THE PAST AND
FUTURE OF AMERICAN
ASTRONOMY

THE WORLD has changed since 1899, but there are few fields which have changed more—in the development of fundamental insights and in the discovery of new phenomena—than astronomy. Here are a few titles of recent papers published in the scientific magazines The Astrophysical Journal and Icarus: “G240-72: A New Magnetic White Dwarf with Unusual Polarization,” “Relativistic Stellar Stability: Preferred Frame Effects,” “Detection of Interstellar Methylamine,” “A New List of 52 Degenerate Stars,” “The Age of Alpha Centauri,” “Do OB Runaways Have Collapsed Companions?,” “Finite Nuclear-size Effects on Neutrino-pair Bremsstrahlung in Neutron Stars,” “Gravitational Radiation from Stellar Collapse,” “A Search for a Cosmological Component of the Soft X-ray Background in the Direction of M31,” “The Photochemistry of Hydrocarbons in the Atmosphere of Titan,” “The Content of Uranium, Thorium and Potassium in the Rocks of Venus as Measured by Venera 8,” “HCN Radio Emission from Comet Kohoutek,” “A Radar Brightness and Altitude Image of a Portion of Venus” and “A Mariner 9 Photographic Atlas of the Moons of Mars.” Our astronomical ancestors would have extracted a glimmer of meaning from these titles, but I think their principal reaction would have been one of incredulity.

WHEN I WAS ASKED to chair the 75th Anniversary Committee of the American Astronomical Society in 1974, I thought it would provide a pleasant opportunity to acquaint myself with the state of our subject at the end of the past century. I was interested to see where we had been, where we are today, and if possible, something of where we may be going. In 1897 the Yerkes Observatory, then the largest telescope in the world, was given a formal dedication, and a scientific meeting of astronomers and astrophysicists was held in connection with the ceremony. A second meeting was held at the Harvard College Observatory in 1898 and a third at the Yerkes Observatory in 1899, by which time what is now the American Astronomical Society had been officially founded.

The astronomy of 1897 to 1899 seems to have been vigorous, combative, dominated by a few strong personalities and aided by remarkably short publication times. The average time between submission and publication for papers in the Astrophysical Journal (Ap. J.) in this period seems to be better than in Astrophysical Journal Letters today. The fact that a great many papers were from the Yerkes Observatory, where the journal was edited, may have had something to do with this. The opening of the Yerkes Observatory at Williams Bay, Wisconsin—which has the year 1895 imprinted upon it—was delayed more than a year because of the collapse of the floor, which narrowly missed killing the astronomer E. E. Barnard. The accident is mentioned in Ap. J. (6:149), but one finds no hint of negligence there. However, the British journal Observatory (20:393), clearly implies careless construction and a cover-up to shield those responsible. We also discover on the same page of Observatory that the dedication ceremonies were postponed for some weeks to accommodate the travel schedule of Mr. Yerkes, the robber-baron donor. The Astrophysical Journal says that “the dedication ceremonies were necessarily postponed from October 1, 1897,” but does not say why.

Ap. J. was edited by George Ellery Hale, the director of the Yerkes Observatory, and by James E. Keeler, who in 1898 became the director of the Lick Observatory on Mount Hamilton in California. However, there was a certain domination of Ap. J. by Williams Bay, perhaps because the Lick Observatory dominated the Publications of the Astronomical Society of the Pacific (PASP) in the same period. Volume 5 of the Astrophysical Journal has no fewer than thirteen plates of the Yerkes Observatory, including one of the powerhouse. The first fifty pages of Volume 6 have a dozen more plates of the Yerkes Observatory. The Eastern dominance of the American Astronomical Society is also reflected by the fact that the first president of the Astronomical and Astrophysical Society of America was Simon Newcomb, of the Naval Observatory in Washington, and the first vice presidents, Young and Hale. West Coast astronomers complained about the difficulties in traveling to the third conference of astronomers and astrophysicists at Yerkes and seem to have voiced some pleasure that promised demonstrations with the Yerkes 40-inch refractor for this ceremony had to be postponed because of cloudy weather. This was about the most in the way of interobservatory rancor that can be found in either journal.

