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Discoveries of Galileo and William Herschel

Astronomical Instruments. Definition

Astronomical knowledge has evolved from time immemorial up to date and it proves to go beyond. Astronomy includes gathering relevant information on celestial objects and relating to our daily lives; how they affect us and the future intuitions. Astronomy as a discipline has experienced major development in instruments or gadgets that make it easy to compile data and do meaningful research. Astronomical instruments are generally grouped in different salient categories. The first grouping includes those gadgets that are used in the real process of gathering visual data from celestial objects. One of the major examples is the meridian transit. It is designed to perform a specific task; that is; the accurate determination of the position of the earth from the observer’s point of view. There are auxiliary instruments that are specifically used to; standardize, record, and statistically analyze gathered raw data by the first category of instruments. Here; accurate time standard is determined, brightness, spectra, and position on photographic plates of heavenly bodies are also determined. However, more gadgets are responsible for making the radiations emitted by stars, planets, and nebulas visible. This paper will give an up-close and candid analysis of the ‘quest of the aperture’ in the making of the telescope. Briefly, the telescope is a gadget that is vital in making invisible objects visible to the naked eye and hence allows the taking of photographs and is easily detected.

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Development of Astronomical Telescopes

Earlier telescopes were developed in Holland during the 17Th Century. Galileo made outstanding improvements on Lipperyshey’s telescopes and used them to observe planets and other invisible celestial bodies like moons of other planets. Refractors in the lenses of the telescopes’ magnification mirrors are meant to gather light and give a focal focus to the ocular state of heavenly bodies. Galileo used a divergent lens to observe, but later improvements were made and convergent lenses were used, although they gave inverted images. Kepler was the first astronomer to see an inverted image in his eyepiece by using a convergent lens. However, this problem was sorted out when scientists added more mirrors to restore the images. It was later discovered that simple lenses distorted the real visible image of the celestial bodies because of the bending of light wavelength. The red and violet lights bend differently hence giving a blurred image. This led to chromatic errors in the earlier telescopes (Kuhn, 1970).

Galileo constructed telescopes that had five centimeters in aperture during his time. The focal length was around 170 centimeters and had a magnifying power of 15 to 30. Today, a normal telescope can magnify a star over 300 times having an aperture of about 50 centimeters. From his time stretching to the William Herschel epoch, the astronomical telescopes have undergone many developments that have improved the viewing of the heavenly bodies (Holmes, 2009). The problem of chromatic aberrations in the images observed in the telescopes was later sorted out when it was found that the higher the focal point the lesser the aberrations. This was a profound finding in ‘the quest of the aperture’ and telescope making. Refracting lenses were constructed and Isaac Newton managed to avoid the chromatic aberrations.

Importance of the Aperture

Before describing the major developments in the ‘quest of the aperture’ it is important to understand the importance and problems in making the aperture of the telescope. The aperture is the most important aspect in determining the optical functioning of an astronomical telescope. The diameter of the aperture is the major aspect that determines the magnification power of a telescope. William Herschel was intrigued with celestial bodies and constructed bigger telescopes that had a wider diameter that determined the size of his telescopes. When an observer gathers a lot of light in the telescopes the bodies observed will be lighter and thus blurred image. However, William Herschel knew the secret behind finer observations. He was able to construct the larger telescopes with higher resolutions that we’re able to observe finer and not fainter details of the celestial. This made him discover Uranus. He was amazed by the rings in Saturn and prompted him to design a more movable and bigger telescope (Holden, 1881).

When a telescope has a higher resolution, it can be used to observe finer details of a heavenly body, even split closely packed double stars. Therefore, a telescope should be built perfectly for it to perform perfectly. The optical performance of a telescope is directly related to the diameter of the aperture and is the ability to avoid much light. Atmospheric unrest limits the aptitude concept of a telescope to amplify facets of the heavenly bodies. However, the aperture becomes contradictory because the usability of a telescope depends on portability. It is also important to note that several irradiations and radiations are emitted from a heavenly body. Using a telescope this facet ideally depends on closeness to the heavenly body’s electromagnetic spectrum. Most optical telescopes are known to increase the visible angular size of celestial planets (Born, 1999).

Major Events from William Herschel

William Herschel had a prodigious mind that assisted him to make a lot of salient discoveries. After abandoning music, he became the father of modern astronomy! Using a Newtonian telescope he could be able to discover Uranus. This telescope was hand-made by him and contained a higher aperture and focal length. He assembled over 400 telescopes and he even gave one as a gift to his sister who did a lot of discoveries on comets and nebula bodies. With this spirit, he was able to make the largest telescope that allowed him to view objects directly when he improved on the reflectivity of his telescope by tilting mirrors. He discovered the Saturn moons. He found out that unfilled telescope apertures can determine the angular resolutions, which gave birth to interferometric imaging. He discovered; Uranus in 1781, Titania in 1787, Enceladus in 1787, and Mimas in 1789 (Hoskin, 2008). He was able to suggest extraterrestrial life in the heavenly bodies. He believed that a species of people lived on the surface of the Sun and had extra-large heads, hence was able to engine the gusto of searching life on other planets. These speculations were able to make scientists find that there was an ocean on the surface of Mars which is a recent finding yet to be proven.


Born, M., & Wolf, E. (1999). Principle of Optics. Cambridge: Cambridge University Press.

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Holden, E. (1881). Sir William Herschel His Life and Works. New York: Charles Scribner’s Sons.

Holmes, R. (2009). The Age of Wonder: The Romantic Generation and the Discovery of the Beauty and Terror of Science. New York, NY: Harper Collins.

Hoskin, M. (2008). New dictionary of Scientific Biography. New York: Charles Scribner’s Sons.

Kuhn, T. (1970). The Structure of Scientific Revolutions. Chicago: The University of Chicago Press.

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