flash vs glint vs flare

Sue J. Worden (worden@uts.cc.utexas.edu)
Wed, 22 Oct 1997 21:08:51 -0500 (CDT) 

Jim Varney wrote:
> Okay, flare fans, can you now outshine glint?

The distinguishing features are the duration of the reflection and
other observed visual characteristics.

The terms "flash" and "glint" are virtually interchangeable.  Both
imply short duration.  The editors of my Webster's Collegiate were
kind enough to provide connative distinctions between similar words.
They say:

   "flash" implies a sudden and transient outburst of bright light
   "glint" implies a cold-glancing light

where

   "glance" suggests a bright darting light reflected from a quickly
      moving surface

I am not sure what they mean by "cold-glancing", however.

By convention, especially in the aerospace fields, the term "glint"
is generally preferred over "flash", possibly because a "glint" is
clearly a reflection of energy, whereas a "flash" could also mean
an emanation of energy from within.

In any case, we on SeeSat-L have adopted "flash" to mean "periodic
flashing" as distinguished from the nonperiodic "glint", so for us,
using "glint" for reflections off solar panels and the phased array
antenna panels (?) on Iridiums seems more appropriate than "flash".

But back to the distinction between "glint" and "flare" for Iridiums.
The keys are, again, duration and visual characteristics.  One of the
definitions for "flare" is "an outburst, a spreading outward".  There
is an implication of extended duration and the visual characteristic
of a "spreading outward" of the light.

Although "glint" may still be more technically correct for Iridiums,
it nevertheless implies very short duration, a "sharp" or "narrow
spike" characteristic in the reflected intensity versus time plot.

Some of the Iridiums I've seen have indeed exhibited what could best
be described as "glints" -- short, sharp changes in brightness.

Other Iridiums, however, have visually been more akin to "flares".
The "monster" I saw last night, for example, slowly ramped up in
brightness over a period of seconds, and I most definitely had the
visual impression of a "spreading outward" of the light, especially
in the latter, brighter stages.

So I propose that both terms, "glint" and "flare", be accepted on
this list to describe the phenomena, with the choice determined by:

                       GLINT        FLARE
   Duration in Time    "short"      "long"
   Duration in Space   "confined"   "expanding"

Respectfully submitted this day... ;-)

--Sue (worden@uts.cc.utexas.edu)