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Optical Projection and Direct Viewing

Projection with binoculars or a telescope. You can form a much sharper and bigger Sun image by projection through a small telescope or binoculars. This is best done outdoors to avoid the distorting effect of a windowpane. To aim the instrument safely, look at its shadow on a white card as you swing the tube around. When the scope's shadow nears its minimum size, a brilliant beam of sunlight will burst out of the eyepiece and fall onto the card. Turn the focus knob and experiment with the card's distance behind the eyepiece until the Sun's disk is sharp and as big as you want. Look for sunspots!

Direct viewing. If you prefer to look directly at the Sun, you can use a square or rectangular arc-welder's glass of shade #13 or #14, available for a few dollars from local welding-supply stores. (Don't get a lower-numbered shade; the Sun will be too bright to look at safely.) Alternatively, special, cheap "eclipse glasses" are widely made from safe solar filter materials.

A solar filter that's designed to be used with a telescope is also safe for viewing with the otherwise unaided eye.

Filters that are not necessarily safe, though sometimes recommended in old books, include smoked glass, stacked sunglasses, crossed polarizing shades, photographic neutral-density filters, or a filter intended to block visible light for infrared photography. While these may greatly dim the Sun's glare, thus appearing to do the job, invisible ultraviolet or infrared radiation may be getting through to damage your eyes. (See the article "Solar Filter Safety" for more details.)

Telescopic viewing. The clearest and best views of the Sun are through a properly filtered telescope.

The filter must be secured over the telescope's front to keep most of the Sun's light and heat out of the instrument. Never use a Sun filter at the eye end, where it could crack or melt in the concentrated heat.

Direct viewing with a telescope and proper solar filter gives the best views of sunspots and the complex details within them, as well as the progress of the Moon's jagged, mountainous edge making its way across the solar disk. Remember, safety is paramount. Never look directly at the Sun without using a safe solar filter. If you don't have one, see our list of suppliers.

3.3.4. Hubble Celebrates 15th Anniversary with Spectacular New Images

When NASA's Hubble Space Telescope was launched in 1990, astronomers anticipated great discoveries, ranging from finding black holes to looking back billions of years toward the beginning of time. Now, 15 years later, the versatile telescope continues to deliver exciting new science, including helping to prove the existence of dark energy, tracing enigmatic gamma-ray bursts to distant galaxies, and sampling the atmospheres of far-flung planets. To celebrate Hubble's 15th anniversary, new breathtaking images will be released of a majestic spiral galaxy teeming with newborn stars and an eerie-looking spire of gas and dust.

The new image of the well-known spiral galaxy M51 (known as the Whirlpool Galaxy), showcases a spiral galaxy's classic features, from its curving arms, where newborn stars reside, to its yellowish central core, a home for older stars. A feature of considerable added interest is the companion galaxy located at the end of one of the spiral arms. The new photograph of the Eagle Nebula shows a tall, dense tower of gas that is being sculpted by ultraviolet light from a group of massive, hot stars.



The pictures are among the largest and sharpest views taken by Hubble. The images, taken by Hubble's Advanced Camera for Surveys, are 20 times larger than a photograph taken by a typical digital camera. The new images are so sharp that they could be enlarged to billboard size and still retain the stunning details.

Mural-sized images of both celestial objects will be unveiled at 100 museums, planetariums, and science centers across the country, from Guam to Maine. The 4-foot-by-6-foot image of M51 and the 3-foot-by-6-foot photograph of the Eagle Nebula will be on display at all the sites. A list of these sites is available on http://hubblesite.org/about_us/unveiling.shtml.

If you cannot see the pictures at a museum or planetarium, catch them on the new "Gallery" at http://hubblesite.org/gallery. Views of M51 and the Eagle Nebula, along with more than 1,000 other glorious Hubble images, can be savored from the comfort of your home. If you want some Hubble pictures to hang in your home, then go to "Astronomy Print Shop." Choose from a list of Hubble images that are specially formatted for printing. Select the image, the size you want (from 4 inches by 6 inches to 16 inches by 20 inches), and download it. Then take it to your favorite print shop to make a copy suitable for framing.

