Crossley telescope
The Crossley telescope is a reflecting telescope located at Lick Observatory in the U.S. state of California. It was used between 1895 to 2010, and was donated to the observatory by Edward Crossley, its namesake.
It was the largest glass reflecting telescope in the United States for several years after its recommissioning in California. Lick Director, James Edward Keeler, remarked of the Crossley in 1900, "... by far the most effective instrument in the Observatory for certain class of astronomical work."
History
"Amateur astronomer Andrew Ainslie Common built the Crossley Reflector in Great Britain in 1879, around the time that the Great Lick Refractor was built. The Great Refractor was one of the last large refractors built, and the Crossley was one of the first large reflectors built. Large reflectors became practical after 1880, when a new technology for making concave, silver-coated glass mirrors was perfected. Prior to this, such mirrors required constant polishing to remain reflective. -- With his reflector, A.A. Common was the first to discover that stars too faint to be seen through a telescope with the eye could be imaged in photographs taken through the telescope using a long exposure time. This discovery is the basis for all modern astrophotography and spectroscopy. For these early astronomical photographs, Common was awarded the Royal Astronomical Society gold medal for Astronomy. -- After deciding to build a larger telescope, Common sold the 36-inch reflector to Edward Crossley in 1885. Crossley built a new dome enclosure to protect the telescope and observers from the harsh Halifax weather, but this climate was far from ideal for observation. After about 10 years, Crossley donated both telescope and dome to Lick Observatory, where it was put into operation in 1896."Given to the Lick Observatory in 1895 by British politician Edward Crossley, it was rebuilt from the ground up as it was on a very flimsy mounting. It was last used in 2010 in the search for extra-solar planets but has been taken out of service due to budget cuts. The mirror, and some of the initial mounts, came from the 36-inch reflector originally mounted in Andrew Ainslie Common's backyard Ealing observatory. He had used it from 1879 to 1886 to prove the concept of long exposure astrophotography. Common sold it to Crossley who had it until 1895.
The 36-inch A.A.Common mirror was made by George Calver for Common, and was ordered after Common wanted one bigger than the 18-inch reflecting telescope, which also had a mirror from Calver. Common completed this telescope by 1879, and went on to make a 60-inch telescope; he sold the 36-inch to Crossley. Crossley set the telescope up in Halifax, England in a new dome.
Meanwhile, at the Lick Observatory in California, Holden, the director, learned that Crossley wanted to sell the well-regarded Common 36-inch telescope. Holden and Crossley exchanged letters and worked out transferring the telescope. Crossley was very impressed by the enhanced observing conditions at Mount Hamilton, and, in April 1895, he formally telegraphed the Lick that he would donate the telescope.
Funds had to be raised to ship the telescope to California, which included money from various donors including many small donations from members of the public, as well as donated services. For example, the heavy parts of the telescope were shipped by The Southern Pacific Company at no cost, a service of over $1,000 USD. Converting the buying power of 1896 dollars to 2017 dollars, that can be estimated at approximately $12,000 USD.
The reflecting telescope type was scarcely used in the United States at the time of the donation, with a noted exception being the work of H. Draper's reflector.
“When the Crossley Reflector first arrived on Mt. Hamilton in 1896, William Hussey, who had been assigned the task of making the Crossley operational, called it a "pile of junk." This attitude was reflected in his work on the Crossley, and it was not until James Keeler arrived in 1898 that serious renovation of the Crossley was begun. The Crossley telescope has now been upgraded to the extent that no original telescope parts remain. Keeler adjusted the inclination of the axis of the telescope to the correct angle for Lick Observatory's latitude, aligning the telescope with the earth's axis. He then adjusted the drive clock, enabling the Crossley to follow star motions more accurately. He also removed the old mirror coating, applied a new reflective surface, and made other upgrades. By 1899, Keeler had taken his series of nebulae images. These were impressive enough to cause a sensation at a meeting of the fledgling American Astronomical Society."
“Keeler used the Crossley to produce early photographs of nebulae, fuzzy-looking areas in the night sky, in the hopes of better understanding their nature. To his surprise, he saw many fainter nebulae in the background of his Orion Nebula images. Previously, astronomers had thought that all nebulae were pretty much the same, and that they were rare phenomena. Keeler’s photos with the Crossley reflector showed that nebulae were in fact quite common. They also showed a variety of different types of "nebulae." Some of these were areas of interstellar dust that we still call nebulae today. Others were actually spiral galaxies filled with billions of stars. Such detailed photographs were possible because this reflecting telescope focused light more effectively than the 36-inch refractor. Thus Keeler’s photos also showed the superiority of reflectors to refractors for modern astronomical research.”
