# What type of telescope can show cliffs on the moon surface from a city location?

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I am a complete novice in this world and I would like a telescope where I could have enough power to view the moon's surface, I don't expect to see the flag or the hover sending signs to me, but perhaps enough to view cliffs, and other details from the surface of it and perhaps from other places.

I honestly don't even know what kind of telescope to purchase. I live in a capital city, so there is a lot of light around here. My apartment is high with a balcony, which is where I would place it and there is nothing in front of me from there.

• What kind of telescope would fit my needs?
• Are there reputable online stores that I could consult?

I have a $500 budget for this and honestly, I have no clue about specs or anything, I am a completely novice in this field. The main things to look for are: • Decent optics (nearly anything except those with plastic lenses). • A steady mount that points where you want to, and moves smoothly. An altitude-azimuth mount is fine because with practice you can guide at high powers. • The eyepieces should be 1 1/4 inch size or more expensive 2 inch. The older 0.96 inch are very hard to find. This lets you upgrade eyepieces later. The larger the aperture the better. Don't worry about magnification. Hint: find your local astronomical society, ask there, go to one of their "star nights", they may even have telescopes on loan. ## Free Shipping on Orders Over$75 & Installment Billing on Orders over $350 (Exclusions Apply) <"closeOnBackgroundClick":true,"bindings":<"bind0":<"fn":"function()<$.fnProxy(arguments,'#headerOverlay',OverlayWidget.show,'OverlayWidget.show')>","type":"quicklookselected","element":".ql-thumbnail .Quicklook .trigger">>,"effectOnShowSpeed":"1200","dragByBody":false,"dragByHandle":true,"effectOnHide":"fade","effectOnShow":"fade","cssSelector":"ql-thumbnail","effectOnHideSpeed":"1200","allowOffScreenOverlay":false,"effectOnShowOptions":"<>","effectOnHideOptions":"<>","widgetClass":"OverlayWidget","captureClicks":true,"onScreenPadding":10>

Of all the celestial sights that pass across the sky, none is more inspiring or universally appealing than our planet's lone natural satellite, the Moon. Remember the rush of excitement that you felt when you first peered at the rugged lunar surface through a telescope or binoculars? (If you haven't, you'll be amazed.) The first view of its broad plains, coarse mountain ranges, deep valleys, and countless craters is a memory cherished by stargazers everywhere.

A New View Every Night
Since the Moon orbits our planet in the same time that it takes to rotate once on its own axis, one side of the Moon perpetually faces Earth. Though the face may be the same, its appearance changes dramatically during its 27.3-day orbital period, as sunlight strikes it from different angles as seen from our standpoint. Due to the sunlight's changing angle, the Moon presents a slightly different perspective every night as it passes from phase to phase. No other object in the sky holds that distinction. (Note that it is actually 29.5 days from New Moon to New Moon the added time is due to Earth's motion around the Sun.)

The Moon is the ideal target for all amateur astronomers. It is bright and large enough to show amazing surface detail, regardless of the type or size of telescopic equipment, and can be viewed just as successfully from the center of a city as from the rural countryside. But bear in mind that some phases are more conducive to Moon-watching than others.

The Best Times to View It
Perhaps the most widespread belief is that the Full Moon phase is the best for viewing, but nothing could be further from the truth. Since the Sun is shining directly on the Earth-facing side of the Moon at this phase, there are no shadows to give the lunar surface texture and relief. In addition, the Full Moon is so bright that it can overwhelm the observer's eye. Although no permanent eye damage will result, the Full Moon is uncomfortable to look at even with the naked eye. Instead, the best time to view the waxing Moon is a few nights after New Moon (when the Moon is a thin crescent), up until two or three nights after First Quarter (First Quarter is when half of the visible disk is illuminated). The waning Moon puts on its best show from just before Last Quarter to the New Moon phase. These phases show finer detail because of the Sun's lower elevation in the lunar sky.