Hubble was placed into Earth-orbit on April 25, 1990. For the first time, a large telescope that sees in visible light began orbiting above Earth's distorting atmosphere, which blurs starlight and makes images appear fuzzy. Astronomers anticipated great discoveries from Hubble. The telescope has delivered as promised and continues serving up new discoveries. During its 15 years of viewing the universe, the telescope has taken more than 700,000 snapshots of celestial objects such as galaxies, dying stars, and giant gas clouds, the birthplace of stars. Astronomers are looking forward to more great discoveries by Hubble.

3.3.5. Really Big Telescopes are Coming

Summary - (Apr 8, 2005) If you think current telescopes are powerful, just you wait. A new class of observatories are in the works that could sport mirrors as large as 100 metres (328 feet) across, and have 40 times the observing power of the Hubble Space Telescope. A new study developed by a commission of European astronomers proposes that instruments this large could be built for approximately 1 billion Euros and take 10-15 years to construct.

Full Story - The largest ground-based optical telescopes in use today use mirrors that are 10 m (33 ft) across. But the prospects for future Extremely Large Telescopes (ELTs) are looking up. According to recent studies by international teams of astronomers and leading astronomical organizations, the next generation of optical telescopes could be 50-100 meters (165 330 ft) in diameter - big enough to fill a sports stadium.

This quantum leap in size has important implications, since astronomers want to capture every photon of light that comes their way, and a 100 m mirror has a collecting area up to 100 times greater than existing instruments. Furthermore, a 100 m telescope would have extremely sharp vision, with the ability to see objects at up to 40 times the spatial resolution of the Hubble Space Telescope.

On Friday 8 April, Dr. Isobel Hook of Oxford University told the RAS National Astronomy Meeting in Birmingham about the compelling scientific case for Extremely Large Telescopes which has been developed at a series of meetings over the past four years. The results of this evaluation process, which involved more than 100 astronomers, have recently been published, coinciding with the start of the European Extremely Large Telescope Design Study.

A team of over 100 European Astronomers has recently produced a brochure summarising the science that could be done, said Dr. Hook. This work is the result of a series of meetings held in Europe over the last 4 years, sponsored by the EC network OPTICON. The new report explains how an ELT will revolutionise all aspects of astronomy, from studies of our own solar system - by producing images of comparable detail to those from space probes - to the edge of the observable Universe.

As the report states: The vast improvement in sensitivity and precision allowed by the next step in technological capabilities, from todays 6-10 m telescopes to the new generation of 50-100 m telescopes with integrated adaptive optics capability, will be the largest such enhancement in the history of telescopic astronomy. The major scientific impact of these new telescopes are likely to be discoveries we cannot predict, so that their scientific legacy will also vastly exceed even that rich return which we can predict today.

Astronomers believe that with an ELT it will not only be possible to find planets orbiting other stars, but also to identify and study habitable Earth-like planets by identifying the presence of liquid water, oxygen and methane. Many of the mysteries about the high-energy Universe will also be answered. An ELT would be able to provide key insights into the nature of black holes, galaxy formation, the mysterious dark matter pervading the Universe and the even more mysterious dark energy that is pushing the Universe apart. An ELT will also be sensitive enough to detect the first galaxies that were born only a few hundred million years after the Big Bang, as well as very early supernova explosions, whose light has travelled for over 10 billion years to reach us.

Some of the most exciting discoveries cannot be predicted now, said Dr. Hook. New astronomical instruments have always surprised us with the unexpected. An ELT would make such advances possible for two main reasons - the large collecting area enables it to detect the faintest sources, and the telescopes huge diameter allows extremely sharp images (provided the effects of atmospheric turbulence are corrected by adaptive optics).

Would it be possible to build such a telescope? Initial studies are very positive, suggesting that a 50-100 m segmented telescope could be built within 10-15 years for a cost of around 1 billion Euros, said Dr. Hook. A major design study is now starting in Europe, aimed at developing the technology needed to build Extremely Large Telescopes. The study has been awarded 8 million Euros from the EC Framework Programme 6 plus additional funds from the participants (the European Southern Observatory, together with universities, institutes and industry around Europe, including the UK).