But in the same period Observatory had a keen nose for American astronomical gossip. From Observatory we find that there was a “civil war” at the Lick Observatory and a “scandal” associated with Edward Holden (the director before Keeler), who is said to have permitted rats in the drinking water at Mount Hamilton. It also published a story about a test chemical explosion scheduled to go off in the San Francisco Bay Area and to be monitored by a seismic device on Mount Hamilton. At the appointed moment, no staff member could see any sign of needle deflection except for Holden, who promptly dispatched a messenger down the mountain to alert the world to the great sensitivity of the Lick seismometer. But soon up the mountain came another messenger with the news that the test had been postponed. A much faster messenger was then dispatched to overtake the first and an embarrassment to the Lick Observatory was, Observatory notes, narrowly averted.

The youth of American astronomy in this period is eloquently reflected in the proud announcement in 1900 that the Berkeley Astronomical Department would henceforth be independent of the Civil Engineering Department at the University of California. A survey by Professor George Airy, later the British Astronomer Royal, regretted being unable to report on astronomy in America in 1832 because essentially there was none. He would not have said that in 1899.

There is never much sign in these journals of the intrusion of external (as opposed to academic) politics, except for an occasional notice such as the appointment by President McKinley of T. J. J. See as professor of mathematics to the U.S. Navy, and a certain continuing chilliness in scientific debates between the personnel of the Lick and Potsdam (Germany) Observatories.

Some signs of the prevailing attitudes of the 1890s occasionally trickle through. For example, in a description of an eclipse expedition to Siloam, Georgia, on May 28, 1900: “Even some of the whites were lacking in a very deep knowledge of things ‘eclipse-wise.’ Many thought it was a money-making scheme and what I intended to charge for admission was a very important question, frequently asked. Another idea was that the eclipse could be seen only from the inside of my observatory … Just here I wish to express my appreciation of the high moral tone of the community, for, with a population of only 100, including the immediate neighborhood, it sustains 2 white and 2 colored churches and during my stay I did not hear a single profane word … As an unsophisticated Yankee in the Southland, unused to Southern ways, I naturally made many little slips that were not considered ‘just the thing.’ The smiles at my prefixing ‘Mr.’ to the name of my colored helper caused me to change it to ‘Colonel,’ which was entirely satisfactory to everybody.”

A board of visitors was appointed to resolve some (never publicly specified) problems at the U.S. Naval Observatory. A report of this group—which consisted of two obscure senators and Professors Edward C. Pickering, George C. Comstock and Hale—is illuminating because it mentions dollar amounts. We find that the annual running costs of the major observatories in the world were: Naval Observatory, $85,000; Paris Observatory, $53,000; Greenwich Observatory (England), $49,000; Harvard Observatory, $46,000; and Pulkowa Observatory (Russia), $36,000. The salaries of the two directors of the U.S. Naval Observatory were $4,000 each, and at the Harvard Observatory, $5,000. The distinguished board of visitors recommended that in a “schedule of salaries which could be expected to attract astronomers of the class desired,” the salary of directors of observatories should be $6,000. At the Naval Observatory, computers (exclusively human at the time) were paid $1,200 per annum, but at the Harvard Observatory only $500 per annum, and were almost exclusively women. In fact, all salaries at Harvard, except for the director’s, were significantly lower than at the Naval Observatory. The committee stated: “The great difference in salaries at Washington and Cambridge, especially for the officers of lower grade, is probably unavoidable. This is partly due to Civil Service Rules.” An additional sign of astronomical impecuniosity is the announcement of the post of “volunteer research assistant” at Yerkes, which had no associated pay but which was said to provide good experience for students with higher degrees.