Using a Moon Filter Improves the View
No matter what the phase of the Moon is, the view is almost always better through a lunar filter. It screws into the barrel of a telescope eyepiece and cuts the bright glare, making for more comfortable observing and bringing out more surface detail. Some lunar filters, called variable polarizing filters, act something like a dimmer switch, permitting adjustment of the brightness to your liking.

Notable Surface Features
The Moon is dominated by large, flat plains known as maria the singular is mare (meaning "sea"), which is pronounced (MAH-ray). Maria were first thought to be large bodies of water. In reality, the maria are ancient basins flooded by long-solidified lava created some three billion years ago when the Moon was still volcanically active. All are relatively free of craters except for a few scars from impacts that have occurred since. Their romantic-sounding names, such as the Sea of Crises, Sea of Fertility, Sea of Serenity, Ocean of Storms, and the Sea of Tranquility, are believed to date back to the mid-17th century.

Surrounding the maria are the lunar highlands, dominated by nearly uncountable craters that measure up to several hundred miles across. Most are believed to have been created when debris from the formation of the solar system collided with the young Moon, leaving a permanent record of the barrage on its surface. Some of the more spectacular lunar craters include Tycho, Copernicus, Kepler, Clavius, Plato, and Archimedes, all named for figures of historical stature. Tycho, Copernicus, and Kepler are especially noteworthy, as each displays a broad pattern of bright rays radiating outward. These are particularly impressive during the Moon's gibbous phases (between Quarter and Full), when the Sun appears high in the lunar sky. The Moon also has several noteworthy mountain ranges, such as the Alps and Apennines, as well as straight cliffs, towering ridges, broad valleys, and small, sinuous rilles.

Focus on the Terminator Region
The greatest amount of detail is visible along the Moon's terminator, the line separating the lighted area of the lunar disk from the darkened portion. It is here that the Sun's light strikes the Moon as the narrowest angle. This casts the longest shadows, increasing contrast of lunar features and showing the greatest three-dimensional relief. Sometimes you will notice a bright "island" surrounded by darkness on the dark side of the terminator. That's a high peak, tall enough to still catch the light of the setting Sun, while the lower terrain around it does not.

A Great Target for Telescopes or Binoculars!
So, the next time the Moon is riding high in the sky, take time to visit our nearest neighbor in space. A binocular provides a terrific view use a tripod or brace it against something to hold it steady. If you have a telescope, begin with a low-power eyepiece. Slowly scan across the lunar disk and try to imagine the emotion that the astronauts must have felt as they orbited that alien world, a world so close to our own, yet so astonishingly hostile and different &mdash "magnificent desolation," as Edwin Aldrin put it during his and Neil Armstrong's historic visit on Apollo 11 in 1969. Then, switch to higher powers for close-up studies of specific areas and features. Get a lunar map or lunar atlas to identify specific craters and features.

An amazing world, our Moon, so rich in detail and so easy to see.

Checklist of Observable Features

1) Maria &mdash Once thought to be oceans of water, these "seas" are actually vast plains of hardened lava. In some of them you will see giant ripples.

2) Craters &mdash Like snowflakes, no two appear exactly alike. In the center of some larger craters, look for peaks formed from the upsurging of molten rock at the impact point. Look for small craterlets inside craters, too.

3) Crater Rays &mdash Long, bright "splash marks" radiating from a few craters, such as Copernicus and Tycho. Best observed at Full or Gibbous phases.

4) Mountains &mdash Several major mountain ranges scar the lunar surface. Check out the largest one, the Apennines, in the southern half of the Moon's disk along the vertical centerline. You can't miss it!

5) Domes &mdash These small, low mounds often have a tiny craterlet in the middle and tend to cluster in groups.

6) Rilles &mdash Filamentous faults and channels, some of which were once meandering rivers of flowing lava.

## A Modern Legacy

The Clark Telescope and the dome that houses it have claimed many notable places in modern pop culture. In season 1 of the popular nerd-core sitcom The Big Bang Theory, a poster featuring the Clark can be seen hanging in the bedroom of Sheldon and Leonard, two of the show’s main characters. The telescope itself has been visited by many notable figures over the years, including poet Carl Sandberg, then First Lady Hillary Clinton, western adventure writer Zane Grey, and astronomy popularizer Neil DeGrasse Tyson.

