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 | | 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. | | |
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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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Using adaptive optics to change the mirror shape
Taft E. Armandroff
- W. M. Keck Observatory
With Nelson’s 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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Well the older telescopes really relied on passive technology in order to compensate for how the mirror shape might change as the mirror pointed to different parts of the sky and the gravity vector was different on the mirror. With Nelson’s 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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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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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. Originally this was requiring a bright star because we had to be able to sample the star two thousand times or more a second in order to correct for the timescales in the atmosphere. This wasn’t really practical because there weren’t enough interesting targets just near bright stars this was perhaps a half a percent of the whole sky was accessible in this manner. So we used sodium lasers to illicit a glow from the sodium layer in the upper atmosphere that is put there by micrometeorites.
We use a sodium laser to excite the sodium layer which is populated by micrometeorites up 90 km in the atmosphere. this creates an artificial guide star anyplace astronomers wanted in the sky, next to the most interesting object, next to the most distant galaxy, next to the star we suspect of having an earth-like planet. So we can use adaptive optics anywhere with this laser guide star technology.
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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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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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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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So 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. This is because we have a larger mirror overall, and once we can use laser guide star adaptive optics to remove the blurring effects of the atmosphere we are limited by the size of the mirror. That’s what matters. So already we have a higher spatial resolution than space-based telescopes, but we also have a cost advantage from the ground where we can easily repair things by technicians. We can be more flexible to advances and things like detector technology, computer technology and we can tailor our science more rapidly to the best science questions of the day because ground based development simply takes less time and less cost than space-based development. So I think you’re going to see ground based telescopes in the future absolutely keeping up with developments in space.
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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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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. So that really stimulated me so by the time I went to university I knew I wanted to be an astronomer. I went to a small liberal arts school, Wesleyan University, where we had a great faculty in astronomy and great telescopes right there to could cut my teeth on. And I knew I was going to go to grad school in astronomy and it just continued in grad school at Yale. So I am very fortunate for the many mentors, scientists who took an interest in helping me over the years, and it has really helped me get to where I am today starting with from high school and on through college and grad school.
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