Then, as now, astronomy was besieged by “paradoxers,” proponents of fringe or crackpot ideas. One proposed a telescope with ninety-one lenses in series as an alternative to a telescope with a smaller number of lenses of larger aperture. The British in this period were similarly plagued but in perhaps a gentler way. For example, an obituary in the Monthly Notices of the Royal Astronomical Society (59:226) of Henry Perigal informs us that the deceased had celebrated his ninety-fourth birthday by becoming a member of the Royal Institution, but was elected a Fellow of the Royal Astronomical Society in 1850. However, “our publications contain nothing from his pen.” The obituary describes “the remarkable way in which the charm of Mr. Perigal’s personality won him a place which might have seemed impossible of attainment for a man of his views; for there is no masking the fact that he was a paradoxer pure and simple, his main conviction being that the Moon did not rotate, and his main astronomical aim in life being to convince others, and especially young men not hardened in the opposite belief, of their grave error. To this end he made diagrams, constructed models, and wrote poems; bearing with heroic cheerfulness the continued disappointment of finding none of them of any avail. He has, however, done excellent work apart from this unfortunate misunderstanding.”

The number of American astronomers in this period was very small. The by-laws of the Astronomical and Astrophysical Society of America state that a quorum is constituted by twenty members. By the year 1900 only nine doctorates had been granted in astronomy in America. In that year there were four astronomical doctorates: two from Columbia University for G. N. Bauer and Carolyn Furness; one from the University of Chicago for Forest Ray Moulton; and one from Princeton University for Henry Norris Russell.

Some idea of what was considered important scientific work in this period can be garnered from the prizes that were awarded. E. E. Barnard received the Gold Medal of the Royal Astronomical Society in part for his discovery of the Jovian moon Jupiter 5 and for his astronomical photography with a portrait lens. His steamer, however, was caught in an Atlantic storm, and he did not arrive in time for the celebration ceremony. He is described as requiring several days to recover from the storm, whereupon the RAS hospitably gave a second dinner for him. Barnard’s lecture seems to have been spectacular and made full use of that recently improved audio-visual aid, the lantern slide projector.

In his discussion of his photograph of the region of the Milky Way near Theta Ophiuchus he concluded that “the entire groundwork of the Milky Way … has a substratum of nebulous matter.” (Meanwhile H. K. Palmer reported no nebulosity in photographs of the globular cluster M13.) Barnard, who was a superb visual observer, expressed considerable doubts about Percival Lowell’s view of an inhabited and canal-infested Mars. In his thanks to Barnard for his lecture, the president of the Royal Astronomical Society, Sir Robert Ball, voiced concern that henceforth he “should regard the canals in Mars with some suspicion, nay, even the seas [of Mars, the dark areas] had partly fallen under a ban. Perhaps the lecturer’s recent experiences on the Atlantic might explain something of this mistrust.” Lowell’s views were not then in favor in England, as another notice in Observatory indicated. In response to an inquiry on which books had most pleased and interested him in 1896, Professor Norman Lockyer replied, “Mars by Percival Lowell, Sentimental Tommy by J. M. Barrie. (No Time for Reading Seriously).”

Prizes in astronomy for 1898 awarded by the Académie Française included one to Seth Chandler for the discovery of the variation in latitude; one to Belopolsky, partly for studies of spectroscopic binary stars; and one to Schott for work on terrestrial magnetism. There was also a prize competition for the best treatise on “the theory of perturbations of Hyperion,” a moon of Saturn. We are informed that “the only essay presented was that by Dr. G. W. Hill of Washington to whom the prize was awarded.”

The Astronomical Society of the Pacific’s Bruce Medal was awarded in 1899 to Dr. Arthur Auwers of Berlin. The dedicatory address included the following remarks: “Today Auwers stands at the head of German astronomy. In him is seen the highest type of investigator in our time, one perhaps better developed in Germany than in any other country. The work of men of this type is marked by minute and careful research, untiring industry in the accumulation of facts, caution in propounding new theories or explanations, and, above all, the absence of effort to gain recognition by being the first to make a discovery.” In 1899 the Henry Draper Gold Medal of the National Academy of Sciences was presented for the first time in seven years. The recipient was Keeler. In 1898 Brooks, whose observatory was in Geneva, New York, announced the discovery of his twenty-first comet—which Brooks described as “achieving his majority.” Shortly thereafter he received the Lalande Prize of the Académie Française for his record in discovering comets.

