SRB05

BIRR / LORD ROSSE

The telescope at Birr, built in 1844/5 was at the forefront of observational astronomy from the late 1840’s to the early 1860’s. Rosse and his team made many new discoveries.
Rosse had developed techniques for casting, grinding and polishing mirrors in the 1830s, training his own workmen. He completed a 36 inch reflecting telescope in 1839, which gave a magnification of 900. Parsons invited several competent observers to use it. One said that it was better than Herschel’s 49 inch telescope.

In 1842, Parsons, now the third Earl, cast a 72 inch mirror, made from speculum metal, a mixture of 4 parts copper and 1 part tin and weighing over four tons, using three crucibles. This broke during cooling, but it was recast and a second mirror was produced.

The mirror was mounted in a 58 foot tube, but there was no way to put this in any kind of universal mounting, so it was mounted between two massive walls.
It could only view a star for about an hour as it crossed the meridian. The tube was 8 feet in diameter in the middle, tapering to 7 feet at the ends, and was made of inch thick wood with iron rings and strengtheners.

The telescope was completed in 1845, but only a few observations could be made before the Famine struck and Rosse devoted most of his efforts to relief for several years, so it was not until 1848 that systematic observations really started. It has often been stated that the telescope was not as good as expected, but this was because the mirror, being outside and uncovered, tarnished quickly and had to be repolished regularly; when it was clean and atmospheric disturbance was absent, it certainly was the best telescope in the world, as attested by numerous users.

It reached magnifications of 650 on good nights and could see ten million light years away. Many of the observations could not be confirmed elsewhere for 50 years. Sadly, it was never adapted for photography, partly because the tracking was not smooth enough for long exposures. The main work of both the 36 inch and the 72 inch was the observation of clusters and nebulae. The 36 inch indicated that some nebulae might be resolvable into stars and the 72 inch made it clear that many of the nebulae were galaxies and first revealed that some had spiral structure. It was Rosse, by the way, who named M1 the Crab nebula.

The efforts of Rosse and his aides were often thwarted by the notoriously bad weather, the “fogs from the bogs” as they were known, which sometimes prevented work being done for days on end.
Ball was an early riser, teaching the boys during the morning and early afternoon, but still with plenty of free time to get acquainted with the Leviathan, as the 72” monster telescope was called.
Whilst at Birr, Robert witnessed a remarkable astronomical event, the like of which was not to be seen again for 100 years. The year was 1866, the month November and on the night of the 13th/14th there was no moon, and the sky was crystal clear. Robert was at the eyepiece some 50 foot up, observing spiral nebula, when he heard one of his assistants shout “Look”............ A meteor had passed overhead, then another. Of course Ball was well aware that these were Leonids, but also knew that they might not come to much, even though the 33 year return was by this time well known. Soon however there were more and Ball concluded his nebula observations. Hurrying to the top of the telescope’s supporting wall, some 60 feet up in the air, he watched in amazement as the shower came thick and fast ....... Lord Rosse was summoned and watched the spectacle for more than 2 hours. Soon Leo was above the horizon and the shower could be seen emanating from that precise spot in the sky.
One of the things that struck Ball at the time, was that you could not demonstrate in a more practical way, the doctrine of parallel lines. The explanation is that all these objects were moving in parallel lines, and that the vanishing point was in Leo. The stars that appeared to be coming straight towards them came actually from the vanishing point. Whenever Ball was asked how to observe meteors, he would say matter of factly, “Why, with your hands in your pockets of course. Instruments are no use whatsoever”.

Ball made much of this spectacle, and included it in many of his lectures during the next 40 years. One wonders what he would have made of the 1833 Leonids which produced a storm, as seen in the US, 20 times greater than the one he witnessed at Birr.