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 | | VERA RUBIN |
| USA (1928 - ) | Vera (Cooper) Rubin is an astronomer who has done pioneering work on galaxy rotation rates. Her discovery of what is known as "flat rotation curves" is the most direct and robust evidence of dark matter. | | |
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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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General relativity and solar observations
Mark Giampapa
- National Solar Observatory
Einstein’s general theory of relativity had an interesting prediction, namely that light rays passing near the sun, passing through the strong gravitational field of the sun would be bent, and this led to the prediction that the apparent positions of stars as their light passed near the sun would shift.
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Einstein’s general theory of relativity had an interesting prediction, namely that light rays passing near the sun, passing through the strong gravitational field of the sun would be bent, and this led to the prediction that the apparent positions of stars as their light passed near the sun would shift. So the best way to observe that phenomenon was during a solar eclipse, when the moon blocked much of the light of the bright sun and astronomers are able to see faint stars near the edge of the sun, so as their light passes we can record the apparent positions of stars near the edge of the solar disk during an eclipse, and see if the predicted shift in their positions is consistent with general relativity.
And indeed this was done by Sir Arthur Eddington initially in an eclipse expedition into Africa in 1919. And their measurements were – while not as precise as we can achieve today – was certainly relatively consistent with Einstein’s predictions. And it was that experiment that really captured the public’s imagination, and brought to their attention the existence and the potential predictive power of general relativity. And of course general relativity, with its unorthodox approach and originality of concept is certainly one of the great intellectual achievements of scientific history.
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George Ellery Hale and sunspots
Mark Giampapa
- National Solar Observatory
George Ellery Hale was the founder of Mt. Wilson Observatory in the early 1900s, where he was to carry out fundamental experiments in solar observational astrophysics.
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George Ellery Hale was the founder of Mt. Wilson Observatory in the early 1900s, where he was to carry out fundamental experiments in solar observational astrophysics. Particularly the observation of the sun, with his newly constructed solar telescope and spectrograph, and he was the first to take photographic spectra of sunspots and he compared the spectra of sunspots with laboratory measurements of spectra in the presence of magnetic fields. And he found they showed very much the same behavior, that is the splitting of spectral lines that occurs in the presence of magnetic fields. But of course, the splitting he observed in sunspot spectra was certainly much greater than what he saw in the lab, and he had indicated intense magnetic fields in sunspots. In fact, the magnetic field strengths he measured were a thousand times greater than the earth’s magnetic field, and really represented the first detection and measurement of magnetic fields beyond the earth.
I would say that George Ellery Hale’s measurements really marked the beginning of solar astrophysics, that is the study of the physics of the sun and fundamental magnetic structures on the sun itself. And these developments occurred nearly 300 years after the beginning of the first observations of the sun.
Hale always had in mind the broad problems of astronomy and his interest was in astronomy so it was no accident that Mount Wilson became a center for stellar astronomy.
We know Hale of course as a builder of great observatories, but really the lasting legacy of Hale are his pioneering investigations in solar physics, particularly the study of the structure of sunspots, and the establishment of Mt. Wilson as a center for stellar astronomy, that is, the astronomy of the sun itself and also its extension to stars. So really it was no accident that new stellar telescopes would be built at Mt. Wilson: the 16-inch telescope and later the 100-inch Hooker telescope. And these telescopes have made fundamental contributions to the study of analogues of solar activity – that is magnetic field-related activity like spots and flares in other stars, and certainly that was a lasting intellectual contribution by Hale, whose work really continues today with more advanced instrumentation and even larger telescopes.
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IYA greeting
Mark Giampapa
- National Solar Observatory
Hi, I’m Mark Giampapa, an astronomer, and I’d like to extend to you on behalf of the National Solar Observatory, our greetings and my own personal greetings and thank you for your participation in the International Year of Astronomy. And I want you to always remember to look up.
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Hi, I’m Mark Giampapa, an astronomer, and I’d like to extend to you on behalf of the National Solar Observatory, our greetings and my own personal greetings and thank you for your participation in the International Year of Astronomy. And I want you to always remember to look up.
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The McMath-Pierce telescope
Mark Giampapa
- National Solar Observatory
Behind me is the McMath-Pierce telescope, the world’s largest solar telescope. It has a primary mirror of 1.6 meters in diameter, which is nearly twice the diameter of currently operating solar telescopes.
