Date: January 17, 2011

Title: Stargazing With the Galileoscope


Podcaster: Rob Sparks

Organization: National Optical Astronomy Observatory


Description: The Galileoscope was created for the International Year of Astronomy (IYA) in 2009. The Galileoscope is a low cost, high optical quality refractor similar in size and magnification to the telescopes used by Galileo in his historic observations. The Galileoscope can be used to observe the Moons of Jupiter, craters on the Moon, the phases of Venus, the rings of Saturn and many other celestial wonders. The Galilesocope project is continuing with teacher workshops around the world and events such as the Galileoscope photo contest.

Bio: Rob Sparks is a Science Education Specialist at the National Optical Astronomy Observatory. A lifelong astronomy enthusiast, he earned a B.A. in physics at Grinnell College and his M.S. at Michigan State University. He taught high school physics, math and astronomy for 11 years at schools on St. Croix, Florida and Wisconsin. He spent the 2001-2002 school year working on the Sloan Digital Sky Survey as a recipient of the Fermilab Teacher Fellowship. He spent the summer of 2003 at the National Radio Astronomy Observatory as part of the Research Experience for Teachers. He has been working as a NASA Astrophysics Ambassador since 2002. He was a member of the Galileoscope Working Group for the International Year of Astronomy.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by John Sandlin. The Sandlin Family wishes you all Clear Skies.


Hi, I am Rob Sparks from the Education and Public Outreach Group at the National Optical Astronomy Observatory (NOAO) in Tucson, Arizona. I would like to welcome you to the first of our podcasts for 2011. NOAO will be producing a different podcast each month that will air on the 17th.

For our first podcast, I would like to talk about the Galileoscope and the Galileocope photo contest currently underway.

The Galileoscope was developed for the International Year of Astronomy (IYA) in 2009. The goal was to create a low cost, high optical quality telescope that could be used by students and amateur astronomers around the world to recreate Galileo’s historic observations. Designing a telescope to meet all the optical and mechanical requirements while keeping the cost down would be a challenge.

The goal of the project was not to make a duplicate of Galileo’s telescope. Galileo’s telescope had many shortcomings. His optics were not high quality and he used a diverging lens for his eyepiece which resulted in a very small field of view. His telescope suffered from chromatic aberration which results in strange color fringes in the image. Most people would find it frustrating to use Galileo’s telescopes. The Galieoscope team wanted to create a telescope similar in size and magnification to Galileo’s but with a modern optical design to give a sharp image with a generous field of view.

Steve Pompea, Doug Arion and Rick Feinberg led a team that included astronomers, optical engineers and educators. Several prototypes were built and tested by astronomers and educators around the U.S. After several iterations, a final design was reached and production began in the first half of 2009.

The final design was a refracting telescope with a 50mm diameter objective lens. The focal length of the telescope is 500mm (making it an f/10 system). The objective is an achromatic lens. An achromatic lens is two lenses made of different types of glass (such as flint glass and crown glass). The two different types of glass have different optical properties that reduce the chromatic aberration that plagued Galileo’s telescope.

The Galieoscope uses a Plossl eyepiece. A Plossl eyepiece uses four lenses to reduce chromatic aberration and provide a larger field of view. The Plossl eyepiece is a diverging lens. Telescopes that use a diverging lens eyepiece are called Keplerian telescopes after Johan Kepler. Keplerian telescopes produce an upside down image.

The Galileoscope’s eyepiece has a focal length of 20mm which gives a magnification of 25x. Galileo used several telescopes that ranged in magnification from 8x to about 30x so he Galileoscope comes in at the upper end of that range. The Galileoscope’s field of view is 1.5 degrees, or about three times the diameter of the full Moon. A large field of makes it easier to find objects in the night sky.

The Galileoscope comes with a second eyepiece. The second eyepiece is a diverging lens. Using the diverging lens, you can make what is known as a Galilean telescope. The diverging lens produces a magnification of 17x, but gives you a right side up image. The disadvantage is that the field of view is only 0.4 degrees, less than the diameter of the full Moon! Having a small field of view makes observing more difficult. It is harder to find objects in the night sky and many star clusters will not fit in this small field of view. The main use of this eyepiece is to illustrate the difference between Galileo’s telescope and modern telescopes.

