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Large Telescopes Pave Way for New Discoveries


May 6, 2021

Up to now we have been living our dreams and expanding our knowledge with the Hubble Space Telescope, a 2.4 meter reflecting mirror lofted out into space in 1990, completely free of the Earth’s atmosphere.  It’s resolution is 0.04 arc seconds, or about 1000 times better than what the human eye can ever resolve.  It has brought in the most distant galaxies at 13.2 billion light years away.

Although these are impressive specs, some wonder why the Hubble couldn’t see objects such as the Apollo lunar landers left behind on the moon from past missions.  As good as the Hubble was designed, it could only see such objects if they were the size of several football fields.

The saying, “out with old, and in with the new” may very well apply as the new James Webb Telescope will tout a 6.5 meter mirror nearing three times the diameter of the Hubble Space Telescope.  It will be made of 18 hexagonal mirror segments made of gold-plated beryllium giving a light collection area over 6 times, and said to be a hundred times more powerful.  It is due to launch into service this year 2021.

If it is one thing that space telescopes have taught us, it is how to hone our practices.

The James Webb Telescope will be placed at Lagrangian point L2, staying in line with the Earth as it orbits the Sun.  

If it is one thing that space telescopes have taught us, it is how to hone our practices.  What scientists have learned from working with the Hubble Space Telescope can now be applied to ground telescopes. This accounts for the unexplained surge of programs to develop larger and larger earth-based ground telescopes that will outsize any current space telescope by many times.

Take for instance the Giant Magellan Telescope which will be constructed at the Las Campanas Observatory in Chile.  It will consist of seven 8.4 m diameter mirror segments yielding the equivalent of a 24.5 m primary mirror.  It will have a resolving power ten times greater than the Hubble.  It is a billion dollar project involving the U.S. in partnership with Australia, Brazil, South Korea, and Chile as the host country.  It is scheduled to begin in 2029.

Another very large telescope is called the Thirty Meter Telescope destined for the Mauna Kea Observatory in Hawaii.  As implied, it will have a 30 meter mirror, over 5 m greater than the Giant Magellan Telescope.  This will give it a collecting area of 7,050 sq ft and a focal length of 450 m.  Since Mauna Kea is the most sacred mountain in native Hawaii, the progress of the project was hindered by ongoing protests.  However, it received court approval to continue its construction, announced by the Hawaiian governor.  It will include an adaptive optics system to help correct image blur caused by Earth’s atmosphere.

On the extreme side of large telescopes is the Extremely Large Telescope (ELT), part of the European Southern Observatory agency and will be located on top of Cerro Armazones in the Atacama Desert of northern Chile.  It will have a segmented primary mirror spanning 39.3 meters across in diameter. When completed it will be the world’s largest telescope for optical and near-infrared use.  It will have around 256 times the light gathering area than the Hubble telescope and stated to provide images 16 times sharper.  The first construction phase will cost about one billion euros and first light1 is planned for 2025.

Comparison of various telescopes in respect to the primary mirror.  Although not shown, the Hubble telescope would appear only slightly larger than Kepler.  All large telescopes are constructed of multiple segmented mirrors.  {Cosmos Magazine}


1. ‘First light’ is when a telescope is first pointed to the night sky for observation or imaging.