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GIOVANNI DOMENICO CASSINI
GIOVANNI DOMENICO CASSINI
Genoa, Italy (1625 - 1712)
Giovanni Domenico Cassini was an Italian mathematician, astronomer, engineer, and astrologer. Cassini was an astronomer at the Panzano Observatory, from 1648 to 1669, professor of astronomy at the University of Bologna and became, in 1671, director of the Paris Observatory. Along with Robert Hooke, Cassini is given credit for the discovery of the Great Red Spot on Jupiter (ca. 1665). Cassini was the first to observe four of Saturn's moons, which he called Sidera Lodoicea. Around 1690, Cassini was the first to observe differential rotation within Jupiter's atmosphere.
 

Enjoy these insightful and educational video clips drawn from over 70 hours of interviews with the world's leading figures in astronomy, shot during the filming of 400 Years of the Telescope.

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Taft E. Armandroff

Using adaptive optics to change the mirror shape
Taft E. Armandroff - W. M. Keck Observatory

With Nelsonís vision and the advances in computer and sensor technology and actuator technology, we are using computers and sensors to constantly adjust the mirrors to compensate for the forces of gravity, to compensate for thermal effects and to adjust for everything that can keep the mirrors from being perfect.

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Taft E. Armandroff

Adaptive optics and the laser guide star
Taft E. Armandroff - W. M. Keck Observatory

Adaptive optics uses a bright source coming from the atmosphere, originally a bright star to go out to something called a wave front sensor that tells us how the atmosphere is defocusing, introducing a stigmatism and other variables into this perfect star image that is hitting the upper atmosphere.

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Taft E. Armandroff

Extrasolar planetary search
Taft E. Armandroff - W. M. Keck Observatory

You know Keck has been really active in discovering planets around nearby stars, and 20 years ago there were no planets known outside of our solar system. So I would predict the next great discovery with Keck is going to be a planet with a mass very similar to the Earth, and I think that is really going to galvanize not only astronomy community interest but public interest in habitable zones in planetary systems and in life elsewhere in the universe.

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Taft E. Armandroff

Ground vs. space-based telescopes
Taft E. Armandroff - W. M. Keck Observatory

Ground based telescopes offer a number of advantages over space-based telescopes. We are already getting resolutions with the Keck telescope that are significantly higher, two-to-four times higher, than with the Hubble space telescope.

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Taft E. Armandroff

Why I became an astronomer
Taft E. Armandroff - W. M. Keck Observatory

I got very interested in astronomy as a junior high school and high school student. I built a radio telescope in my own back yard. And I was very fortunate because my school district would send people to a place called Talcat Mountain science center during on the weekends where they would get people who were interested in science from a variety of schools, and pair them with scientists and engineers to work on special projects.

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Taft E. Armandroff

Adaptive vs. active optics at Keck
Taft E. Armandroff - W. M. Keck Observatory

Active optics compensate for slowly varying influences on the telescope optical system, so the mirrors and the mechanical systems that hold the mirrors into place. So these change rather slowly over the course of the night with the direction of telescopes pointed or with temperature.

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Taft E. Armandroff

Keck telescopes overview
Taft E. Armandroff - W. M. Keck Observatory

The Keck telescopes are the two largest fully stirrable optical infrared telescopes in the world. They were the first of the new generation of large telescopes.

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Taft E. Armandroff

Astronomy answers at Keck
Taft E. Armandroff - W. M. Keck Observatory

How do stars form and evolve? How does the galaxy form and evolve nearby galaxies? What are the real influences? What makes one galaxy a spiral and another an elliptical? What makes one star live a hundred thousand years and another live sixteen billion years?

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Taft E. Armandroff

Segmented mirror technology
Taft E. Armandroff - W. M. Keck Observatory

Jerry Nelson developed a revolutionary technique for instead of having one mirror as all telescopes had before Keck and following the prescription of say, the classic telescopes like the Palomar 200 inch, the Mt. Wilson 100 inch, and the Kitt Peak and Cerra Tololo four meters to make it much more achievable in terms of issues like weight, in terms of cost to break the mirror into segments.

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Taft E. Armandroff

The 30-meter telescope
Taft E. Armandroff - W. M. Keck Observatory

The 30-meter telescope plans to use segmented mirror technology just like Keck, and between Keck and 30 meter telescope we have a great interchange of technical knowledge on topics like controls systems, for keeping the mirrors precisely positioned, working on illuminizing the segments and adaptive optic systems.

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