Henderson, the first distance to a star and Scottish confidence

One hundred and seventy five years ago a Scottish astronomer published the result that he would become famous for. Unfortunately it was the timing of the result that was the most note-worthy thing.

Thomas Henderson didn’t follow what we would now consider a typical astronomical career. He started out in Dundee as an apprentice to a lawyer. Six years later he moved to Edinburgh to further his law studies eventually becoming secretary to the Lord Advocate (similar to the Attorney General in other countries). All the while Henderson had been developing his astronomical hobby, focussing on computational methods. It was his brilliance in this that resulted in him determining more accurate methods to work out the timing of the Moon’s passage infront of stars. This calcualtion brought him to the attention of Thomas Young who at the time was running the Naval Almanac Office, in-charge of accurately calculating the timing of astronomical events. He applied for a job at the Almanac Office after a posthumous reccomendation by Young but was turned down. He was also turned down for a job at Edinburgh University around this time. Henderson then took a job working at the Cape Observatory (yes, he had to move halfway round the world to stay in astronomy, how modern). He spent a year there, working ridiculous hours making a massive number of astronomical observations. This appears to have burnt him out and he moved back to Edinburgh to become the first Astronomer Royal for Scotland. But he brought back with him the dataset that would see his name go down in history.
The distance to stars can be pretty hard to measure. While the noted astronomers of antiquity had noted “the fixed stars” as opposed to the wandering planets, by Henderson’s time it was understood that stars moved slowly across the sky. This indicated that the stars weren’t infinitely far away and (due to its high motion) that Alpha Centauri was probably quite close. The best way to estimate the distance to a star is using trigonometric parallax, taking advantage of the subtle changes in the point of view a star is observed from at different stages in the Earth’s orbit.
This first step on the stellar distance ladder became one of the big science goals of the mid-19th century. Henderson was one of the best in the world in astronomical calculations and soon after returning from the Cape, he had noticed an oscillation in the position of Alpha Centauri. This was about an arcsecond, roughly the size of a Coke can viewed 440km away. This made Alpha Centauri about 3.25 light years away (compared to the true distance of 4.4 light years). However Henderson wasn’t sure, he thought his instrument may be suspect so he waited for more observations from the Cape to confirm his results. Unfortunately his lack of confidence bit him, he was beaten to the first parallax measurement by the Prussian astronomer Friedrich Wilhelm Bessel nipped in and measured the parallax of another fast-moving star 61 Cygni in 1838, two months before Henderson’s publication.
Henderson’s lack of confidence may have stemmed from previous parallax measurements which were later shown to be nonsense. However it may have stemmed from the inherent lack of confidence Scots have. Scottish people are among the least confident in the developed world, Scottish satire writers pick “Lloyd, I’m ready to be heartbroken” to sum up the Scottish national football team. Perhaps the best summation of this is Gordon McIntyre’s, “I hate the way we expect to fail, and then we fail, and then we get bitter because we fail.” A nation defined by glorious failure, shy about its history of discovery, doesn’t produce risk takers.All that said, if I’d have been in Henderson’s position, I would have done the same. We’ve all seen massive “discioveries” knocked down by data released soon after and in science it should be more important to be right than to be first at all costs.

The astronomer prince of Samarkand

Sweeping conquests in the style of Genghis Khan, a shining city at the crossroads of east and west and amongst it all, one of the great astronomers of his age……

I should start by saying that I came across the subject for this post from listening to the BBC radio series A History of the World in 100 Objects as a podcast. The particular episode was on the jade cup of Ulugh Beg. The owner of the object in question was the descendant of one of the most successful military campaigners of the late middle ages and was himself one of the great Islamic astronomers.

In the late 14th century Central Asia was a patchwork of successor states to the great Mongol Empire. In this period the Turco-Mongol military leader Tamerlane waged campaigns of conquest from India to Mesopotamia. In doing so he founded the Timurid Empire which in stretched from Baghdad and the Black Sea in the west to Kashmir in the east and from the Indian Ocean to the Aral Sea.

After Tamerlane’s death, his son Shah Rukh took over most of empire covering Iran and Central Asia. Rather than rule his territories from Tamerlane’s capital of Samarkand in what is now Uzbekistan, he moved his capital to Herat in modern-day Afghanistan. He then sent his sixteen year old son Ulugh Beg to rule over Samarkand.

When I think of the great Islamic astronomers and centres of learning I automatically envisage Cairo, Baghdad and Damascus. Samarkand by contrast conjures up images of bussling commerce and great wealth due to its position on the Silk Road. But, like his father and grandfather before him, Ulugh Beg was a patron of the arts and sciences. He founded an Islamic school (madrasa) in Samarkand but was also interested in pursuing science himself.

