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Telescopes and Spacecraft

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Learning Goals Students will: 1) understand the technology used in Ancient and Modern Astronomy. 2) understand how different wavelengths of the electromagnetic spectrum are used to study space.

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Success Criteria Students will show their understanding of leaning goals by: 1) understand the technology used in Ancient and Modern Astronomy. 2) understand how different wavelengths of the electromagnetic spectrum are used to study space.

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Tools of Astronomy 1) Radiation (All wavelengths of the Electromagnetic Spectrum) Telescopes (Light, X-ray, Radio, Infrared, Ultraviolet) 2) Spacecraft Satellites Unmanned probes Human Spaceflight Hubble Space Telescope Apollo Space Capsule Very Large Array Radio Telescope

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The Naked Eye From before the dawn of history until less than 400 years ago, our Universe consisted of what we could see with our eyes: a sky filled with objects in constant motion. The Earth seemed to rest at the center of a starry sphere, and the Sun, Moon, planets, and stars appeared to move around the Earth. People used measuring instruments to map the stars and to plot the changing positions of the Sun, Moon, and planets in order to understand and predict their motions.

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The Naked Eye Our early ideas about the Universe were largely based on what we learned from these ancient tools. Also remember that the use of electric lighting was almost absent until the 20 th century and there was no light pollution. The night sky was filled with stars unobscured by the light of cities and highways. Take a look at the star maps and ask yourself if you actually see that many stars. How many people in this room have seen the Milky Way?

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The Naked Eye In ancient times, nature was held in awe, often in God-like status and thus changes in the sky or the movement of celestial objects were held as omens of the future or the will of God. Almost all ancient societies have Creation myths and stories to explain the structure of the universe. The sky was also used as a guide or calendar with certain stars or groups of stars called constellations indicating direction or marking important events, such as the harvest or planting times.

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Constellations Ancient societies grouped stars together to form the shape of people, animals or objects. Different societies had different constellations. The common constellations that we see today are Greek and Roman constellations. The 12 constellations of the Zodiac appear in the night sky at different times of the year (many of us know these constellations and the times they appear in the sky yet many of us have never actually seen the constellation itself).

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The Zodiac Most of us are aware of the signs of the Zodiac from Astrology Astrologers predict the future and define behaviours based on the location of stars and other celestial objects and your birth date. Ancient farmers used these constellations as a calendar. Today, light pollution means that we cannot see most zodiac constellations.

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The Zodiac The dates related to each sign of the zodiac coincide with the position of the sun in front of that constellation

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The Astrolabe Astrolabes served as mechanical maps of the Universe. Sophisticated, hand-held instruments, they were used for centuries to teach people about the sky. The back side had a moveable sighting arm and a scale of degrees for measuring altitude. The front side was engraved with a flattened map of the heavens, which was used with other moveable parts to solve practical astronomical problems. This astrolabe has several interchangeable plates, each engraved with the celestial coordinates for a different latitude. The pointers on the top plate indicate the positions of 22 bright stars. The top plate can rotate to show where those stars will appear at different times or dates, much like a modern paper or plastic star finder. The instrument could also be used to predict when the Sun or certain bright stars would rise or set on any date. Islamic Astrolabe

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Tycho Brahe "Amazed, and as if astonished and stupefied, I stood still...with my eyes fixed intently upon it.... When I had satisfied myself that no star of that kind had ever shone forth before, I was led into such perplexity by the unbelievability of the thing that I began to doubt the faith of my own eyes." Danish astronomer Tycho Brahe's observations of the bright new star that appeared in the sky of 1572 proved the heavens were not changeless. His observations of a comet in 1577 proved that comets moved about freely through the realm of the planets, a discovery that shattered the centuries-old notion of solid, transparent heavenly spheres.

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Tycho Brahe Observing was Tycho's passion, and precision was his obsession. Supported by the king of Denmark, he built two major observatories and filled them with the finest instruments, many of which he designed himself. He cataloged the positions of a thousand stars and tracked the motions of the Sun, Moon, and planets. The accuracy of his measurements remained unsurpassed until the invention of the telescope. This image depicts Tycho's huge mural quadrant, one of his most accurate tools for measuring heights of celestial objects. Brahes data was used by Copernicus and Galileo to make their conclusions. Brahes massive astrolabe used to collect the most detailed cosmic observations ever made

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Galileo and the Telescope In 1609 Galileo began using a new kind of instrument that magnified distant objects: a telescope. When he trained it on the heavens, he saw countless stars and other faint objects never before seen. Suddenly, the Universe was no longer limited to what the naked eye could see. As telescopes improved, astronomers continued to push back the boundaries of the known Universe, peering ever deeper into the surrounding sea of stars known as the Milky Way.

