JOHN JACKSON CBE, MA, DSc, FRS
John Jackson Image source: not known
If, like me, you cannot really get your head round the intricacies of astronomy, cosmology, astrophysics etc, you may find it hard to appreciate Dr John Jackson, but the work he did was hugely important as a basis for future studies and discoveries. In this piece I have tried to keep the science very simple for ease of reading, but if you want the technical information about any of the astronomy topics, Wikipedia has detailed articles on all of them.
It may surprise you to learn that, officially, the first 'solar observatory' was the Goseck circle in Germany, dating back approximately to the 49th Century BC. This was, of course, fairly rudimentary (i.e. ditches and wooden palisades), but its existence shows just how long we have been questing after knowledge of the solar system and beyond - we are still questing. Another amazing fact is that Pluto was not discovered until 1930.
John Jackson retired to Ewell (he lived at 30 Arundel Avenue) in 1950, having spent virtually his whole adult life in the field of astronomy, but it had not been his intended career.
Early life and education
John was born in Paisley, Renfrewshire on 11 February 1887, the fifth of eight children of mechanical engineer Matthew Jackson and his wife Jeanie (nee Millar). He was a bright lad and attended Paisley Grammar School, passing the entrance examination for the University of Glasgow when he was just 16. He studied mathematics and physics, graduating in 1907 with an MA (1st Class Honours), and was awarded a fellowship for further study. Continuing his studies, he graduated from Glasgow with a BSc in 1908.
John attended the classes of Ludwig Becker, who was Regius Professor of Astronomy at Glasgow from 1893 to 1935. Becker had the knack of engaging and inspiring students and John became interested in mathematical astronomy. In simple terms, among other things this involves counting objects in the sky and calculating distances, a task which is anything but simple. Becker described his pupil as the most brilliant student he had ever taught. Then, in 1909, John went up to Trinity College, Cambridge as an undergraduate to study mathematics and astronomy. He graduated with distinction in 1912 and was awarded the Tyson Gold Medal for astronomy.
In 1913 John became a research student at the Royal Society and made the first reliable determination of the orbit of the eighth satellite/moon of Jupiter (now known as Pasiphae), which had been discovered only in 1908. With apologies for the use of terminology, Pasiphae is what is known as a retrograde irregular satellite: this means basically that it orbits in the opposite direction from Jupiter, its 'parent planet', and the orbit is inclined. The difficulty of the task was compounded by the fact that Pasiphae is visually faint and also that its orbit is highly disturbed.
In 1914 he was appointed as a Chief Assistant to the Astronomer Royal, Frank Watson Dyson (the man who introduced the Greenwich time pips), and his first important work concerned the observations of binary (or double) stars that had been made in the past. A binary star is a star system which has two stars, one brighter than the other, orbiting round their common centre of mass (i.e. they are bound together by gravity). The illustration below shows the Sirius (Dog Star) binary system, which is the brightest star in the night sky. Sirius A is in the centre of the picture and the much fainter Sirius B, known as a white dwarf, is the faint blob at bottom left. Interestingly, Sirius B was once the bigger of the two but consumed its resources and became what is known as a red giant; it then shed its outer layers and became a white dwarf. When did this happen? About 120 million years ago, apparently.
As many junior staff at Greenwich had joined the forces, John performed a lot of observations personally, particularly on something known as the Airy transit circle. Like many terms in astronomy, this one gives you no clue whatsoever as to what it might be, but it is actually an instrument.
The Airy transit circle. Image source: The Illustrated London News, 21 April 1923.
There are any number of mind-bogglingly complicated explanations of how the Airy transit circle worked and what it was for, but we are interested in what John Jackson did with it. Fundamentally this instrument stood on the Meridian line at Greenwich and measured the angle at which stars crossed the meridian. Simultaneously a clock known as a regulator recorded the time at which this happened. The end result of this process was the ability to chart the stars, which was of use in navigation (satellites and other electronic aids have now superseded celestial navigation, although the science is still taught to some degree).
In 1917 John was commissioned into the Royal Engineers and served as a trigonometrical survey officer in France, which involved plotting for artillery. He returned to Greenwich in February 1919 and one project he worked on was the performance of the new (1921) Shortt free pendulum clock.
A Shortt free pendulum clock. Image source: National Institute of Standards and Technology via Wikimedia Commons.
Without getting into the technical details (and way out of my depth), a pendulum which is not actually inside the clock has a more regular and constant swing, so that in theory it should keep perfect time. In fact, the Shortt model was the most accurate type of mechanical clock ever produced. The proposition was that this clock could be used in making a reliable determination of the variability in the earth's rotation, but John showed that this was unlikely. He also conducted research into the rotation of Neptune, which had been something of a mystery planet since its discovery in 1846. It is the farthest planet from the sun and we are now aware that it revolves around the sun once in every 165 years. Nothing much was known about Neptune until the space probe Voyager 2 passed by in 1989. Incredibly Voyager 2 was launched in August 1977 and at the time of writing is still up there, as is Voyager 1. If you want to know where they are at any time you can find out at http://voyager.jpl.nasa.gov/where/. I think you will be amazed.
In 1933 John became His Majesty's Astronomer and then Director at the Royal Cape Observatory, Cape Town, where he carried out work on the positions and motions of the stars, known as the stellar parallax programme. This is horrendously difficult work but the underlying problem is the same as any parallax issue - that observation with the naked eye or an optical device distorts the relative positions of objects. And when you are talking about objects that are light years away from us (one light year being equivalent to about 6 trillion miles or about 9.5 trillion kilometres), you begin to see the scale of the problem.
The main building of the Royal Observatory in Cape Town. Photo by Janek Szymanowski via Wikimedia Commons.
One of John's keen interests was the observation of total eclipses of the sun. The dates of such eclipses can be predicted but you need to be in the right place on earth to see them. In the whole 20th century there were just four total eclipses that could be seen in Britain and John saw the second of them, in 1927, at Giggleswick, North Yorkshire: it lasted for a mere 24 seconds. In 1929 he travelled to Alor Star, Malaya to see another one, but it was obscured by cloud, and then he saw more - Canada in 1932, Cape Province in 1940 and Sweden in 1954. Most of us will not be around for the next one visible in the UK on 23 September 2090, but, if you are, then Cornwall is the place to see it (remembering not to look at it directly).
Total solar eclipse 1999, as seen in France. Image source: Luc Viatour via Wikimedia Commons.
A photograph of the 1929 eclipse taken by John Jackson's expedition is available on Flickr
John was a Member of the Council of the Royal Astronomical Society for 12 years and its secretary from 1924 to 1929; he became a Fellow of the Royal Society of South Africa in 1934, served on its council and was president in 1949. He became a Fellow of the Royal Society in the UK in 1938 and was awarded the CBE in 1950, the year he retired to Ewell. His wife, whom he married in 1920, was Mary Beatrice Marshall. There was one son of the marriage who sadly died shortly after his birth.