When you read this, I will be in the United States, either celebrating the arrival of the New Year in Gettysburg, Pennsylvania, or participating in the 215^th conference of the American Astronomical Society in Washington, DC.

I have never been to an AAS meeting before, and as they represent major events on the astronomical calendar, this will be an exciting experience. I will give an invited talk in the Historical Astronomy Division of the AAS, on the theme of the first hundred years of astronomical spectroscopy.

One of the most famous astronomers to graduate from the University of Canterbury in New Zealand has undoubtedly been Beatrice Tinsley (née Hill). Beatrice was born in England in 1941 and with her parents and two sisters, Rowena and Theodora, she migrated to New Zealand in 1946.

A famous old telescope has spent nearly half a century in New Zealand while awaiting a new home. There is now a good chance that a new life for the 18-inch (45-cm) Brashear refractor will be found.

The telescope has an illustrious history. It was installed in 1897 at the Flower Observatory in Pennsylvania, which was owned by the University of Pennsylvania. The mechanical construction took place in 1895-96 at the Warner and Swasey Co. in Cleveland Ohio. The optics were figured by John Brashear (1840-1920) in Pittsburgh. He was the famous American optical engineer and the equal of Alvan Clark. Together Clark and Brashear built some of the largest refractors of the late nineteenth and early twentieth centuries.

In an earlier article written for Cosmic Diary I gave my personal list of the top 25 discoveries in astronomy and astrophysics of the twentieth century (see Cosmic Diary for 18 June: http://cosmicdiary.org/blogs/john_hearnshaw/?p=96). The list was originally prepared for a seminar on this topic, but in compiling my list of 25, I actually considered a larger list of at first 50, which grew to 51 after the seminar!

So in this blog I am going to present what are the most important discoveries between numbers 26 and 51. The criteria for selection were only to include astronomy and astrophysics of the Sun, stars and beyond. Cosmology is of course included, but solar system exploration of planetary bodies by spacecraft was not part of my deliberations (important though that may be). By importance I am referring to impact in discovering something completely new, such as a new phenomenon or type of object, and research which went on to spawn a whole new branch of subsequent investigations. For sure, my judgement is very arbitrary, and I have not done a more careful analysis based on citations, though that would have created its own set of biases.

Most astronomers, when asked the question of who first published a Hertzsprung-Russell diagram would probably guess that it was Ejnar Hertzsprung, the famous Danish astronomer who went to Göttingen in 1908 to visit Karl Schwarzschild. In 1911, Hertzsprung published colour-magnitude diagrams for both the Hyades and Pleiades clusters. A few might guess that it was Henry Norris Russell at Princeton, who independently published a diagram of absolute visual magnitude against Harvard spectral type for nearby field stars using trigonometric parallaxes. However Russell’s first publication of his diagram was in 1914, several years after Hertzsprung.

Whether you answer Hertzsprung or Russell, your answer is wrong!

In an earlier blog on Cosmic Diary I published my personal list of the 25 greatest discoveries in astronomy of the 20^th century. See my article of 18 June at http://cosmicdiary.org/blogs/john_hearnshaw/?p=96 on this topic.

In that article I listed my choice of the 25 major discoveries of the last century, and broke the list down into 42 key papers. These papers represented fundamental discoveries of new phenomena, or new types of object, each of which resulted in the development of a major new field of investigation or branch of astronomy. Certainly much subjectivity went into the selection, but I suspect many others who go through this exercise would choose many of the same groundbreaking discoveries, perhaps in a slightly different order.

The University of Canterbury (my home institution) is fortunate to have a venerable old telescope of outstanding pedigree. It is the Townsend telescope, a 6-inch equatorially mounted refractor made by Thomas Cooke (1807-1868) of York, England in 1864. The telescope is in excellent working order and in essentially its original condition, with a mechanical weight drive and twin-ball governor for the polar axis. It is used now for public outreach. It is one of my favourite old telescopes, and any astronomical aficionado who likes antique telescopes should visit the Townsend in Christchurch.

The Townsend 6-inch telescope, 1864.

And now for something completely different! On a recent visit to Ondřejov Observatory near Prague (see my Cosmic Diary blog of 2 July) I was introduced to the Czech writer Jan Neruda (1834-91). As well as a writer, he was a poet, journalist and Czech patriot.

Jan Neruda published a series of poems in 1878 entitled Cosmic Songs (or Písně Kosmické) and Cosmic Song number 22 is entitled ‘Do frogs exist there too?’ I was introduced to Jan Neruda because he was a friend of the founder of the Ondřejov Observatory, Josef Frič. One of the original buildings at Ondřejov is a house whose exterior wall depicts a scene from Neruda’s poem. It shows frogs sitting around a pond with their frog teacher delivering a discourse on the marvels of the universe above, with stars and the Milky Way.

One of the highlights of my visit to Spain has been a recent visit to el Real Instituto y Observatorio de la Armada, or in English, the Royal Naval Observatory in San Fernando near Cádiz. I spent a week working in the magnificent library there at the end of June.

Real Observatorio de la Armada at San Fernando. The building dates from 1798 and houses the library and historical archives. Francisco Gonzalez is standing on the steps in front of the building.

First some history: el Real Observatorio de la Armada, or ROA for short, was founded in 1753 in Cádiz. In 1798 it moved to a far superior site in San Fernando, some 8 km from central Cádiz. For those who know the topography of the area, Cádiz is built on an island on Spain’s Atlantic coast, and connected to the mainland by a long and narrow sandspit. Essentially the city is fully built out and land is at a premium. San Fernando is also an island of sorts (la Isla de León) but a narrow channel separates it from the mainland proper.

This article discusses two classical papers in the history of astronomy, namely Christian Doppler’s (1803–53) announcement in May 1842 of the effect named after him, and a major article by Hermann Carl Vogel (1841–1907), which appeared in May 1892. Vogel’s work represented the first successful application of the Doppler effect to stars, to determine their space velocities in the line of sight.

Doppler’s theoretical paper and Vogel’s painstaking instrumental technique have together provided the basis for our knowledge not only of stellar motions, but have also indirectly contributed to our knowledge of stellar rotation, of thermal and turbulent Doppler line broadening in stellar (and other) spectra, of stellar masses in many binary stars, of galaxy masses from their rotation or velocity dispersion, of the missing mass problem in galaxies and clusters, of the expansion of the universe, of the nature of quasi-stellar objects and of the existence of the Big Bang. Indeed astronomical knowledge would almost certainly be vastly poorer if Doppler’s principle had never been applied in astronomy.