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Radiation The Electromagnetic Spectrum

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The Electromagnetic Spectrum The electromagnetic spectrum is a continuum of all electromagnetic waves arranged according to frequency and wavelength. The sun, earth, and other bodies radiate electromagnetic energy of varying wavelengths. Electromagnetic energy passes through space at the speed of light in the form of sinusoidal waves. The wavelength is the distance from wave crest to wave crest Hotter, more energetic objects and events create higher energy radiation than cool objects. Only extremely hot objects or particles moving at very high velocities can create high-energy radiation like X-rays and gamma- rays.

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Radiation Electromagnetic Spectrum Celestial objects produce radiation in a wide variety of wavelengths. Humans can detect only visible light which occupies a very narrow band of the electromagnetic spectrum (400 700 nm or 4.0 x10 -7 7.0 x 10 -7 m wavelength)

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Radio: Sun in Radio Light This is an image of the Sun at radio wavelengths. Since our eyes do not see these wavelengths, colour is added to help us understand the image, in this case, yellow and red. In this picture, red represents stronger radio emissions and green represents weaker emissions. This image was taken by the NRAO 12 Meter Telescope at Kitt Peak, AZ.

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Radio Wavelengths Radio waves are very long compared to waves from the rest of the spectrum. Most radio radiation reaches the ground and can be detected during the day as well as during the night. Radio telescopes use a large metal dish to help detect radio waves. The study of the radio universe brought us the first detection of the radiation left over from the Big Bang. Radio waves also bring us information about supernovae, quasars, pulsars, regions of gas between the stars, and interstellar molecules.

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Infrared Radiation: Sun in Infrared This image of the Sun was taken at a wavelength near 1 micrometer (1/1,000,000 of a meter) with a ground-based telescope at US National Solar Observatory on Kitt Peak in Arizona. The observatory is on top of a 6,875 foot mountain.

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Infrared Wavelengths Only a few narrow bands of infrared light can be observed by ground-based observatories. To view the rest of the infrared universe we need to use space based observatories or high-flying aircraft. Infrared is primarily heat radiation and special detectors cooled to extremely low temperatures are needed for most infrared observations. Since infrared can penetrate thick regions of dust in space, infrared observations are used to peer into star- forming regions and into the central areas of our galaxy. Cool stars and cold interstellar clouds which are invisible in optical light are also observed in the infrared.

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Visible Light: Sun in Visible Light This is what the Sun looks like in a very narrow region of visible light at 0.6560 micrometer, in the orange-red part of the spectrum. Astronomers are interested in this wavelength because hydrogen atoms, when they change energy levels, put out radiation at this wavelength. So this image shows hydrogen atoms on the surface of the sun. The gas spilling out on the right is due to an explosion on the sun, which happens rather frequently. This image was taken by instruments aboard Skylab.

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Visible Light Obviously most of the early astronomers and astronomers right up until the early 20 th century used visible light as the only source of astronomical data. The visible light from space can be detected by ground-based observatories during clear sky evenings. Advances in techniques have eliminated much of the blurring effects of the atmosphere, resulting in higher-resolution images. Hubble Space Telescope

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Visible Light Although visible light does make it through our atmosphere, it is also very valuable to send optical telescopes and cameras into space. In the darkness of space we can get a much clearer view of the cosmos. We can also learn much more about objects in our solar system by viewing them up close using space probes. Visible light observations have given us the most detailed views of our solar system, and have brought us fantastic images of nebulae and galaxies. European Extremely Large Telescope - 10 m

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Using Visible Light Radiation With the development of photography, images of stars could be developed on photographic plates and stars could be catalogued. To increase the graphic detail of the images, three things could be done: 1) increase the size of the telescope 2) increase the length of the exposure time (time for collecting light. 3) Position the telescope above the blurring effect of the atmosphere. 4) Employ precise optics with better focusing ability Where would you locate a telescope?

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1) Increasing Exposure Time In order to collect light from a single star for a long period of time the telescope must be pointed at the star for a long period of time. However, we know that stars change position at night since the planet is rotating. Thus the telescope must be on a rotating mechanism (a clock drive) that rotates at the same rate.

