Sky Talk July 2010: Reliving Telescope History

With all the telescopes of superb optical quality in widespread use by stargazers today, few have ever had the opportunity of going back in time to when this magical instrument first appeared and experience firsthand the enormous quantum leap that’s been made in its performance. But thanks to a unique product offered through Edmund Scientifics print and online catalogs, you can relive some of those early days of celestial exploration using primitive optics.

As is well known, the first telescopes that were invented (some would say discovered) were simple refractors using very primitive single-element spectacle lenses. Such lenses produced obvious colored fringes around objects viewed (especially the Moon, planets and bright stars) — a defect known as “color aberration.” They also suffered from being unable to bring all rays to the same focus due to zones in the lenses. Known as “spherical aberration,” this caused images to appear “soft” and fuzzy. While no one today would purposely use single-element lenses for either a telescope objective or its eyepiece, it’s both fun and instructive to look through such an instrument. And the Telescope Kit makes this possible at the very affordable price of just $12.95.

After assembling this 8x refractor from the do-it-yourself kit, your first target should definitely be the Moon. And while your initial look may leave you shaking your head at the poor quality of the image produced, closer inspection will reveal all the major lunar features including craters and mountain ranges. While surface detail stands out in relief best when the Moon is at First-Quarter (half-full), all the phases offer something worth viewing — from the “Earthshine” visible on the dark part of the Moon when a crescent to the vast system of rays seen splashing out of the brighter craters when Full.

Next come the planets, especially Jupiter with its retinue of four bright satellites (those discovered by Galileo). A magnification of 8x is enough to show Jupiter’s disk as non-stellar and the moons as little stars nearly engulfed in the glare of the planet itself. The outer satellites are most obvious, and their configuration changes from night to night as they orbit the planet. This telescope is not powerful enough to show the rings of Saturn, but when they are wide open (as they will be again in few years) the planet looks egg-shaped. And when Venus is closest to us, its thin crescent can be made out. Finally, look at some of the brightest stars. Despite its inherent color aberration, this scope will reveal that some of them have obvious colors of their own. In July’s sky, look at blue-white Vega in Lyra, golden-orange Arcturus in Bootes and fiery-red Antares in Scorpius, for starters. (Use your Scientifics Star and Planet Locator to identify them. Also note that for optimum results, all of these observations require that the telescope be mounted in some way rather than hand-held.)

–James Mullaney
Former assistant editor at Sky & Telescope magazine and author of seven books on stargazing.


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