Simulated Space Travel

Simulated Space Travel

The man-made planetarium sky provides an excellent setting for presenting achievements in the greatest adventure of all time – the physical conquest of space. A variety of planetarium shows con be devised to stimulate space travel and, in the light of present knowledge, give a preview of conditions on the moon and other worlds. The younger generation, for whom space ships and interplanetary expeditions have become fairly common topics of conversation, take to these shows like ducks to water. But once again eager curiosity and enthusiasm have to be directed toward the goal of understanding and critical evaluation.

The growing general interest in space travel and space studies led Carl Zeiss Jena to introduce a planetarium instrument that was more versatile and sophisticated than earlier models. It can be used to stimulate orbital flight around the earth and also to portray the sky and the movements of the sun and planets as seen from the moon. When spectators see these effects they can also be persuaded into thinking that they are astronauts on their way to a successful lunar landing.

At the Morehead Planetarium, University of North Carolina, Chapel Hill, the Zeiss instrument was specially adapted to brief astronauts training for Project Mercury. In the first stages of the instruction the astronauts learned to identify stars and constellations, particularly those adjacent to the proposed orbital space path. A similar although greatly simplified training was available to space-minded youngsters at the McLaughlin Planetarium in Toronto, Ontario, Canada. They may never become astronauts but they should at any time and place be able to orientate themselves by the stars.

Deep Space. Illustration by Elena

Star Navigation

Long ago sailors learnt to steer by the stars. Later, they tried to fix their position in uncharted waters by using the stars, but progress in this field was slow and difficult. In the 18th century two great inventions, the sextant and the chronometer, together with the introduction of more accurate astronomical tables, heralded big advances. Among the latter were some of the modern methods in star- or astronavigation which made possible the determination of both latitude and longitude. These quantities can now be obtained from aboard ship by making simultaneous observations of the altitudes of two stars, or from two altitudes of the same star taken at different times.

Lectures in astronavigation can play an important part in the life and work of a planetarium. The planetarium sky represents part of a celestial sphere and can therefore be used as a background for showing the celestial meridian, celestial equator, part of the right ascension-declination framework, and the nautical of PZS triangle. Consequently, it is an easy matter to illustrate concepts like altitude, azimuth, hour angle, and the angles of a spherical triangle. The ecliptic and mean sun can also be shown, thereby providing a good basis for demonstrating basic ideas and methods in the measurement of time. To what extent these and similar facilities are used in any given planetarium will depend largely on the demand. They should be of particular interest to sailors, yachtsmen, pilots, surveyors and students of astronomy. At a more popular level, its highly instructive to watch the planetarium sun move along the ecliptic and/or through the constellations of the zodiac. By compressing time so that the events of a year occur in a matter of minutes, and by keeping the sun on the meridian, the sun is seen to swing up and down the meridian as the seasons progress. The movements demonstrate in a most striking way the significance of the equinoxes and solstices, and the precise way in which the earth revolves around the sun. Alternatively, the planetarium sun can be kept permanently below the horizon, thereby bringing about a state of perpetual night. In this way the changing aspect of the night sky as seen from Toronto or any other place for the period of a whole year con be shown.

Variety with Integrity

Constellation figures, eclipses of the sun and moon, the phenomenon of the harvest moon, artificial satellites, space probes, comets, the precession of the equinoxes, the motions of the planets about the sun, sunspots, meteor showers, star clusters, nebulae, galaxies… these and many more things can be seen in the planetarium. In fact, anything that pertains to astronomy is appropriate material for presentation in the star theatre. Yet it would be comparatively easy to produce a series of spectacular although completely unrelated effects. The stately panorama of the starry skies could be paraded as a meaningless jumble of events. Sun, moon, and planets can be made to career across the dome in a fantastic way, the precessional cycle of 25,800 years can be compressed into one and a half minutes, and eclipses and constellation figures can be made to order by flicking appropriate switches. These things, however interesting in themselves, must be presented in context, that is, in their proper places and with suitable introduction and straightforward explanation. Only by exercising restraint and due care can astronomical events in the planetarium be invested with meaning and presented with integrity.

