TEMPERATURE CONVERSION CHART -------------------------- John Pazmino NYSkies Astronomy Inc firstname.lastname@example.org www.nyskies.org 2010 August 8j
Introduction ---------- Altho y the turn of he 21st century astronomers are quite thoroly moved along to metrics, there are a few lingering writers still employing oldstyle measures. Of course, there is a mass of legacy writing with oldstyle but I mean here the newer material of this century. In the 20th century it was common for astronomy textbooks and references to have chart and tables to convert between oldstyle and metric units. These occupied tens of pages at the back of the book. Newer works generally omit this section, having in the stead a review of the more uncommon metric concepts.
Temperature scales ---------------- The oldstyle scale of temperature is either the Fahrenheit or the Rankine scale. Fahrenheit stars at 32 degree for water-ice equilibrium and continues thru 212 degree for water-steam equilibrium. These are for one atmosphere pressure, like in, ambient air. Zero degrees was supposedly the coldest mixture of chemical in water possible. 100 was the warmest internal body of a mammal. The scale extends indefinitely on the hot end and pins at absolute zero at the cold end. The Rankine scale is the 'absolute Fahrenheit' scale, starting at absolute zero and running positively hotwaord. This is the temperature needed for thermodymanic formulae. In metrics the scale is either the Celsius or Kelvin scale. Celsius, also still called centigrade, has 0 degree at ice-water and 100 at water-steam, both in ambient air. Kelvin is the absolute scale with zero at absolute zero, -273 degree Celsius. This is what thermodynamics equations need. Technicly the INTERVAL or UNIT of temperature is the Kelvin but the SCALE or NUMBER of degrees can be the Kelvin or Celsius, according as its zero point. For very high temperature, like for stars, the Kevin and Celsius are often interchangeable. The Sun's temperature is 6,000K or 6,000C, with the 273 degree offset neglected. It is usually unnecessary to see a Kelvin temperature and subtract 273 to translate to Celsius. By the 21st century, metrics are so prevalent among both home and campus astronomers that no longer do they convert 'scientific' units to 'customary' units. Even the public, thanks to routine overseas travel and business and to continuing immigration, knows metrics.
Temperature conversion -------------------- Converting from oldstyle is usually a multiplication of the oldstyle measure by a factor. The anseer is the metric equivalent. This is how we shifted pounds (of mass) to grams, pound (of force) per square inch to pascals, feet to meters, and so on. Temperature had a peculiar process, a subtract and a multiply. Or was it a multiply and then the subtract? For some reason it was tough to recall the correct formula! The glitch is that the Fahrenheit and Celsius scales are zeroed at different points. Many of us remember one equivalence, like 68F equals 20C. Then we tried the one or other version of the formula to make sure we got the right result
(68F) --> [one of the versions] -?-> (20C)
If it didn't we worked with the other version. This was a real pain in the ass when dealing with many numbers to shift across to metric. Mind that before the 1970s we did not yet have electronic calculettes!
New York method ------------- When I was new to astronomy my elders taught me a wonderful way to convert oldstyle temperature to metric. The metric scale of temperature was then called 'centigrade'. In the 1960s the new name Celsius' was adopted. happily both words begin with 'C'. We can continue to refer to temperatures as 'such-&-such C' The one defect is that it converts only within the range of human comfort on Earth. It fails completely for other planets. It does in deed cover the extreme of cold and heat expected in New York City. I never knew who invented this method but it had to be after about 1917, for a reason I'll explain later. It was presented as a handy, quick, simple method already in wide use among astronomers in New York. It was also described as unique to the City. No where else does this scheme work!
