Sky and Telescope - August 2018 - 61

400

500

600

700

SPECTRU M: G REGG DINDER M A N (S&T ); SCIEN TIFIC PA PER: THE SCIENTIFIC
PAPERS OF SIR WILLIAM HUGGINS, K.C.B., O.M. (19 0 9) / PUBLIC DO M AIN

Wavelength (nanometers)

with which, after a few moments of hesitation, I put my eye
to the spectroscope. Was I not about to look into a secret
place of creation?
"I looked into the spectroscope. No such spectrum as I
expected! A single bright line only! At ﬁrst I suspected some
displacement of the prism, and that I was looking at a reﬂection of the illuminated slit from one of its faces. This thought
was scarcely more than momentary; then the true interpretation ﬂashed upon me. The light of the nebula was monochromatic, and so, unlike any other light I had yet subjected
q RECORDED LIGHT William Huggins sketched the emission lines he
detected in NGC 6543 with his 8-inch Clark refractor and visual spectroscope. He determined that the brightest line coincided with nitrogen
and the faintest with hydrogen. "37. H IV Draconis" is William Herschel's
designation for NGC 6543.

p STELLAR SPREAD The spectrum of Vega showing its most obvious absorption bands. The colors look even brighter through the
author's spectroscope.

to prismatic examination, could not be extended out to form
a complete spectrum. . . . A little closer looking showed two
other bright lines on the side towards the blue, all three lines
being separated by intervals relatively dark.
"The riddle of the nebulae was solved. The answer,
"This is a
which had come to us in
memorable
the light itself, read: Not
an aggregation of stars, but
observation
a luminous gas."
not only for
Everything had come
duplicating
together for this second
breakthrough. His ongoHuggins's
ing laboratory work with
observation,
Miller, his observations
but that I can
of terrestrial, solar, and
stellar spectra, and now
(do it) so easily
a bright spectrum from a
and with such
planetary nebula had given
an inexpensive
Huggins the means to
recognize what the emisspectrograph . . ."
sion line spectrum of NGC
6543 and other planetary
nebulae meant. About planetary nebulae in general he wrote:
". . . we must probably regard these objects, or at least
their photo-surfaces, as enormous masses of luminous gas
or vapor." Only "matter in the gaseous state" emits "light
consisting of certain deﬁnite refrangibilities only." (In this
instance "refrangibilities only" means light refracted into
discrete emission lines.)
Bingo.

153 Years Later
I can't help but get caught up in the excitement of Huggins's
account, and in 2017 I recreated his observation of NGC
6543. To do so, I purchased a relatively inexpensive, lowresolution diffraction grating spectroscope that attaches to a
1.25-inch eyepiece like a ﬁlter and had a look for myself.
I started by examining the spectra of Vega (spectral class
AOV) and Altair (A7V) to become familiar with continuous
stellar spectra. They appear nearly identical as bright, beautiful rainbow streaks with several dark absorption bands.
sk yandtelescope.com * AUGUST 2 018

http://www.skyandtelescope.com

Sky and Telescope - August 2018

Table of Contents for the Digital Edition of Sky and Telescope - August 2018