The newest chapter in the Clark Telescope’s legacy began with the announcement of a new private stargazing experience: Clark Telescope Premium Access. This experience allows groups of up to 10 cohabitating or cotraveling guests to view the cosmos through Mars Hills most storied telescope. Tickets are available now, so don’t wait—reserve your place in the Clark’s history today!

## Sharjah Centre for Astronomy and Space Sciences

The centre opened in 2015 as a small optical observatory with one telescope to observe the galaxies, stars and planets.

Since then, it has grown to include two more: one to observe the sun and moon and the other, which is mainly used for a specific type of solar observations.

Encased in a golden dome – said to have been designed by Sheikh Dr Sultan bin Muhammad Al Qasimi, Ruler of Sharjah, himself – the centre is actively involved in space research.

It also monitors the crescent moon throughout the year to contribute findings that determine when Islamic events, including Ramadan and Eid, begin.

The academy is currently closed to visitors due to the coronavirus outbreak.

## Apollo 11 Moon Landing Site Seen in Unprecedented Detail

The clearest view yet of the famous Apollo 11 landing site on the moon was captured by a NASA spacecraft in orbit around our planet's natural satellite.

The agency's Lunar Reconnaissance Orbiter (LRO) zeroed in on Mare Tranquillitatis, or the Sea of Tranquility — the place where humans first touched down on the lunar surface on July 20, 1969. The new image from LRO captures amazing details of the historic site, even revealing the remnants of Neil Armstrong and Buzz Aldrin's first steps on the moon.

In the image, the astronauts' tracks are the dark regions around the Lunar Module that lead to and from various scientific experiments that were set up on the surface of the moon.

LRO's camera snapped the picture as the probe flew only 15 miles (24 kilometers) above the moon's surface. The image, which was released on March 7, provides the best look yet at humanity's first venture to another world, NASA officials said in a statement.

One of the experiments that can also be made out in the image is the Passive Seismic Experiment Package, which provided the first lunar seismic measurements and continued to return data for three weeks after the Apollo 11 astronauts departed from the moon.

The discarded cover of the Laser Ranging RetroReflector is also highlighted in the image. This experiment allows precise measurements to be collected from the moon to this day, NASA officials said. [Photos: New Views of Apollo Moon Landing Sites]

The astronauts' tracks also lead toward Little West crater, which is located about 164 feet (50 meters) east of the Lunar Module. This was part of an unplanned excursion, when Armstrong bounced over to get a look inside the crater, near the end of the 2.5 hours that the duo spent on the surface of the moon.

The new image also clearly shows how restricted Armstrong and Aldrin were in their exploration of the area. Interestingly enough, their tracks cover less area than a typical city block, according to NASA officials.

Later, during Apollo 12 and 14, the astronauts were given more time to spend on the surface, and on the Apollo 15, 16 and 17 missions, the crews were equipped with a Lunar Roving Vehicle that enabled them to explore beyond the landing site.

The Apollo 11 astronauts returned valuable rock samples from the Sea of Tranquility landing site that revealed the moon's fiery past for the first time. The samples showed that this region of the moon was once the site of volcanic activity, and that thin flows of lava had once flowed where Armstrong and Aldrin had roamed.

LRO has captured images of other Apollo landing sites before, including fascinating pictures that show tracks left by the Apollo 17 astronauts and their lunar rover.