The chart ------- The method is to picture a chart laid down in two stages. The first is here:
|----|----|----|----|----|----|----|----|----|----| 14 23 33 42 51 59 68 77 86 96 103
This bizarre sequence of numbers makes utterly no sense for the reader of this article any where on this planet EXCEPT within New York City. Oh, it's meaningful if you frequent the City, like coming to the NYSkies Seminar from Jersey City, New Jersey. Otherwise, you may scratch your head about this string of numbers somehow being 'easy' to recall at the instant. The next step is to lay down this sequence in steps of five:
-10 -5 0 +5 +10 +15 +20 +25 +30 +35 +40 |----|----|----|----|----|----|----|----|----|----| 14 23 33 42 51 59 68 77 86 96 103
This equally odd sequence at least has equispaced numbers. But why in hell is it zeroed at the '33' mark? Now comes the magic. The upper set of numbers is the Celsius, centigrade, temperature.The lower set is the oldstyle temperature. Try it. What is 77F in Celsius? Bingo! It's 25C. How about 19F? Bingo! It's between -5C and -10Fc, say, -7C. This is not exact, but close within a degree or two, which is really what we need in mental conversion. The method IS approximate, but entirely adequate for cotidian life. The marvel of this method is that it requires NO MATH, a point that makes it attractive for many lay people, like those attending public astronomy sessions.
Outside the comfort range ----------------------- Much colder or hotter than the range -5C to +40C, the subtract part of the temperature formula is usually skipped. Just the multiply, like for most other conversions, is needed. You'll find that in everyday goings about the comfort range is 99-4/100 percent of the occasion to shift temperature readings.
Some weird history ---------------- In the 1870s New York, then consisting of just Manhattan and the South of Bronx, started building its rapid transit system. It constructed els in 2nd and 3rd Avenues on Manhattan's eastern flank and els in th and th Avenue on the spine and west flank. These els, at first of only two tracks each, quickly saturated with riders as the City grew. Consolidation with Brooklyn and other boros in 1898 and massive immigration in the early 20th century swelled ridership to choke the rail lines. At first, the subway company added express tracks to the els. This was a major relief but not nearly enough. The City built an underground line in Lexington Av, now the green line, to supplement the els. With now ten lanes of rail (3 in 2nd Av, 3 in 3rd Av, 4 in Lexington Av) on the east side of the island, rail capacity was about adequate. Because of the density of traffic, stations on the els and underground wr closely spaced, only several hundred meters apart. This on the green line averaged to nine short city block apart. This Lexington Av line opened in sections starting in 1917. The els were in time demolished with intent to replace them by subways. This ws accomplished for the 6th/9th Av els, but not for the 2nd/3rd Av els. Today there is only the 4-track green line to work a district on Manhattan of greater urban activity than all of Boston or San Francisco. As a result, the green line must handle all of the rapid transit traffic, making it by far the world's busiest single transit line. It moves about 1.6 million riders per day. By itself it would be the 2nd busiest transit system in the United States, surpassing Washington or Chicago.
The key ----- The first step in the temperature conversion is to picture the Lexington Av line from is 14th street station to its 103rd St station. Stations downtown from 14th St are not numbered, but have proper names North of 103rd St the spacing is a bit irregular. The reader form the City will instantly notice that one station is omitted. Where's 28th St? This is a half-stop in City mindset. It pairs with 18th St station of certain other lines In fact, on most other lines the 18th St station was long ago removed from service. The upper scale of number is nothing but a 5x5 numbering. 33rd St is nearly 32F, which is 0C That's why the upper scale is zeroed there. The 9-block station spacing combined with the 5x5 spacing is close to the 5/9 factor is the oldstyle/metric conversion formula! SO the chart is like the dual scale of a regular thermometer!
Conclusion -------- I do not claim invention for this method, It was shown to me in the 1980s as already in use However, no one seems to know how it came about. It is not at all obvious, specially when all three transit lines worked the Manhattan east side. The 2nd Av line was removed in 1940;3rd Av, 1955. The replacement subway is now under construction, with trepidations, under 2nd Av. It's a 2-track stub from 63rd St to 96th St, to open maybe in 2015. The downtown end connects to the existing 63rd St line to reach midtown and points south.