Richard Brinsley Sheridan, a Bathonian, opens his comedy, The Rivals, with a social sneer. Fag, the stylish apostle of bon ton, meets his fellow servant Thomas, a clodhopping yokel, and exclaims: “Why Thomas … But who the deuce thought of seeing you in Bath?”. One might ask the same of William Herschel, the Hanoverian bandsman’s son, who, having discovered Uranus, was to pass the last forty years of his life as a Crown pensionary, living just outside Windsor. How did Herschel come to spend his formative scientific years in Bath, resort of the giddy and the gay? How did he come to discover Uranus there?

In 1784 Jean-Dominique Cassini, who as Director of the Paris Observatory was one of the foremost professional astronomers of his day, wrote

The history of astronomy knows great telescope builders, great observers, and great theorists; but only William Herschel falls indisputably into all three categories. When he became a professional astronomer in the summer of 1782, he had already demonstrated his skills in the construction of big reflectors: the mounting of his 20ft still left much to be desired, but otherwise his mirrors, his eyepieces, and his mountings combined to give him a head start over any other astronomer in the examination of distant and therefore faint objects. And in little over a year after his arrival near Windsor Castle where he was to be available on occasion to show the heavens to the Royal Family, he completed one of the great telescopes of all time: his ‘large’ 20ft reflector, with mirrors of 18 inches diameter, and soon to be equipped with a stable ladder-type mounting so that telescope and observing platform could be rotated together by a single workman. This mounting he further improved and refined in the years to come, and meanwhile the telescope was his favourite instrument and in constant use during his twenty-year systematic search of the sky for nebulae. In his extreme old age it was refurbished under his direction by his son John, who resurveyed his father’s nebulae and then took the telescope to the Cape of Good Hope to extend the coverage to the southern skies. John’s General Catalogue of Nebulae and Clusters of Stars (1864) led to the New General Catalogue that astronomers use today.

In his Astronomisches Jahrbuch for 1784, Johann Elert Bode summarises the scanty information that had reached Berlin concerning the recent discovery on 13 March 1781 of a new heavenly body by a still-unidentified observer in England. Its easterly progress through the Milky Way during the interim six months had been parallel to the ecliptic, and thus entirely consistent with the view - hitherto based only upon its brightness and clearly-defined disc - that it was a planet and not a comet. Bode therefore asks why this sixth-magnitude object had not been previously detected, and raises the question of whether it had in fact been observed by earlier astronomers but misidentified as a star. He himself had already scanned the star-catalogues of Tycho Brahe, Johann Hevelius, John Flamsteed, and Tobias Mayer; and had come to suspect that a missing sixth magnitude star in the constellation Capricorn, observed by Tycho on 20 November 1589, might have been the planet. A second possibility which still required investigation was Mayer’s star No. 964, observed in Aquarius on 25 September 1756.

The discovery of Uranus was a very much more important event than the addition of one primary planet to the Solar System. Indeed, it was to greatly influence future developments in a number of diverse regions. In this paper we shall consider its impact in three such areas: (l) the research on, and the acceptance of, the Titius-Bode Law; (2) the search for, and subsequent discovery of, a planet exterior to Uranus and (3) the direction of William Herschel’s own career.

Several cosmogonic theories are examined for their ability to explain the details of Uranus’ composition as inferred from observations and interior models. Suggestions are made as to how future work may enable us to decide among competing scenarios.

We present an updated study of Uranus interior models using current information about the planet’s gravity field and rotation rate. The most plausible model, both from the point of view of recent data and cosmogony, has a central core of iron and magnesium silicates, an outer envelope of liquid water, methane, and ammonia, and a deep “atmosphere” of almost four earth masses of hydrogen, helium, and methane. The “atmosphere” contains a gravit at ionally nonnegligible amount of methane — about 40% by mass. All plausible models are most consistent with a rotation period of ~15 to 16 hours.

The magnetosphere of a planet, as the name implies, is the region surrounding the planet in which the planetary magnetic field plays a dominant role in determining the behaviour of the medium. The inner boundary of a magnetosphere is the surface of the planet if it has no significant atmosphere (as in the case of Mercury), or the lower ionosphere in the case of planets with atmospheres. The outer boundary, usually termed the “magnetopause”, is shaped by stresses exerted by the solar wind, being blunt on the upstream side, with normal stresses playing a dominant role, and extending in a comet-like “magnetotail” on the downstream side away from the Sun largely as a result of the action of shear stresses. The characteristic size of a magnetosphere, namely the distance Lm (in planetary radii) to the subsolar point is determined approximately by balancing solar wind ram pressure and the magnetic pressure:

where n is the ion number density and Vs the speed of the solar wind, m is the average ion mass, Bo the (dipole) field strength at the surface of the planet and C is a constant of order unity.

From the start of this century until the mid-1970’s the rotation rate of Uranus was reported to be 10.8 h in a retrograde sense (see, for example, Allen, 1955), but a cursory examination of the origin of this datum reveals that little confidence should be placed in it.

