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Describes “star parties” and night sky observation reference materials, such as star charts. At the Stoney Ridge Observatory in the southern California mountains; produced by the Jet Propulsion Laboratory.
Public domain film from NASA, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
A Dobsonian telescope is an alt-azimuth mounted Newtonian telescope design popularized by John Dobson starting in the 1960s credited with vastly increasing the size of telescopes available to amateur astronomers . 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 visually observing faint deep sky objects such as nebulae. This type of observation requires a large objective diameter (i.e. light-gathering power) of relatively short focal length and portability for travel to relatively less light polluted locations.
Dobsonians are intended to be what is commonly called a “light bucket” operating at low magnification, and therefore the design omits features found in other amateur telescopes such as equatorial tracking. Dobsonians are popular in the amateur telescope making 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 “Dobsonian” is currently used for a whole range of large-aperture Newtonian reflectors that use some of the basic Dobsonian design characteristics, regardless of the materials from which they are constructed…
Dobson’s design innovations
Dobson’s design allows a builder with minimal skill to make an extremely large telescope out of common items. Dobson optimized the design for visual observation of faint objects such as star clusters, nebulae, and galaxies (what Amateur Astronomers call deep sky objects). These dim objects require a large objective mirror able to gather a large amount of light. Because “deep sky” observing often requires travel to dark locations away from city lights, the design benefits from being more compact, portable, and rugged than standard large Newtonian telescopes. John Dobson’s telescopes combined several innovations to meet these criteria, including:
Thin mirrors: Instead of costly Pyrex mirror blanks with the standard 1:6 thickness ratios (1 cm thick for every 6 cm in diameter) so they won’t flex and sag out of shape under their own weight, Dobson used mirrors made out of surplus glass ship porthole covers usually with 1:16 thickness ratios. Since the telescope design 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.
Construction tubes: 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 comparatively large sizes. Dobsonian scopes are intended to be transported out to dark sky locations, and Sonotubes are claimed to be more rugged than aluminum or fiberglass tubes which can dent or shatter from impacts. Sonotubes 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.
A square “mirrorbox”: Dobson used a plywood box for the tube base and mirror housing. This gave a rigid flat surface to attach the “carpet” support for the porthole mirrors he was using, and made it easy to attach the altitude bearings.
A simple alt-azimuth mount: Dobson opted for a simple to build and use altazimuth mount. He used a “gun carriage type” design…
The design of Dobsonian telescopes has evolved over the years (see Derivative Designs), but most commercial or amateur-built “Dobsonian” telescopes follow many or most of the design concepts and features listed above…
John Lowry Dobson (September 14, 1915 – January 15, 2014) was an amateur astronomer and is best known for the Dobsonian telescope, a portable, low-cost Newtonian reflector telescope…