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2)Increasing Telescope Size In the 1930s, astronomical observatories housed larger and larger telescopes. Most of these new observatories were built at high elevation to be above the clouds, blurring effects of heat and away from the lights of cities. 1930, the Hale Observatory was built at Mt. Palomar in California with a 200 inch (over 5 meter) diameter. In started a revolution in Astronomy. How much more light can a 50-cm reflector collect as compared to a 10-cm reflector? Todays largest telescopes haves mirrors that are 10 m in diameter (Keck telescopes the mirrors weigh more than 14 tons) 8.4 meter telescope mirror - optical perfect and polished to within micrometers of perfection

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Astronomical Observatories Large telescopes are housed in observatories that can swivel to observe celestial objects in any part of the sky.

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Types of Telescope s 1)Reflector the image is focused by a mirror(s). Light is reflected by a concave mirror. 2)Refractor the image is focused by a lens. Light is refracted by a double convex (converging) lens onto the eyepiece. 3)Astronomers tend to use reflecting telescopes due to weight limitations

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Limitations of Light Telescopes 1)Light pollution (from cities, the moon, etc.) lowers the resolution of pictures. 2)Air distorts optical images (Think of the shimmer off of hot pavement) 3)Stars and other celestial objects emit other types of radiation that cannot be seen with the eye but give us information that cannot be determined using visible light. 4)Where would you employ a light telescope?

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Blurring due to heat in the atmosphere

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Ultraviolet: Sun in Ultraviolet This image of the Sun was taken in ultraviolet light from the SOHO (Solar and Heliospheric Observatory) telescope that is in orbit above the Earth's atmosphere. Since our eyes do not see these wavelengths, the image is shown in orange. The telescope observes the hot atmosphere of the Sun and its corona which extends far above the visible surface. The images below show a galaxy at visible and UV wavelengths.

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Ultraviolet Radiation Most of the ultraviolet light reaching the Earth is blocked by our atmosphere's ozone layer and is very difficult to observe from the ground. To study light in this region of the spectrum astronomers use high- altitude balloons, rockets, and orbiting observatories. At ultraviolet wavelengths, most stars fade from view because they are too cool to emit such high energy light. But very young massive stars, some very old stars, bright nebulae, white dwarfs stars, active galaxies and quasars shine brightly in the ultraviolet.

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Ultraviolet Radiation Ultraviolet observations have contributed to our understanding of the Sun's atmosphere and tell us about the composition and temperatures of hot, young stars. Light from this part of the spectrum (left image) also gives astronomers information about the chemical composition, densities, and temperatures of interstellar gas and dust. Discoveries have included the existence of a hot gaseous halo surrounding our own galaxy.

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X-Rays: Sun in Soft X-Rays This is an X-Ray image of the Sun taken by the Yohkoh Soft X-Ray Telescope, which is in orbit above the Earth's atmosphere. Since our eyes do not see these wavelengths, we can choose any color we like to show the image, in this case, red. This orbiting telescope is a joint mission of three different countries, Japan, Great Britain, and the United States. Its purpose is to observe the energetic events taking place in the Sun's solar flares using X-Ray images.

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X-Ray and Gamma Ray Radiation Since high-energy radiation like X-rays and gamma rays are absorbed by our atmosphere, observatories must be sent into space to study the Universe at these wavelengths. X-rays and gamma rays are produced by matter which is heated to millions of degrees and are often caused by cosmic explosions, high speed collisions, or by material moving at extremely high speeds. This radiation has such high energy that specially made, angled mirrors must be used to help collect this type of EM wavelength. X-ray and gamma-ray astronomy has led to the discovery of black holes in space, and has added much to our understanding of supernovae, white dwarfs and pulsars. High-energy observations also allow us to study the hottest regions of the Sun's atmosphere.

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Image Comparisons Spiral Galaxy using Infrared, Visible Light and UV The UV detects the star forming regions towards the center of the galaxy

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Image Comparisons The Crab Nebula at all wavelengths

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Which wavelengths are absorbed by our atmosphere? Most wavelengths are absorbed by our atmosphere - thus space based telescopes are required to collect data at many EM wavelengths.

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Advances in Astronomy Progress in Astronomy meant that further exploration using light spectra to determine the composition and distance of stars. (We will discuss this in future classes) Astronomers begin to use telescopes that collect data at other EM wavelengths radio, infrared, ultraviolet, X-rays and gamma rays. Data is collected digitally and analyzed with computers to allows millions of times more information to be studied.

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Telescopes Employing Other Wavelengths 1) Radio Telescopes VLA (Very Large Array) computers have linked together many radio telescopes to create the equivalent of a single massive telescope. 2) Infrared Telescopes 3) Visible Light Telescopes 4) Ultraviolet Telescopes 5) X-ray Telescopes 6) Gamma Ray Telescopes