“James Lick telescope”的意思、由来-开放百科全书

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James Lick telescope

释义

Construction
Major discoveries
References
External links

The James Lick Telescope is a refracting telescope built in 1888. It has a lens {{convert|36|in|cm}} in diameter- a major achievement in its day. The instrument remains in operation and public viewing is allowed on a limited basis. Also called the "Great Lick Refractor" or simply "Lick Refractor", it was the largest refracting telescope in the world until 1897 and now ranks third, after the 40-inch unit at the Yerkes Observatory and the Swedish 1-m Solar Telescope. The telescope is located at the University of California's Lick Observatory atop Mount Hamilton at an elevation of {{convert|4209|ft|m}} above sea level. The instrument is housed inside a dome that is powered by hydraulic systems that raise and lower the floor, rotate the dome and drive the clock mechanism to track the Earth's rotation. The original hydraulic arrangement still operates today, with the exception that the original wind-powered pumps that once filled the reservoirs have been replaced with electric pumps. James Lick is entombed below the floor of the observing room of the telescope.

Here are some excerpts from an 1894 book describing the telescope:^[1]

The height of the marble floor of the main building above mean sea level is 4209 feet. On a closely connected peak half a mile to the east of the Observatory, and 50 feet higher, are the reservoirs from which water for household and photographic purposes is distributed. A spring about 350 feet below and one mile to the northeast of the Observatory supplies excellent water. Another peak seven-eighths of a mile to the east is the summit of Mount Hamilton; it is 180 feet higher than the Observatory, and supports the reservoirs supplying power for moving the dome, raising the movable floor, and winding the driving clock of the great telescope. This system receives its supply from the winter rains falling on the roofs; the water being pumped to the reservoirs on the higher peak by means of windmills.

The movable floor in the dome is the first of the kind to be constructed. It is {{convert|60|ft|m}} in diameter, and can be raised or lowered through a distance of {{convert|16+1/2|ft|m}}, its purpose being to bring the observer within convenient reach of the eye end of the telescope.

Construction

The fabrication of the two-element achromatic objective lens, the largest lens ever made at the time, caused years of delay.^[2] The famous large telescope maker Alvan Clark was in charge of the optical design. He gave the contract for casting the high quality optical glass blanks, of a size never before attempted, to the firm of Charles Feil in Paris. One of the huge glass disks broke during shipping, and making a replacement was delayed. Finally, after 18 failed attempts, the lens was finished, transported safely across country, and on December 31, 1887, was carefully installed in the telescope tube. The builders had to wait for three days for a break in the clouds to test it. On the evening of January 3 the telescope saw first light,^[2] and users found that the instrument couldn't be focused. An error in the estimation of the lens' focal length had caused the tube to be built too long. A hacksaw was procured, the great tube was unceremoniously cut back to the proper length and the star Aldebaran came into focus.

Major discoveries

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These are some of the discoveries made with the Lick telescope, as described in the same 1894 book:^[1]

Amalthea, the fifth satellite of Jupiter was discovered in September, 1892.^&91;3&93;^&91;4&93;
The speed of the planetary nebulae in their motions through space is of the same order of magnitude as the speed of the stars.
Twenty-five comets—17 unexpected and 8 periodic—have been discovered.
The unequaled Lick series of comet photographs has taught us more as to the structure, formation, and dissolution of comets' tails than had been learned in all previous time.
About 1300 new double stars have been discovered.
The period of revolution of the double star delta Equulei has been shown to be 5{{fraction|3|4}} years, the shortest period previously known for any double star being 11.4 years. It is therefore in many ways the most interesting double star under observation.
Spectroscopic observations have shown that the atmosphere of Mars is of low density—probably much less dense at the surface of Mars than the Earth's atmosphere at the summit of the highest peak in the Himalayas.
The average speed of the brighter stars is {{convert|21|mi/s}}.
The North Polar Star was found to be a triple star, in 1899, by means of spectroscopic observations. Two of its members are invisible in our largest telescopes. The bright star and one dark companion revolve around each other in four days; and these in turn revolve around the other dark body in several years.
Capella was discovered, in 1899, to be a spectroscopic binary star, period 104 days, the two nearly equal components being inseparable in our largest telescopes.
About 40 spectroscopic binaries—that is, stars seen single in ordinary telescopes, but proven to be double by means of the spectroscope—were discovered in 1898–1902. At least one star in seven has an invisible component, observable thus far only by spectroscopic means.
About 10,000 nebulae have been discovered in the past at the various observatories; but the Lick photographs show that fully 100,000 nebulae await discovery. These photographs led to the unexpected discovery that the majority of the nebulae have a spiral form—undoubted evidence of their rotation.
The light of the inner portion of the solar corona is largely inherent, whereas the light of the outer portion is largely reflected sunlight, as proven at the Sumatra eclipse by means of spectroscopic and polariscopic observations.
It has been shown that the principal "New Stars" have been converted into nebulae.
The extraordinary motion in the nebula surrounding Nova Persei was discovered from the photograph of November 7–8, 1901.
Many thousands of very accurate positions of stars have been secured with the meridian circle.
Very extensive and accurate observations of double stars, comets, planets, etc., have been made.
Very extensive additions have been made to our knowledge of the spectra of nebulae, of comets, of new stars, of bright-line stars, etc.
The speeds in the line of sight of about four hundred of the brighter stars in the northern sky have been measured by means of the spectroscope.

References

1. ^¹[https://books.google.com/books?id=BbA2AQAAIAAJ A Brief Account of the Lick Observatory of the University of California]. The University Press, 1894.
2. ^¹{{cite web | last = Misch | first = Tony | authorlink = |author2=Remington Stone | title = The Building of Lick Observatory | work = Lick Observatory website | publisher = Univ. of California | year = 1998 | url = http://collections.ucolick.org/archives_on_line/bldg_the_obs.html | doi = | accessdate = 2008-06-30}}
3. ^{{cite journal| doi = 10.1086/101715| last = Barnard| first = E. E.| date = 12 October 1892| title = Discovery and observations of a fifth satellite to Jupiter| journal = The Astronomical Journal| volume = 12| issue = 11| pages = 81–85| bibcode = 1892AJ.....12...81B| ref = harv}}
4. ^{{cite book|author=Lick Observatory|title=A Brief Account of the Lick Observatory of the University of California|url=https://books.google.com/books?id=BbA2AQAAIAAJ&pg=RA7-PA27|year=1894|publisher=The University Press|page=7}}

External links

Photographs of the James Lick telescope from the Lick Observatory Records Digital Archive, UC Santa Cruz Library's Digital Collections

2 : Optical telescopes|Lick Observatory

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