3.3.6. Sedna Untouched for Millions of Years

Summary - (Apr 13, 2005) Most objects in the Solar System have been resurfaced by collisions with asteroids, smaller rocks and comets. But Sedna, on the other hand, has spent its lifetime in the remote reaches of the Solar System, and probably hasn't had many impacts at all. It's only been weathered by cosmic rays and solar ultraviolet radiation. Astronomers think that Sedna started out icy, like Pluto and Charon, but was then baked for millennia, until the ice was transformed into a complex hydrocarbon similar to asphalt.

Full Story - Recent spectroscopic studies of infrared light reflected from the surface of Sedna reveal that it is probably unlike Pluto and Charon since Sedna's surface does not display evidence for a large amount of either water or methane ice. Due to Sedna’s extreme distance from the Sun, the frigid surface has probably been untouched for millions of years by anything except cosmic rays and solar ultraviolet radiation.

Gemini Observatory astronomer Chad Trujillo led an effort by the same California Institute of Technology research team responsible for Sedna's original discovery to obtain spectra of this distant planetoid using the Near Infrared Imager (NIRI) on Gemini North. Their aim was to better understand the surface of this distant world and how it has evolved since its formation. “It is likely that Sedna has experienced an extremely isolated life in the outskirts of our solar system,” said Trujillo. “Out there beyond what we used to think was the edge of the solar system, interactions or collisions between bodies are probably very rare. Our observations confirm what you would expect from a surface that has been so far out in our solar system for such a long time and exposed to space weathering.”

The data could reveal something of Sedna's evolutionary history in the outer solar system. Astronomers think that objects like Sedna start out with icy surfaces. Over time cosmic rays and solar ultraviolet radiation “bake and burn” the surfaces into black hydrocarbon-rich substances similar to asphalt, which do not reveal themselves well in infrared spectra. Such a history might explain why Sedna doesn't exhibit traces of methane and water ice, whereas Pluto and Charon do.

“Like a sandblaster operating for several billion years, most of the objects out as far as Pluto are constantly being resurfaced by impacts and collisions which expose and supply fresh surface materials before the black stuff can get baked on,” said Michael Brown of California Institute of Technology, who is the Principle Investigator of the team that originally discovered Sedna. “Pluto and its moon Charon provide an excellent example of this process, with Pluto displaying a strong methane ice signature in its spectrum and Charon dominated by water ice.”

The team does not rule out the possibility that longer-duration (deeper) observations might reveal evidence of methane or water ice on Sedna. However, the Gemini data indicate that if they do exist their extent is limited.

3.3.7. The Art of Using a Telescope

Once you've obtained an astronomical telescope, what can you expect of it? Both less and more than many new owners realize. One of the fun parts of being an amateur astronomer is showing off the heavens to others. The "oohs" and "aahs" as people get their first good look at the Moon or Saturn are a pleasant reward for the proud telescope owner. Sometimes there's a temptation to show people more typical objects "to give them an idea of real astronomy." The reactions then are not so encouraging, even when viewers are told they're looking at a recently recovered comet or a galaxy 50 million light-years away.

The truth is that most of the thousands of objects visible in amateur instruments are not the least bit spectacular. Anyone who gets a telescope expecting dramatic visual thrills is in the wrong hobby. The riches that astronomy offers are of a different sort. Visual observing outdoors in the dark usually means working to detect something that's extremely faint, tiny, hard to find, or all three. The more difficult the task, however, the greater the rewards of success. The excitement lies in finding and seeing, first-hand, remote marvels far beyond our planet — and in gaining skills and knowledge as an amateur scientist.

Too many people buy a telescope as if it were a TV, expecting it to show pictures all by itself. It's more like a piano, which gives back only as much value as the work you put into it. Learning to use a telescope well is much easier than learning a musical instrument, however. If you practice the techniques described here, you'll soon master the skies.


Date: 2015-12-18; view: 593


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