The LBT: Large Binocular Telescope – Two Mirrors for enhanced observations achieves first light

The idea for the LBT was conceived in the late 1980’s and in the early 90’s a coalition of several countries and a number of universities formed to get the project underway. The construction on the observatory began in 1997, and was completed in 2002. For the next three years the support structure and equipment were added, with the first primary mirror being placed in 2004. In 2005, with the calibration of the first primary mirror complete, the observatory achieved its first light (first official images taken) on October 12, 2005. The target for first light was an edge-on spiral galaxy, NGC891, 24 million light years distant, shown in blue light in Figure 3.

In 2005 the second primary mirror was installed and on March 6, 2008 images were released of the first light event for the complete binocular telescope. A spiral galaxy, 120 million light years distant, NGC2770 was to commemorate the event. (See Figure 4) The image is a composite of ultraviolet, green and deep red images taken by the telescope.

The non-traditional design of the telescope offers many advantages over a conventional Newtonian telescope.

• With the two primary optical paths, one target can be photographed in two different parts of the spectrum at the same time, reducing the amount of observing time needed to collect the images. See Figure 5 for the focal path of the telescope.
• Taking spectrographs will also be quicker because of this arrangement. Each primary will have the same unique mask for the target field being observed - one using visible light, the other infrared.
• The most important mode that can be used is to combine the images from both primary mirrors using a technique called interferometry. This allows the telescope to have the resolving power of a single telescope with a primary mirror 22.8 meters (74.8 feet) in diameter. This resolution is ten times what the Hubble Space Telescope has.
• This design allows different secondary mirrors to be stored on the telescope for quick change over as the observing conditions change.
• The design of the telescope and its supporting structure allowed for a smaller building (less cost) to house the system than would be needed for a conventional telescope with similar capabilities.

The LBT will use adaptive optics on its secondary mirrors to accommodate the changing viewing conditions. The control system will monitor the atmospheric turbulence and adjust the mirrors at a rate of about 1000 times per second utilizing 672 electromagnetic adjusters on the back of the mirrors. Figure 6 shows a drawing of the LBT assembly.

What wonders will the LBT unveil? Only time will tell. The LBTI, or Large Binocular Telescope Interferometer, has just been installed and once fully functional should produce some amazing images. If the Hubble Space Telescope is any indication, we have a wonderful time ahead of us!

For more information on the LBT, its unique construction, history and amazing images check out this link.

Figures 1, 3, 4, 5, 6: http://medusa.as.arizona.edu/lbto/index.htm

Figure 2: Credit & Copyright: Stefan Seip (TWAN)

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