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Behind me is the McMath-Pierce telescope, the world’s largest solar telescope. It has a primary mirror of 1.6 meters in diameter, which is nearly twice the diameter of currently operating solar telescopes. Robert R. McMath, from the University of Michigan, was a pioneer in the building of solar telescopes and in fact the founding of Kitt Peak National Observatory. He certainly had this dream to build the world’s largest solar telescope to study the solar spectrum at the highest dispersions possible – that is the features in the sun’s spectral lines – at the greatest possible precision. And this is what this telescope accomplishes, from the near ultraviolet to the far infrared. So it’s a unique facility.
Later, the name of Keith Pierce, who was a notable solar astronomer at Kitt Peak National Observatory, was added to that of McMath to honor his contributions as well, in the building of this great solar facility.
McMath-Pierce has this unique sundial-like design with a heliostat of 82 inches on top, which tracks the sun during the course of the day and reflects the sun’s light down a long shaft that goes over 150 feet into the ground, and then is reflected back up to an intermediate mirror, which then reflects the light back into our instrumentation. And by doing this we achieve a certain image scale that allows us to study the solar spectrum at very high precisions. It’s all-reflecting design is unique as well. Most solar telescopes right now have a window and a vacuum tower that allows excellent seeing to be achieved. However, with the all-reflecting design of the McMath-Pierce, we can see all wavelengths while vacuum tower telescopes typically cut off in the infrared wavelengths.
In contrast to the Dunn solar telescope at Sacramento Peak, with its evacuated tower and very good seeing at that site, so it’s able to obtain very high spatial resolutions on the sun, to see the granulation and inside the granulation, and the inner granular lanes, and all the dynamic activity that occurs there. The McMath-Pierce telescope, with its larger aperture, is able to achieve very high precisions in the measurement of magnetic fields of the sun from the visible to the infrared, and it’s particularly well-suited for infrared observations, where we can attain the highest possible spatial resolutions with this particular telescope. In fact at the diffraction limit of its 1.6 meter aperture, using adaptive optics in the infrared. So in that sense, it plays a role that no other solar telescope currently plays in the world, with its combination of large apertures so it can gather a lot of photons from the sun and get what we call very high signal-to-noise ratio, that is very high quality observations at all wavelengths.
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Studying the sun
Mark Giampapa
- National Solar Observatory
Among all the astronomical objects that we observe, the sun is certainly the most important astronomical object to all of humankind. The sun supplies the energy for life on Earth, to sustain our lives on the Earth, and it’s the driver of the climate on Earth. And so it’s extremely important for us to understand all aspects of the variability of the sun.
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Among all the astronomical objects that we observe, the sun is certainly the most important astronomical object to all of humankind. The sun supplies the energy for life on Earth, to sustain our lives on the Earth, and it’s the driver of the climate on Earth. And so it’s extremely important for us to understand all aspects of the variability of the sun.
And therefore we must build the kind of telescopes that we need to give us insight on the physics of the sun and to compare what we’ve learned through observations with what we’re learning with theoretical models using the most powerful computers available today. And those kinds of models have outstripped the ability of our current telescopes to gather data to compare with them.
A fundamental goal in science is to gain predictive power, and to gain that kind of level of understanding to make reliable predictions, we have to develop our physical models to the point where they can be verified with actual observations. So we need telescopes such as the Advanced Technology Solar Telescope (ATST) to do exactly that.
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Digital photography and computing power in astronomy
Mark Giampapa
- National Solar Observatory
Transcript in progress
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Since I began my career in astronomy, there were two major technological changes. The first was the transition from photographic plates to electronic detectors. And that had a huge impact on astronomy with the higher sensitivity, greater dynamic range, digital detectors, and the ability to process the data more rapidly and with greater ease than with photographic plates.
The other technological innovation was certainly the tremendous advancement in computing power. Today’s computers or even handheld devices can handle enormous amounts of data and do complex calculations in relatively short times.
So those two advances have remarkable impact on astronomy and really enabled small telescopes to once again become very powerful instruments in astronomical research.
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The telescope, Galileo and solar observations
Mark Giampapa
- National Solar Observatory
Galileo was among four initial users of the telescope, and observed sunspots with his newly invented telescope. And that really marked the beginning of solar astronomy.
