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O Stars in the Firmament, Release Your Secrets

Photonics Spectra
Nov 2008
Lynn Savage, Features Editor, lynn.savage@laurin.com

Nearly 400 years ago, Galileo Galilei kicked the development of optical telescopes into high gear. Since then, there has been a steady stream of progress both in the technology behind what Galileo first termed the “perspicillum” and in our knowledge about the objects Earth-bound observers have sought in the night sky.

The most recent pinnacle – certainly in terms of capturing the public’s interest – has been the Hubble Space Telescope, which in the past decade and a half has delivered one amazing view of the universe after another. As good as the Hubble has been, however, its instruments and optics have not been state of the art since the early 1990s, and its primary mirror is just 2.4 m in diameter. Compare that with the mirrors in the future space telescopes, such as the James Webb, which has a primary mirror measuring 6.5 m across – thus providing more than seven times the light-collecting power.

StarField_HubbleFull.jpg

The new state of the art for telescopes will be driven by advances in mirrors. Terrestrial telescopes, such as the Giant Magellan Telescope, will employ extremely large primary mirrors that comprise many smaller segments. Smaller pieces are easier and faster to make, even with high polishing and fitting tolerances, and they make it possible to add adaptive optics (AO) systems to improve image resolution. AO systems have hundreds, even thousands, of mechanical actuators that move individual mirror segments in such a way that aberrations caused by atmospheric haze are nearly obliterated.

Space-bound telescopes also will employ segmented mirrors, primarily to enable reflective areas larger than the 2.4-m mirror in the Hubble.

What follows is an overview of several of the telescopes on the drawing board for future astronomy.

Fig1_2_Herschel.jpg

Herschel Space Telescope
Location: L2 Lagrange point
Launch: 2009
First Observations: 2010
Principal Investigator: European Space Agency
Primary Mirror Diameter: 3.5 m
Observed Wavelength Range: 60 to 670 μm
Purpose: Once known as FIRST (Far-Infrared and Submillimeter Telescope), the Herschel Space Observatory was planned for an operational life of only two or three years. It has, however, several interesting distinctions: At the time of launch, it will have the largest mirror on a space-based platform as well as the only one to cover the far-infrared to submillimeter range. It will be used to study galactic formation in the early universe, to investigate stellar creation activity, and to analyze the chemical composition of the atmospheres and surfaces of planets and their satellites as well as of comets.

Fig2_phot06a03.jpg

Atacama Large Millimeter/ Submillimeter Array (ALMA)
Location: Cerro Chajnantor, Atacama, Chile
Construction: Under way since 2003
First Observations: 2011
Principals: Because of its size and expense, ALMA is a partnership that includes contributions from the US National Science Foundation, the National Research Council of Canada, the European Southern Observatory (ESO) and Spain. Construction and operations are led by the National Radio Astronomy Observatory and by ESO.
Total Collecting Area: up to 7240 m2
Resolution: 10 milliarcsec
Observed Wavelength Range: 0.3 to 9.6 mm
Purpose: Comprising 50 to 64 twelve-meter radio antennas, ALMA will enable studies of the early universe by imaging redshifted dust from evolving galaxies, by providing spectroscopic information about star-forming gases in the Milky Way galaxy, and by seeking out and examining the photospheres and chromospheres of giant and supergiant stars.

Fig7_gmtpredawnlarge300.jpgGiant Magellan Telescope (GMT)
Location:
Cerro Las Campanas, Chile
Construction: Under way
First Observations: 2016
Principals: A consortium that includes Carnegie Observatories, Harvard University, Smithsonian Astrophysical Observatory, University of Arizona, University of Michigan, MIT, University of Texas at Austin, Australian National University and Texas A&M
Primary Mirror Diameter: 8.4 m (× 7)
Field of View: 20 to 30 arcmin
Resolution: 0.21 to 0.3 arcsec at 500 nm
Observed Wavelength Range: 320 to 25,000 nm
Purpose: Likely the first of the new outsized telescopes, the GMT will be used to search for and image extrasolar planets as well as to determine their basic chemical compositions. It will also be used to study several of the fundamental building blocks of galaxies, the formation of black holes, and the dynamics of dark matter and dark energy.

Fig6_ATSTMeesRender.jpgAdvanced Technology Solar Telescope (ATST)
Location: Haleakala, Hawaii
Construction: 2009
First Observations: 2016
Principal Investigator: National Solar Observatory
Primary Mirror Diameter: 4.24 m
Field of View: 5 arcmin
Resolution: 30 km, or 5× the current state of the art
Observed Wavelength Range: 300 to 28,000 nm
Purpose: According to its designers, the ATST will “study the outer solar atmosphere where magnetic activities manifest themselves as sunspots and other changing phenomena that can affect life on Earth.” The primary mirror will likely be made of Corning’s Ultra Low Expansion material or Schott AG’s Zerodur; the telescope’s secondary mirror will be made of silicon carbide. Although scheduled for initial construction in 2009, the NSO and its collaborators are still negotiating with local conservationists who believe that Haleakala does not need another observatory breaking up the scenic yline or disturbing the spiritual beauty of the locale. Proponents of the observatory say that the ATST will be the first new solar facility in a generation and will be the largest such telescope yet built.

