Newton's reflector

Newton's reflector
A replica of Newton's second reflecting telescope that he presented to the Royal Society in 1672 described as the better of the two instruments Newton built[1].

The first reflecting telescope built by Sir Isaac Newton in 1668[2] is a landmark in the history of telescopes, being the first known successful reflecting telescope[3][4]. It was the prototype for a design that later came to be called a newtonian telescope.

Contents

Description

Isaac Newton built his reflecting telescope as a proof for his theory that white light is composed of a spectrum of colors[5]. He had concluded that the lens of any refracting telescope would suffer from the dispersion of light into colors (chromatic aberration). The telescope he constructed used mirrors as the objective which bypass that problem. To create the primary mirror Newton used a custom composition of metal consisting of six parts copper to two parts tin, an early composition of speculum metal[3]. He devised means for shaping and grinding the mirror and may have been the first to use a pitch lap[6] to polish the optical surface. He chose a spherical shape for his mirror instead of a parabola to simplify construction: he had satisfied himself that the chromatic, and not the spherical aberration, formed the chief faults of refracting telescopes. He added to his reflector what is the hallmark of the design of a "Newtonian 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. This unique addition allowed the image to be viewed with minimal obstruction of the objective mirror. He also made all the tube, mount, and fittings.

Newton described his invention as:

The diameter of the sphere to which the Metal was ground concave was about 24 English Inches, and by consequence the length of the Instrument about six Inches and a quarter. The Eye-glass was Plano-convex, and the diameter of the Sphere to which the convex side was ground was about 1/5 of an Inch, or a little less, and by consequence it magnified between 30 and 40 times. By another way of measuring I found it magnified 35 times. The concave Metal bore an Aperture of an Inch and a third part, but the Aperture was limited not by an Opake Circle, covering the limb of the Metal round about, but be an opake Circle, placed between the Eyeglass and the Eye, and perforated in the middle with a little round hole for the Rays to pass through to the Eye. For this Circle being placed here, stopp'd much of the erroneous Light, which other wise would have disturbed the Vision. By comparing it with a pretty good Perspective of four Feet in length, made with a concave Eye-glass, I could read at a greater distance with my own Instrument than with the Glass. Yet Objects appeared much darker in it than in the Glass, and that partly because more Light was lost by Reflexion in the Metal, than by Refraction in the Glass, and partly because my Instrument was overcharged. Had it magnified but 30 or 25 times, it would have made the Object appear more brisk and pleasant.

Newton describes a telescope with an objective concave primary mirror diameter of about 1.3 inches (33 mm) ground to fit a sphere that was 24 inches in diameter giving it a radius of 12 inches and a focal length of 6 inches (152 mm). It had a flat diagonal secondary mirror bouncing the light at a 90° to a Plano-convex eyepiece[7]. Newton completed this reflecting telescope in late 1668 and first wrote about it in a February 23, 1669 letter to Henry Oldenburg (Secretary of the Royal Society)."[8].

Newton found that he could see the four Galilean moons of Jupiter and the crescent phase of the planet Venus with his new little telescope[7]. Newton's friend Isaac Barrow showed the telescope to small group from the Royal Society of London at the end of 1671. They were so impressed with it they demonstrated it for Charles II in January of 1672. The last record Newton made of having it was in 1704, but the final fate of Newton's first reflecting telescope is unknown.[1] It was recorded as having been seen for a while at an instrument makers shop (Mr. Heath's) in Strand, London before 1723 but nothing further is known about it[1].

The practical potential of Newton's first telescope was made more clear by the end of the 18th century, when the largest reflector had grown to nearly 50 inches aperture (126 cm)[9] while the largest achromatic lens objective was not more than about 5 inches (13 cm).[10]

Specifications

See also

  • Isaac Newton Telescope, a 2.5m Telescope named for Isaac Newton, completed in 1967
  • List of largest optical telescopes in the 18th century


References

  • Smith, Warren J., Modern Optical Engineering, McGraw-Hill Inc., 1966, p. 400

External links


Wikimedia Foundation. 2010.

Игры ⚽ Поможем решить контрольную работу

Look at other dictionaries:

  • Newton, Sir Isaac — (4 ene. 1643, Woolsthorpe, Lincolnshire, Inglaterra–31 mar. 1727, Londres). Físico y matemático inglés. Hijo de un pequeño terrateniente, fue criado por su abuela. Se educó en la Universidad de Cambridge (1661–65), donde descubrió la obra de René …   Enciclopedia Universal

  • Isaac Newton — Sir Isaac Newton …   Wikipedia

  • Telescopio reflector — Telescopio espacial Hubble. Un telescopio reflector es un telescopio óptico que utiliza espejos en lugar de lentes para enfocar la luz y formar imágenes. No se sabe con certeza cuál es el primer telescopio reflector, pero la idea de la… …   Wikipedia Español

  • Parabolic reflector — Parallel waves coming in to a parabolic mirror are focused at a point F A parabolic reflector (or dish or mirror) is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular… …   Wikipedia

  • Isaac Newton — Para otros usos de este término, véase Newton. Sir Isaac Newton …   Wikipedia Español

  • Laser Ranging Retro-Reflector — Fotografía del retrorreflector láser instalado en la Luna por el Apolo 11. Laser Ranging Retro Reflector. También denominado LR 3, se trata de un experimento instalado en el ALSEP de tres de las misiones Apolo (Apolo 11, 14 y 15), si bien no… …   Wikipedia Español

  • Telescopio reflector — Un telescopio reflector es un telescopio óptico que utiliza espejos en lugar de lentes para enfocar la luz y formar imágenes. Sir Isaac Newton diseñó el primer reflector alrededor de 1670. Este primer reflector fue diseñado para evitar el… …   Enciclopedia Universal

  • Schmidt-Newton telescope — The optical design of the Schmidt Newton telescope combines elements from both the Schmidt camera and the Newtonian telescope. In this system the parabolic primary mirror common in newtonian reflector is replaced by a spherical mirror, which… …   Wikipedia

  • Observatory Vsetín — The Observatory Vsetín was found in 1950 by the local branch of Czechoslovak Astronomical Society. Contents 1 Brief history 2 Scientific equipments 3 Scientific activities 4 Populariza …   Wikipedia

  • History of the telescope — The earliest known working telescopes appeared in 1608 and are credited to Hans Lippershey and Zacharias Janssen, spectacle makers in Middelburg, and Jacob Metius of Alkmaar. The design of these early refracting telescopes consisted of a convex… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”