The Lunar Reconnaissance Orbiter has been in orbit around the moon since June 2009. The $504 million car-sized spacecraft first captured close-up images of the Apollo landing sites in July 2009, which revealed new details about the sites and even spotted hardware that was left behind on the lunar surface. The workhorse probe is currently on an extended mission through at least September 2012. ## On the Lunar Surface &ldquoThe surface is fine and powdery. I can pick it up loosely with my toe. But I can see the footprints of my boots and the treads in the fine sandy particles.&rdquo &mdashNeil Armstrong, Apollo 11 astronaut, immediately after stepping onto the Moon for the first time. The surface of the Moon is buried under a fine-grained soil of tiny, shattered rock fragments. The dark basaltic dust of the lunar maria was kicked up by every astronaut footstep, and thus eventually worked its way into all of the astronauts&rsquo equipment. The upper layers of the surface are porous, consisting of loosely packed dust into which their boots sank several centimeters (Figure (PageIndex<7>)). This lunar dust, like so much else on the Moon, is the product of impacts. Each cratering event, large or small, breaks up the rock of the lunar surface and scatters the fragments. Ultimately, billions of years of impacts have reduced much of the surface layer to particles about the size of dust or sand. Figure (PageIndex<7>) Footprint on Moon Dust. Apollo photo of an astronaut&rsquos boot print in the lunar soil. (credit: NASA) In the absence of any air, the lunar surface experiences much greater temperature extremes than the surface of Earth, even though Earth is virtually the same distance from the Sun. Near local noon, when the Sun is highest in the sky, the temperature of the dark lunar soil rises above the boiling point of water. During the long lunar night (which, like the lunar day, lasts two Earth weeks 1 ), the temperature drops to about 100 K (&ndash173 °C). The extreme cooling is a result not only of the absence of air but also of the porous nature of the Moon&rsquos dusty soil, which cools more rapidly than solid rock would. Learn how the moon&rsquos craters and maria were formed by watching a video produced by NASA&rsquos Lunar Reconnaissance Orbiter (LRO) team about the evolution of the Moon, tracing it from its origin about 4.5 billion years ago to the Moon we see today. See a simulation of how the Moon&rsquos craters and maria were formed through periods of impact, volcanic activity, and heavy bombardment. ## How to see the ISS Large satellites The satellites which are the most comfortable for watching are the largest: The International Space Station (ISS), space shuttles (STS - No more!) and the Hubble Space Telescope (HST). The ISS is orbiting at an altitude of 350 km, with many visible transitions. At its peak, the station can reach brightness magnitude up to -4 (brighter than Jupiter and almost as bright as Venus). Space shuttle travels to the ISS occasionally. When the shuttle and the station had not yet joined, or soon after they parted, the pair can be seen as two successive points of light chasing one after the other on the same path within a few seconds to a minute difference. Repeated observations over two or three days will show how the two dots receding or approaching each other. During one of the launches of a space shuttle, I noticed that it is already dark here at Israel. Although there were no data for the pass, I went up to the roof immediately after viewing the launch at NASA site and looked toward the approximate place where the shuttle had to appear (by my own calculations). In about 20 minutes after launch, a bright dot of light appeared exactly as expected. Much to my surprise soon after, another bright spot appeared on a similar route but dimmer. After thinking I concluded that the second point was none other than the external fuel tank of the shuttle. After a shuttle launch, its main fuel tank separate after about ten minutes, losing speed and altitude and finally falls into the Indian ocean waters. Since the phenomenon which I watched is quite rare (Because It can be seen only for about 20 minutes and at most of them from unpopulated areas), I found no other amateurs who viewed it. But I found confirmation that it exists in the following picture. Due to the low number of remaining shuttle missions the chance to see this behavior again is little (at least until the next generation of shuttles will be operational). Even the Hubble Space Telescope can be seen with the naked eye. The HST cruise in higher orbit than the ISS (600 km) and is much smaller. Therefore, its visible magnitude is only about 1.5 at most. Space shuttle mission STS-125 in October 2008 was to upgrade and repair the telescope, giving him at least 5 more years to serve and sends more amazing pictures and data. Iridium Flares Another type of observation is on Iridium satellites. The Seattleites are in polar orbits (moving around the earth at an angle of 90 degrees to the equator), passing over the poles. The Iridium satellites are used for communication purpose from anywhere on Earth. Not all of them are operational but all still orbits the earth (except one which crashed in space with Russian satellite). The satellite brightness