Page 33 - Life beyond the Karman

Three main optical types:
• The refracting telescope which uses lenses to form an image;
• The reflecting telescope that uses an arrangement of mirrors to form an image;
• The catadioptric telescope which uses mirrors combined with lenses to form an image.
Here are a few of the most significant and well-known telescopes in the world:
Galileo’s telescope
In May 1609, Galileo Galilei learned of a remarkable new invention from the Netherlands that used lenses to make far- off objects appear close by. After that, he made his own version and upped the magnification to 20 times.
Galileo’s telescope allowed him to see craters and mountains on the moon’s grey surface, which was one of his initial aims. Jupiter, the next brightest object in the night sky, was also visible to him.
On 7 January 1610, he discovered that “three fixed stars, totally invisible by their smallness” had joined it, appearing to line up precisely with the planet. He discovered during the following few nights that they weren’t fixed at all and instead moved in tandem with Jupiter.
On 13 January, he observed a fourth. These moons, which would subsequently be referred to as the Galilean Moons, were orbiting the earth rather than stars.
Galileo presented his findings in his ground-breaking book Sidereus Nuncius, which offered convincing evidence that Copernicus was correct to propose that the sun, not Earth, is at the centre of the universe and that the telescope would be the most potent instrument ever created for cosmos exploration.
Isaac Newton’s telescope
In 1668, Isaac Newton presented a model of the first reflecting telescope to the Royal Society.
By the middle of the 17th century, astronomers were frequently lamenting the existence of coloured bands at the edge of their
telescope’s field of view.
It dawned on Sir Isaac Newton that the distortion was caused by the telescope lens’s edge dividing the star’s white light into multiple colours.
The theory was sound but proved difficult to put into practice.
Ideally, one would need a parabolic mirror, but these were hard to produce by hand. Newton used a spherical mirror, which was easier to grind. This corrected the chromatic aberration but also created spherical aberration—an uneven focus in the image—an additional optical flaw.
In order to make viewing the image from the side of the telescope easier, Newton also utilised a secondary mirror. When Newton displayed his telescope to the Royal Society of London in 1671, it was so well- received that he was invited to show it to King Charles II. Fifty years later, in 1721, John Hadley, another astronomer, figured out how to make parabolic mirrors, which removed spherical aberration. Nearly all reflecting telescopes on the market now are based on the Newtonian design.
Daniel K. Inouye Solar Telescope
LIFE BEYOND THE KÁRMÁN LINE - OUTER SPACE
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