Many large-scale planetariums are not just a theatre of the skies. Exhibits and displays in the exhibition areas supplement the demonstrations given in the star chamber. A reference library and information centre enables books on astronomy, star charts, star atlases, moon maps, and astronomical photographs to be studied at leisure. In the basement a lecture room capable of seating dozens of people is usually available for meetings, courses, and special lectures on astronomy. Also optical workshops are usually operated in the building, where members of the public, at relatively low cost to themselves, can grind, polish, test their own telescope mirrors under expert guidance. A sales desk offers literature on astronomy to suit almost every need, particularly books for children, photographs of astronomical objects, seasonal star charts, star finders, and literature about exhibits, facilities and future events…

Another Sense of Space and Time

Another Sense of Space and Time

Planetarium shows can add another dimension to our thinking. They allow us to make journeys in imagination far from the earth and to acquire a deeper sense of space and time than that provided by the world around us. These shows enable us to look back at mankind, to contrast human trials and endeavours with the impersonal cosmic background and, indeed, to lose sight of man altogether. Under their influence we find ourselves adopting a universal rather than local viewpoint. What we once called the physical universe, the universe of ordinary experience, is seen to be only a tiny part of a much greater complex. Man, and in turn, the earth, the solar system and the entire galaxy of stars, shrink almost to nothing. What we once thought was a long period of time in human affairs is seen to be no more than a fleeting moment. In astronomy a million years is as brief as the tick of a cosmic clock.

Since a major aim of a planetarium show is to inform, we must not feel overawed, and still less overwhelmed, but what we see and hear. Rather, we can appreciate more fully the accomplishments of men, and marvel that creatures so small should, in so short period of time, have discovered so much. We begin to echo the sentiments of the German philosopher Immanuel Kant. “Two things,” he wrote, “fill my mind with ever new and even greater wonder and reverence, the oftener and the longer I allow my mind to dwell on them – the starry heavens above, and the moral law within me.”

A blue sky. The modern sky, whether real or artificial, is not so much a sky to look at as one to think about. Illustration: Elena

A Stirring Spectacle

The planetarium is a first-class medium for introducing young and old alike to the basic components and movements of the sky. But it is one thing to see a starry sky and quite another to be able to interpret its various parts in the light of modern knowledge. Appearances may greatly impress us, yet for all their grandeur they are only appearances. Our main concern in astronomy and, therefore, in what is shown in the planetarium, must be with interpretation and understanding, with causes and laws, and with the probable nature and structure of the universe of stars.

The modern sky, whether real or artificial, is not so much a sky to look at as one to think about. Visitors who come to a planetarium merely to see the sun, moon, planets and stars “perform” usually are disappointed. But those who turn both eyes upwards will have an experience as mentally stimulating as it is visually remarkable. As Dr. Philip Fox, first director of the Adler Planetarium, Chicago, once wrote: «Visitors come to see a stirring spectacle, the heavens brought within the confines of museum walls. Not a trivial plaything, a mimic aping firmament, but the heavens portrayed with great dignity and splendour, dynamic, inspiring, in a way that dispels the mystery but retains the majesty”.

McLaughlin Planetarium

The McLaughlin Planetarium

(the planetarium was closed in 1995, this text has an historical value)

Royal Ontario Museum, Toronto

The planetarium at the Royal Ontario Museum is only one of Robert Samuel McLaughlin’s many philanthropic gifts. A McLaughlin Foundation finances postgraduate study overseas for about 40 Canadian doctors yearly; he has given generously to hospitals, the Red Cross, the Community Chest, the Boy Scouts, and to numerous civic projects in Oshawa, Ontario.

