TImeline Of Telescopes

By Philip Matheson
  • 3500 BCE

    Glass Discovered

    3500 B.C. Phonenicians cooking on sand discover glass

  • Hans Lippershey

    1608--In the Netherlands, Hans Lippershey discovers that holding two lenses up some distance apart bring objects closer. He applies for a patent on his invention. This is the first documented creation of a telescope.

  • Johannes Kepler

    1611--Johannes Kepler switches from a concave eyepiece to a convex eyepiece. This not only allowed a larger field of view, but it allowed for the projection of images (such as the sun) onto a flat white screen. Although the images are inverted, Kepler demonstrates how a third convex lens turns the images right-side-up again. The use of a third lens also degrades the images, so this form of the telescope is not widely used. For terrestrial applications, particularly military applications

  • James Gregory

    1663--James Gregory designed a telescope using a concave primary mirror (slightly hyperboloid) concave ellipsoidal secondary mirror. The first mirror gathers the light and reflects it onto the secondary. The secondary mirror focuses the light back through a hole in the primary mirror. This is the basis for many telescopes made today, but the opticians of his time were not able to produce mirrors of high enough quality to give good results.

  • Robert Hooke

    1668--Robert Hooke demonstrates how to shorten the tube by using three or four perfectly flat mirrors to reflect the image back and forth in a shorter tube. A 60-foot long telescope can be reduced to 12 feet long, greatly simplifying support and stability.

  • Christian Huygens

    1675--Christian Huygens suggests getting rid of the supporting structure and mounting the objective lens on the top of a long pole. These were called "aerial telescopes" because they were open to the air. They were also much easier to build and use. At the same time, Huygens developed a compound negative eyepiece using two air-spaced convex lenses. This arrangement cancelled out some of the chromatic aberration that occurred in a single lens eyepiece.

  • Chester Moor

    1729--Chester Moor Hall develops an achromatic lens. Two pieces of glass with different indices of refraction can be combined to produce a lens that tends to focus most colors at a very close (though not exact) point. Red and Green neatly blended at a point, but blue-violet still missed that point by a small amount. The result was a much sharper image with violet halos around brighter objects. Refractors are suddenly popular again. The images still show simple optical distortion around the edges

  • James Short

    1730--The Scottish Instrument maker James Short invents the first parabolic and elliptic, distortionless mirror ideal for reflecting telescopes. Short accomplished this in a very practical manner: Since parallel rays nearer the centre of a spherical mirror overshoot the marginal rays coming from the edge of the mirror, why not just deepen the centre to bring all the rays of light to the same point of focus? James Short built over 1,360 telescopes. All had speculum mirrors.

  • Sir William Herschel

    1789--Sir William Herschel constructs a forty foot long telescope with a four-foot diameter mirror. Reflector telescopes have become popular again because they can be built with enormous mirrors, capable of gathering hundreds or even thousands of times more light than a refractor. Today we call them "light buckets."

  • H. Dennis Tayloe

    1893--H. Dennis Taylor, optical manager of T. Cooke & Sons of York, makers of astronomical telescopes, designed and patented the revolutionary, and now famous, triplet design (British patent no. 1991). This lens eliminated the optical distortion at the outer edge of lenses. The Cooke Triplet was a significant improvement of the Dolland triplet of more than a century earlier. The cooke triplet, seen at left, is made of three different types of glass.