Back in 2009, I partnered with Richard Fienberg (American Astronomical Society) to launch Galileoscope as an international cornerstone project for the International Year of Astronomy. These low-cost, high quality telescope kits have been an important instrument for engagement with astronomy ever since.
Galileoscope was also selected as an international cornerstone for the 2015 International Year of Light. Continuing production has seen more than 270,000 Galileoscope’s in use in over 110 countries. A wide range of educational guides and materials have been created, along with instructions in multiple languages, and are available through the project website found here.
Galileoscopes are 50mm diameter, 500mm focal length refractors with glass doublet objectives, a Plössl 20mm FL eyepiece (giving 25x), and a 2x Barlow lens (giving 50x) that doubles as a Galilean eyepiece, so one can experience what Galileo did when he first turned a telescope to the heavens (although his telescope wasn’t optically anywhere as good as a Galileoscope!).
Galileoscopes have been particularly great for engaging youngsters and students with astronomy (see Image 2 of a recent workshop with students at the Compass Academy in Franklin, NH), as well as for science teachers, astronomy clubs and public outreach, and in education from elementary school through college, especially in Astro 101 courses.
A couple of years ago Scott Roberts and Explore Scientific took over manufacturing and distribution from us. This has greatly expanded availability of Galileoscopes, as Rick Fienberg and I had volunteered our time, effort, and personal resources to launch and manage the project on top of our regular positions for a decade – which is one of the reasons it has been available at such low cost.
Galileoscope Kits with Sun Filters
Working with Explore Scientific we offer a Galileoscope kit package that includes a safe solar filter and sunshade. The Galileoscope is a wonderful telescope for sunspots on any sunny day (and the Moon, planets, and other celestial highlights on any clear night).
These kits have helped thousands of people affordably and safely view the 2023 (annular) and 2024 (total) solar eclipses and are also suitable for observing the increase in solar activity over the next few years. Indeed, one of Galileo’s accomplishments was observing sunspots on the Sun!
To ensure eye safety, Explore Scientific has developed a safe solar filter – one that meets the transmission requirements of the ISO 12312-2 international standard – that fits snugly inside the Galileoscope’s dew cap, along with a sunshade that keeps bright sunlight off your face while observing and that doubles as a pointing aid so that you can safely aim your Galileoscope at the Sun without risk to your eyes.
In addition to solar-capable Galileoscope kits, Explore Scientific is also offering economical tripods, and, for those who already have or are reselling Galileoscopes, solar filters and sun shades as add-on accessories. The Image 1 shows the Galileoscope solar kit with the solar filter and sun shield installed.
An In Depth Look At The Galileoscope
As mentioned, the Galileoscope is a refracting telescope, or refractor: a long tube with a big lens (the objective) at the front end and a small lens (the eyepiece) at the back end. The great Italian scientist Galileo’s telescopes were refractors, too, but the Galileoscope improves upon his 400-year-old design in several important ways.
The field of view is the angular diameter of the circle of sky you see when you look into the telescope’s eyepiece. The full Moon is about ½° wide, so the Galileoscope’s field at 25x is three Moons wide, just big enough to encompass the splendid Pleiades star cluster in Taurus, one of the objects Galileo marveled at 400 years ago. If you double the magnification to 50x using the included Barlow lens, the width of the field of view is correspondingly halved. Image 3 shows simulated views of the Moon at 50x, the Pleiades star cluster at 25x, and Jupiter and its moons at 50x in the Galileoscope.
Eye relief is the distance behind the eyepiece that you need to put your eye to see the entire circular field of view. The Galileoscope’s ample eye relief of 16 mm at 25x and 22 mm at 50x should enable anyone, including children, to observe comfortably with or without eyeglasses.
We’ve designed the Galileoscope to accept accessories with the standard 1¼-inch barrel common to most commercial telescopes. This means that you can substitute your own eyepieces of various focal lengths for the supplied 20-mm eyepiece, giving you additional options for magnification and field of view.
Galileo built each of his telescopes with a convex (magnifying) objective lens and a concave (demagnifying) eyepiece lens. This combination produces an image that is both right-side up and correct left-to-right, but the field of view is uncomfortably narrow – as if you’re looking at the sky through a drinking straw. Image 4 is a photo shows one of Galileo’s telescopes on display in Florence, Italy.
