The Telescope Revolution

Timelines of Events

  • 1576
    • Tycho Brahe constructed a large observatory on the island of Hveen, from which he conducts observations for the next 20 years.
  • 1600
    • Giordano Bruno, an Italian friar, is burned at the stake as a heretic after expressing his belief that the sun and Earth are not central or unique in the universe.
  • 1608
    • Hans Lippershey, a Dutch eyeglass manufacturer, seeks a patent for a three-times magnification telescope.
  • 1610
    • Galileo Galilei discovered four moons orbiting Jupiter using a telescope magnified 33 times.
  • 1619
    • The three laws of planetary motion proposed by Johannes Kepler describe the elliptical orbits of planets.
  • 1639
    • Jeremiah Horrocks, an English astronomer, watches Venus pass across the face of the sun.
  • 1659
    • Christiaan Huygens, a Dutch astronomer, was the first to accurately describe the structure of Saturn's rings.
  • 1675
    • Giovanni Domenico Cassini correctly deduces that Saturn's rings are not solid after spotting a gap in them.
  • 1676
    • Dane Ole Rmer observes the eclipses of Jupiter's moon Io to determine the speed of light.
  • 1687
    • In his book Principia, Isaac Newton outlines his general law of gravitation.
  • 1705
    • Edmond Halley, an English astronomer, forecasts the return of the comet that bears his name.
  • 1725
    • James Bradley demonstrates that the Earth is moving by demonstrating a phenomenon known as stellar aberration.

Introduction

  • Tycho Brahe, a Dane, was the last great astronomer before the invention of the telescope.
  • At the time of Tycho's death in 1601, the realm of celestial bodies appeared remote and inaccessible to astronomers.
  • In 1608, the invention of the telescope brought the vast and distant universe into a much closer look.
  • Telescopes have two key advantages over human eyes alone:
    • greater light-gathering capacity; and
    • resolve finer details.
  • In 1610, the telescope became the main astronomical instrument, when Galileo made his first telescopic observations of the planets, the moon's rough surface, and the Milky Way star clouds, creating previously unimaginable vistas.

Planetary Dynamics

  • After Tycho Brahe passed away, his assistant Johannes Kepler received the records of his observations. Kepler was persuaded by Copernicus's justifications that the planets orbit the sun.
  • Kepler used his aptitude for mathematics and intuition to deduce that planetary orbits are not circular but rather elliptical.
  • He had developed his three laws of planetary motion, which describe the geometry of how planets move, by 1619.
  • Kepler had found a solution to the problem of how planets moved, but the reason for their motion remained a mystery.
  • Ancient Greeks believed that the planets were carried on intangible spheres, but Tycho's observation of comets' free passage through interplanetary space appeared to refute this notion.
  • Kepler believed that the planets were propelled by the sun in some way, but he lacked the scientific terminology to describe it.

Gravitation

  • Isaac Newton was tasked with describing the force behind the motion of the planets, and it was his theory that was upheld until Albert Einstein.
  • Newton came to the conclusion that celestial bodies are attracted to one another, and he mathematically demonstrated that Kepler's laws are a logical conclusion if the pulling force between two bodies decreases in proportion to the square of their distance.
  • The Latin word, gravitas, means weight — is where the word gravity came from.

Telescopic Improvements

  • Newton used his mathematical method of describing how objects move to develop a new theoretical framework for astronomers and solve practical problems.
  • Although it helped make the telescope incredibly long, early telescope makers found it impossible to obtain images free from colored distortion with their simple lenses. For instance, Giovanni Domenico Cassini observed Saturn in the 1670s using long "aerial" telescopes without a tube.
  • In 1668, Newton designed and built the first working version of a reflecting telescope that did not have the color problem.
  • In the 18th century, reflecting telescopes of Newton's design were widely used after John Hadley developed techniques for fabricating sizable, precisely curved mirrors from shiny speculum metal.
  • James Bradley, Oxford professor, astronomer, and later Astronomer Royal, was impressed with telescopes and acquired a reflector.
  • In the early 18th century, Chester Moore Hall, an English inventor, created a two-part lens that significantly reduced color distortion.
  • John Dollond, an optician, used this discovery to create significantly better refracting telescopes.
  • Practical astronomy has changed as a result of the accessibility of high-quality telescopes.