is a good candidate for cleanup by the community - it's messy and seems redundant towards the end. Unless I'm missing something, I think the article could be re-written as much more concise and clear. --ABQCat 16:44, 31 Aug 2004 (UTC)
January 0
What does January 0 mean in this article?? Georgia guy 02:38, 27 Feb 2005 (UTC)
- 1900 January 0 = 1899 December 31. Furthermore, the rest of the definition has a specific astronomical meaning which is not obvious. I'll revise the subsequent paragraph. — Joe Kress 03:31, Feb 27, 2005 (UTC)
Not derived units?
Interesting... SI uses the term 'derived units', but apparently some other field does not? Which would then be the preferred term? See also SI derived units. Radiant_* 12:58, May 26, 2005 (UTC)
- What are you talking about? In metrology jargon, a "derived unit" is a unit to measure some other quantity than the quantity measured by the "base units", and the "derived unit" is built up from some combination of those "base units". For example, in SI the SI derived unit of the quantity force is the newton, which is built up from the base units for the quantities mass, length, and time as 1 kg·m/s².
- The units formed by adding prefixes to the root word (note that this is not to the base unit, as we can see in the case of centimeters in cgs systems and kilograms in mks systems including SI) is something entirely different. Though they may be in some senses of the word "derived", they are not "derived units"—a term with more specific meaning in metrology jargon. Gene Nygaard 13:21, 26 May 2005 (UTC)