Mr. McLaughlin was born September 8, 1971 at Enniskillen, Ontario. In 1876 his father’s carriage-building plant was moved to Oshawa and the young McLaughlin served his apprenticeship in it as an upholsterer. When automobiles began to appear, Samuel persuaded his father to switch to auto production. The McLaughlin Motor Company was formed in 1907 with R.S. McLaughlin as president. In 1918 the company was sold to General Motors Corporation and Mr. McLaughlin was named president of General Motors of Canada. In 1945 he became company chairman. Mr. McLaughlin was a director of several corporations and he was Life Honorary Colonel of the Ontario County Regiment (Tanks). His gift of the planetarium contained only one stipulation: that it be the best. Visitors will agree this request was fulfilled.

Seeing Stars

Just over 200 years ago, James Ferguson, a humble Scots farm lad, made his first attempts to know the stars. “I went into a field with a blanket over me”, he wrote, “lay down on my back, and stretched a thread with small beads upon it at arm`s length between my eye and the stars.” He moved the beads so they covered various bright stars and then transferred their positions to paper. In this way he came to know and to love the stars so well that astronomy became his life-long interest.

In those old days star maps and books were few in number and known only to the educated. People who, like Ferguson, wished to learn something about the stars, had to study and interpret the night sky for themselves. Today, in contrast, several hundred people at a time can seat in comfort beneath an artificial sky and have its wonders described to them in clear straightforward terms.

This approach to an age-old science is provided by the planetarium, where on a great dome the night sky can be reproduced with such remarkable realism that spectators feel they are sitting outdoors on the clearest of nights. Some 3,000 stars shine overhead and the Milky Way spans the sky like a giant bridge of pearly light. At the touch of a switch, the sky turns slowly to bring into view more stars while others dip below the horizon. Perhaps the moon and one of the planets appear, perhaps a “shooting star” traces a lonely path, or polar lights flicker in the north. For the visitor, the auditorium is transformed into a “theater of the skies” in which the sun, moon, planets and stars are the actors and the vault of heaven is the stage.

The Zeiss Instrument

Most visitors to any planetarium are slightly overawed when they first see the Zeiss projector. This is not surprising. The massive dumb-bell looks like some double-headed monster of science fiction, especially when the lighting is low. This feeling is maintained even during a show, for there is still little to suggest that the stars and other objects on the dome are formed by the instrument at the centre. Yet, the performance of the instrument depends on the application of comparatively simple principles.

The Zeiss projector used in planetariums consists basically of a long dumb-bell supported by slender but extremely rigid steel struts. The two “balls” of the dumb-bell are hollow globes from which the stars are projected. The connecting lattice-work “bar” contains projectors for the sun, moon, and five naked-eye planets.

McLaughlin Planetarium building

Star Globes

Between them the two star globes project well over 8,900 stars, although only half of this number can be seen at any one time, the rest being hidden below the horizon. These stars are positioned relative to each other and graded in size to correspond to the stars in the real sky for our epoch. They include all the stars which can be seen by a keen eye on an exceptionally clear and dark night, a range which extends from the brightest to faint stars of magnitude 6.5. A visitor to the star theatre can see about 4,500 stars at any one time; in the real sky under good conditions he would see only 2,500 to 3,000.

The planetarium stars are the images of tiny holes punched in copper foil 0.015mm thick. The foil is the sandwiched between two glass plates to form what is known as a “star field plate”. To reproduce the different brightness of the stars in the real sky the holes range from 0.023 to 0.452 mm in 52 different sizes. Some of the star field planets also have small stippled areas to represent star clusters and nebulae visible to the unaided eye (e.g. the globular star cluster in Hercules, the Great Nebula in Orion, and the Clouds of Magellan). Illumination is provided by a 1500-watt lamp mounted at the center of each globe. Light from this is collected by 16 radially placed aspherical condenser lenses and passed through the same number of star plates with their associated f/4.5 Zeiss projection lenses.

