263:: Dobson replaced the traditional aluminum or fiberglass telescope tube with the thick compressed paper tubes used in construction to pour concrete columns. "Sonotubes", the leading brand employed by Dobson, are less expensive than commercially available telescope tubes and are available in a wide variety of sizes. For protection against moisture, the tubes were usually painted or coated with plastic. Sonotubes are claimed to be more rugged than aluminum or fiberglass tubes which can dent or shatter from impacts during transport. They have the added advantage of being thermally stable and non-conductive, which minimizes unwanted convection currents in the light path caused by handling of the tube assembly.
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telescope and keep the eyepiece in a relatively easy to access position on the side of the telescope. The altazimuth mount design used in
Dobsonian designs also adds to simplicity and portability; there is no added mass or need to transport counter weights, drive components, or tripods/pedestals. Setting up for hard tube dobs simply involves placing the mount on the ground, and setting the tube on top of it. The weight of the Dobsonian style altazimuth mount is distributed over large simple bearing surfaces so the telescope can move smoothly under finger pressure with minimal backlash.
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center-bolt (Fig.1, dark green) keeps the rocker box centered and allows it to pivot above the ground board. On opposing sides of the rocker box, semicircular depressions are cut out from the top edge of each wall (the rocker box is open on the top and on the back). Each depression has a widely spaced pair of supports installed in the cut (Fig.1, top yellow). The telescope optical tube assembly (OTA, Fig.1, light blue) has two large round
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assembly, which contains the secondary mirror, and focuser, held in place by several rigid poles over a mirror box which contains the objective mirror. The poles are held in place by quick-disconnecting clamps which allow the entire telescope to be easily broken down into its smaller components, facilitating their transport by vehicle or other means to an observing site. These truss tube designs are sometimes incorrectly called a
199:: Instead of a standard mount using axial bearings, Dobson opted for a very stable design that was simple to build, and which had fewer mechanical limitations when used with large and heavy telescopes. He modified the classical fork mount into a free-standing three-piece construction, which holds the telescope steady on seven discrete support points and allows for easy and safe repositioning of a large and heavy telescope.
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offer models of 24 inch (610 mm) aperture and greater. Truss
Dobsonians are the largest telescopes commercially available today. A massive 36 inch (914 mm) aperture Hybrid model from New Moon Telescopes was displayed at the 2018 Northeast Astronomy Forum. In 2019, a huge 50 inch (1270 mm) aperture folded Newtonian from Canadian based Optiques Fullum was installed in New Jersey.
344:: The Dobsonian design of maximized objective diameter combined with portability makes the design ideal for observing dim star clusters, nebulae, and galaxies (deep sky objects), an activity that requires large objectives and travel to dark sky locations. Since these objects are relatively large, they are observed at low magnifications that do not require a clock-driven mount.
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The result has been a proliferation of larger telescopes which would have been expensive to build or buy, and unwieldy to operate, using "traditional" construction methods. Whereas an 8 inch
Newtonian telescope would have been considered large in the 1970s, today 16 inch systems are common,
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The original intent of the
Dobsonian design was to provide an affordable, simple, and rugged large-aperture instrument at low cost. These same attributes facilitate their mass production. One of the first companies to offer Dobsonian telescopes commercially was the now defunct company Coulter Optical
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Many designs have increased portability by shrinking the altazimuth (rocker box) mount down to a small rotating platform. The altitude trunnion style bearing in these designs becomes a large radius roughly equal to or greater than the radius of the objective mirror, attached to or integrated into the
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mirror blanks with the standard 1:6 thickness ratios (1 cm thick for every 6 cm in diameter) so they don't flex and sag out of shape under their own weight, Dobson used mirrors made out of glass from surplus ship porthole covers usually with 1:16 thickness ratios. Since the telescope design
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The use of Teflon over textured material combines with gravity-produced wedging forces to create a unique smooth action, transitioning from rock steady to smooth motion and back. Thus a clamp mechanism is not needed to prevent unintentional motion of the telescope, unlike most other telescope mounts.
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Solid tube commercial
Dobsonians typically have a maximum aperture of 12 inches (305 mm) due to the size of the tube. Truss Dobsonians of 12 to 18 inches (305 to 457 mm) are the most popular sizes, as they offer substantial aperture yet can still be easily set up by one person. Several manufacturers
358:. Most Dobsonian telescopes have enough friction in the bearings to resist a moderate amount of imbalance; however, this friction can also make it difficult to position the telescope accurately. To correct such imbalance, counterweights are sometimes hooked or bolted onto the back of the mirror box.