Fig5_SAFIR_telescope.jpgSingle Aperture Far-Infrared Observatory (SAFIR)
Location:
L2 Lagrange point
Launch: Between 2015 and 202
Principals: NASA/Jet Propulsion Laboratory
Primary Mirror Diameter: 10 m
Field of View: 10 to 30 arcmin diameter
Resolution: 0.04 parsec
Observed Wavelength Range: 20 μm to 1 mm
Purpose: According to NASA’s Jet Propulsion Laboratory, SAFIR will enable astronomical observations in the wavelength range between those probed by the James Webb Space Telescope and those observable with telescopes on the ground, such as ALMA (1 mm and above). SAFIR will explore the formation of the first stars and galaxies in the early universe and reveal planetary system formation in the Milky Way galaxy. It will also help study the connections between black holes and the galaxies in which they reside and look for evidence of prebiotic molecules in planet-forming regions of space. The telescope will use cryogenic cooling to help keep the mirrors at a consistent 5 K or less.

Fig4_LSSTtelescope_withpath.jpgLarge Synoptic Survey Telescope (LSST)
Location: Cerro Pachón, Chile
Construction: Undergoing preliminary design review, though mirror blanks are under way
First Observations: 2015
Principal Investigator: LSST Corp.
Primary Mirror Diameter: 8.4 m
Field of View: 9.6 degrees square
Observed Wavelength Range: 320 to 1050 nm
Purpose: The LSST will cover the entire available sky once every three nights, providing a complete picture of more than half of the sky each time. The images the telescope acquires with its 3.2-gigapixel camera will also be used to explore the role of dark matter in the universe by tracing apparent distortions in the shapes of remote galaxies. Through a partnership with Google, more than 1 terabyte of information will be posted on the Internet every day for public use during the operation of the telescope.

Fig9_TMTobservatory-concept.jpgThirty-Meter Telescope (TMT)
Location: Either Cerro Armazones in Atacama, Chile, or Mauna Kea, Hawaii
Construction: 2010
First Observations: 2017
Principals: Caltech, University of California and the Association of Canadian Universities for Research in Astronomy
Primary Mirror Diameter: 30 m
Field of View: 15 arcmin
Resolution: 0.04 arcsec at 1200 nm
Observed Wavelength Range: 310 to 28,000 nm
Purpose: Designed, in part, to work as a complement to the James Webb Space Telescope, the TMT will be a general-purpose telescope that will support research efforts. It will be used to examine a multitude of “first light” objects near the center of the universe, to help develop a time line of the formation of black holes and to provide a star-by-star analysis of galaxies up to 10 million parsecs from Earth.

Fig3_jwst_new1.jpgJames Webb Space Telescope (JWST)
Location: The Earth–Sun L2 Lagrange point
Launch: 2013
Principals: NASA, European Space Agency, Canadian Space Agency
Primary Mirror Diameter: 6.5 m
Observed Wavelength Range: 600 to 27,000 nm
Purpose: Once known as the Next Generation Space Telescope because it was intended to be the chief successor to the Hubble, the JWST was renamed for the former NASA administrator. It will use a suite of near- and mid-infrared instruments to study every phase of the history of the universe.




Fig10_OWLB.jpgOverwhelmingly Large Telescope (OWL)
Location: To be determined, likely Chile or Canary Islands
Construction: Currently in design stage
First Observations: 2020
Principal Investigator: European Southern Observatory
Primary Mirror Diameter: 60 or 100 m, spherical
Field of View: 30 arcsec to 10 arcmin
Resolution: 1 milliarcsec
Observed Wavelength Range: 320 to 12,000 nm
Purpose: The OWL will be designed to image solar system objects at resolutions comparable to those of space-based viewers, but over much longer time periods. It will not only study extrasolar planetary atmospheres but also determine whether they support biological molecules. As with all of the large ground-based telescopes in development, the OWL will use adaptive optics to account for atmospheric blurring. However, because of the complexity and risks involved in funding and building a 100-m telescope, the ESO is concentrating first on the 42-m E-ELT.

Fig8_E-ELT-3_2008.jpgEuropean Extremely Large Telescope (E-ELT)
Location:
To be determined, likely Chile or Canary Islands
Construction: Scheduled to begin in 2010
First Observations: 2017
Principal Investigator: European Southern Observatory
Primary Mirror Diameter: 42 m
Field of View: 10 arcmin diameter
Resolution: 0.001 to 0.6 arcsec
Observed Wavelength Range: Visible to near-IR
Purpose: The five-mirror E-ELT will be used to study general astronomical objects, including early galaxies and first-light regions of the universe, but it will also be used to study the atmospheres of extrasolar planets scattered throughout the Milky Way galaxy.


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