Lenses, Mirrors & Mountains

A HISTORY OF AMERICAN OBSERVATORIES

The late Allan Chapman, Faculty of History at the University of Oxford, was a member of Wadham College and an Astronomy Now contributing consultant. Please see page 20 for an appreciation of his life and work.

Travelling across the United States of America from east to west, the astronomical observatories become increasingly ambitious. They symbolise an age of scientific philanthropy with wealthy donors seeking to build larger and larger telescopes. Allan Chapman tells the story of these wonderful constructions.

One might perhaps argue that the oldest observatories on the American land mass were those sun-reverencing Andean peak centres such as Machu Picchu, dating from long before Europeans set foot on the American continent in 1492. But they were places of worship, and not of scientific study.

And while not especially astronomical, Thomas Harriot, the mathematical and linguistic friend of Sir Walter Raleigh, delivered the first ‘modern’ science lecture on the American continent to a group of elders of the Algonkian nation in 1588, having first learned their language. It took place in present-day Virginia and the subject was ‘modern’ technology: magnetism, optics, clocks and such.

In the late seventeenth century, the gentlemen of the early Harvard College, Boston, would have received some teaching on astronomy as it was then understood, with astrolabes, armillary spheres, and small telescopes, but there was nothing resembling an ‘observatory’ as a fixed institution until the early nineteenth century.

Between 1763 and 1769, however, fixed astronomically-determined observation points were established in the surveying of that demarkation line separating Pennsylvania and Maryland by the English astronomers Charles Mason and Jeremiah Dixon: the Mason– Dixon Line.

But once the survey was completed, the geodetic survey points did not become permanent astronomical observatories. It was not until c.1830 that the boom in American observatory building took off, largely as a result of the establishment and flourishing of benefactor-driven private colleges, in the wake of Harvard.

Observatory building takes off

Several other factors played a prominent role, one of which must surely have been North America’s low geographical latitude. At its most northerly point, bordering Canada, America is approximately 45 degrees north, and extends to 25 degrees south. This places it more to the south than anywhere in Great Britain, making the celestial equator that much higher in the sky. Some years ago, getting out of a car amidst the high pines of Bemidji, Minnesota, after a long flight from Gatwick, I gasped in amazement at the brilliant starry sky – the like of which could never have been seen in England. There was the Milky Way in all its glory, along with the Orion Nebula, and an aurora borealis which resembled a town on fire!

With such skies above, it is hardly surprising that the enquiring young minds of the rapidly expanding American cities and academic institutions desired astronomical departments equipped with great telescopes.

Although at this time William Herschel’s discovery of Uranus and spectacular galactic discoveries were setting the scientific world ablaze, they could only really be seen and made sense of when viewed with large speculum-mirror reflecting telescopes. The optical construction of these telescopes was very much a Herschel secret, and when commissioned from him they ranged in price from £110 to more than £3000. They were also complicated to use and maintain.

This meant that refracting telescopes, which use lenses instead of mirrors, were much more versatile optical instruments, making them the obvious choice for a new observatory in a distant location. The breakthrough in refracting telescope technology had come back in 1758, when John Dollond announced and patented his achromatic lens.

Achromatic lenses combine two types of glass (crown and flint) to bring different colours of light to the same focus. This greatly reduced the coloured fringes that had been seen around bright celestial objects with simple lenses.

Yet pure crown and flint glass blanks of more than three or four inches in diameter that were free from streaks and striations were hard to produce. It was Joseph Fraunhofer, while head of the Benediktbeuern glassworks, Munich, after 1800, who developed techniques for the production of larger slabs of pure, striation-free glass. This made possible object glasses of 9.6 and more inches in diameter, such as those that Fraunhofer built for his pioneering equatorially-mounted clock-driven telescope of 1824.

Unleash the refractors

This unleashed a wave of new large-aperture refracting telescope construction, on both sides of the Atlantic. And it was this, I would suggest, that initiated the ongoing stream of observatory building in the USA, the great majority of which were refractor-based. Refractors, moreover, were easier to use, at least before large silver-on-glass mirrors with electrical controls were developed in the late nineteenth century.