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

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 experimental observations of the infrared opacity of carbon dioxide and water vapor were performed in this period by Rubens and Aschkinass, who essentially discovered the v₂ fundamental of carbon dioxide at 15 microns and the pure rotation spectrum of water.

There is preliminary photographic spectroscopy of the Andromeda nebula by Julius Scheiner at Potsdam, Germany, who concludes correctly that “the previous suspicion that the spiral nebulae are star clusters is now raised to a certainty.” As an example of the level of personal vituperation tolerated at this time, the following is an extract from a paper by Scheiner in which W. W. Campbell is criticized: “In the November number of the Astrophysical Journal, Professor Campbell attacks, with much indignation, some remarks of mine criticizing his discoveries … Such sensitiveness is somewhat surprising on the part of one who is himself given to severely taking others to task. Further, an astronomer who frequently observes phenomena which others cannot see, and fails to see those which others can, must be prepared to have his opinions contested. If, as Professor Campbell complains, I have only supported my views by a single example, I was only withheld by courteous motives from adding another. Namely, the fact that Professor Campbell cannot perceive the lines of aqueous vapor in the spectrum of Mars which were seen by Huggins and Vogel in the first place, and, after Mr. Campbell had called their existence in question, were again seen and identified with certainty by Professor Wilsing and myself.” The amount of water vapor in the Martian atmosphere that is now known to exist would have been entirely indetectable by the spectroscopic methods then in use.

Spectroscopy was a dominant element in late-nineteenth-century science. Ap. J. was busily publishing Rowland’s solar spectrum, which ran to 20,000 wavelengths, each to seven significant figures. It published a major obituary of Bunsen. Occasionally the astronomers took note of the extraordinary nature of their discoveries: “It is simply amazing that the feeble twinkling light of a star can be made to produce such an autographic record of substance and condition of the inconceivably distant luminary.” A major topic of debate for the Astrophysical Journal was whether spectra should be shown with red to the left or to the right. Those who favored red to the left cited the analogy of the piano (where high frequencies are to the right), but Ap. J. opted gamely for red to the right. Some room for compromise was available on whether, in lists of wavelengths, red should be at the top or at the bottom. Feelings ran high, and Huggins wrote to say that “any change … would be little less than intolerable.” But the Ap. J. won anyway.

Another major discussion in this period was on the nature of sunspots. G. Johnstone Stoney proposed that they were caused by a layer of condensed clouds in the photosphere of the Sun. But Wilson and FitzGerald objected to this on the ground that no conceivable condensates could exist at these high temperatures, with the possible exception of carbon. They suggested instead and very vaguely that sunspots are due to “reflection by convection streams of gas.” Evershed had a more ingenious idea. He thought that sunspots were holes in the outer photosphere of the Sun, permitting us to see to much greater and hotter depths. But why are they dark? He proposed that all the radiation would be moved from the visible to the inaccessible ultraviolet. This, of course, was before the Planck distribution of radiation from a hot object was understood. It was not at this time thought impossible that the spectral distributions of black bodies of different temperatures should cross; and some experimental curves of this period indeed showed such crossing—due, as we now know, to emissivity and absorptivity differences.

Ramsay had recently discovered the element krypton, which was said to have, among fourteen detectable spectral lines, one at 5570 Å, coincident with “the principal line of the aurora.” E. B. Frost concluded: “Thus it seems that the true origin of that hitherto perplexing line has been discovered.” We now know it is due to oxygen.

There were a great many papers on instrumental design, one of the more interesting being by Hale. In January 1897 he suggested that both refracting and reflecting telescopes were needed, but noted that there was a clear movement toward reflectors, especially equatorial coude telescopes. In a historical memoir, Hale mentions that the 40-inch lens was available to the Yerkes Observatory only because a previous plan to build a large refractor near Pasadena, California, had fallen through. What, I wonder, would the history of astronomy have been like if the plan had succeeded? Curiously enough, Pasadena seems to have made an offer to the University of Chicago to have the Yerkes Observatory situated there. It would have been a long commute for 1897.

