Broca's Brain - Carl Sagan [141]
In 1897, in connection with an exhibition in Brussels, the Belgian government offered prizes for the solutions of certain problems in astronomy. These problems included the numerical value ofred prizes for the solutions of certain problems in astronomy. These problems included the numerical value of the acceleration due to gravity on Earth, the secular acceleration of the Moon, the net motion of the solar system through space, the variation of latitude, the photography of planetary surfaces, and the nature of the canals of Mars. A final topic was the invention of a method to observe the solar corona in the absence of an eclipse. Monthly Notices (20:145) commented: “… if this pecuniary reward does induce anyone to solve this last problem or in fact any of the others, we think the money will be well spent.”
However, reading the scientific papers of this time, one gets the impression that the focus had shifted to other topics than those for which prizes were-being given. Sir William and Lady Huggins performed laboratory experiments which showed that at low pressures the emission spectrum of calcium exhibited only the so-called H and K lines. They concluded that the Sun was composed chiefly of hydrogen, helium, “coronium” and calcium. Huggins had earlier established a stellar spectral sequence, which he believed was evolutionary. The Darwinian influence in science was very strong in this period, and among American astronomers T. J. J. See’s work was notably dominated by a Darwinian perspective. It is interesting to compare Huggins’ spectral sequence with the present Morgan-Keenan spectral types:
HUGGINS’ STELLAR SPECTRAL SEQUENCE
Order of
Increasing Age Star (and modern spectral type in
parentheses)
Young Sirius (A1V)
…….…
Altair (A7 IV-V)
Rigel (B8Ia)
Deneb (A2Ia)
…….…
…….… Vega (A0V)
Capella (G8, G0)
Arcturus (K1 III)
Aldebaran (K5 III) Sun (G0)
Old Betelgeuse (M2 I)
Note: The modern stellar spectral sequence runs, from “early” to “late” spectral types, as O, B, A, F, G, K, M. Huggins was very nearly right.
We can see here the origin of the present terms “early” and “late” spectral type, which reflect the Darwinian spirit of late Victorian science. It is also clear that there is a reasonably continuous gradation of spectral types here, and the beginnings—through the later Hertzsprung-Russell diagram—of modern theories of stellar evolution.
There were major developments in physics during this period and readers of Ap. J. were alerted to them by the reprinting of summaries of important papers. Experiments were still being performed on the basic radiation laws. In some papers, the level of physical sophistication was not of the highest caliber, as, for example, in an article in PASP (11:18) where the linear momentum of Mars is calculated as the single product of the mass of the planet and the linear velocity of the surface. It concluded “the planet, exclusive of the cap, has a momentum of 183 and 3/8 septillion foot pounds.” Exponential notation for large numbers was evidently not in wide use.
In this time we have the publication of visual and photographic light curves, for example, of stars in M5; and experiments in filter photography of Orion by Keeler. An obviously exciting topic was time-variable astronomy, which must then have generated something of the excitement that pulsars, quasars and X-ray sources do today. There were many studies of variable velocities in the line of sight from which were derived the orbits of spectroscopic binaries, as well as periodic variations in the apparent velocity of Omicron Ceti from the Doppler displacement of H gamma and other spectral lines.
The first infrared measurements of stars were performed at the Yerkes Observatory by Ernest F. Nichols. The study concludes: “We do not receive from Arcturus more heat than would reach us from a candle at a distance of 5 or 6 miles.” No further calculations are given. The first