Fernrohr

Henry Ward Beecher once said, “The soul without imagination is what an observatory would be without a telescope.”

Astronomy, which one often enters into, with fantastic ideas about that which is celestial, is a field that helps us look beyond the physical realms that we find around us; a field for imaginative, for the keen-sighted, for the industrious students of science (for even the most famous Astrophysicists were arguably just that – students of science – even at the ends of their careers, given the leaps and bounds that we have taken over the years, in Astrophysics, in particular, and for that matter most of science, in general). For some reason, I was never too much into Astrophysics in my undergraduate days, but lately have got more interested in Cosmology and Astronomy, primarily because of them providing us with testing grounds for various possible unified theories of physics: a path one must humbly and cautiously try to tread. Observations and experimentation form a fundamental pillar of this field of research and study, given the importance empirical data has on making new theories in this domain. A telescope, or `Fernrohr’ as it is popularly called in German, is a vital element in the toolkit of an astronomer, and be it Galileo’s perspicillum (the term Galileo used for the telescope in the Sidereus Nuncius, a short treatise published in March, 1610) or the Cassegrain telescope or the Fermi Gamma Ray Space Telescope, the telescope has evolved as an instrument over the centuries since its conception (or should I say millennia, given a recent claim about the 3000 year old Assyrian Nimrud Lens being a part of a telescope?).

Recently I got the opportunity to get to see and learn about two of the oldest functioning telescopes in Cambridge: Northumberland and Thorrowgood telescopes, as part of the Cambridge University Astronomical Society (CUAS) induction, with a good friend – Sargam Mulay, on 16 October 2016. We were shown both telescopes and told about the various elements that constitute them by a CUAS member, before we went for life memberships, each. In this article, I would like to briefly talk about the same.

Northumberland

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The Northumberland Telescope is around 180 years old (having been erected when the Duke of Northumberland expressed his interest to build a telescope for the newly founded University Observatory in 1833) and is one of the oldest surviving and functional telescopes of the Cambridge University Observatory. A quick historical tit-bit of interest is that it was for a few years one of the world’s largest refracting telescopes with an accurate clock-driven equatorial mounting to follow a star in its diurnal motion across the sky.

The telescope was built in the ‘English’ form to support a fairly rigid structure that could support an achromatic doublet lens of 11.6 inches aperture and focal length 19 feet and 6 inches that had been made by Cauchoix of Paris, at the behest of the then Director G. B. Airy. The University provides us with some technical details of the structure in the following words:

“…The polar axis is composed of two massive triangular prisms. The main structure was built by the engineers Ransomes of Ipswich, and the fine mechanical work by the London instrument makers Troughton and Simms. The polar axis frame and the telescope tube are of Norwegian fir. The observing chair which gives access to the eyepiece in all positions is the original. The polar axis points upwards to the North celestial pole, at an altitude equal to the latitude of the Observatory (+52degrees 13minutes). A small electric motor, now replacing the original mechanical clock, turns the polar axis once in a sidereal day. Once directed to a star the telescope tube remains in a fixed orientation in space, while the Earth turns beneath it. The original Cauchoix lens is not (by present day optical standards) very good and it is now in store. The optics on the telescope are modern: a 12 inch aperture visual achromatic doublet designed by Dr R.V. Willstrop of the Institute and constructed by the local firm A.E. Optics Ltd. was installed to mark the 150th anniversary of the telescope.” 

Upon entering, and being so used to high-precision-automation, one of my first questions was related to whether the telescope had been upgraded to include such facilities. Incidentally, it has been and has had a facility to track celestial objects with a computer terminal within the structure, which was established in 2001.

northumberland_telescope_detailFigure: Schematic of Northumberland

Our demonstrator showed us how to operate the movement of the dome and the slit that opens up to let the telescope aim out into the skies, using ropes! It was fascinating to see these old technologies very much in use. Even the telescope had to be accessed using ladders and the lens cap had to be removed by hand. There was a small motor, as mentioned above, and options to move from the ‘lunar’ to the ‘sidereal’ modes and vice versa. Not to forget, the reclining observation chair was quite comfortable to sit in, by the looks of it.

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Figure: The Eyepiece, Northumberland Telescope, University Observatory

Apparently, the steel dome was a later addition after the original wooden dome had deteriorated by within a century of the establishment of the telescope. Moreover, due to the ‘English’ form, the telescope has limited manoeuvrability and there is a ‘dark portion’ of the sky that cannot be seen by this telescope due to the impossibility of moving the lens in that direction, given structural frames and inclined posts.

Thorrowgood

The Thorrowgood Telescope is also around a hundred and fifty years old, built by T. Cooke & Sons of York & London in 1864. It is housed in a smaller chamber, with a wooden, movable roof and has a ‘German’ form of equatorial mounting. The telescope is famous for its role in the study of double stars by Rev. William Rutter Dawes in 1855. William John Thorrowgood (1862 – 1928) was the last private owner of this telescope and the telescope is named after him, as it stands to this day. Interestingly, the telescope is technically still on an extended loan to the University Observatory, as it was offered to Professor Eddington, the Director in 1929, by the Royal Astronomical Society, initially for a period of 10 years.

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Figure: Thorrowgood (on the right) and Northumberland (on the left) Telescopes

The roof is moved using a rope-and-pulley mechanism, installed at multiple points in the cabin, and the slit-door can be opened using long sticks with handles and metallic tops to support the slit door when closed. We had a small guest on our trip to Thorrowgood, in the form of a hornet, and so half the time, the guide and our group were busy making sure that it stays put (when it did fly eventually, you should have been there to see our guide run! Ha ha!). We soon walked out as well.

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Figure: The Thorrowgood Telescope

Thorrowgood is smaller than Northumberland and has a problem in that when an object crosses the meridian between the zenith and the pole, it is usually necessary to interrupt the observations to reverse the position of the telescope tube, though there is a greater manoeuvrability that it provides over its ‘English’ form counterpart nearby.

All in all (sans the hornet), it was a fairly calm, informative session, and after passing the CUAS test (which allows one anytime access to both), I hope to use my knowledge to stargaze and know the world there yonder to a point of greater familiarity.

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