AT THE END of the nineteenth century, solar system studies displayed the same mixture of future promise and current confusion that the stellar work did. One of the most notable papers of the period, by Henry Norris Russell, is called “The Atmosphere of Venus.” It is a discussion of the extension of the cusps of the crescent Venus, based in part on the author’s observations with the 5-inch finder telescope of the “great equatorial” of the Halsted Observatory at Princeton. Perhaps the young Russell was not yet considered fully reliable operating larger telescopes at Princeton. The essence of the analysis is correct by present standards. Russell concluded that refraction of sunlight was not responsible for the extension of the cusps, and that the cause was to be found in the scattering of sunlight: “… the atmosphere of Venus, like our own, contains suspended particles of dust or fog of some sort, and … what we see is the upper part of this hazy atmosphere, illuminated by rays that have passed close to the planet’s surface.” He later says that the apparent surface may be a dense cloud layer. The height of the haze is calculated as about 1 kilometer above what we would now call the main cloud deck, a number that is just consistent with limb photography by the Mariner 10 spacecraft. Russell thought, from the work of others, that there was some spectroscopic evidence for water vapor and oxygen in a thin Venus atmosphere. But the essence of his argument has stood the test of time remarkably well.

William H. Pickering’s discovery of Phoebe, the outermost satellite of Saturn, was announced; and Andrew E. Douglass of the Lowell Observatory published observations that led him to conclude that Jupiter 3 rotates about one hour slower than its period of revolution, a conclusion incorrect by one hour.

Others who estimated periods of rotation were not quite so successful. For example, there was a Leo Brenner who observed from the Manora Observatory in a place called Lussinpiccolo. Brenner severely criticized Percival Lowell’s estimate of the rotation period of Venus. Brenner himself compared two drawings of Venus in white light made by two different people four years apart—from which he deduced a rotation period of 23 hours, 57 minutes and 36.37728 seconds, which he said agreed well with the mean of his own “most reliable” drawings. Considering this, Brenner found it incomprehensible that there could still be partisans of a 224.7-day rotation period and concluded that “an inexperienced observer, an unsuitable telescope, an unhappily chosen eyepiece, a very small diameter of the planet, observed with an insufficient power, and a low declination, all together explained Mr. Lowell’s peculiar drawings.” The truth, of course, lies not between the extremes of Lowell and Brenner, but rather at the other end of the scale, with a minus sign, a retrograde period of 243 days.

In another communication Herr Brenner begins: “Gentlemen: I have the honor to inform you that Mrs. Manora has discovered a new division in the Saturnian ring system”—from which we discover that there is a Mrs. Manora at the Manora Observatory in Lussinpiccolo and that she performs observations along with Herr Brenner. Then follows a description of how the Encke, Cassini, Antoniadi, Strove and Manora divisions are all to be kept straight. Only the first two have stood the test of time. Herr Brenner seems to have faded into the mists of the nineteenth century.

AT THE SECOND CONFERENCE of Astronomers and Astrophysicists at Cambridge, there was a paper on the “suggestion” that asteroid rotation, if any, might be deduced from a light curve. But no variation of the brightness with time was found, and Henry Parkhurst concluded: “I think it is safe to dismiss the theory.” It is now a cornerstone of asteroid studies.

In a discussion of the thermal properties of the Moon, made independently of the one-dimensional equation of heat conduction but based on laboratory emissivity measurements, Frank Very concluded that a typical lunar daytime temperature is about 100°C—exactly the right answer. His conclusion is worth quoting: “Only the most terrible of Earth’s deserts where the burning sands blister the skin, and the men, beasts, and birds drop dead, can approach noontide on the cloudless surface of our satellite. Only the extreme polar latitudes of the Moon can have an endurable temperature by day, to say nothing of the night, when we should have to become troglodytes to preserve ourselves from such intense cold.” The expository styles were often fine.

