[vsnet-chat 1960] Re: (fwd) Sequence for M88 supernova / magnitude IR ?

[bas@lowell.Lowell.Edu (Brian Skiff)]

     As Kato-san correctly notes, the request for "infrared" observations
of the reddened supernova in M88 does indeed refer to wavelengths in the
2 to 5 micron range covered by the JHK standard passbands.
     When the photometric passbands redward of V were established in the
1960s by Johnson, "infrared" was considered to be somewhere in the 7000A to
1 micron range.  Thus it was natural for him to call the passband there "I"
(infrared).  When detectors became available to extend the photometry out to
5 and 10 microns, he named the passbands by simply extending the lettering
from I, thus JHKLMN... (although I could never figure out why 'H' got stuck
between 'J' and 'K'!).
     In the CCD era, where ordinary detectors are sensitive to about 1 micron,
and observations are regularly made at 5, 10, 50, even 100 microns, the term
"infrared" now commonly refers to wavelengths past 1 micron, often divided
further into "near-infrared" (1-5 microns), "thermal-IR" (5-20 microns, etc.
     In view of this, I would suggest thinking of the range covered by the
usual R and I passbands as "far-red".

\Brian

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