normally is barley seen with a naked eye but they have relatively large radio antennas which return the sunlight like a mirror to the area along an imaginary strip over the earth. Whoever found within the stripe or a short distance away, will see a flash in the skies for a few seconds. The closer to the center of the strip, the flash intensity is higher and take longer. Iridium flares can be seen almost every day. Particularly bright flashes can be seen even in daylight if the location of the flare in the sky is far enough from the sun (angular distance). This is the time to note that caution is required in observations that occur while the sun is in the sky, as it might cause irreversible damage to eye of the observer without protective measures. Communications Satellites Communications satellites are Geostationary. They circle the earth around the equator and remain at the same point in the sky all the time (Their speed is identical to the earth own rotation speed and their height is about 36,000 km). Such satellites are difficult to see and they will appear as a dim star. Their movement speed is very slow, in fact, they will move in the direction opposite the movement of the sky. If photographed without star tracking they will be sees as a single point (compared to stars which will produce arcs). If tracking is used they will appear as an arc while the starts are fixed as dots. How to photo satellites Photographing satellites is relatively easy. It requires aiming the camera at the corresponding area in the sky (using a wide field lens). It is best to find a nice constellation that the satellite will pass through, or integrate an Iridium flare with a lovely landscape (buildings, landscape, etc.). Use a long exposure of several seconds, or preferably in manual mode. The result is a strip of light passing through the constellation or in the landscape. Iridium satellite flares start as a narrow point, become wider and narrow again as can be seen in the photo.  Iridium flare in the constellation Lyra When aiming the camera at the area of the satellite leaves or enters Earth's shadow, see how the brightness changed from white to red  The Space station in the Virgo constellations. Entrance to the earth shadow is changing the brightness. For telescopes owners It is hard to observe satellites with a telescope due to the high speed of the object. Small satellites will look only as a bright dot, but the International Space Station structure can be seen at 60x magnifications and higher. Another interesting option is to watch satellite on as they move across the sun. This course requires use of special solar filter. Do not look at the sun without appropriate equipment or you will damage your eyes. Satellite's passage over the sun take around a second, but at least you know where to aim your well protected scope similarly, one can see passes on the surface of the moon. How to find satellites You can of course watch the sky looking for satellites. When observing from a dark area you will usually see several satellites during the hour’s right after sunset or before sunrise. However, it is better to come prepared and download location information from the Internet before starting the observation. Here's an example of two recommended sites. HeavensAbove: Registration is not mandatory, but it helps to keep your data for future use. The use is required to choose is location (by country and city, or exact coordinates). The site is very friendly and easy to use, and provides detailed maps showings where every satellite should pass the sky (including the direction and height of the starting points, peak and end). The site includes information on the movement of planets and comets as well. CalSky:This site is rich in information. You can perform queries and receive a detailed report that includes watching a lot of events. The reports are little harder to read but it provides much more information such as transitions over the sun or moon. ## Our shows Moon Apogee and Perigee: Grades 5+ Have you ever noticed that sometimes the Moon looks bigger or smaller on the sky? Why does this happen? With this introduction, we look at the Moon's orbit and how the Moon appears at different times. Night Sky Tonight: Grades K+ Take a look at what's up in the sky tonight. We'll take you on a tour of our night sky, including stars, planets, galaxies, and more. See objects invisible to the naked eye and get up close and personal with some of our cosmic neighbors. ### Special Topics include: ### Featured films include: Accidental Astronauts: Grades K-3 | 32 minutes | Trailer Black Holes: Grades 5+ | 22 minutes | Trailer The Dark Matter Mystery: Grades 9+ | 38 minutes | Trailer Learn why the Sun rises and sets, examine the Moon’s orbit, craters, phases and eclipses, and explore past and future space travel to the Moon and beyond with the help of Coyote, an amusing character adapted from Native American oral traditions, who has many misconceptions about Earth and its neighbors. Earth's Wild Ride: Grades 2-4 | 20 minutes | Trailer Einstein's Gravity Playlist: Grades 9+ | 22 minutes | Information From Earth to the Universe: Grades 9+ | 30 Minutes| Trailer Larry Cat in Space: Grades K-3 | 30 minutes | Trailer Larry Cat In Space is a playful, imaginative