An enthusiastic scholar of astronomy and mathematics Ulugh Beg’s madrasa was a place with a vibrant academic culture attracting great minds such as the Persian mathematician al-Kashi. To satisfy his growing interest is astronomy he build a magnificent observatory. Before telescopes astronomical measurements could be difficult. The positions of stars were measured by timing them crossing their highest point and using sextants to measure their height while they did this. Ulugh Beg’s observatory had a massive sextant over 35 metres in diameter. This was used to measure the length of the astronomical year and the tilt of the Earth’s axis more accurately than later, more famous astronomers such as Copernicus and ol’ Mr. Brassnose Tycho Brahe. Ulugh Beg also catalogued nearly a thousand stars and determined trigonometric relations to astonishing accuracy.

Ulugh Beg's Observatory in Samarkand

The observatory also produced great thinkers of its own. One such was Ali Qushji, the son of Ulugh Beg’s royal falcon trainer. He challenged the orthodox astronomical thinking of the time, trying to break astronomy free from the shackles of Aristotle’s model of the world and making it an independent science. He also postulated that the Earth was not stationary based on his observations of comets.

Ulugh Beg was one of the great scientists of the Middle Ages, however he was not a successful ruler. After his father’s death he lost several important battles and was eventually killed after his own son moved against him. The Timurid Dynasty would survive thanks to his great-nephew Babur, who founded the Mughal dynasty in India. This did not officially fall until the Sepoy Rebellion in 1857. Just to put that into context, Tamerlane and Ulugh Beg’s dynasty lasted from before the European Renaissance to the time of Queen Victoria.

If you want to read more on Ulugh Beg, I found this article from the University of St. Andrews very informative.

That’s for Jan Brueghel the Elder…….

This post was chosen as an Editor's Selection for ResearchBlogging.org

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OK so yet again I’m blogging on a topic I don’t know terribly much about but that I found interesting. A month ago this paper by Paolo Molaro and Pierluigi Selvelli from Trieste Observatory appeared outlining the interesting case of early telescopes in paintings.

The paper focusses on the work of Jan Brueghel the Elder and in particular two works made between 1608 and 1617. My knowledge of Flemish painters is limited to Jan van Eyck and Hieronymus Bosch (and most if the latter comes from watching In Bruge) so forgive me if I can’t discuss the finer technical points of the art, there does appear however that there could be be a fascinating story behind the paintings.

In the early 17th century the Eighty Years’ War had reached stalemate. Most of what is now The Netherlands was held by the new Dutch Republic while their Spanish opponents and former overlords remained in control of Flanders to the south. It was in this environment that the telescope was first invented. Who invented it is not certain, but we do know that the first public demonstration was in Den Haag in 1608.

Around this time Jan Brueghel the Elder was working as the court painter for Archduke Albert VII (the sovereign of the Spanish/Austrian portion of the Low Countries). At some time in-between 1608 and 1611 he painted “Extensive Landscape with View of the Castle of Mariemon” (I can’t find a picture online, see the original paper). In this the archduke is seen viewing the scenery through a telescope. Given the date it is likely this is one of the earliest such device. The authors then go on to speculate that this device could have been made by the inventor of the telescope. One letter from a Papal envoy to a nephew of Pope Paul V claims that, having seen the telescope being demonstrated in Den Haag while he was there negotiating a peace deal with Dutch Stadthouder Maurice of Nassau, Ambrosio Spinola (the Genoese commander of the Spanish Army in the Low Countries) was impressed and managed to obtain one of these “spyglasses”. Another letter written by a Udine nobleman (to Galileo of all people) claims this came from the inventor himself.

Brueghel also worked on a series of paintings in collaboration with Ruebens. In The Allegory of Sight (1617, see below),

he paints a long, silver telescope. The authors deduce from its style and dimensions that this instrument could be one of the first Keplerian Telescopes (one where the eyepiece as well as the objective lens is convex). These were first described in principle by Kepler in 1611 and could have been manufactured shortly after. They suggest that Christoph Scheiner, one of the first people to observe sunspots, had presented Keplerian telescopes to Archduke Albert’s brother in Innsbruck. A Keplerian Telescope produces an image which is upside down, Scheiner added a third lense to flip the image to the correct orientation. So again it is quite possible that this is one of the first ever device of its type ever made.

I hope I’ve given a reasonable run-down of a subject, if you want to know the full story from a much better source then I urge you to read the original paper. And if you understand what the title of this post is a nod to, don’t complete it in the comments thread (please).

Paolo Molaro, & Pierluigi Selvelli (2009). The mystery of the telescopes in Jan Brueghel the Elder’s paintings Memorie della Società Astronomica Italiana arXiv: 0908.2696v1