Telescope Evolution
ACE
In June 1609, Galileo Galilei, an Italian physicist heard of the “Dutch perspective glass” which could make objects far way nearer and bigger. He then made his first telescope by fitting a convex lens in one extremity of a leaden tube and a concave lens in the other one. Afterwards, Galileo publicised his invention in Venice and presented a better version of his first one to the doge Leonardo Donato. He made telescopes that each increased with power and the last telescope he made was able to magnify thirty-three diameters. In 1960, he used this telescope to discover the satellites of Jupiter and spots on the Sun, phases of Venus and hills and valleys of the Moon.
At about 1611, Johannes Kepler showed that a convex objective and convex ocular, combined with another convex lens could make an inverted image erect. Christoph Scheiner then experimented with convex oculars to make his telescope images erect. However, his image of the Sun was too bright and too big a field of view for the telescope. People preferred the Galilean telescope as it could be interchangeably used for both terrestrial and celestial viewing, while the latter caused more defects in the image as there were more lens. In the second half of the seventeenth century, the Galilean telescope was used for terrestrial purposes. It had four convex lenses: objective, ocular, erector lens, and a field lens (which enlarged the field of view even further).
Increased magnification had to be achieved by increasing the focal length of the objective as the curvature of the lenses had to be minimized due to the optical defects it caused. From 1640s onwards, telescopes started to increase in size. From the typical Galilean telescope of 5 or 6 feet in length, they rose to about 15 or 20 feet. Then, further increases in magnification had to be stopped as the field of view would be too restricted. The field lens had to be utilised. This helped in building of much bigger telescopes that could even reach 140-feet.
In June 1609, Galileo Galilei, an Italian physicist heard of the “Dutch perspective glass” which could make objects far way nearer and bigger. He then made his first telescope by fitting a convex lens in one extremity of a leaden tube and a concave lens in the other one. Afterwards, Galileo publicised his invention in Venice and presented a better version of his first one to the doge Leonardo Donato. He made telescopes that each increased with power and the last telescope he made was able to magnify thirty-three diameters. In 1960, he used this telescope to discover the satellites of Jupiter and spots on the Sun, phases of Venus and hills and valleys of the Moon.
At about 1611, Johannes Kepler showed that a convex objective and convex ocular, combined with another convex lens could make an inverted image erect. Christoph Scheiner then experimented with convex oculars to make his telescope images erect. However, his image of the Sun was too bright and too big a field of view for the telescope. People preferred the Galilean telescope as it could be interchangeably used for both terrestrial and celestial viewing, while the latter caused more defects in the image as there were more lens. In the second half of the seventeenth century, the Galilean telescope was used for terrestrial purposes. It had four convex lenses: objective, ocular, erector lens, and a field lens (which enlarged the field of view even further).
Increased magnification had to be achieved by increasing the focal length of the objective as the curvature of the lenses had to be minimized due to the optical defects it caused. From 1640s onwards, telescopes started to increase in size. From the typical Galilean telescope of 5 or 6 feet in length, they rose to about 15 or 20 feet. Then, further increases in magnification had to be stopped as the field of view would be too restricted. The field lens had to be utilised. This helped in building of much bigger telescopes that could even reach 140-feet.
Another challenge surfaced- such long telescopes had lens that were almost impossible to align.
After about 1975, astronomers removed the telescope tube and mounted it on buildings/poles instead. These were called “aerial telescopes”. The 1730s marked a new era of the reflecting telescope.
Scientists started to place mirrors as emphasis on building telescopes. Issac Newton added to his reflector (in telescope) a secondary "diagonal" mirror near the primary mirror's focus to reflect the image at 90° angle to an eyepiece mounted on the side of the telescope. The objective mirror then could not disrupt the image much. He could see the four Galilean moons of Jupiter and the crescent phase of the planet Venus. Encouraged by this success, he made a second telescope with a magnifying power of 38x which he presented to the Royal Society of London in December 1672.
This is called a Newtonian telescope. Newton was also the first one to produce a successful reflecting telescope. However, since his mirrors were made with copper and tin, they would tarnish and rust easily. His mirrors also did not bring all the rays of light to common focus.
After about 1975, astronomers removed the telescope tube and mounted it on buildings/poles instead. These were called “aerial telescopes”. The 1730s marked a new era of the reflecting telescope.
Scientists started to place mirrors as emphasis on building telescopes. Issac Newton added to his reflector (in telescope) a secondary "diagonal" mirror near the primary mirror's focus to reflect the image at 90° angle to an eyepiece mounted on the side of the telescope. The objective mirror then could not disrupt the image much. He could see the four Galilean moons of Jupiter and the crescent phase of the planet Venus. Encouraged by this success, he made a second telescope with a magnifying power of 38x which he presented to the Royal Society of London in December 1672.
This is called a Newtonian telescope. Newton was also the first one to produce a successful reflecting telescope. However, since his mirrors were made with copper and tin, they would tarnish and rust easily. His mirrors also did not bring all the rays of light to common focus.
Sir William Herschel constructed a forty foot long telescope with a 4-foot diameter mirror. The humongous mirrors used by this type of telescope could gather hundreds/thousands times more light. H. Dennis Taylor, maker of astronomical telescopes, designed and patented the revolutionary and current triplet telescope design in 1893. This lens cleared distortion at the outer edge of lenses. The lenses are air-spaced (not touching each other).
In April 24 1990, the Hubble Space Telescope (HST) was launched and it is the first telescope to orbit the Earth. As it is in the atmosphere, it is able to get a better view of the sky than a telescope on the ground. It is named after the U.S. astronomer Edwin Hubble and can observe the Earth 24 hours a day. It is a very powerful telescope that can observe things very far away. Scientists have written thousands of papers on important things like the age of the universe, size of black holes, and the shapes of countless stars. It first shot into orbit on April 24, 1990.