Earlier in the decade, Maurice Loewy and Pierre Puiseux at the Paris Observatory had published an atlas of lunar photographs, the theoretical consequences of which were discussed in Ap. J. (5:51). The Paris group proposed a modified volcanic theory for the origin of the lunar craters, rills and other topographic forms, which was later criticized by E. E. Barnard after he examined the planet with the 40-inch telescope. Barnard was then criticized by the Royal Astronomical Society for his criticism, and so on. One of the arguments in this debate had a deceptive simplicity: volcanoes produce water; there is no water on the moon; therefore the lunar craters are not volcanic. While most of the lunar craters are not volcanic, this is not a convincing argument because it neglects the problem of possible repositories for water. Very’s conclusions on the temperature of the lunar poles could have been read with some profit. Water there freezes out as frost. The other possibility is that water might escape from the Moon to space.

This was recognized by Stoney in a remarkable paper called “Of Atmospheres upon Planets and Satellites.” He deduced that there should be no lunar atmosphere because of the very rapid escape to space of gases from the low lunar gravity, or any large build-up of the lightest gases, hydrogen and helium, on Earth. He believed that there was no water vapor in the Martian atmosphere and that Mars’ atmosphere and caps were probably carbon dioxide. He implied that hydrogen and helium were to be expected on Jupiter, and that Triton, the largest moon of Neptune, might have an atmosphere. Each of these conclusions is in accord with present-day findings or opinions. He also concluded that Titan should be airless, a prediction with which some modern theorists agree—although Titan seems to have another view of the matter (see Chapter 13).

In this period there are also a few breath-taking speculations, such as one by the Rev. J. M. Bacon that it would be a good idea to perform astronomical observations from high altitudes—from, for example, a free balloon. He suggested that there would be at least two advantages: better seeing and ultraviolet spectroscopy. Goddard later made similar proposals for rocket-launched observatories (Chapter 18).

Hermann Vogel had previously found, by eyeball spectroscopy, an absorption band at 6183 Å in the body of Saturn. Subsequently the International Color Photo Company of Chicago made photographic plates, which were so good that wavelengths as long as H Alpha in the red could be detected for a fifth-magnitude star. This new emulsion was used at Yerkes, and Hale reported that there was no sign of the 6183 Å band for the rings of Saturn. The band is now known to be at 6190 Å and is 6v₃ of methane.

Another reaction to Percival Lowell’s writings can be gleaned from the address of James Keeler at the dedication of the Yerkes Observatory:

The address of Simon Newcomb on this occasion contains some remarks which apply generally, if a little idealistically, to the scientific endeavor:

AFTER READING through the publications of astronomers three-quarters of a century ago, I felt an irresistible temptation to imagine the 150th Anniversary Meeting of the American Astronomical Society—or whatever name it will have metamorphosed into by then—and guess how our present endeavors will be viewed.

In examining the late-nineteenth-century literature, we are amused at some of the debates on sunspots, and impressed that the Zeeman effect was not considered a laboratory curiosity but something to which astronomers should devote considerable attention. These two threads intertwined, as if prefigured, a few years later in G. E. Hale’s discovery of large magnetic field strengths in sunspots.

Likewise we find innumerable papers in which the existence of a stellar evolution is assumed but its nature remains hidden; in which the Kelvin-Helmholtz gravitational contraction was considered the only possible stellar energy source, and nuclear energy remained entirely unanticipated. But at the same time, and sometimes in the same volume of the Astrophysical Journal, there is acknowledgment of curious work being done on radioactivity by a man named Becquerel in France. Here again we see the two apparently unrelated threads moving through our few-years snapshot of late-nineteenth-century astronomy and destined to intertwine forty years later.

There are many related examples—for instance, in the interpretation of series spectra of nonhydrogenic elements obtained at the telescope and pursued in the laboratory. New physics and new astronomy were the complementary sides of the emerging science of astrophysics.

Accordingly, it is difficult not to wonder how many of the deepest present debates—for example, on the nature of quasars, or the properties of black holes, or the emission geometry of pulsars—must await an intertwining with new developments in physics. If the experience of seventy-five years ago is any guide, there will already be people today who dimly guess which physics will join with which astronomy. And a few years later, the connection will be considered obvious.

