Galileo Galilei

In 1609, an Italian mathematics professor named Galileo Galilei constructed an amazing instrument. He called it “telescopio”, Greek for “to see at a distance”. Inspired by the newly invented spyglass used by naval officers to spot distant ships, Galileo turned his gaze upward, to examine the stars and planets more closely than ever before.

Galileo’s telescope had a simple but revolutionary design. It was a tube with two lenses — the convex primary lens that curved outward, and the concave eyepiece lens that curved inward. It had about 30x power.

With his telescope, Galileo was able to observe the cratered landscape of our moon, as well as discovering several moons of Jupiter, distant stars in the Milky Way, and the rings of Saturn.

He also observed that Venus had distinct phases, much like the Earth’s moon. This was important evidence in support of Copernicus’ Heliocentric (Sun-centered) model of the Universe. This discovery brought Galileo into conflict with the authorities, who supported the incorrect Geocentric (Earth-centered) model.

This Telescope Observation book belongs to:

Interested in bringing a group to learn more about telescopes and how they work? Call us and book a date soon!

L. C. Bates Museum at Good Will-Hinckley

14 Easler Road / Hinckley, ME 04944

(207) 238-4250 lcbates@gwh.org

www.gwh.org/lcbates

Open Wednesday - Saturday, 10am - 4:30pm and Sunday, 1 - 4:30pm

@LCBatesMuseum www.facebook.com/lcbates

Telescopes

Galileo’s telescope was a refractor. Observe a distant object without the Galileoscope,

and record your findings below:

Now observe the same object with the Galileoscope, and record your findings below:

Refraction is the bending of light as it passes from one

substance to another. Here, the light ray passes from air

to glass and back to air. The bending is caused by the

differences in density between the two substances.

When light passes through a prism, it is dispersed into its

many colors. The curved shape of a lens causes some of

these colors to focus at different points, creating a ring

of color around the distant object you are trying to view.

This optical illusion is known as chromatic aberration.

In a telescope like Galileo’s, the lenses which refract light are referred to as convex and concave.

Experiment with different lenses — can some of them cause objects to appear farther away? Can other lenses distort light like a funhouse mirror? Legend has it that an early spyglass was invented when some children were playing around with eyeglass lenses, and realized by accident that by combining them, they could see the weathervane on top of a distant church!

Below is the light path of Galileo’s telescope, demonstrating the effect of combining a set of convex and concave lenses.

Galileo was the first astronomer to use a telescope to

study the heavens. His observations strengthened his

belief in Copernicus' theory that Earth and all other

planets revolve around the Sun. Can you navigate to

the center of our solar system?

Telescope Vocabulary

Concave - Concave means to curve inward, like the inside of

a circle. Remember, a cave is a hollowed out space!

Convex - Convex is the opposite of concave, like the outside

of a circle or sphere.

Reflection - Reflection occurs when light changes direction

as a result of "bouncing off" a surface like a mirror.

Refraction - Refraction is the bending of light as it passes

from one substance to another. Have you ever seen something

(like a drinking straw) look funny and distorted when it’s

underwater? That’s refraction!

Lens - A lens is a piece of glass with curved sides (either con-

cave or convex) for concentrating or dispersing light rays. One

convex lens by itself is a magnifying glass—we put multiple lenses

together to build a telescope.

Mirror - A mirror is a reflective surface, such as brightly

polished metal.

Focal point - The focal point is the point at which rays or

waves meet after reflection or refraction.

Chromatic aberration - Chromatic aberration is a ring

of color around the bright object being viewed through a tele-

scope. It is caused by light being broken up as it passes through a

curved prism.

Galileo’s refractor telescope inspired generations of astronomers to explore our universe, and to come up with their own improved telescope designs. Galileo’s original tele-scope was only a few feet long, but less than a century later, astronomers were building refractors up to 150 feet in length!

These gigantic refractors were unwieldy and difficult to use—there had to be a better way!

In the 1680’s, English scientist Isaac Newton came up with a solution for making powerful telescopes that were also more compact. His design is called a reflecting telescope.

Newton’s reflector design solved the old problem of chromatic

aberration. This is because he used mirrors instead of lenses.