Observations by Keeler helped establish large reflecting telescopes with metal-coated glass mirrors as astronomically useful, as opposed to earlier cast speculum metal mirrors. Great refractors were still in vogue, but the Crossley reflector foreshadowed the success of large reflectors in the 1900s. Other large reflectors followed, such as the Harvard 60-inch Reflector, also with a mirror by A.A. Common, or the 1 Meter Spiegelteleskop of the Hamburg Observatory. At this time the 72-inch Leviathan of Parsonstown was the largest by aperture, but it used a metal mirror. Despite the accomplishments of reflectors under Herschel, in the 19th century much of the astronomical community used relatively small refractors, often just a few inches in aperture, save for a few larger ones.
After Keeler died unexpectedly in 1900, William W. Campbell, now Lick Observatory's astronomer-in-charge, assigned Assistant Astronomer Charles Dillon Perrine "to take charge of all duties in connection with the Crossley" including completing Keeler's observation of the near-Earth asteroid 433 Eros, for the determination of the solar parallax. Perrine further significantly reconstructed the telescope from 1902 to 1905. Perrine would use the rebuilt Crossley to great effect in discovering eight comets and the sixth and seventh satellites of Jupiter. The Crossley was so effective that when Perrine became the director of the Argentine National Observatory in Cordoba in 1909, he established a program to install a 60-inch reflecting telescope in Argentina. At that time it would have been equal to the largest reflector on Earth. After a world war and national economic crisis the "Perrine telescope" at the Bosque Alegre astrophysical station was inaugurated in 1942 when it was the largest reflector in South America.
In the 1930s, the Crossley mirror was tested with vapor-deposited aluminum for reflection, rather than coated by using a silver metal precipitated out of a solution. The telescope was aluminized in 1934, 1938, 1946, and 1951.
Nicholas Mayall was a long time user of the Crossley and added a slitless spectrograph to extend its usefulness in the face of larger telescopes.
Discoveries & Observations
was first photographed between 1898 and 1900 by James Edward Keeler with the Crossley reflector.Other early photographic imaging targets, dating to 1899, include GC 4628 and GC 4964, GC 4373, and the "Ring nebula in Lyra." Keeler notes that in a 4 hour exposure, 16 new nebulae were found, seeing objects that were normally much to hard to make out with the reflector visually.
1899: As an example of its performance, Keeler noted that in a two-hour exposure of the "cluster in Hercules" made on July 13, 1899, he could count 5400 stars on the photograph. Keeler noted how with long exposure on this telescope the "swarms of minute stars" that gave it a nebulous look were resolved.
In 1900, Assistant Astronomer Charles Dillon Perrine took hundreds of photographs of the near-Earth asteroid 433 Eros for the determination of the solar parallax.
From 1902-05, after significant reconstruction by Perrine, he discovered eight comets and the sixth and seventh satellites of Jupiter.
1928: "The photograph of the Orion Nebula, taken with the Crossley reflector in 1928, illustrates the fine detail that the Crossley is capable of imaging. This photograph is frequently used in science educational materials and amateur astronomy publications."
1940: Mayall's Object was discovered by American astronomer Nicholas U. Mayall of the Lick Observatory on 13 March 1940, using the Crossley reflector.
In 1990, the Crossley was used to test the photometric detection of exoplanets, including around the star CM Draconis.
Comets known to have been photographed using the Crossley include:
- 1931 I was found on plates taken in January 1931.
- 1941 IV was observed visually and photographed in July 1941, after the comet re-emerged from around the Sun.
- 1946 III was observed visually in July 1946.
- 1946 IV was recorded on plates taken in June and July 1946.
Contemporaries on debut
Legend
| Name/Observatory | Aperture cm | Type | Location | Extant* |
| Leviathan of Parsonstown | 183 cm | reflector – metal | Birr Castle; Ireland | 1845–1908* |
| National Observatory, Paris | 120 cm | reflector – glass | Paris, France | 1875–1943 |
| Yerkes Observatory | 102 cm | achromat | Williams Bay, Wisconsin, USA | 1897 |
| Meudon Observatory 1m | 100 cm | reflector-glass | Meudon Observatory/ Paris Observatory | 1891 |
| James Lick telescope, Lick Observatory | 91 cm | achromat | Mount Hamilton, California, USA | 1888 |
| Crossley Reflector Lick Observatory | 91.4 cm | reflector – glass | Mount Hamilton, California, USA | 1896 |
| A.A. Common Reflector | 91.4 cm | reflector – glass | Great Britain | 1880–1896 |
| Rosse 36-inch Telescope | 91.4 cm | reflector – metal | Birr Castle; Ireland | 1826 |
| Grande Lunette, Paris Observatory | 83 cm + 62 cm | achromat x2 | Meudon, France | 1891 |