There is a third observing configuration as well. The Gaileoscope comes with a small tube that lets you use the diverging lens to make a Barlow lens. A Barlow lens increases the magnification of you telescope, in this case by a factor of 2. By using the diverging lens and the Plossl eyepiece together, you can create a telescope with a magnification of 50x. Increasing the magnification decreases your field of view to ¾ of a degree and produces a dimmer image. For bright objects such as the Moon and planets, this configuration can show pleasing details.

The Galieloscope has a standard ¼ – 20 nut that will attach to any camera tripod. It is very difficult to hold the Galileoscope steady so putting it on a tripod is very important.

The end result is a telescope that can see a wide variety of objects. The Moon is always a good target. Jupiter’s two main belts are easily visible as are the four Galilean Moons. Saturn’s rings are a pleasing site and you can watch the phases of Venus change over time.

There are many objects outside the solar system that are pleasing sites as well. Many of the Messier objects are good targets. The Galileoscope’s wide field of view is particularly well suited to the Pleaides. The Andromeda Galaxy is a surprisingly good target if you have dark skies. The Orion Nebula is not to be missed. For a more extensive list of targets and observing tips, you can download the Galileoscope Observing Guide from the Teaching With Telescopes website at

In 2010, Rick and Jean Edelman donated 15,000 Galileoscopes for students around the United States. These Galileoscopes were distributed through the National Earth Science Teacher’s Association, Project Astro sites, and directly to teachers. We thank the Edelman’s for their generosity.

Over 200,000 Galileoscopes have been sold (and counting). They have been used by students, teachers and amateur astronomers around the world and are still available by visiting

The Galileoscope made an appearance at the White House Star Party in 2009. In January of 2010, we built almost 500 Galileoscopes in Tucson as part of the Math Moves You program with our partners Raytheon and the University of Arizona MESA program. Science Foundation Arizona sponsored a star party in Flagstaff where we built 400 Galileoscopes and had a wonderful evening of observing with hundreds of students and their families. There have been many smaller star parties featuring the Galileoscope in Tucson and around the country.

One of the current projects we are working on is the Galileoscope Photo and Sketching contest. The National Earth Science Teacher’s Association and the National Optical Astronomy Observatory launched the contest in December of 2010 and various contests run through April of 2011. The goal is to encourage students to record their observations made through the Gailoeoscope either by taking photographs with a digital camera or by sketching their observations like Galileo. There are separate categories for different objects and different ages. You may enter either the sketching contest or the photo contest.

To take photos with the Galileoscope, you do not need fancy equipment. Inexpensive digital cameras can produce good results. Even cell phone cameras can work if you have a steady hand. Be sure to turn off your camera’s flash before attempting to take a picture through the Galileoscope.

I recommend practicing some daytime shots before you try photos at night. Pick a distant object and focus the Galileoscope on it. Be sure to use just the Plossl eyepiece. Don’t try to go for the higher magnification. Turn off the your camera’s flash (every camera is different so you will have to find out who to do that…generally, look for a button or setting on a dial that has a little lightning bolt symbol and try it). The tricky part is lining up the camera with the eyepiece. You have to make sure it points directly into the eyepiece and is close enough to see the image. You can use your camera’s zoom feature. I have found zooming in about 3-4x with the camera makes it easier to line up.

If your camera has a low light setting, you can turn it on. Use the highest ISO you can if you camera allows you to change it. If your camera doesn’t have these settings, don’t worry. I have taken pleasing pictures of the Moon and Saturn using all automatic settings so they are not essential.

You can try taking video as well. Since Earth’s atmosphere is constantly in motion, you get what we call atmospheric distortion. Taking a video allows you to look for video frames with the least distortion and use it. There are even free programs that will automatically look for the best frames and let you combine them to make a really super image. Registax ( ) is a good example.

There are various contests going on. You can image the Moon, Jupiter or Saturn. A separate category is called Galileo’s Choice where you can image or sketh whatever you like. For full details, see the National Earth Science Teacher’s Association website (

That’s about all the time we have for this month. We’ll be back on February 17th with another podcast. In the upcoming months, we will be interviewing a variety of NOAO astronomers about their cutting edge research.

End of podcast:

365 Days of Astronomy
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