Dr. Tony Phillips, Space Directorate, Marshall Space Flight Center, NASA
copy to: Ron Koczor, Marshall Space Flight Center, NASA
Dear Dr. Phillips,
I found your article at
http://science.msfc.nasa.gov/headlines/y2001/ast15feb_1.htm
regarding the heliomagnetic field and its recent flip to be extremely
interesting and serendipitously timely for my Introductory Physics
classes. I intend to distribute copies of the article to them and
discuss it on Monday (with credits intact, of course) as part of my
pre-test review in our study of magnetism.
However, I am going to have to explain an obsolete unit that you used in
the article -- the gauss. We no longer teach our students to use gauss;
instead we use the SI unit, the tesla, for magnetic flux density.
Their textbooks do not mention or define the gauss. In fact, we no
longer mention that people once used the gauss! I'll have to convert
this for them. In the future, though, would you please use only SI
units and not use the obsolete cgs units that used to be common a few
decades ago? It's bad enough that we have to put up with NASA
information occasionally using statute miles, yards, feet, and pounds
(especially information coming out of Johnson Space Center!), but to
have to put up with yet a third system of units -- cgs -- would tax our
lecture time limits. If your older instruments are still reading out in
gauss, you would be doing educators and students a favor to convert the
information to teslas behind the scenes and prior to release to the
public.
By the way, the SI symbol for the astronomical unit (a non-SI unit
accepted for use with the International System) is ua, not AU.
References for my comments above are:
International Bureau of Weights and Measures (BIPM):
http://www.bipm.fr/pdf/si-brochure.pdf
National Institute of Standards and Technology (NIST):
http://physics.nist.gov/Pubs/SP811/sp811.html
American Institute of Physics (AIP):
http://commerce.aip.org/metric.htm
International Astronomical Union (IAU):
http://www.iau.org/units.html
Note especially paragraph 5.16 of the last reference which lists the
gauss as obsolete. Inexplicably, it lists the symbol for astronomical
unit as au (but not AU) instead of ua in Table 5.
Again, my compliments and thanks for your otherwise excellent material.
regards,
James R. Frysinger
--
James R. Frysinger University/College of Charleston
10 Captiva Row Dept. of Physics and Astronomy
Charleston, SC 29407 66 George Street
843.225.0805 Charleston, SC 29424
http://www.cofc.edu/~frysingj [EMAIL PROTECTED]
Cert. Adv. Metrication Specialist 843.953.7644
