Astronomy is perhaps the most ubiquitous of human endeavors. Regardless of time or location, people have studied the night sky for an understanding of the universe. All five continents contain ancient sites used for astronomical purposes. From the ancient Egyptians noting the simultaneous rising of Sirius and the Sun to predict seasonal flooding, Chinese observation of the supernova that produced the Crab Nebula on July 4, 1054, Islamic astronomers high-precision measurements of celestial objects for time-keeping, astronomy has been a truly multi-cultural endeavor. The next generation of 30-meter telescopes promises to continue that heritage.
During the 20th century, large scale astronomy was dominated by the United States. When the 200-inch Mt. Palomar telescope opened for business in 1948, the next largest telescope outside the U.S. was the 74-inch David Dunlap Observatory just north of Toronto. The two World Wars created economic chaos across Europe and Asia. At the same time, the vision of George Ellery Hale enabled the U.S. to surge ahead of the world in building large telescopes. These two factors conspired to cause a listing of astronomy research towards the U.S. during this period.
From 1897 to 1993, the largest telescope in the world would be one designed by George Ellery Hale*. The first would be the 40-inch refracting telescope at Yerkes Observatory. This remains the largest refractor in the world. The final would be the 200-inch reflecting telescope at Mt. Palomar. In between was the 100-inch telescope at Mt. Wilson where galaxies outside the Milky Way and the expansion of the universe was discovered. These telescopes stretched the limits of the single mirror design. A new type of mirror was required to construct larger telescopes, and the segmented mirror was the answer.
The 10-meter Keck Observatory in Hawaii ushered in the era of the segmented mirror design. The next generation of 30-meter telescopes, due to commence operations in the next decade, will radically expand Earth-based observatory capabilities. In fact, these giant mirrors, combined with adaptive optics technology to remove atmospheric turbulence from their imaging, promise to have resolution capabilities several times that of the Hubble Space Telescope.
The first question one might ask is what is a segmented mirror? Lets take a look at the image below:
This is the 200-inch (5 meter) Palomar mirror as it is removed to be aluminized. Its total area is about 20 square meters. Single mirrors larger than this are problematic as the weight requires a massive support structure. Another factor is economics. When the Keck Observatory was in the planning stage during the late 1970’s, a 10-meter mirror was estimated to cost $1 Billion ($2.9 Billion in 2015 dollars). Funding prospects for that amount were rather bleak.
Now take a look at the mirror below:
This is the 10-meter Keck mirror. As you can see, rather than a single mirror like Palomar, it consists of 36 hexagonal segments 1.8 meters wide. Each mirror segment is also very thin at 75 mm. The impact is two-fold as the total weight of the Keck mirror array is the same as the single Palomar mirror. As a result, the cost of the Keck Observatory was reduced to $270 million. The cost reduction enabled the Keck Observatory to obtain funding from the William M. Keck Foundation in 1985. When the Keck I opened in 1993, it was the first non-Hale telescope to become the world’s largest in 96 years.
The video below has an inside look at the Keck and its accomplishments:
Since the Keck, the Gran Telescopio Canarias 10.4-meter telescope was built in the Canary Islands as well as the 9.2-meter South African Large Telescope (SALT) in the Northern Cape region. The Gran Telescopio Canarias became the first world’s largest telescope outside the United States since the 1800’s. That telescope was funded mostly by the government of Spain, along with minor contributions from Mexico and the University of Florida. The SALT was funded by a partnership between South Africa, United States, Germany, Poland, India, United Kingdom and New Zealand. The next generation of telescopes will continue the trend of international partnerships for funding.