Perhaps the first significant American observatory was that donated by Albert Hopkins of Williams College Massachusetts in 1836–8, which housed a 7-inch refractor. Then, in 1842, Ormsby MacKnight Mitchel, along with private and civic subscribers, established a fine civic observatory in Cincinnati, with a superb Merz and Mahler 11-inch refractor. Indeed, in 1842, US President John Quincy Adams beseeched the citizens of the USA to be like those of Cincinnati, and build ‘Light Houses’, or astronomical observatories.

It would have been interesting to know what the novelist Charles Dickens would have made of the great Cincinnati Observatory, but he had visited the burgeoning ‘City of Seven Hills’ in April 1842, shortly before its construction. He recorded his visit in American Notes, where he praised the civic pride and elegance of the new American city. Had the Cincinnati Observatory been built and open to the public when Dickens visited, one wonders how awe-struck he might have been!

New observatories began to abound, and were invariably the products of the prosperity brought by burgeoning entrepreneurial activities, such as the railroads, tramcars, great river steamboats, manufacturing, and the completion of the trans- continental railroad in 1869.

In the early 1840s, it was felt that Harvard College required an observatory similar to the Berlin and Pulkova ones in Europe, and William Cranch Bond, a Rochester clock manufacturer and astronomer, was approached. Bond built a fine observatory, largely in the wake of the astronomical enthusiasm generated by the appearance of the Great Comet of 1843, which led to Harvard commissioning the ‘Pulkova Twin’, after the great telescope at St Petersburg. This telescope, also built by Merz and Mahler back in Europe, had a 15-inch lens and saw its first light in 1847. For several years it would rank as America’s largest telescope.

Some years ago, at a conference, I was given a personal guided tour of the early Harvard Observatory instruments by a former senior staff member, and was deeply impressed by this superlative great refractor.

Wider technological innovations

Astronomy, and the foundation of new observatories, benefited from several other new technologies that were a wider part of nineteenth century life, but to which the sheer vastness of the continent conferred especial research potential. These included railways (railroads), steamships, photography, telegraphy, and, at the very end of the century, petrol-engined rough-road motor vehicles.

After 1893, Harvard established a high- elevation, clear-sky observatory at Arequipa, in Peru, with its command of the southern hemisphere skies. Harvard astronomers could now travel by train to a western coastal port, and then by train on Chile’s post-1840 burgeoning mineral railway system. Or, more productively, observational data collected beneath crystal-clear southern hemisphere skies, such as about the Magellanic Clouds, could be photographed and otherwise recorded, and then telegraphed or dispatched for a team of female astronomers to analyse the complex spectral and other data in a Harvard laboratory.

Perhaps the most distinguished of these Harvard astronomers were Annie Jump Cannon and Henrietta Swan Leavitt, who did astronomy from a photographic-plate-measuring microscope on a table-top. Henrietta Leavitt measured many thousands of plates and stars, transforming our understanding of the deep-sky universe. This was founded on her discovery of the period-luminosity relationship for Cepheid variable stars. Cepheids are variable stars whose maximum and minimum brightness make them ‘periodic variables’, with fixed luminosity cycles, and Henrietta Leavitt computed the synchronising of their cycles with their distance. This allowed astronomers to establish ‘measuring rods’ into deep space.

Annie Jump Cannon’s especial skill was measuring photographic spectra to establish the specific chemical composition and sequencing of stars, especially from Arequipa. Indeed, by 1900 these women, working indoors under the Harvard Observatory Director Edward Pickering in a room with plate-measuring instruments, were doing astronomy with greater comfort than could have been imagined in 1845.