Three independent techniques for measuring the rotation rate are available, each very difficult and not including the most direct method of observing the motion of features across the disc. Visual observers have reported features from time to time (see Alexander, 1965, for a full historical account), but the mean diameter of Uranus is only 3.6 arcsec and large high contrast features are rare in the visible spectrum, if they exist at all.

Measurements of the gross properties of Uranus are enough to show that it is a planet with quite unique characteristics. The best estimates of its radius (24900 km; Danielson, Tomasko and Savage, 1972) and of its mass (14.54 Earth masses; Klepczynski, Seidelmann and Duncombe, 1970) imply an interior structure and overall composition that set it clearly apart from Jupiter and Saturn (Hubbard and MacFarlane, 1980).

Observations of the minute disks of Uranus and Neptune from the surface of the earth present a major challenge to any observatory site and require the most advanced techniques in optical imaging instrumentation. Less than 4 arcsec across, the disk of Uranus would fit within the Great Red Spot of Jupiter in the focal plane of a terrestrial telescope; the smaller disk of Neptune, less than 2.5 arcsec in diameter, is scarcely more than half again that of Ganymede, the largest of the Galilean satellites. At present, both planets are situated at far southerly declinations, making them even more difficult objects for Northern Hemisphere observatories.

One of the fundamental problems in atmospheric physics is concerned with providing improved weather forecasts for the Earth and predicting the future climate of our planet. However, this is a particularly difficult task since the meteorology of the Earth is affected by a wide range of physical factors - clouds, oceans, continents, polar caps, deserts and forests - all of which respond differently to ‘the solar energy which drives the weather systems. In addition, external factors, such as the changing energy from the sun, are thought to strongly influence the Earth’s meteorology. To provide a broader understanding of atmospheric phenomena, detailed studies of planetary atmospheres have been conducted, since they provide a unique opportunity to investigate these basic problems in fluid dynamics under boundary conditions which are quite different from those found on the Earth.

The Uranian satellite system contains five known members, all of which are difficult to study owing to their faintness and proximity to Uranus. The photometry of these objects is not in a satisfactory state, nor is the photovisual spectrophotometry. Infrared observations are in some sense easier and more precise because Uranus itself is faint in the near infrared and interferes but little with the satellite studies. The near infrared work reveals water ice or frost on the satellite surfaces, perhaps in a very pure state. The satellites are most similar to Ganymede in terms of the strength of the ice bands, but subtle differences, now under study, may be present. The diameters and masses of the satellites, while not readily measurable directly, can be estimated from generalizations about the surface geometric albedos, assumed mean densities, and certain dynamical arguments. Most of the data and theories are consistent with bodies with radii in the range 160-520 km (similar to the larger asteroids) and albedos on the order of 0.5, consistent with ice and snow. The mean densities are probably similar to those of the icy Saturn satellites, about 1.3 g/cm3. Uranus’ satellites probably formed after the event that caused the planet to tilt to the presently observed obliquity.

One of the very exciting discoveries in astronomy and planetary sciences in recent times is the detection of a series of narrow rings around Uranus. During more than three centuries, the rings of Saturn have had a special fascination and symbolism and an enormous amount of literature has been devoted to studies of their nature, properties and origin. The discovery of Uranus’s rings, and two years later of Jupiter’s rings has not only renewed interest but also raised a number of new cosmogonical questions.

Since their discovery in 1977 (Elliot 1979), the dark, narrow rings of Uranus have intrigued dynamicists. The main enigma has been how the rings can remain so narrow - only a few km wide - when particle collisions and the Poynting-Robertson effect should cause the particles to disperse. The Uranian rings have posed other problems as well, and have proved to be a unique system for developing dynamical models of rings. The reason for this theoretical interest is the high precision and time coverage of the data available from occultation observations. With occultations we obtain a spatial resolution of 1 km in the position of ring segments and a resolution of 4 km in their structural details. These high-resolution data are available sufficiently often to be useful for dynamical purposes - at the rate of 1-2 events per year. This spatial resolution is somewhat better than that obtained by Voyager imaging of Jupiter’s and Saturn’s rings (Owen et al. 1979; Smith et al. 1981). Ground-based images of the Uranian rings, obtained by Matthews, Nicholson, and Neugebauer (1981), have a spatial resolution of ~50,000 km. Although unable to resolve individual rings, these data have established the mean geometric albedo of the rings at 0.030 ± 0.005.

The Space Telescope Observatory, scheduled for launch in 1985, is described. The advantages of the space environment and the consequent features of ST performance are given, with Uranus observations as examples. The first generation instruments, including two cameras, two spectrographs and a high speed photometer, are discussed. The Space Telescope Science Institute, which will manage the Observatory, is discussed briefly. The potential scientific interaction with the Voyager 2 encounter of Uranus is also considered.