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We have seen that the astronomical observational objections presented a serious obstacle to the acceptance of the key Copernican thesis of the earth’s motion. Galileo was impressed as much as anyone by the power of these anti-Copernican arguments. Nevertheless, he was able to find a way out of these difficulties. This was a long, arduous, and tortuous process. To understand and assess how Galileo defended Copernicus in this regard, we have to examine how his attitude toward Copernican astronomy and astronomical observation evolved in the course of his life, especially in his earlier career. To this we now turn.

In the previous two chapters, we covered problems related to the physical notion of time in (i) philosophy and (ii) Newtonian mechanics. Our contention is that a theoretical analysis of the concept of time in Newtonian theory is and was of greater relevance than the Michelson-Morley experiment in understanding the special theory of relativity. Here we argue in support of the latter part of the contention. The Michelson-Morley experiment, though relevant, was not intended to test the constancy of the speed of light. Rather, the experiment attempted to distinguish between the theories of Fresnel and Stokes, both of which used the aether hypothesis. Michelson concluded that the Stokes theory was valid, while Miller was awarded a prize for his claim to have detected an aether drift, which was widely disbelieved.

The most significant basis of the reputation of a scientific organization is the accuracy and influence of its work. From a comparison of values of certain astronomical constants and stellar parallaxes obtained at Pulkovo and elsewhere, the extremely high weight given to the Pulkovo values (e.g. by Newcomb) is further justified in retrospect given the small deviations between Pulkovo values and the “modern” values accepted a century later.

The precision obtained in equating a very precise linear dimension to a very small and imprecise angular dimension sets a limit on the precision of the distance scale of the Universe. Within the Solar System, errors in distances are of the order of one part in one hundred million, but beyond its limits only a single star, Barnard’s star, has a distance known to better than one part in one hundred, and distances known to one part in twenty from parallaxes are limited to only a few hundred nearby stars. Yet most other distance methods and results must ultimately be calibrated against distances to nearby stars derived from the heliocentric parallax method and its observations and uncertainties.

Thirty-six percent of the 1641 visual components nearer than 22.5 parsecs listed in 1969 were members of systems. Meanwhile for an extension to 25 pc of the Sun about 2000 additional objects are found, however, only 22% of them are known today as members of systems. Angular separations are observed from a few tenths of an arcsec to more than one degree. The widest linear separations at the sphere seem to be larger than 105 astronomical units. The observed frequency distribution of the projected separations for all nearby stars is given and compared with the frequency distribution of more complete subsamples. The 32 presumable systems with the widest separations are discussed with respect to their astrometric and spectroscopic properties.

In recent years, the Van Vleck Observatory has undertaken a program of broad-band photoelectric photometry of the stars on its parallax program and of similar stars which are possible members of nearby clusters. Most of the cluster and field stars are K and M dwarfs inhabiting the lower main sequence. The photometry includes the R and I bands of the Kron system as well as the normal B and V magnitudes. The data has been obtained with the 1.3m and no. 20.9m telescopes of the Kitt Peak National Observatory and the 0.6m Perkin telescope of the Van Vleck Observatory.

The stars in the FK4- and FK4Sup-Catalogue are supplied with visual magnitudes and spectral types essentially on the basis of the Henry Draper Catalogue. There are several good arguments, to compile additional astrometric, photometric and spectroscopic data for these stars. Not only to detect astrometric effects, which can produce errors in the fundamental system, like magnitude equation, colour equation, and foreshorthening effect. For the last one distances and radial velocities have to be known. But also to study the kinematics of the FK4/FK4Sup stars, in profiting from their high precision in proper motion.

Progress in science depends to a great extent on planed programs of research. However we must not ignore the role played by serendipity. Significant discoveries now and than are made unintentionally, as an unexpected byproduct, of a program planned for a different purpose. A classical example is the discovery of stellar aberration in 1726 by James Bradley. Intent on finding stellar parallax, which later proved to be below Bradley’s attainable accuracy, he did find the yearly aberration effect, differeing 90° in phase from parallactic displacement, with a total amplitude of 41″ (Chapter 3).

In 1957 I have published a catalogue of 915 stars — single and multiple systems — nearer or apparently nearer than 20 parsecs. The 1969 edition was extended to 22.5 parsecs with 1328 objects. In the last decade new trigonometric parallax programs have yielded first results and their accuracy has been increased. In 1981 the number of stars with known parallaxes exceeding 0.044 is estimated close to 1700. Certainly, that are not yet thirty per cent of the stars really existing in this volume. But time seems to be ripe for a third edition which should be extended to 25 parsecs now.

Trigonometric parallaxes are reported for ten bright, southern late-type MK giant stars. The plate material was obtained with the 66 cm Yale-Columbia refractor at the Mt. Stromlo Observatory and measured with the PDS 1010A at Mt. Stromlo. The ten stars include HR 794 (KO III), HR 1247 (M2 IIIab), HR 2245 (M2.5 III), HR 2773 (K3 Ib), HR 3518 (K3 III), HR 3803 (K5 III), HR 5287 (K2 III-IIIb), HR 5603 (M3 IIIa), HR 6832 (M3.5 III), and HR 6913 (K1 IIIb). The modern parallaxes are compared with earlier results and the luminosity calibration for these stars is discussed.

Combining the information from the speckle interferometric and spectroscopic binary βCrB a mass of 1.82 solar masses and an absolute visual magnitude Mγ = 1m.42 is found, indicating that the star may be in that state of evolution, when the stellar core has shrinked after hydrogen exhaustion in it and the energy generation mainly comes from the envelope. The question whether all magnetic Ap stars are in that special evolutionary state is revived.

The stellar intensity interferometer at Narrabri Observatory was used to measure the angular diameters of 32 stars in the spectral range 05f to F8 and brighter than about V = +2.6. The results were combined with measurements of absolute flux and, in a few cases parallax, to find the emergent flux, effective temperature, radius and luminosity of the stars. The methods used to calibrate these measurements and their uncertainties are discussed. It is shown that in measuring emergent flux and effective temperature the major uncertainties were most frequently in the measurements of angular size.

Although we are familiar with the fundamental facts concerning Copernicus and his work, history is not, nor was it ever, a closed book. This is all the more true with regard to the history of scientific discoveries, for they assume different shades and colors as the body of scientific knowledge grows. That is one of the reasons why we so frequently go back in thought to those who played a decisive role in the development of science, to the men of the Renaissance, among whom one of the brightest lights is Copernicus.

The President, after welcoming members to the meeting of the Commission, invited discussion on the draft report. The report from the Leander McCormick Observatory had not been received in time for inclusion in the draft report.

Distances in astronomy are usually so enormous, that they can only be measured by means of large instruments and a very careful measuring technique. We shall imitate the method of working on an enormously enlarged scale and with artificial light-sources.

The work of Copernicus represents not only the beginning of modern astronomy but also the beginning of the modern science of the universe and of nature. Awareness that nature is governed by laws emerged through study of the heaven and through observation of the Sun, the stars and the planets, for it is there that the laws are most striking.