The success of the segmented mirror has prompted the design of 25-39 meter telescopes. This is an expansion of telescope size unprecedented is in modern times. Thirty years after the 100-inch Mt. Wilson telescope was built, the 200-inch Mt. Palomar telescope doubled aperture size for the world’s largest telescope. The planned 39-meter European Extremely Large Telescope (E-ELT) will nearly quadruple Keck’s mirror size in the same time frame. Three telescopes of this class are set to commence operations in the next decade and they are:
The design of this telescope is quite interesting as it uses the upper end of monolithic mirror design as the basis for a segmented mirror. The GMT will package seven 8.4 meter mirrors into an array 24.5 meters wide. The telescope will be located at Las Campanas Peak in the Atacama Desert. The total cost will be $1 billion and funding is provided by the Carnegie Institute for Science (who also funded both Mt. Wilson and Mt. Palomar), Smithsonian Institution, and several American, Australian, Korean, and Brazilian universities. The GMT will begin observations in 2021 and will be fully operational in 2024. The image below provides a good perspective on the size of the mirror array:
This telescope will be located in Hawaii on the summit of Mauna Kae where the Keck Observatory is located. Appropriate from an astronomy standpoint, as the TMT is the successor to Keck in that its mirrors will consist of 492 segments 1.44 meters wide. The location has also become problematic as a result of protests by indigenous Hawaiians who consider the peak of Mauna Kae to be a scared site. The protests have stopped construction for now. While its more than likely the 18 story high TMT will eventually be built, its unknown what impact the current impasse will have on its planned timeline to be completed in 2024. The TMT is expected to cost $1.4 billion to build and is funded by a consortium including Caltech and partners from China, India, Japan, Canada.
The E-ELT will be the granddaddy of the next generation of telescopes. Like the GMT, the E-ELT will be located in the Atacama Desert in Chile. Its mirror will be 39 meters wide and consist of 798 hexagonal mirrors each 1.45 meters wide. The cost of the E-ELT is expected to be 1.1 billion Euro. The telescope will be funded by the European Southern Observatory with contributions from its 16 member nations. Currently, the member nations are all from Europe with pending applications from Poland and Brazil. First light is expected in 2026. An artist conception of the E-ELT is below. It is an ideal site to observe the Milky Way.
The northern Chile desert provides the desired combination of dry air, high altitude, and lack of light pollution. Currently, the ESO operates the Very Large Telescope (VLA) in the Atacama Desert. The VLA has four telescopes each with 8.2 meter mirrors. Also located there is the large 66 antennae ALMA radio telescope array which is run by a consortium consisting of the United States, Canada, Japan, ESO member states and Chile. The Astronomical Tourism website has a list of the remarkable number of observatories in Chile here. Among some of the advantages of being in the Southern Hemisphere is that the Milky Way can arch overhead making it a very easy target to observe. By 2025, it is expected that half of the world’s observing power will be located in Chile. Below is a video that demonstrates the awesome clarity of the Chilean skies.
All three observatories will utilize adaptive optics system. This is a means to eliminate the twinkle in stars caused by atmospheric turbulence during observations. While the twinkling of stars can have great aesthetic value, it hampers the performance of a telescope. Adaptive optics works by shooting a laser into the sky near the observation target. This laser excites sodium atoms located about 60 miles above the Earth’s surface. The excited atoms then release the energy in the form of light causing an artificial star to be created in the sky. The artificial star is used as a baseline to measure atmospheric turbulence. This in turn is used to adjust a small deformable mirror in the instrument package of the telescope. This deformable mirror removes most of the twinkling from the observed object prior to being imaged. The picture below shows the galactic center before and after adaptive optics from the Keck Observatory is applied.
The large mirrors combined with adaptive optics is expected to give these telescopes resolution several times that of the Hubble Space Telescope. In fact, the E-ELT is expected to provide 15 times the resolution ability of the Hubble. To put the E-ELT in proper perspective, this telescope will collect more light than all the existing 8-10 meter telescopes combined. Among the science objectives of these telescopes will be to peer into the farthest regions of the universe to study the first galaxies formed to the detection of Earth-sized planets and characterization of exoplanet atmospheres. The latter could possible provide evidence of bio-signatures.
The cost of this science is not cheap. However, it is not more expensive than other large scale infrastructure projects. For example, the total cost of the three new observatories combined ($3.5 billion) is identical as the new Detroit-Windsor bridge to be built during the same period. Nonetheless, the cost of large observatories are now on the scale that international partnerships must be used for funding. American society, competitive as it is, tends to fret when it comes to the possible loss of a dominant leadership position in any given field. However, this recent development simply puts astronomy back at its natural state. Rather than being an American endeavor, large scale astronomy research is now a global venture, just as it was during ancient times. And that is exactly as it should be.
*There were other telescopes larger than Yerkes in 1897 such as the 72-inch Leviathan of Parsonstown, but those had fallen into disrepair and were no longer in use.
**Image on top of post is the E-ELT compared to the VLA and Statue of Liberty. Credit: ESO.