Unique among available telescope kits, the Galileoscope can be assembled in either a Galilean configuration or a Keplerian configuration so that you can compare the two designs yourself. The Galileoscope is really two telescopes in one!
The Galileoscope’s 50-mm f/10 objective lens is an achromat made from two types of glass. The 20-mm (25x) eyepiece employs two achromats – a total of four lenses – made from two types of plastic. This four-element configuration is similar to that of the popular Plössl eyepiece, a high-quality design rarely seen on any telescope costing less than $100.
In addition to the main eyepiece, the Galileoscope comes with another plastic achromat that can be used in either of two ways: as a 17x eyepiece in the Galilean configuration, or as a 2x Barlow lens to double the magnification of the Galileoscope to 50x in its normal Keplerian configuration.
We’ve designed the Galileoscope so that it can be assembled in 5 minutes or less by young children with some adult supervision. Assembly requires no tools, no glue, and no adhesive tape – everything snaps into place easily.
As noted, the Galileoscope’s objective is a two-lens glass achromat. It comes as a single unit with the two elements glued together. The twin two-element plastic achromats for the main eyepiece, and the two-element plastic achromat for the Galilean eyepiece/Barlow lens, come as individual lenses, so that’s six more pieces. Except where noted, all other parts in the Galileoscope kit are made of ABS plastic, a durable material commonly used in injection molding.
The complete 31-piece parts list includes:
– Lens shade/dew cap
– Eyepiece-barrel halves (2)
– Objective lens
– Eyepiece field-stop ring
– Main tube halves (2)
– Eyepiece clamp ring
– ¼-20 mounting nut
– Eyepiece eye-end ring
– V bases/stands (2)
– Barlow tube
– Main-tube clamp ring
– Galilean eyepiece/Barlow lenses (2)
– Main-tube O-rings (2)
– Galilean eyepiece tube halves (2)
– Focuser tube halves (2)
– Galilean eyepiece clamp ring
– Focuser tube O-rings (2)
– Galilean eyepiece/Barlow eye-end ring
– Eyepiece lenses (4)
– Sun-warning sticker
All parts except the lenses (of course) and mounting nut are black. The tube halves fit together with tongues and grooves to prevent light from seeping in through the sides and the main tube includes multiple internal baffles. In addition, the insides of the telescope and focuser tubes are roughened to minimize internal reflections. These features, designed to reduce glare and the amount of stray light reaching the eyepiece, make the Galileoscope an ideal urban telescope for use in even the most light-polluted cities and are usually found only on telescopes costing much more.
The Galileoscope can be put together in 5 minutes or less. A 10-year-old child can assemble the telescope with minimal adult supervision, and younger children with a bit more supervision. Moreover, the kit can be assembled and disassembled multiple times – making it well suited for classroom use.
To assist with aiming the telescope at celestial targets, the main tube has a traditional notch-style sight along the top edge.
Eyepieces and other accessories are held securely in the focuser by self-adjusting spring-loaded tabs molded into the tube. The focuser assembly slides in and out with a comfortable amount of friction and can be moved in very tiny steps to achieve precise focus. If you’re nearsighted or farsighted and prefer to look through a telescope without wearing eyeglasses, you’ll appreciate the Galileoscope’s extra-long focuser tube, which accommodates a wide range of focus positions.
The ¼-20 mounting nut enables the Galileoscope to be affixed to a standard photo tripod or any other mount with a ¼-20 threaded post.
The bases/stands serve several purposes. They can simplify assembly by cradling the main tube on a tabletop or display the telescope by supporting it on a shelf or mantel. They also can enable students to partially assemble the telescope on a table and see what’s happening inside the instrument as it forms an image of a distant object.
No tools are needed to assemble the Galileoscope – all the parts fit together by hand in just a few minutes, with the tube halves held together by snap-fit plastic rings and/or rubber O-rings. A sheet of English-language instructions is included, but a set of graphical instructions is available in our Assembly Instructions section, so you don’t need to read English to assemble the scope.