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tube and a collapsible design. Collapsible "truss tube" Dobsonians appeared in the amateur telescope making community as early as 1982 and allow the optical tube assembly, the largest component, to be broken down. As the name implies, the "tube" of this design is actually composed of an upper cage
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The altazimuth mount does have its own limitations. Un-driven altazimuth mounted telescopes need to be "nudged" every few minutes along both axes to compensate for the rotation of the Earth to keep an object in view (as opposed to one axis for un-driven equatorial mounts), an exercise that becomes
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tube assembly which lowers the overall profile of the mount. The advantage of this is that it reduces the total telescope weight, and the telescope's balance becomes less sensitive to changes in the weight loading of telescope tube from the use of heavier eyepieces or the addition of cameras etc.
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From its inception, telescope makers have been modifying the
Dobsonian design to fit their needs. The original design fit the needs and available supplies of one person—John Dobson. Other people devised variants that fit their own needs, abilities, and access to parts. This has led to significant
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of the telescope OTA. The trunnions (commonly known as altitude bearings) rest atop the aforementioned four supports in the top cutouts of the rocker box. To raise the telescope (altitude), just lift the tube and the trunnions will slide over the four supports. To move the telescope left or right
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The classical
Dobsonian mount (refer to Fig.1) consists of a flat horizontal "ground board" platform (Fig.1, black) on top of which are attached three of the seven supports (Fig.1, bottom yellow). Upon these three supports rests a box construction called a "rocker box" (Fig.1, dark blue). A loose
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The
Dobsonian design is considered revolutionary due to the sheer size of telescopes it made available to amateur astronomers. The inherent simplicity and large aperture of the design began to attract interest through the 1970s since it offered the advantage of inexpensive large instruments that
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in 1989. Later
American manufacturers included StarStructure, Webster Telescopes, AstroSystems, Teeter's Telescopes, Hubble Optics, Waite Research, and New Moon Telescopes. These low-volume builders offer premium objective mirrors, high-end materials and custom craftmanship, as well as optional
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with clock drive was left out of the design. Equatorial mounts tend to be massive (less portable), expensive, complicated, and have the characteristics of putting the eyepiece of
Newtonian telescopes in very hard to access positions. Altazimuth mounts cut the size, weight and cost of the total
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photography, the large apertures of the Dobsonian have dramatically increased the number of objects observed as well as the amount of detail in each object observed. Whereas the amateur astronomer of the 1970s and 1980s typically did not explore much beyond the Messier and brighter
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Classical Dobsonian mount parts are typically made from plywood and other cheap materials which are glued, screwed, or even nailed together. In contrast to other telescope mount types, no precision-machined mechanical parts are required. For smooth sliding motions, small
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style altitude axis and a broadly supported azimuth axis, both making use of material such as plastic, Formica, and Teflon to achieve smooth operation. Many derivative mount designs have kept this basic form while heavily modifying the materials and configuration.
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It is hard to classify the Dobsonian Telescope as a single invention. In the field of amateur telescope making most, if not all, of its design features had been used before. John Dobson, credited as having invented this design in 1965 pointed out that
228:(PTFE) blocks are used for the seven supports. Their surface sizes can be precisely calculated for the particular OTA weight. To improve the smoothness and steady position-holding, the bottom of the rocker box is typically covered with micro-textured
465:-based digital setting circles has allowed any altazimuth mounted telescope to be fitted or retrofitted with the ability to accurately display the coordinates of the telescope direction. These systems not only give the user a digital read-out for
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The steadiness of the classical Dobsonian is unparalleled, as the telescope is actually not rotating on two axes as other mounts but instead statically standing on seven solid blocks (until pushed to a new position). Only the
130:, he preferred to call the design a "sidewalk telescope". Dobson combined all these innovations in a design focused towards one goal: building a very large, inexpensive, easy to use, portable telescope, one that could bring
453:
Since the late 1990s many innovations in mount design and electronics by amateur telescope makers and commercial manufacturers have allowed users to overcome some of the limitations of the Dobsonian style altazimuth mount.
