Galilean Telescope
3.Galileo Galilei |
Galileo Galilei was the first astronomer to use a telescope to study the heavens. Galileo made a number of observations that finally helped convince people that the Sun-centered solar system model (the heliocentric model), as proposed by Copernicus, was correct.
What is a Galilean telescope?
The original design Galileo Galilei came up with in 1609 is commonly called a Galilean telescope. Galileo’s telescope with which Jupiter's moons could be observed was made with a plano convex objective (the lens toward the object) with a focal length of about 30 to 40 inches, and a plano-concave eyepiece with a focal length of about 2 inches. The eyepiece was in a small tube that could be adjusted for focusing. The objective lens was stopped down to an aperture of 0.5 to 1 inch. , and the field of view was about 15 arc-minutes (about 15 inches in 100 yards). The instrument's magnification was 15-20. The glass was full of little bubbles and had a greenish tinge (caused by the iron content of the glass); the shape of the lenses was reasonable good near their centers but poor near the periphery (hence the restricted aperture); the polish was rather poor. The limiting factor of this type of instrument was its small field of view--about 15 arc-minutes--which meant that only a quarter of the full Moon could be accommodated in the field. Over the next several decades, lens-grinding and polishing techniques improved gradually, as a specialized craft of telescope makers slowly developed. But although Galileo’s telescope, and variations of it, were made with higher magnifications, they were practically useless because of the small field of vision.
Galileo's Telescope
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How does a Galilean
Galileo Galilei was the first astronomer to use a telescope to study the heavens. Galileo made a number of observations that finally helped convince people that the Sun-centered solar system model (the heliocentric model), as proposed by Copernicus, was correct.
What is a Galilean telescope?
The original design Galileo Galilei came up with in 1609 is commonly called a Galilean telescope. Galileo’s telescope with which Jupiter's moons could be observed was made with a plano convex objective (the lens toward the object) with a focal length of about 30 to 40 inches, and a plano-concave eyepiece with a focal length of about 2 inches. The eyepiece was in a small tube that could be adjusted for focusing. The objective lens was stopped down to an aperture of 0.5 to 1 inch. , and the field of view was about 15 arc-minutes (about 15 inches in 100 yards). The instrument's magnification was 15-20. The glass was full of little bubbles and had a greenish tinge (caused by the iron content of the glass); the shape of the lenses was reasonable good near their centers but poor near the periphery (hence the restricted aperture); the polish was rather poor. The limiting factor of this type of instrument was its small field of view--about 15 arc-minutes--which meant that only a quarter of the full Moon could be accommodated in the field. Over the next several decades, lens-grinding and polishing techniques improved gradually, as a specialized craft of telescope makers slowly developed. But although Galileo’s telescope, and variations of it, were made with higher magnifications, they were practically useless because of the small field of vision.
Galileo's Telescope
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How does a Galilean