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Galileo was among four initial users of the telescope, and observed sunspots with his newly invented telescope. And that really marked the beginning of solar astronomy. Galileo in particular made very careful observations of sunspots, and was able to do very detailed drawings, drawings that showed the shape of the dark umbra sunspots, and the irregularities in the shape, and even the fine structure of the penumbra, the somewhat less dark area that surrounds sunspots. And through his work and his observations of the changes in sunspots as they traverse the solar disk, he was able to emphatically refute the claims that spots were planets transiting across the disk. And so he really firmly established sunspots as a purely solar phenomena.
Sunspot observation has a rich history, going back to certainly ancient times where during periods of particular cloudiness combined with large spots on the sun, people could get a glimpse of them through the clouds. But later it was Galileo was one of four people who first observed sunspots with the telescope. Certainly Galileo performed the most detailed initial studies with the telescope, especially with the superior quality of his instrument compared to others at the time.
If I could describe some more of the observations of sunspots that Galileo did – as he watched them go across the solar disk, he realized that they were moving across in a periodic fashion – that is, they were carried across the solar disk once every 27 days, and he concluded that the sun rotates, but in philosophy though, his observations of sunspots had profound implications. These blemishes on the sun made the sun appear as a less perfect, or certainly imperfect object. It was no longer the “pure orb”.
Observations of sunspots by Galileo certainly had profound philosophical implications. These blemishes, or spots on the sun, were simply not consistent with the image of the sun as a pure, perfect, celestial body orbiting in the heavens, and it contradicted the prevailing dogma of the time. And so the observation of sunspots by Galileo in a sense paved the way intellectually for the eventual acceptance of an even more revolutionary idea, espoused by Galileo, and namely the Copernican system which placed the sun at the center of our solar system, with the planets orbiting around it.
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What is astronomy?
Mark Giampapa
- National Solar Observatory
Well, astronomy is the study of the stars, planets, and basically the contents of the cosmos. Their composition, their evolution, and the large-scale structure of the universe.
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Well, astronomy is the study of the stars, planets, and basically the contents of the cosmos. Their composition, their evolution, and the large-scale structure of the universe.
Astronomy has a history that goes back to the ancients, when they first looked up in the sky and wondered about the bright lights they saw, some of which moved. And they began to see systematic behavior, that is, regular patterns, in the sky and during seasons.
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Why I became an astronomer
Mark Giampapa
- National Solar Observatory
I became an astronomer because I really enjoyed physics and mathematics as a kid, and especially in high school. I found though that I tended to like the physics problems in space more than the physics problems in the lab.
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I became an astronomer because I really enjoyed physics and mathematics as a kid, and especially in high school. I found though that I tended to like the physics problems in space more than the physics problems in the lab.
My interest was certainly stimulated when I was a freshman in high school and I received a telescope as a gift, as a Christmas gift in fact. While it may seem unbelievable, I pointed the telescope at a bright object in the sky, the first time I ever looked through a telescope, and the first object I saw in that telescope was Saturn. It was unbelievably impressive to look through a telescope at Saturn and see its rings, it’s magnificent rings. And that telescope really hooked me on astronomy. Just like I think the telescope certainly captured Galileo’s interest and imagination in the structure and nature of the entire universe. I think that’s what many astronomers are motivated by.
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Copernicus and Aristarchus
Owen Gingerich
- Harvard University
In Copernicus’ day, one didn’t want to be too radical an innovator.
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In Copernicus’ day, one didn’t want to be too radical an innovator. So Copernicus looked around to see if anybody else had similar ideas in the past and he did read that Aristarchus, a Greek astronomer, had done something of the sort; but what Copernicus had was only a line or two in another book that wasn’t at all explicit and in the end when Copernicus was editing his book he switched at that point to a passage in Greek which made the book more aerodite but didn’t happen to mention Aristarchus. So Aristarchus got wiped out of the forward of the book. If Copernicus had been sure that Aristarchus had a heliocentric system he would have felt more comfortable in not being alone with the idea and so comparatively isolated. But we don’t even know exactly why it was that Aristarchus got that idea. It was so early in the development of planetary theory that the ideas weren’t fully in place.
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