543:(now part of Murnaghan Instruments). In the 1980s, they helped popularize the design with "Odyssey" models of various sizes, with tubes made of Sonotube and following Dobson's original concept of simplicity. By the 1990s,
50:. Dobson's telescopes featured a simplified mechanical design that was easy to manufacture from readily available components to create a large, portable, low-cost telescope. The design is optimized for observing faint,
271:: Dobson often used a plywood box for the tube base and mirror housing, into which the Sonotube was inserted. This gave a rigid flat surface to attach the mirror supports, and made it easy to attach the trunnions.
232:. The altitude trunnions often have a large diameter, and can also be covered with textured material. For larger telescopes, semicircular wood pieces or arc-shaped rails can be used instead of round trunnions.
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and other manufacturers began to introduce upgraded Dobsonian models. These imported mass-produced scopes included such niceties as metal tubes and more refined hardware, and are still very affordable.
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for ease of tracking, and with careful polar alignment sub-arc second precision CCD imaging is entirely possible. Roeser Observatory, Luxembourg (MPC observatory code 163) have contributed hundreds of
392:"Classic" design tube assemblies would require a large van for transport. Designers started coming up with disassembleable or collapsible variants that could be brought to the site with a small
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is currently used for a range of large-aperture Newtonian reflectors that use some of the basic Dobsonian design characteristics, regardless of the materials from which they are constructed.
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away from city lights, the design benefits from being more compact, portable, and rugged than standard large Newtonian telescopes of times past, which typically utilized massive
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has an alt-azimuth mount, the mirror only has to be supported in a simple cell with a backing of indoor/outdoor carpet to evenly support the weight of the much thinner mirror.
1214:– The book treats the "why" as importantly as the "how", sharing Dobson's philosophy on the importance of popular access to astronomy for proper appreciation of the universe.
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Dobson's design allows a builder with minimal skills to make a very large telescope out of common items. Dobson optimized the design for observation of faint objects such as
350:: Designs that have the telescope tube fixed in relationship to its altitude bearings can be put out of balance by the addition or subtraction of equipment such as cameras,
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Since the 1990s, manufactured Dobsonians using the truss tube design have become increasingly popular. The first commercial truss Dobsonian was released into the market by
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and others. Mostly manufactured in China, they offer good quality and value while being considerably less expensive than the premium scopes described above. In 2017,
313:, mainly because a large movement of the azimuth axis is needed to move the telescope pointing by even a small amount. Altazimuth mounts are also not well suited for
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This ratio ensures that per inch of objective diameter, a Dobsonian will weigh less and require less space than other types and is thus the most portable design.
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community, where the design was pioneered and continues to evolve. A number of commercial telescope makers also sell telescopes based on this design. The term
212:(azimuth), push or pull the top rim of the OTA (some have a dedicated handle) so that the pivoting rocker box slides over the ground board's three supports.
423:, but since the main truss is not built with an opposing mirror cell truss it only performs one function of that design, i.e. keeping the optics parallel.
330:: The Dobsonian design's structure as measured in volume and weight is relatively minimal for any given objective diameter when compared to other designs.
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A modified Dobsonian from 1983 that features a collapsible open tube assembly with integrated bearing surface and a very compact "rocker box" mount.
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The main attribute of a Dobsonian's mount is that it resembles a "gun carriage" configuration with a "rocker box" consisting of a horizontal
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objects, thanks in part to Dobsonians, modern amateur astronomers routinely observe dim objects listed in obscure catalogues, such as the
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to help in aiming the telescope at the coordinates of known objects. They are known for being difficult to point at objects near the
279:), but most commercial or amateur-built "Dobsonian" telescopes follow many or most of the design concepts and features listed above.
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207:(or arc-shaped rails for larger telescopes) secured on the left and right sides (Fig.1, red). Their common axis intersects the
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to give a current graphical representation of where the telescope is pointing, allowing the user to quickly find an object.
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Two Dobsonians that combine a truss tube, compact "rocker box", large radius altitude bearings, and a collapsible design.
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336:: From a cost perspective, a user typically gets more objective diameter per unit of cost with the Dobsonian design.
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1178:"Digital Setting Circles Revisited – Lumicon Sky Vector I – JMI NGC-MAX – Celestron Advanced Astro Master"
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s). These dim objects require a large objective mirror able to gather a large amount of light. Because "
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more difficult with higher magnifications. The altazimuth mount does not allow the use of conventional
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Dobson identified the characteristic features of the design as lightweight objective mirrors made from
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404:. This innovation allowed the amateur astronomy community access to even larger apertures.