cartoon presentation about an inquisitive cat Oasis in Space: Grades 3-7 | 24 minutes | Trailer The Secrets of Gravity: Grades 3+ | 28 minutes | Trailer Solar Superstorms: Grades 5+ | 24 minutes | Trailer A fury is building on the surface of the Sun – high-velocity jets, a fiery tsunami wave that reaches 100,000 kilometers high, rising loops of electrified gas. What's driving these strange phenomena? How will they affect planet Earth? Find the answers as we venture into the seething interior of our star. Stars of the Pharaohs: Grades 6+ | 35 minutes | Trailer Supervolcanoes: Grades 5+ | 24 minutes | Trailer Tales of the Maya Skies: Grades 5+ | 35 minutes | Trailer Two Small Pieces of Glass: Grades 3+ | 23 minutes | Trailer Ultimate Universe: Grades 5+ | 33 minutes | Trailer *description provided by the Fulldome Database, **description from Montana State © 2021 West Virginia University. WVU is an EEO/Affirmative Action employer — Minority/Female/Disability/Veteran. Last updated on June 23, 2021. Our Parkes radio telescope has been in operation for nearly 60 years. Thanks to regular upgrades, it continues to be at the forefront of discovery. Just outside the town of Parkes in the central-west region of New South Wales, about 380 kilometres from Sydney, is our Parkes radio telescope. It's one of four instruments that make up the Australia Telescope National Facility. With a diameter of 64 metres, Parkes is one of the largest single-dish telescopes in the southern hemisphere dedicated to astronomy. It started operating in 1961, but only its basic structure has remained unchanged. The surface, control system, focus cabin, receivers, computers and cabling have all been upgraded &ndash some parts many times &ndash to keep the telescope at the cutting edge of radio astronomy. The telescope is now 10,000 times more sensitive than when it was first commissioned. #### Research with Parkes radio telescope Its large dish surface makes the Parkes telescope very sensitive and it is ideally suited to finding pulsars, rapidly spinning neutron stars the size of a small city. Half of the more than 2000 known pulsars have been found using the Parkes telescope. The introduction of a multibeam receiver, a revolutionary instrument designed and built by CSIRO, enabled Parkes to be used for large-scale surveys of the sky. These surveys include the HI Parkes All-Sky Survey that found over 2500 new galaxies in our local region, and the Galactic All-Sky Survey that successfully mapped the hydrogen gas in our Galaxy in high detail. #### Tracking spacecraft with Parkes radio telescope While it is operated primarily for astronomy research, the Parkes telescope has a long history of being contracted by NASA and other international space agencies to track and receive data from spacecraft. In 1962 it tracked the first interplanetary space mission, Mariner 2, as it flew by the planet Venus, and in July 1969 it was a prime receiving station for the Apollo 11 mission to the Moon. The fictional film 'The Dish' was based on the real role that the telescope played in receiving video footage of the first Moon walk by the crew of Apollo 11. Most recently, in 2018-19 the telescope supported NASA's Canberra Deep Space Communication Complex in receiving data from Voyager 2 as the spacecraft crossed into interstellar space. ## Contents Hale supervised the building of the telescopes at the Mount Wilson Observatory with grants from the Carnegie Institution of Washington: the 60-inch (1.5 m) telescope in 1908 and the 100-inch (2.5 m) telescope in 1917. These telescopes were very successful, leading to the rapid advance in understanding of the scale of the Universe through the 1920s, and demonstrating to visionaries like Hale the need for even larger collectors. The chief optical designer for Hale's previous 100-inch telescope was George Willis Ritchey, who intended the new telescope to be of Ritchey–Chrétien design. Compared to the usual parabolic primary, this design would have provided sharper images over a larger usable field of view. However, Ritchey and Hale had a falling-out. With the project already late and over budget, Hale refused to adopt the new design, with its complex curvatures, and Ritchey left the project. The Mount Palomar Hale Telescope turned out to be the last world-leading telescope to have a parabolic primary mirror. [2] In 1928 Hale secured a grant of$6 million from the Rockefeller Foundation for "the construction of an observatory, including a 200-inch reflecting telescope" to be administered by the California Institute of Technology (Caltech), of which Hale was a founding member. In the early 1930s, Hale selected a site at 1,700 m (5,600 ft) on Palomar Mountain in San Diego County, California, US, as the best site, and less likely to be affected by the growing light pollution problem in urban centers like Los Angeles. The Corning Glass Works was assigned the task of making a 200-inch (5.1 m) primary mirror. Construction of the observatory facilities and dome started in 1936, but because of interruptions caused by World War II, the telescope was not completed until 1948 when it was dedicated. [3] Due to slight distortions of images, corrections were made to the telescope throughout 1949. It became available for research in 1950. [3]

