Astronomy

What is Asias Largest Telescope



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As so often happens, the answer to a question depends on just what the words in the question mean to the person making the inquiry.  It is true here as well.  To avoid comparing apples and oranges, let’s agree now to concentrate on optical telescopes.  Radio telescopes are certainly much larger, but fall into a different category.

The largest optical telescope in Asia is widely identified to be the Vainu Bappu telescope (VBT), located at the Vainu Bappu Observatory in the Javadi Hills near Kavalur in the Indian state of Tamil Nadu.  Manali Kallat Vainu Bappu was an Indian astronomer who, in the latter half of the 20th Century, was instrumental in the establishment of the Indian Institute of Astrophysics and the funding and construction of several observatories, the largest of which was named after him to honor his scientific contributions to India.  It would be fair to label him as the father of modern astronomy in India. 

The Vainu Bappu telescope has a primary mirror having a diameter of 2.346 meters, or about 923 inches.  The telescope can be used at prime focus, where it has a focal ratio of f/3.25, or at a Cassegrain focus with a focal ratio of f/13.  Although it was mounted in a horseshoe equilateral mount similar to that of the 200 inch Hale telescope, optically the VBT is a near match for the 100-inch Hooker telescope. 

Does the VBT have any rivals for the honor of being Asia’s biggest telescope?  Well, the Lijiang telescope, which saw first light in 2007, ekes out a win over the VBT.  Located in China’s Yunnan Province, the Lijiang telescope has a 2.45 meter primary mirror, and is the largest fully automated observatory designed solely for remote operation.  The telescope has Ritchey-Chretien optics with a Cassegrain focal ratio of f/8. 

Are there any other contenders?  Another arguably bigger telescope is the Chinese Large Sky Area Multi-Object Fibre Spectroscopic Telescope, or LAMOST.  LAMOST’s aperture is 4 meters, making it clearly bigger than the VBT.  It is a Schmidt telescope designed to image huge regions of the sky at once.  The focal plane is 1.75 meters in diameter, corresponding to a field of view of about 5 degrees of arc.  The light from a given celestial object is collected by an optical fiber, which directs the light into a spectrograph.  The spectra of some 4000 separate objects within the field of view can be simultaneously recorded.  LAMOST is designed to take spectroscopic surveys of celestial objects, thus offering a new window on the large-scale structure of the Universe.  However, it is a highly specialized telescope, not capable of imaging studies.  Given that instruments having limited scope are generally easier to build, it is not clear that a size competition with the general-purpose VBT is appropriate.   

Finally, there is the 6-meter BTA-6 (large altazimuth telescope) located just on the north side of the Caucasus Mountains in southern Russia.  The BTA-6 is a much larger telescope than is the VBT, and is also a general-purpose telescope, not specialized to a particular field of study.  However, it is not entirely clear if it is located in Asia or in Europe.  The boundary between these two continents is rather poorly defined, since there is no tectonic plate boundary separating them.  As fate would have it, the Caucasus Mountains are squarely in the middle of a highly disputed region.  Not being geographers, we won’t argue either side of the dispute.  BTA-6 could well be Asia’s biggest telescope or not, depending on the stand taken about the Europe-Asia boundary.

Although it is not clear which telescope is Asia’s biggest, we can at least be reasonably confident that it is not the VBT, despite it being so identified in many sources.  The largest telescope is a moving target, as a vast array of new telescopes come on line with great regularity.  For the moment, the reader must decide which of the telescopes mentioned is truly “Asia’s biggest” as of December 2009.  Be assured, the answer will change in the next few years.

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