TEMPERATURE CONVERSION CHART
--------------------------
John Pazmino
NYSkies Astronomy Inc
nyskies@nyskies.org
www.nyskies.org
2010 August 8j
Introduction
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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.