A functioning one tenth scale model of the telescope was also made at Corning. [4]

The 200-inch (510 cm) telescope saw first light on January 26, 1949, at 10:06 pm PST [5] [6] under the direction of American astronomer Edwin Powell Hubble, targeting NGC 2261, an object also known as Hubble's Variable Nebula. [7] [8] The photographs made then were published in the astronomical literature and in the May 7, 1949 issue of Collier's Magazine.

The telescope continues to be used every clear night for scientific research by astronomers from Caltech and their operating partners, Cornell University, the University of California, and the Jet Propulsion Laboratory. It is equipped with modern optical and infrared array imagers, spectrographs, and an adaptive optics [9] system. It has also used lucky cam imaging, which in combination with adaptive optics pushed the mirror close to its theoretical resolution for certain types of viewing. [9]

One of the Corning Labs' glass test blanks for the Hale was used for the C. Donald Shane telescope's 120-inch (300 cm) primary mirror. [10]

The collecting area of the mirror is about 31,000 square inches (20 square meters). [11]

The Hale was not just big, it was better: it combined breakthrough technologies including a new lower expansion glass from Corning, a newly invented Serruier truss, and vapor deposited aluminum.

### Mounting structures Edit

The Hale Telescope uses a special type of equatorial mount called a "horseshoe mount", a modified yoke mount that replaces the polar bearing with an open "horseshoe" structure that gives the telescope full access to the entire sky, including Polaris and stars near it. The optical tube assembly (OTA) uses a Serrurier truss, then newly invented by Mark U. Serrurier of Caltech in Pasadena in 1935, designed to flex in such a way as to keep all of the optics in alignment. [12] Theodore von Karman designed the lubrication system to avoid potential issues with turbulence during tracking.

### 200-inch mirror Edit

Originally, the Hale Telescope was going to use a primary mirror of fused quartz manufactured by General Electric, [13] but instead the primary mirror was cast in 1934 at Corning Glass Works in New York State using Corning's then new material called Pyrex (borosilicate glass). [14] Pyrex was chosen for its low expansion qualities so the large mirror would not distort the images produced when it changed shape due to temperature variations (a problem that plagued earlier large telescopes).

The mirror was cast in a mold with 36 raised mold blocks (similar in shape to a waffle iron). This created a honeycomb mirror that cut the amount of Pyrex needed down from over 40 short tons (36 t) to just 20 short tons (18 t), making a mirror that would cool faster in use and have multiple "mounting points" on the back to evenly distribute its weight (note – see external links 1934 article for drawings). [15] The shape of a central hole was also part of the mold so light could pass through the finished mirror when it was used in a Cassegrain configuration (a Pyrex plug for this hole was also made to be used during the grinding and polishing process [16] ). While the glass was being poured into the mold during the first attempt to cast the 200-inch mirror, the intense heat caused several of the molding blocks to break loose and float to the top, ruining the mirror. The defective mirror was used to test the annealing process. After the mold was re-engineered, a second mirror was successfully cast.