The 16 projection lenses of each star globe together form a mosaic of 16 separate but completely integrated star fields. Each projector forms a pentagonal or hexagonal-shaped portion of the sky. Ideally the star field plates should be at the center of curvature of the dome. The fact that they are several feet away from the center means that their tiny holes have to be displaced by calculated amounts. Each star field plate has a built-in distortion, so to speak, which compensates for the effect of its distance from the center of the dome.

In earlier Zeiss Jena instruments only Sirius, the brightest star in the night sky had its own projector. This was partly because the projector was designed to illustrate the apparent displacement of a nearby star due to the diameter of the earth’s orbit (an effect known as annual parallax), and to the velocity of the earth in its orbit in relation to the finite velocity of light (ab effect known as the aberration of light). These effects can be illustrated with different stars. The brightest stars have comparatively small but bright disks and therefore look highly realistic. They possess their characteristic colours. Betelgeuse and Antares, for example, shine with a reddish light, Capella looks yellow, and Rigel and Spica have a blue colour.

A Moving Sky

The dumb-bell can be moved in three ways. The most important is rotation about a polar axis, or axis parallel to the axis of the earth. This reproduces the daily or diurnal motion of the stars and the regular succession of night and day. In nature the starry sky rotates once in about 24 hours. In the planetarium, the period is reduced to a maximum of 12 minutes, and is continuously variable down to about 30 seconds.

In another movement, generally referred to as the polar altitude motion, the dumb-bell is rotated on a horizontal east-west axis. This corresponds to a change in terrestrial latitude, and, like the diurnal motion, is continuously variable up to a maximum of 12 minutes for one complete turn of the dumb-bell.

The third movement takes care of the precession of the equinoxes. The term “precession” refers to a slow wobble of the earth as it rotates on its axis. The earth makes one complete wobble in 25,800 years, during which time a celestial pole makes one revolution about the corresponding pole of the ecliptic. One result of this is that the night sky will present a new face to people living in the far distant future. Different stars take turns in becoming the north pole star, and stars which for us rise slightly above the southern horizon will eventually disappear for thousands of years. Another result is that the verbal equinox moves along the ecliptic in a general east to west direction at a rate of about 1% degrees a century. To meet this requirement the dumb-bell is made to rotate on its long axis, and the precessional cycle can be reproduced in any period from one to 15 minutes.

Of course, during these movements the star images must be confined to the dome, otherwise they would run across the faces of spectators and spill themselves over the wall and floor. To achieve this each star field projector is fitted with a mechanical eyelid. As the projector approaches the level of the planetarium skyline a gravity-controlled shutter moves across the aperture of the lens and gradually reduces the brightness of the star images until they disappear completely. Similar shutters are also fitted to the approximately 20 individual star projectors.

Zeiss projector installed in Montreal Planetarium

Sun, Moon and Planets

Inside the lattice structure connecting the star globes are projectors for the sun, moon, and five naked-eye planets. The projectors for Saturn, the sun and the moon occupy the upper or northern cage; those for Mercury, Venus, Mars and Jupiter occupy the southern cage. The projectors are all doubles or paired, for the struts of the lattice, although thin, would otherwise cause appreciable dimming. Each pair of projectors is designed and aligned to produce a single, sizable disk of light. The image of Mars is red, Jupiter appears with cloud belts, and Saturn with a semblance of rings. Mercury and Venus do not show phases but are distinguishable in size and, along with Mars, have brightnessnes which are in relation to their distance from the earth and also to their phase angles.

The planetarium sun is formed by four projectors – two in tandem to produce the sun’s disk, and two to form a halo or aureole of diffuse light around the sun. The first two also contain glass prisms which reflect some of the light to two small supplementary projectors to produce the Gegenschein, or counter-glow, a nebulous patch of light diametrically opposite to the position of the sun.