188:. John Dobson's telescopes combined several innovations to meet these criteria, including:
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Dobsonians are intended to be what is commonly called a "light bucket". Operating at low
1592:
And the Skylark Sings with Me: Adventures in Homeschooling and Community-based Education
1521:
1514:
Classic Telescopes: A guide to collecting, restoring, and using telescopes of yesteryear
1639:
Seeing in the Dark: How Amateur Astronomers Are Discovering the Wonders of the Universe
1590:
1279:
1130:
462:
1177:
699:
A light bucket is a telescope with a large aperture, used mainly for visual observing.
367:
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In the 21st century, truss Dobsonian models are also mass-produced by Meade, Orion,
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strips and other low-cost materials. Since he built these telescopes as aids in his
81:, and therefore the design omits features found in other amateur telescopes such as
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651:(and discovery) to the amateur wishing to contribute minor planet positions to the
159:
1659:
The Dobsonian Telescope: A practical manual for building large aperture telescopes
636:, and others once considered reference works only for professional astronomers.
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systems. Some also produce "ultra-light" models that offer greater portability.
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in 1965 and credited with vastly increasing the size of telescopes available to
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24:
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The Largest Portable Dobsonian Telescope in the World (42 inch - 107 cm)
106:"for hundreds of years, wars were fought using cannon on 'Dobsonian' mounts".
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204:
142:
123:
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1499:
Visual Astronomy Under Dark Skies: A new approach to observing deep space
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the difficulties using a Dobsonian for short-exposure (≲ 1 hr)
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In combination with other improvements in observing equipment, such as
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are obviated. This has opened up the field of high precision asteroid
70:) of relatively short focal length and portability for travel to less
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1537:
A Buyer's and User's Guide to Astronomical Telescopes and Binoculars
1408:"16-inch f/4.5 collapsible-truss Dobsonian from New Moon Telescopes"
240:
mount invented later can rival the steady smoothness of a Dobsonian.
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The design of Dobsonian telescopes has evolved over the years (see
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525:
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655:. It also makes possible searches for new, faint objects such as
1054:. South East Queensland Astronomical Society Inc. Archived from
1049:"Recommendations for Beginning Amateur Astronomers, page 4"
850:
DiBona, Chris; Stone, Mark; Cooper, Danese (21 October 2005).
214:
1079:
Hamberg, Ivar (Fall 1982). "An Extremely Portable 17⁄
517:
using a home-built 20" dobsonian on an equatorial platform.
1454:"News & Views from the 2018 Northeast Astronomy Forum"
1163:"Arduino bluetooth digital setting circles for telescopes"
473:(dec.), they also interface with digital devices such as
1440:"Sky-Watcher's Stargate Truss-Tube Dobsonian Telescopes"
287:
The Dobsonian design has the following characteristics:
1516:. Springer Science & Business Media. p. 127.
1484:
Bunch of Amateurs: A search for the American character
1469:"Huge 50" Newtonian Telescope Installed in New Jersey"
1231:
Know Thy Dob: Choosing and Using a Dobsonian Telescope
1200:
How and Why to Make a User-Friendly Sidewalk Telescope
16:
Type of Newtonian telescope popularized by John Dobson
1708:
1573:. Springer Science & Business Media. p. 21.
1501:. Springer Science & Business Media. p. 156.
821:; Aguirre, E. (September 1995). "Walden of the Sky".
412:
Many designs have combined the advantages of a light
1589:
1375:"Review of Hubble Optics UL16 Dobsonian Telescope"
1129:
1016:
729:
727:
725:
592:in the back of a small car and set up in minutes.
449:Overcoming the limitations of the altazimuth mount
427:Modifications to the altazimuth mount (rocker box)
1694:Complete Plans for Building a Dobsonian Telescope
596:and huge 32 inch systems not all that rare.
1560:A Salesman for the Heavens Wants to Rope You In
1224:
1222:
1220:
958:Newton, Jack; Teece, Philip (19 January 1995).
734:Newton, Jack; Teece, Philip (19 January 1995).
497:: The use of equatorial platforms (such as the
1202:. Everything in the Universe. pp. 61–62.
575:introduced its line of large Stargate models.
323:Large objective diameter compared to mass/cost
538:Commercially custom-built 16" truss Dobsonian
8:
1003:Dobson ... promoting causal visual observing
485:using live ephemeris calculating / charting
62:. This type of observation requires a large
964:. Cambridge University Press. p. 288.
