In the Land of the (Overwhelmingly Large) Giants
Sky & Telescope, Aug 2000, Cover Story: "Giant Eyes of the Future"
This article is a roundup of the next generation of fantastically large telescopes being planned or now under construction. For the near term there will be several 10-meter giants, such as the 10.4-m "Gran Telescopio Canarias" on the Canary Islands. Thirty-six hexagonal mirrors will form the reflective surface of this telescope that is scheduled for completion in 2002. Joining the large mirror club, with an 11-m span (9.1-m clear aperture) of segmented mirrors, the "Southern African Large Telescope" is being constructed over the next five years. One of the most fascinating scopes currently under construction must be the "Large Binocular Telescope" on Mt. Graham in Arizona. Consisting of twin 8.4-m telescopes, it will have the resolution of a 23-m telescope when the light beams are commingled through interferometry. It has a 2004 "first light" date.
But
even more spectacular super-giant telescopes are being planned. The
"California Extremely Large Telescope" is a 30-m "light
bucket" made up of hundreds of small hexagonal segments. Funding for the
$400 million project has yet to be finalized. The U.S. Decadal Review of
Astronomy Committee also recommends building a 30-m scope -- the "Giant
Segmented Mirror Telescope." Corporate donors are being sought to pay half
the cost of this National Science Foundation sponsored instrument. The Swedes
have been studying the "Extremely Large Telescope" since 1991. It is
similar to the "California" scope with 600 segments making up the
dish. Still in preliminary planning stages, the National Optical Astronomy
Observatory is considering a 30 to 50-m facility dubbed the "Maximum
Aperture Telescope". The 50-m design may cost $1 billion. The 30-m
telescope under consideration is large enough to have its own moniker: the
"Extremely Large Telescope" -- confusingly the same name as the
Swedish telescope. It would cost possibly only $250 million and have a spherical
mirror of 127 segments. To save money it would only see 70% of the sky and
objects could only be tracked for an hour. Not to be outdone by the preceding
50-m scope designs, the European Southern Observatory is planning a 100-m
"Overwhelmingly Large Telescope." The $1 billion monster would consist
of 2,000 spherical segments. A corrector, by itself larger than any existing
telescope in the world, would remove the spherical aberration inherent in the
design. The complete structure would be over 30-stories tall. It is quite
possible that the large telescope designers will run out of acronyms involving
the word "large" before running out of ideas for more grandiose
instruments.
Designed to image large areas of the sky, new survey scopes are also being developed. The British built "Visible and Infrared Survey Telescope for Astronomy", a name contrived to form the acronym "VISTA", will be built in Chile. The 4-m mirror will yield a 1.7-degree field of view. The "Large Sky Area Multi-Object Spectroscopic Telescope" is to be built in China close to the great wall. As the name suggests, this survey telescope will be dedicated to spectroscopy. Equipped with a 4-m stationary primary, it will have a 5-degree field of view. It will can the heavens by way of a steerable mirror that directs light from the sky to the primary. A 6.5-m "Large-aperture Synoptic Survey Telescope" will have a very wide field. Recommended by the Decadal Revue Committee, the instrument will hunt for supernova and asteroids by imaging the whole sky down to 24th magnitude every week. It should be able to track down 90% of all near-Earth asteroids larger than 300-meters. A relative of this scope is the 8.4-m "Dark Matter Telescope." The 3-degree field of view is designed to study distant galaxy fields for signs of gravitational lensing caused by dark matter.
Old Probes Never Die…
Sky & Telescope, Aug 2000, Mission Update: "The Outer Solar System,” “The Inner Solar System” and “Near-Earth Space”
This
month’s Mission Update proves that money invested to operate
instruments in the harsh environment of space can be well spent.
Highlighted are satellites from earlier eras of the space age that still return
useful data. Launched in 1965, the “Pioneer 6” spacecraft is still
monitoring the solar wind by getting as close to 0.8 a.u. of the Sun. This
makes it the closest operational spacecraft to that body. Another veteran,
the “Interplanetary Monitoring Platform 8,” was placed in high Earth orbit
to monitor the solar wind in this region of space. It has been functioning
since 1973. Twenty-eight year-old “Pioneer 10” is 75 a.u. from Sol and
used as a training tool for spacecraft controllers. Voyagers 1 and 2,
launched in 1977, are respectively 76 and 61 a.u. from Sol searching for the
heliopause – the Solar System boundary where the solar wind meets interstellar
space.
King Seeks Crown Back
Central Bureau for Astronomical Telegrams; July 20, 2000; International Astronomical Union Circular 7460: "S/1999 J 1"
Skypub.com; July 21, 2000; Current Astronomical News: "A New Moon for Jupiter"
A
July 20th "Circular" from the IAU announced to the world that Jupiter
has one more known satellite. Images from the University of Arizona's Kitt
Peak Spacewatch telescope are being examined for the purpose of discovering new
moons around the planet. Pay dirt was hit when an object initially thought to be
an asteroid was found to orbit Jupiter instead. 
Designated "S/1999
J1," the estimated 10-km diameter moon never gets closer than 21-million km
to the giant planet.
The "King of Planets" now has 17 known moons, but it has not reigned as the undisputed "Moon King" since the regions around the outer planets have been made visible by space probes and modern imaging systems. Uranus presently holds that distinction with 20 satellites -- two just recently confirmed.
Run Away from the Light
The Canadian Press; July 17, 2000: "Laser Eye Surgery May Damage Night Vision Long-Term: Study"
This
article should cause amateur astronomers to think very seriously before having
one of the common forms of surgical vision correction performed. It reports
several studies that show decreased night vision years after the surgery. A
study by opthamologist Dr. William Jory, working out of the London Centre for
Refractive Surgery in England, warns that 58% of patients that had LASIK or PRK
fail night vision tests. The study was of 38 persons that had moderate to severe
corrections done two to seven years prior. University of Ottawa Eye Institute's
Dr. Evanne Casson found similar results for patients that underwent PRK between
1996 and 1998. Sixty percent had reduced night vision up to two-years after
surgery. Early results from another study show 30% of people were likewise
affected. Dr. Casson said it is not known how aging will affect eyes corrected
though these surgeries and called for an international study of such affects.
Not all doctors agree that a problem exits. The director of the Bochner Eye Institute in Toronto says: "I sometimes tell patients to drive with the overhead light on at night, or I give them drops to make the pupils smaller." Dr. Stein said night vision problems are more common in patients with large pupils. A study of 1,300 people by Dr. Michel Pop revealed 50% had night vision problems the first month, but that decreased to 5% after a year. Dr. Pop, who performs the surgery at his clinic, said the latest surgical lasers are addressing the problem. "It's not as big an issue as it was five years ago," he said.
It may be difficult for laser designers to solve the problem because there is no consensus on why the surgery has this side effect in some people.