The phases of the moon are formed by a projector which contains a concave mirror about which rotates a close-fitting hemispherical cap or shutter. As the cap rotates on its axis its projected edge gives rise to the moon terminator, or edge between light and darkness. In nature we see the sun from a moving earth. The sun therefore appears to move in a west to east direction against the background of stars, but the motion is by no means uniform owing to the slightly elliptical form of the earth’s orbit. 

The sun’s path, or the ecliptic, is inclined at about 23 ½ degrees to the celestial equator. This behaviour of the sun is well shown in the planetariums, for there the sun can be seen in a darkened sky along with the stars. The correct orientation of its path is assured by the design of the Zeiss instrument, the axis of the dumb-bell being at all times inclined to the polar axis at an angle of 23 ½ degrees.

In a planetarium the celestial drama is produced by a composite optical projector mounted at the center of the circular theatre. This giant instrument, made by the firm of Karl Zeiss, is shaped like a dumb-bell and contains nearly 150 individual projectors. The whole programme is operated by remote control from the lecturer’s console near the north wall of the theatre. When the dumb-bell with its projectors is made to move in one of several prescribed ways, the images on the dome move collectively to reproduce the general march of the stars and other objects across the face of the sky.

The projectors for the sun, moon and five naked-eye planets (Mercury, Mars, Venus, Jupiter and Saturn) can also be moved relative to the dumb-bell. When this is done, the corresponding optical images drift in a general west-to-east direction among the planetarium stars, and the spectator sees what is tantamount to a moving picture of the universe.

So great is the versatility of the Zeiss projector that it can faithfully reproduce the starry sky as seen from any place on earth and for any time – past, present, or future. In a matter of minutes the night sky for Toronto can be changed for that at the North Pole, where the stars neither rise nor set, or for one far south, where the Southern Cross and Clouds of Magellan rise high. With the earth as a footstool and time at one’s command, the effects of the passage of centuries can be squeezed into minutes. One can see the night sky of 14,000 A.D. when the bright star Vega will be the North Pole Star and the Big Dipper will no longer remain permanently above the skyline of New York. Or one can, in effect, go back 20 centuries to stand with the shepherds on the hills outside Bethlehem, and bridge even 40 centuries to see the stars familiar to Abraham as he gazed across the plains of Chaldea.

The instrument of the McLaughlin Planetarium (today closed) was the first Carl Zeiss Jena planetarium projector to have motion about a vertical axis. This was achieved by mounting its supports on a turntable which could be rotated either clockwise or anti-clockwise through 360 degrees by a variable speed motor. The turntable, and hence the entire instrument, runs on rubber wheels and has an associated sound-baffle system for noiseless operation. As the instrument rotates it can be made to project the letters of the four compass points on the base of the dome, so the problem of N.S.E.W. orientation never arises. By using this motion it is possible to demonstrate the aspect and apparent movement of the starry sky as seen from a spacecraft, a feature which enables spectators to escape more easily from the restrictions of the old earth-centered viewpoint.

Planetary Motions

Planetary Motions

Planetarium Sky

We see the planets from a moving earth. Their earth-centered or geocentric movements are therefore a combination of their own individual motions through space and the motion of the earth about the sun. In addition, the planes of their orbits are inclined at comparatively small angles to the plane of the earth’s orbit. Relative to the fixed stars, therefore, the planets are seen to trace quite complex paths. They advance in right ascension, become stationary, and then regress, moving in pendulations and loops which lie near the ecliptic.

All these geocentric movements can be seen in any planetarium. They are made possible in principle by mounting each pair of planet projectors on two concentric gear plates. One plate is mechanically coupled to the sun projector and represents the orbit of the earth. The other moves at a different rate and represents the orbit of the planet. Pins on the gear plates represent the relative positions of the earth and the planet. By connecting the pins with an adjustable rod arranged parallel with the projectors, the latter can be made to reproduce the geocentric aspect of the planet in the planetarium sky. For showing the motion of Venus only two gear plates are required. The other planets, owing to the more eccentric or oval form of their orbits, require three.

