Talk:Conversion of units/Archive 2013

Humble Suggestions:

A medimnus is one-and-one-half bushels or 12 gallons. A choenix is one-and-ninety-two-hundredths pints. A hin is five-and-seven-tenths liters. An ephah is 35 liters. A talent is 60 minas, or 26 kilograms. A mina is 60 shekels. A shekel is two bekehs. A bekeh is 10 gerahs. A gerah is 6.43014932 grains. — Preceding unsigned comment added by Nodmonk (talk • contribs) 06:43, 1 February 2013 (UTC)

We would need one or more reliable sources which state the conversions above, and give us some idea of how important the units are, to decide if they are important enough to put in this article. Jc3s5h (talk) 17:05, 1 February 2013 (UTC)

Removal of "In Fiction" Section

Do I really need to justify this? Tripe. — Preceding unsigned comment added by 75.172.62.216 (talk) 22:45, 3 October 2013 (UTC)

ISO 80000-3

The standard defines "year" as either 365 d or 366 d. It also defines "tropical year" as "the duration between two successive passages of the Sun through the mean vernal equinox." Dondervogel 2 (talk) 22:19, 13 October 2013 (UTC)

Please quote sufficient text from the standard so we can understand if they are documenting the generally understood meaning of "year" and "tropical year" or if the decided to create their very own year and tropical year. If they created their own, please document that their unique definition is notable. Jc3s5h (talk) 23:55, 13 October 2013 (UTC)

The text is from a table, which has an entry for year (symbol a) that is then followed by the following definition

• a := 365 d; 366 d
• One tropical year is the duration between two successive passages of the Sun through the mean vernal equinox.
• This duration is related to the corresponding difference in mean longitude of the Sun, which depends on time in a not exactly linear form; i.e. the tropical year is not constant but decreases at a rate of nearly 0,53 s per century. The tropical year is approximately equal to 365,242 20 d =~ 31 556 926 s.

Notability comes from the affect that it is from the ISO 80000 series of international standards, which is the defining series of standards for the International System of Quantities, underpinning (among other things) the SI.

The text "a := 365 d; 366 d" is my shorthand for "a := " followed by opening curly brackets in which two options are offered "365 d" and "366 d". I interpret that as meaning both definitions of "year" are recognised by this ISO standard. Dondervogel 2 (talk) 08:34, 14 October 2013 (UTC)

It seems to me that tables of units in standards can be of three sorts:

1. mentioning for reference commonly accepted values that were established outside the standard
2. providing a lawful, binding definition of units which might have been established informally, in a non-binding way, in other ways, or which might have been established in prior laws which are now being updated, or which might be new
3. providing specialized definitions for those who choose to adopt the standard (for example, the ISO 8601 date format, for those who choose to use it)

It seems to me that in the case of a year being 365 or 366 days long, the standard is merely collecting a convention that was established by Julius Caesar. In the case of the tropical year, the definition is poorly stated and does not agree with the definition used by modern astronomers.

As for International System of Quantities, I think you've got it backward. The SI defines units, and ISO/IEC 80000 is one of many lists of units. ISO/IEC 80000 might be considered authoritative in certain situations for selected units, but I think the weight given to that standard would have to be examined on a unit-by-unit basis.

I see no indication that ISO 8601 is defining a new kind of year for some specific application, rather, it is just including the year in a list compiled from many sources. It is like a dictionary. So it might be used as a citation, but certainly doesn't deserve a separate line in a table in this article, because it is not defining a different kind of year. Jc3s5h (talk) 14:27, 14 October 2013 (UTC)

I think you misunderstand the signifance of ISO/IEC 80000. Reading this BIPM page might help clarify its status. Dondervogel 2 (talk) 14:52, 14 October 2013 (UTC)

The BIPM page pointed out by Dondervogel 2 states in part:

The system of quantities, including the equations relating the quantities, to be used with the SI, is in fact just the quantities and equations of physics that are familiar to all scientists, technologists, and engineers. They are listed in many textbooks and in many references, but any such list can only be a selection of the possible quantities and equations, which is without limit.