We also see in the nineteenth-century material a number of cases where the observational methods or their interpretations are clearly in default by present standards. Planetary periods deduced to ten significant figures by the comparison of two drawings made by different people of features we now know to be unreal to begin with is one of the worst examples. But there are many others, including a plethora of “double-star measurements” of widely separated objects, which are mainly physically unconnected stars; a fascination with pressure and other effects on the frequencies of spectral lines when no one is paying any attention to curve of growth analysis; and acrimonious debates on the presence or absence of some substance based solely upon naked-eye spectroscopy.

Also curious is the sparseness of the physics in late-Victorian astrophysics. Reasonably sophisticated physics is almost exclusively the province of geometrical and physical optics, the photographic process, and celestial mechanics. To make theories of stellar evolution based on stellar spectra without wondering much about the dependence of excitation and ionization on temperature, or attempting to calculate the subsurface temperature of the Moon without ever solving Fourier’s equation of heat conduction seems to me to be less than quaint. In seeing elaborate empirical representations of laboratory spectra, the modern reader becomes impatient for Bohr and Schrödinger and their successors to come along and develop quantum mechanics.

I wonder how many of our present debates and most celebrated theories will appear, from the vantage point of the year 2049, marked by shoddy observations, indifferent intellectual powers or inadequate physical insight. I have the sense that we are today more self-critical than scientists were in 1899; that because of the larger population of astronomers, we check each other’s results more often; and that, in part because of the existence of organizations like the American Astronomical Society, the standards of exchange and discussion of results have risen significantly. I hope our colleagues of 2049 will agree.

The major advance between 1899 and 1974 must be considered technological. But in 1899 the world’s largest refractor had been built. It is still the world’s largest refractor. A reflector of 100-inch aperture was beginning to be considered. We have improved on that aperture only by a factor of two in the intervening years. But what would our colleagues of 1899—living after Hertz but before Marconi—have made of the Arecibo Observatory, or the Very Large Array, or Very Long Baseline Interferometry (VLBI)? Or checking out the debate on the period of rotation of Mercury by radar Doppler spectroscopy? Or testing the nature of the lunar surface by returning some of it to Earth? Or pursuing the problem of the nature and habitability of Mars by orbiting it for a year and returning 7,200 photographs of it, each of higher quality than the best 1899 photographs of the Moon? Or landing on the planet with imaging systems, microbiology experimentation, seismometers and gas chromatograph/mass spectrometers, which did not even vaguely exist in 1899? Or testing cosmological models by orbital ultraviolet spectroscopy of interstellar deuterium—when neither the models to be tested nor the existence of the atom that tests it were known in 1899, much less the technique of observation?

It is clear that in the past seventy-five years American and world astronomy has moved enormously beyond even the most romantic speculations of the late-Victorian astronomers. And in the next seventy-five years? It is possible to make pedestrian predictions. We will have completely examined the electromagnetic spectrum from rather short gamma rays to rather long radio waves. We will have sent unmanned spacecraft to all of the planets and most of the satellites in the solar system. We will have launched spacecraft into the Sun to do experimental stellar structure, beginning perhaps—because of the low temperatures—with the sunspots. Hale would have appreciated that. I think it possible that seventy-five years from now, we will have launched subrelativistic spacecraft—traveling at about 0.1 the speed of light—to the nearby stars. Among other benefits, such missions would permit direct examination of the interstellar medium and give us a longer baseline for VLBI than many are thinking of today. We will have to invent some new superlative to succeed “very”—perhaps “ultra.” The nature of pulsars, quasars and black holes should by then be well in hand, as well as the answers to some of the deepest cosmological questions. It is even possible that we will have opened up a regular communications channel with civilizations on planets of other stars, and that the cutting edge of astronomy as well as many other sciences will come from a kind of Encyclopaedia Galactica, transmitted at very high bit rates to some immense array of radio telescopes.

But in reading the astronomy of seventy-five years ago, I think it likely that, except for interstellar contact, these achievements, while interesting, will be considered rather old-fashioned astronomy, and that the real frontiers and the fundamental excitement of the science will be in areas that depend on new physics and new technology, which we can today at best dimly glimpse.