The planetarium sun can be made to circuit the ecliptic once in any time with the range 15 seconds to 10 minutes. When this “annual motion” is used it is automatically coupled with that for precession but is quite free from the diurnal motion. When the diurnal motion is used it is automatically coupled with the annual and precessional motions. On the other hand, the precessional motion can be operated on its own. In view of these accomplishments it is small wonder that Bauersfeld, when he designed the first fixed latitude instrument, covered 600 folio sheets with basic astronomical and technical calculations!

Added refinements

If a modern planetarium instrument is to merit the name “universal” it must be able to project more than just the sun, moon, planets, and stars. A planetarium sky would not be complete without a representation of the Milky Way. Star identification is helped by being able to project constellation figures, and various circles of the celestial sphere are important features. These and many other additions can be found in modern planetariums.

The Milky Way is formed by two drum-type projectors, one at the side of each star globe. A drawing based on photometric measurements of the Milky Way was photographed to form two diapositives, each of which was wrapped round a glass cylinder. Inside the cylinder is a lamp surrounded by a glass tube. The latter has a hollow wall half full of mercury which effectively screens off that part of the Milky Way beneath the horizon. Lenses are deliberately left out since the Milky Way is essentially an irregular band of faint, diffuse light.

At the extreme end of the dumb-bell, attached to each star globe, is a smaller sphere for forming constellation figures and a precession circle. The sphere has 16 projectors, each fitted with a gravity-controlled shutter. Also attached to the star globes are individual optical projectors which reproduce the light changes of three well-known variable stars – Delta Cephei; Beta Persei, or Algol; Omicron Ceti, or Mira. Further projectors on or near the dumb-bell reproduce the appearance and motion of Comet Donati 1858, moving clouds, the celestial meridian, celestial equator, part of the declination system, the ecliptic, nautical triangle, mean sun, horizon circles, compass points, and a geographical latitude map.

In addition to the main instrument, many planetariums contain a number of auxiliary projectors to show eclipses of the sun and moon, the total eclipses of the sun being accompanied by views of prominences and the corona, f.i. Others produce the artificial skyline, a shower of shooting stars, the main types of aurorae, and an earth satellite capable of motion along any prescribed path. One projector takes the form of an optical orrery and shows the solar system as seen from a viewpoint well outside the orbit of Saturn. When this is used spectators can watch the relative heliocentric motions of the planets and, by means of a “light line” which connects the earth and any other circling planet, see how these motions give rise to the geocentric paths of the planets.

A giant planet. The planets appear to describe loop-shaped paths against the background of stars. Illustration: © Elena

At the Console

During a planetarium show, the lecturer has remote control over each and every projector. Sitting at the console near the northern face of the dome, he acts as a guide for spectators seated in the theatre. Whether he is pointing out interesting objects in the night sky, illustrating the ways of the planets, or describing objects in deep space, the story he tells is dictated by the changes which he alone initiates in the planetarium sky. He seldom refers to notes and scarcely even reads from a script. He requires no light to find the controls. Like a car driver at night his hand reaches out unerringly to touch the required knob or switch. As in driving, full coordination comes with experience, but as the lectures drives the machinery in the planetarium he must maintain a running commentary of what is being shown. This means that before he gives a presentation he must memorize the proposed schedule of events, translate them into operations, and plan the general content, scope and level of his discourse.

The voice of the lecture, alive and compelling, is an integral part of planetarium experience. The lecturer identifies himself with his audience. He provides the interpretation, answers silent questions and anticipates new ones, appreciates the requirements and limitations of his audience, and never once loses sight of his main objective – to give an increasing number of people from all walks of life some insight into the nature, structure and extent of the astronomical universe. So although planetariums have projectors for their heart, their spirit is astronomy, and their life comes from the people who operate beneath their domes.

