Ground versus Space Telescopes
Almost
all astronomical research and discovery prior to 1950 was made by
optical telescopes on the ground. The leading observational advances
in the period of 1900-1950 came from telescopes located in the
southwestern United States using photographic methods.
After World War II, the
technologies developed for radar and rocketry were applied to
astronomy, opening the whole electromagnetic spectrum to
observation, as well as allowing direct exploration of the solar
system. These advances, along with the development of electronic
imaging, revolutionized astronomy at all wavelengths. However, no
significant advances were made in ground-based telescope design; no
telescopes more powerful than the Palomar 200-inch, completed in
1947, were built.
Today the pace of technological advances in space has slowed;
future instruments in space, more powerful than the Hubble Space
Telescope (HST) or similar
observatories operating at other wavelengths, will be very expensive
and slow in coming. It has been realized worldwide that, for optical
and infrared observations, new advanced mountaintop telescopes offer
huge potential for future discovery, at a much smaller cost. Light
grasp more than an order of magnitude larger than HST can be
obtained from the ground, allowing detailed analysis of fainter,
more distant sources. Moreover, taking advantage of the latest
sensors and fast computers adaptive optics allows the potential of
correcting atmospheric blurring and enormously improving image
sharpness to a level far exceeding that of the HST. Mountaintop
telescopes are entering a new golden era.
The image above shows the spiral galaxy NGC 4535 moved to a
redshift of 1.0 and synthetically imaged with various telescopes at
a wavelength of 2 microns. The upper left frame shows the
ground-based seeing limit under excellent conditions (0.4 arcsec).
The upper right frame is the galaxy imaged by HST (a 2.4 meter
telescope) with 0.2 arcsec resolution. The lower two frames show how
the galaxy will appear with LBT. The lower left frame gives the
appearance of the galaxy with full adaptive correction of a single
8.4 meter mirror (0.06 arcsec diffraction limit), while the lower
right frame shows the detail attainable with a near infrared beam
combiner which provides the diffraction limit of the full 22.8 meter
baseline (0.02 arcsec). These images were provided by Drs.
Hans-Walter Rix and Tom Herbst of MPIA Heidelberg who are part of a
team studying the near infrared beam combiner design.
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Ground Telescope: Design Optimization Challenge
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