So ISO/IEC 80000 is to be a list of quantities and units used with SI, and is a collection of "quantities and equations of physics that are familiar to all scientists, technologists, and engineers." Thus the purpose of the standard is not to create new units, but just to collect existing ones. This is the same purpose as a good dictionary (but more specialized) so it could be used in a citation, just as a dictionary could be used in a citation. But the year as defined in ISO/IEC 80000 ought not to be a different kind of year from those already established, and thus, ought not to have a separate line in the table.(talk)

You questioned the notability of ISO 80000-3. The extract from the BIPM site relevant to notability reads "The revised harmonized standard will be known as ISO/IEC 80000, Quantities and Units, in which it is proposed that the quantities and equations used with the SI will be known as the International System of Quantities." In other words, ISO/IEC 80000 is the vehicle through which BIPM has chosen to document the definitions of units and quantities to which you refer. You might not like to read those words, but it does not get much more notable than that. Dondervogel 2 (talk) 05:29, 15 October 2013 (UTC)

The crucial words are "used with the SI". Units "used with SI" are units that are not part of SI. Except for a few metric units that were deprecated, like the angstrom, the BIPM and its boss, the CGPM, were not involved in the creation or definition of these units. They just decided it's OK to use some of them (like day and hour) with SI and others (like foot) should not be used with SI. This is all explained in their brochure. Since the SI has no authority to define "year" or "tropical year" they have no authority to delegate to ISO or IEC, and so the ISO/IEC 80000 standard is just one more opinion. This differs from, say, the meter. The countries who are members of the CGPM have signed a treaty to allow CGPM to exist, they fund it, and they pass laws making the SI units the lawful units in those countries. I am not aware of any country that has recognized ISO/IEC 80000 as the law of the land.

Of course, the BIPM's decision to allow or not allow the use of certain non-SI units with SI is just an opinion. If a country defines additional units other than SI, it would be the laws of that country, and not BIPM, which would determine if SI and non-SI units can be used together.

But looking at it line by line, ISO/IEC 80000 says a year can be 365 or 366 days. Is there any evidence the standard is trying to define a different kind of year from the ones that have existed since 46 BC? I see no reason to think so, so there is no reason for a different line in the table. Jc3s5h (talk) 14:25, 15 October 2013 (UTC)

A comment about the ISO/IEC 80000 entry for tropical year as quoted by Dondervogel 2: "One tropical year is the duration between two successive passages of the Sun through the mean vernal equinox" and the corresponding value: "65,242 20 d =~ 31 556 926 s." The entry acknowledges the tropical year changes, but neglects to state what year the stated value is valid for, hardly what one would expect to find in a definitive work. It also neglects to state if the seconds are SI seconds or seconds of UT1. If the year was 2000 and if SI seconds were used, the stated value corresponds to the mean tropical year computed as the time required for the mean longitude of the sun to increase 360 degrees, and does not correspond to the value for the purported definition of successive passages through the vernal equinox (see our Tropical year article). So the ISO/IEC 80000 is clearly not up to the task of providing the standard definition for a tropical year. It is merely providing an informal description inexpertly culled from other sources. Jc3s5h (talk) 14:46, 15 October 2013 (UTC)

The different definitions of "year" in the WP table all look like averages to me. By comparison ISO 80000-3 makes no attempt to define an average year. It just says a "year" is sometimes 365 d and sometimes 366 d. Simple, intuitive, and filling a gaping hole in the existing table that Jc3s5h chooses not to acknowledge. Dondervogel 2 (talk) 17:12, 15 October 2013 (UTC)

OK, I can see the merit of putting common and leap years in as individual lines. I have done so. I used as a source a book I have on hand; while ISO 800000-3 might also be acceptable as source if it explains about common and leap years, I don't have ISO 800000-3 so I can't cite it. It's common knowledge anyway, the citation is pro forma.

I also noted that certain values for conversion into seconds will be dependent on any leap seconds that might occur during the period being converted. This applies to common and leap years in the Gregorian calendar, since for civil purposes, time is almost always kept according to UTC which contains leap seconds. Jc3s5h (talk) 18:22, 15 October 2013 (UTC)

I think you have found a good solution. I'm not sure about that note though, about the uncertainty in the number of seconds. It seems to contradict the definition as precisely 365 (or 366) d. The definition and the note cannot both be correct. Dondervogel 2 (talk) 18:45, 15 October 2013 (UTC)

Year: leap seconds

A Gregorian calendar year might be a common year or a leap year. Either way, it is mostly used for civil purposes, and the precise beginning and end would be found by using a time piece set to the civil time legally in force in a particular location. This is almost always based on UTC, with appropriate time zone offsets. This means that one of the 365 or 366 days that make up the year might have contained a leap second. (In 1972 there were two leap seconds.) So depending on the precision required, it may be necessary to account for this when converting between years and seconds.

Precise conversions would also have to consider daylight saving time; depending on the particular period involved, the number of spring clock advances might not equal the number of autumn clock turnbacks. Jc3s5h (talk) 19:01, 15 October 2013 (UTC)