740:. Cambridge University Press. p. 287.
588:could be carried to dark sky locations and
583:The Dobsonian's effect on amateur astronomy
582:
669:Central Bureau for Astronomical Telegrams
530:Commercially mass-produced 10" Dobsonian
85:tracking. Dobsonians are popular in the
1715:
856:. "O'Reilly Media, Inc.". p. 351.
721:
692:
505:work. Such platforms can incorporate a
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1657:Kriege, David; Berry, Richard (1997).
1360:"Teeter's Telescopes Custom Dobsonian"
1136:. Cambridge University Press. p.
937:. New Society Publishers. p. 93.
813:
811:
114:glass, and mountings constructed from
1551:35 Who Made a Difference: John Dobson
791:Star Clusters and how to Observe Them
180:" observing often requires travel to
7:
1687:San Francisco Sidewalk Astronomers'
1615:Woodruff, John (2003). "Dobsonian".
1486:. Crown/Archetype. pp. 231–234.
1128:Newton, Jack; Teece, Philip (1995).
23:A Dobsonian telescope on display at
1456:. Sky & Telescope. 23 Apr 2018.
1442:. Sky & Telescope. 30 Oct 2017.
1362:. Sky & Telescope. 18 Jan 2016.
1704:World's Largest Backyard Telescope
1642:. Simon and Schuster. p. 37.
1596:. New Society Publishers. p.
788:Allison, Mark (21 December 2005).
767:. Simon and Schuster. p. 39.
137:
14:
1683:Sidewalk Astronomers Organization
1161:Andico, Orly (January 11, 2012).
931:Albert, David H. (January 1999).
384:diversity in "Dobsonian" design.
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1754:
1742:
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1467:Parkerson, Stuart (2 Jul 2019).
1426:"Obsession 18-inch UC telescope"
1388:Harrington, Phil (27 Jul 2015).
1373:Parkerson, Stuart (2 Jun 2019).
1198:(1991). Sperling, Norman (ed.).
334:Low cost to objective size ratio
328:Low mass to objective size ratio
218:Fig.1 Dobsonian mount schematics
1329:Bonandrini, Dave (8 Aug 2009).
761:Ferris, Timothy (8 July 2003).
170:(what amateur astronomers call
1549:Moser, Don (November 1, 2005)
1132:The Guide to Amateur Astronomy
961:The Guide to Amateur Astronomy
883:. Inc NetLibrary. p. 17.
737:The Guide to Amateur Astronomy
1:
1621:. Firefly Books. p. 60.
1471:. Astronomy Technology Today.
1424:Shibley, John (19 May 2009).
1413:. Astronomy Technology Today.
1406:Allis, Damian G. (May 2013).
1377:. Astronomy Technology Today.
1176:Ward, Peter (December 1993).
985:Knoll, Peter (30 July 1996).
934:And the Skylark Sings with Me
904:Knoll, Peter (30 July 1996).
1618:Firefly Astronomy Dictionary
1390:"Waite Research Renegade 20"
1344:Shinn, Brett (16 Dec 2008).
1293:Nelson, Anthony (May 2005).
877:Fred Watson (October 2007).
601:narrow-pass optical filters
440:Compact "rocker box" mounts
388:Collapsible tube assemblies
138:Dobson's design innovations
1805:
1570:The New Amateur Astronomer
1567:Mobberley, Martin (2004).
880:Why is Uranus Upside Down?
296:equatorial telescope mount
1588:Albert, David H. (1999).
1558:Moser, Don (April 1989) "
1539:(1 ed.). p. 38.
1023:. Firefly Books. p.
342:Good "Deep Sky" telescope
277:§ Derivative designs
134:astronomy to the masses.
1636:Ferris, Timothy (2003).
1562:", Smithsonian Magazine.
1535:Mullaney, James (2009).
1331:"Webster Telescopes D18"
991:. Springer. p. 25.
910:. Springer. p. 25.
794:. Springer. p. 74.
354:or even unusually heavy
186:German equatorial mounts
87:amateur telescope making
1689:telescope building page
837:1995S&T....90c..84L
681:List of telescope types
663:in local galaxies, and
459:Digital setting circles
1512:English, Neil (2012).
1497:Cooke, Antony (2006).
1346:"Astrosystems Telekit"
1280:"Obsession Telescopes"
1229:English, Neil (2011).