The Red Planet and its canals

In 1877, Mars made one of its periodic ‘bypasses’ of the earth, and Giovanni Schiaparelli of the Milan Observatory in Italy argued that one could see ‘canali’ in the Martian deserts. Although ‘canali’ simply means straight lines, the English-speaking world interpreted them as artificially-dug waterways. So, was Mars a drying-out world, and were the ‘canals’ built to drain water from the icy poles to the arid equator, allowing the Martians to practise agriculture? The idea of super-intelligent Martians grabbed the global imagination, fuelling such novels as H. G. Wells’s The War of the Worlds (1898). Were the Martians vicious aggressors or poor, hungry, thirsty victims? The question would continue to be asked by the general public well into the twentieth century.

One Boston millionaire with an interest in the sciences, Percival Lowell, set himself the task of demonstrating the reality or otherwise of the Martian ‘canali’. Lowell built one of the most powerful refractors in private hands, in a ‘prime sky’ location beneath the Arizona desert, near to a US survey point at Flagstaff, in 1894. This telescope had a 24-inch-aperture object glass by Alvan Clark, and opened up a superlative view of Mars and the other planets.

No Martian canals were ever seen with Lowell’s 24-inch, though it and other Flagstaff instruments went on to make other discoveries. The first sighting of Pluto was made by Clyde Tombaugh, using the Flagstaff 13-inch, in 1930.

The fashionable Drapers

Dr John William Draper, a leading St Helens, England-born New York physician, chemist, and astronomer, took the first photograph of the Moon in 1840. His son Henry followed in his footsteps, and married Mary Anna Palmer, who was both a New York socialite and an accomplished astronomer and photographer. Indeed, the Drapers were similar to Sir Willam and Lady Margaret Huggins in England, who were well-off married Grand Amateur astronomers, where the wife was a pioneer of photography and of daytime spectrum-plate measurement.

The Drapers lived in fashionable New York City, where they had a fine observatory attached to their house. But searching for clearer skies, they built a major private observatory on their property at Hastings-on-Hudson, outside NYC, and undertook original photo-spectroscopic research with a fine Alvan Clark telescope. Henry and Anna, just like Sir William and Lady Huggins, worked as a team.

Wishing to take advantage of the unpolluted skies of the West, Draper led an expedition aimed at building another new observatory. However, the overworked, self-driving Draper became ill once back in New York, and the eminent doctor died of pleurisy in 1882. Following Henry’s death, Anna bequeathed their observations to Harvard.

Aperture fever

American astronomy was in so many ways an astronomy of increasingly large-aperture refracting telescopes from the 1840s onwards. This was made possible by several opticians, most notably Alvan Clark, who mastered and perfected the casting, figuring, and polishing of increasingly large crown and flint glass blanks. The progress of the big refractors culminated in the instruments of the Lick and Yerkes Observatories in the 1880s.

James Lick had acquired his fortune through piano manufacturing in San Francisco, and built the first mountain-top observatory on Mount Hamilton, with its 36-inch-aperture Alvan Clark object glass, in 1888. Then soon afterwards, the Yerkes 40-inch-aperture effectively saw the refractor reach its limit, both from an optical and from an engineering perspective.

And so the next step forward in optical astronomy could only come from a reappraisal and a fresh approach towards reflecting telescopes. This demanded very large glass blanks, along with a re-design of the mount that would hold the telescopes. George Ellery Hale the astrophysicist, who was involved with the Yerkes refractor and recognised its limitations, therefore turned his attention to the development of a new large-aperture reflector on a radically re-engineered mount.

The real transformation in technology and research potential came in 1908 with the 60-inch-aperture instrument on Mount Wilson: the mighty camera that could see deeper into space than anything before it. The California mountain top would later be the home of the 100-inch Hooker in 1917, while the great 200-inch-aperture Hale reflector on Mount Palomar would come to be the world’s largest telescope in 1948.

Though multi-mirror instruments subsequently enabled greater apertures to be built, it was the Hubble Space Telescope, named after Edwin Hubble, the galaxy-discovering astronomer, that took astronomy into air-less space. And this, when combined with new electronic technologies, and rocketry, led to wonders hitherto unimagined.