As noted, the Galileoscope’s 1¼-inch (31¾-mm) barrel enables the use of standard commercial accessories such as additional eyepieces, Barlow lenses, and camera adapters. A 1¼-inch focuser is one of the key factors that distinguishes a serious telescope from a toy. (Another is achromatic optics, and the Galileoscope has those, too!) There are thousands of 1¼-inch accessories on the market today, giving the Galileoscope virtually limitless versatility.
One accessory that does not work with the Galileoscope, at least not in most cases, is a star diagonal. That’s a right-angle mirror or prism that goes between the telescope and eyepiece and enables you to avoid having to crane your neck when observing celestial objects high overhead. The Galileoscope is designed for straight-through viewing. There’s not enough “in focus” to permit the use of most star diagonals. We recommend sitting in a chair with the Galileoscope on a tripod that can be extended to a height of at least 150 cm (60 inches). That way, observing objects high in the sky will be comfortable even without a star diagonal.
A Galilean eyepiece is included in the Galileoscope kit which offers a custom accessory consisting of a plastic two-element achromat with a two-piece plastic holder, a plastic ring, and a plastic tube. The lens has a negative focal length of 30 mm. This accessory can be used in either of two ways. If you assemble it without the tube, you get a Galilean eyepiece that gives a magnification of 17x and a right-side-up field of view less than ½° wide. With this eyepiece, you can have the rather frustrating “Galileo experience” of looking at the heavens one very tiny piece at a time. This will make you really appreciate the advance represented by today’s wider-field designs!
If instead you assemble the parts using the tube, you get a 2x Barlow lens which, when used with the regular supplied eyepiece, increases the Galileoscope’s magnification to 50x. In addition to providing more detailed views of the Moon, Jupiter, and other targets, the Barlow lens will make plain the rings of Saturn. When Galileo looked at 20x to 30x, he couldn’t quite figure out that he was seeing a ringed planet – he described Saturn as “tri-form.”
As experienced stargazers know, a telescope is only as good as its mounting. Because a telescope gives a highly magnified view, the tiniest vibration looks like a major earthquake in the eyepiece. Even at a relatively modest 25x, the Galileoscope needs to be firmly attached to something stable. Because the instrument is so lightweight, an inexpensive photo tripod – the type you’ll find at most discount stores – should be sufficient. The tripod should have a pan head that moves smoothly in altitude (up-down) and azimuth (left-right), so that you can aim the telescope anywhere in the sky and make small adjustments without jerking things around.
Looking for a cheap alternative to a tripod? Astronomy blogger Shannon Murphy (University of Michigan) has posted detailed instructions for building a cardboard box mount at https://aquillam.wordpress.com/2010/01/04/a-cheap-tripod-alternative.
To Close
The Galileoscope enables kids of all ages (adults included) to build and observe with a telescope similar to (but much better than) Galileo’s. Sharing these observations with as many people as possible, and encouraging parents, teachers, students, and others to think about their importance, addresses one of the main goals of the Galileoscope Initiative – to promote widespread access to new knowledge and observing experiences.
Douglas Arion, PhD
Douglas Arion, PhD is the Executive Director of Mountains of Stars, and is Professor Emeritus of Physics and Astronomy and Donald D. Hedberg Distinguished Professor Emeritus of Entrepreneurial Studies at Carthage College. He is deeply concerned about human impact on the environment, and founded Mountains of Stars to change attitudes and actions of the public by creating ‘environmental awareness from a cosmic perspective’. He co-founded Galileoscope, a worldwide project to provide high quality, low cost telescopes for worldwide promotion of science education and outreach. More than 260,000 are now in use in over 110 countries. He was the driving force in the creation of the AMC Maine Woods International Dark Sky Park, which protects over 75000 acres of land in the last dark sky region of the eastern United States.
Looking to learn more about observing and imaging the Sun? Check out The Definitive Equipment Guide to Viewing and Imaging the Sun which can be found here. It provides an easy-to-consume introduction to the technological options for enhancing your solar imaging and observing experience. We cover the gamut of options available including building your own solar viewer, solar glasses, smart phones, DSLR cameras, astronomy telescopes, solar telescopes, binoculars, solar filters (including a DYI filter option), solar imaging cameras, solar mounts, solar accessories and so much more!