After cooling several months, the finished mirror blank was transported by rail to Pasadena, California. [17] [18] Once in Pasadena the mirror was transferred from the rail flat car to a specially designed semi-trailer for road transport to where it would be polished. [19] In the optical shop in Pasadena (now the Synchrotron building at Caltech) standard telescope mirror making techniques were used to turn the flat blank into a precise concave parabolic shape, although they had to be executed on a grand scale. A special 240 in (6.1 m) 25,000 lb (11 t) mirror cell jig was constructed which could employ five different motions when the mirror was ground and polished. [20] Over 13 years almost 10,000 lb (4.5 t) of glass was ground and polished away reducing the weight of the mirror to 14.5 short tons (13.2 t). The mirror was coated (and still is re-coated every 18–24 months) with a reflective aluminum surface using the same aluminum vacuum-deposition process invented in 1930 by Caltech physicist and astronomer John Strong. [21]

The Hale's 200 in (510 cm) mirror was near the technological limit of a primary mirror made of a single rigid piece of glass. [22] [23] Using a monolithic mirror much larger than the 5-meter Hale or 6-meter BTA-6 is prohibitively expensive due to the cost of both the mirror, and the massive structure needed to support it. A mirror beyond that size would also sag slightly under its own weight as the telescope is rotated to different positions, [24] [25] changing the precision shape of the surface, which must be accurate to within 2 millionths of an inch (50 nm). Modern telescopes over 9 meters use a different mirror design to solve this problem, with either a single thin flexible mirror or a cluster of smaller segmented mirrors, whose shape is continuously adjusted by a computer-controlled active optics system using actuators built into the mirror support cell.

### Dome Edit

The moving weight of the upper dome is about 1000 US tons, and can rotate on wheels. [26] The dome doors weigh 125 tons each. [27]

The dome is made of welded steel plates about 10 mm thick. [26]

The first observation of the Hale telescope was of NGC 2261 on January 26, 1949. [28]

Halley's Comet (1P) upcoming 1986 approach to the Sun was first detected by astronomers David C. Jewitt and G. Edward Danielson on 16 October 1982 using the 200-inch Hale telescope equipped with a CCD camera. [29]

Two moons of the planet Uranus were discovered in September 1997, bringing the planet's total known moons to 17 at that time. [30] One was Caliban (S/1997 U 1), which was discovered on 6 September 1997 by Brett J. Gladman, Philip D. Nicholson, Joseph A. Burns, and John J. Kavelaars using the 200-inch Hale telescope. [31] The other Uranian moon discovered then is Sycorax (initial designation S/1997 U 2) and was also discovered using the 200 inch Hale telescope. [31]

In 1999, astronomers used a near-infrared camera and adaptive optics to take some of the best Earth-surface based images of planet Neptune up to that time. [32] The images were sharp enough to identify clouds in the ice giant's atmosphere. [32]

The Cornell Mid-Infrared Asteroid Spectroscopy (MIDAS) survey used the Hale Telescope with a spectrograph to study spectra from 29 asteroids. [33] An example of a result from that study, is that the asteroid 3 Juno was determined to have average radius of 135.7±11 km using the infrared data. [34]

In 2009, using a coronograph, the Hale telescope was used to discover the star Alcor B, which is a companion to Alcor in the famous Big Dipper constellation. [35]

In 2010, a new satellite of planet Jupiter was discovered with the 200-inch Hale, called S/2010 J 1 and later named Jupiter LI. [36]

In October 2017 the Hale telescope was able to record the spectrum of the first recognized interstellar object, 1I/2017 U1 ("ʻOumuamua") while no specific mineral was identified it showed the visitor had a reddish surface color. [37] [38]

### Direct imaging of exoplanets Edit

Up until the year 2010, telescopes could only directly image exoplanets under exceptional circumstances. Specifically, it is easier to obtain images when the planet is especially large (considerably larger than Jupiter), widely separated from its parent star, and hot so that it emits intense infrared radiation. However, in 2010 a team from NASA's Jet Propulsion Laboratory demonstrated that a vortex coronagraph could enable small scopes to directly image planets. [39] They did this by imaging the previously imaged HR 8799 planets using just a 1.5 m portion of the Hale Telescope.