Courage of Kepler and Galileo

The courage of Galileo and Kepler in promoting the heliocentric hypothesis was not evident in the actions of others, even those residing in less fanatically doctrinal parts of Europe. For example, in a letter dated April 1634, René Descartes, then living in Holland, wrote: Doubtless you know that Galileo was recently censored by the Inquisitors of the Faith, and that his views about the movement of the Earth were condemned as heretical. I must tell you that all the things I explained in my treatise, which included the doctrine of the movement of the Earth, were so interdependent that it is enough to discover that one of them is false to know that all the arguments I was using are unsound. Though I thought they were based o very certain and evident proofs, I would not wish, for anything in the world, to maintain them against the authority of the Church… I desire to live in peace and to continue the life I have begun under the motto To live Well you must live unseen.

The connection between Holland as an exploratory power and Holland as an intellectual and cultural center was very strong. The improvement of sailing ships encouraged technology of all kinds. People enjoyed working with their hands. Inventions were prized. Technological advance required the freest possible pursuit of knowledge, so Holland became the leading publisher and bookseller in Europe, translating works written in other languages and permitting the publication of works proscribed elsewhere.

Adventures into exotic lands and encounters with strange societies shook complacency, challenged thinkers to reconsider the prevailing wisdom and showed that ideas that had been accepted for thousands of years – for example, on geography, – were fundamentally in error.

In a time when kings and emperors ruled much of the world, the Dutch Republic was governed, more than any other nation, by the people. The openness of the society and its encouragement of the life of the mind, its material well-being and its commitment to the exploration and utilisation of new worlds generated a joyful confidence in the human enterprise. This exploratory tradition may account for the fact that Holland has, to this day, produced far more that its per capita share of distinguished astronomers, among them Gerard Peter Kuiper, who in the 1940’s and 1950’s was the world’s only full-time planetary astrophysicist. The subject was then considered by most professional astronomers to be at least slightly disreputable, tainted with Lowellian excesses. Carl Sagan was grateful to have been Kuiper’student.

Universal Gravitation

Universal Gravitation

Copernicus had another great champion in Johannes Kepler, a German astronomer and mathematical genius whose study of the observations of Tycho Brahe led him to discover that the planets move in elliptical orbits. Kepler determined the nature of the motions in these orbits and in so doing dispensed completely with the Greek concept of uniform motion in a circle. The elaborate system of circles used by Ptolemy and Copernicus to account for the observed motions of the planets were reduced to six ellipses, and the solar system acquired its modern form.

The next major step was made between 1665 and 1687 by Isaac Newton who, from observation of a falling apple, deduced that the earth exerted a pull of “force of gravitation” on the moon. Under the action of this force the moon would simply fall to the earth but was prevented from doing so by its speed in its orbit. In a similar way, each planet was under the gravitational control of the sun. Newton`s calculations showed that since each planet moves in an eclipse, the force of gravitation varied directly as the product of the masses of the sun and planet, and decreased as the square of the distance between them increased.

Newton’s Telescope. Replica of Newton’s reflecting Telescope

Armed with this law Newton was able to put the theory of the tides, the precision of the equinoxes, the complex motions of the moon, and numerous other events on a sound dynamical basis. In effect he demonstrated that the principle and relationships found in terrestrial mechanics could be applied in celestial places. To him the physical universe was a great machine whose parts were controlled by the forces acting on them, but whose construction and working demonstrated the design and purpose of God.

Newton also established optics as a science. He invented and made a new type of telescope, the reflecting telescope, and discovered that the sunlight is composed of the different rainbow colours of the spectrum. Through the development of the first, astronomers were able to probe further into the immensity of space than ever before. Through the second they learned how to analyze starlight and discover the physical natures of the stars – their surface temperatures, chemical composition, sizes, masses and even how they shine.

Sir Isaac Newton (1642-1726)