Of the many important developments in space astronomy during the past three years perhaps the most dramatic was the voyage of the Mariner II which passed less than 35 000 km from the surface of the planet Venus on 14 December 1962 and from which valuable measurements were made of the mass and magnetic field of Venus of the structure of its atmosphere and of conditions in the interplanetary medium. A second event of great importance to solar physics was the successful launching in March 1962 of the first of NASA’s Orbiting Solar Observatories’ the first satellite to be especially designed as a stabilized platform for solar observation. Six additional satellites in this series are planned between 1964 and 1966. Striking advances in the range and quality of rocket solar spectra have also been achieved. Soft X-ray spectra have been photographed to a short-wave limit of 13·8Å and the resolving power at longer wavelengths has been improved by as much as a factor of 10.

The principal recommendations of this Report on the system of astronomical constants are in accordance with the resolutions passed at Symposium no. 21 (Paris, May 1963). We first of all give a reference list of the constants of the system and a set of explanatory notes. We have used the term ‘primary constant’, rather than ‘fundamental constant’, since the latter has a connotation in astronomical usage that is inappropriate to the manner of selection of the primary constants. In choosing the values for the primary constants we have, perhaps, adopted a conservative view of the likely errors of their determinations, but even so the new system should be of adequate accuracy for astronomical studies for many years. Limits within which the true values are believed to lie are indicated in a later section, in which we also give expressions for differential corrections to the derived constants. Finally we discuss the manner in which this system should be introduced into the national and international ephemerides.

The discovery of magnetic fields on the Sun made by George Ellery Hale in 1908 (1) is undoubtedly one of the most outstanding events in the astronomy of this century. It is well worth mentioning that the geomagnetic field was a unique example of cosmical magnetic fields before this discovery. But during the last two decades, it became known through Babcock’s work (2) that numerous stars have also magnetic fields amounting to several thousand gauss on the average over the star’s surface and thus considerably exceeding solar magnetic fields concentrated mainly in sunspots.

My first encounter with what has come to be known as Space Astronomy took place at the Harvard Observatory in 1937 at a colloquium by Dr M. N. Saha on ‘A Stratosphere Solar Observatory,’ in which he described some of the advantages that astronomy would gain if the solar spectrum could be photographed from a balloon at a height of 40 kilometers, or above what was then thought to be the altitude of the ozone layer. As Saha put it, ‘the great intensity of the Balmer series and the associated continuous spectrum in the chromosphere has given rise to a large number of speculative theories.’ He then went on to suggest that if only the Lyman lines could be observed, the problem of hydrogen excitation in the Sun and stars would probably be completely explained, and the problems of stellar atmospheres would be nearer solution.