988:Induced Seismic Events
907:Induced Seismic Events
539:
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522:Commercial adaptations
380:
372:
219:
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42:design popularized by
28:
1428:. Astronomy Magazine.
1395:. Astronomy Magazine.
1100:"The 17.5" Dobsonian"
1019:Moon Observer's Guide
1015:Grego, Peter (2004).
537:
529:
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217:
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68:light-gathering power
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1553:– Smithsonianmag.com
1255:"The Odyssey 8 Site"
667:(for reports to the
560:computer controlled
557:Obsession Telescopes
513:measurements to the
487:planetarium software
269:A square "mirrorbox"
250:: Instead of costly
150:built Dobsonians at
1522:2013ctgc.book.....E
1482:Hitt, Jack (2012).
824:Sky & Telescope
653:Minor Planet Center
641:equatorial platform
639:When mounted on an
515:Minor Planet Center
494:Equatorial platform
461:: The invention of
48:amateur astronomers
40:Newtonian telescope
33:Dobsonian telescope
1302:Astronomy Magazine
764:Seeing in the Dark
569:Explore Scientific
540:
532:
381:
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363:Derivative designs
261:Construction tubes
220:
156:
154:in the early 1980s
128:sidewalk astronomy
37:altazimuth-mounted
29:
27:in the early 1980s
1661:. Willmann-Bell.
1649:978-0-684-86580-5
1607:978-0-86571-401-4
1580:978-1-85233-663-9
1240:978-1-4419-8785-3
1147:978-0-521-44492-7
1034:978-1-55297-888-7
545:Meade Instruments
503:astrophotographic
209:center of gravity
126:of instructional
97:Origin and design
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1106:. Archived from
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1085:Telescope Making
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645:astrophotography
549:Orion Telescopes
479:tablet computers
315:astrophotography
292:Altazimuth mount
52:deep-sky objects
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1182:Sky & Space
1180:. Test Report.
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467:right ascension
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420:Serrurier truss
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307:setting circles
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283:Characteristics
193:Nontraditional
173:deep sky object
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66:diameter (i.e.
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1083:" Dobsonian".
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1313:. Retrieved
1306:the original
1301:
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1263:. Retrieved
1259:the original
1249:
1233:. Springer.
1230:
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1123:
1112:. Retrieved
1108:the original
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1063:. Retrieved
1056:the original
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831:(3): 84–87.
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248:Thin mirrors
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1761:Outer space
1749:Spaceflight
819:Levy, David
603:, improved
573:Sky-Watcher
511:astrometric
507:clock drive
483:smartphones
477:computers,
471:declination
195:alt-azimuth
74:locations.
44:John Dobson
1315:2020-06-22
1265:2020-06-22
1114:2009-02-25
1065:2009-02-25
716:References
661:supernovae
649:astrometry
238:Ball-Scope
152:Stellafane
83:equatorial
25:Stellafane
1725:Astronomy
1104:telia.com
634:Minkowski
605:eyepieces
469:(RA) and
398:hatchback
356:eyepieces
205:trunnions
124:avocation
91:Dobsonian
64:objective
1783:Category
675:See also
630:Kohoutek
613:infrared
433:trunnion
178:deep sky
168:galaxies
132:deep-sky
112:porthole
60:galaxies
54:such as
1711:Portals
1518:Bibcode
833:Bibcode
609:visible
481:, and
230:Formica
164:nebulae
148:Amateur
116:plywood
56:nebulae
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665:comets
475:laptop
311:zenith
226:Teflon
166:, and
120:Teflon
35:is an
1737:Stars
1411:(PDF)
1393:(PDF)
1309:(PDF)
1298:(PDF)
1059:(PDF)
1052:(PDF)
687:Notes
657:novae
626:Abell
414:truss
402:sedan
294:: An
252:Pyrex
197:mount
1663:ISBN
1644:ISBN
1623:ISBN
1602:ISBN
1575:ISBN
1235:ISBN
1204:ISBN
1142:ISBN
1029:ISBN
993:ISBN
966:ISBN
939:ISBN
912:ISBN
885:ISBN
858:ISBN
796:ISBN
769:ISBN
742:ISBN
611:and
562:GoTo
146:Two
58:and
1138:289
671:).
618:NGC
394:SUV
1785::
1600:.
1598:92
1300:.
1219:^
1140:.
1102:.
1027:.
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829:90
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810:^
724:^
659:/
632:,
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622:IC
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31:A
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