J. E. van Zyl’s scientific contributions

Besides the method of naming stars, described on page 165, it was decided that capital letters before the genitive of the Latin name of the constellation be used only from A to Q. Letters from R to Z were to be reserved for variable stars, such as R Coronae Borealis, U Geminorum, etc.

Good progress was made in the development of the telescope during the first half of the 17th century. The first telescopes were refractors, having an objective lens and ocular, or eyepiece, on the optical axis. The principle of the refractor is illustrated in Figure 4.1.

Unveil the Universe includes material on almost every aspect of astronomy, beginning from first principles. It is unique in providing a level of scientific accuracy and detail found in no other introductory book, in addition to a wealth of material on instruments, theory, observation, space exploration, and cosmology. It is encyclopaedic in the breadth of its coverage, yet still contains detailed explanations of the underlying theories. With its many colour illustrations it will capture the intere st of any reader, and the clear, concise text provides the reader with a fascinating, easy-to-read, and scientifically accurate description of the fundamentals of astronomy.

When the telescope came into use, a nearly endless series of discoveries followed. In one of the unpublished manuscripts of Thomas Harriot, mention is made of the fact that he saw Jupiter’s four large moons before Galileo mentioned his discovery in 1610. Harriot also discovered sunspots. Galileo kept his discovery of sunspots secret, out of fear for his life! How could he dare say that the immaculate Sun had blemishes? In 1665 Christiaan Huygens discovered the large moon of Saturn, Titan. Giovanni D. Cassini (1625–1712) discovered a gap in Saturn’s rings. He also discovered four of Saturn’s moons: Iapetus (1671), Rhea (1672), Dione and Tethys (1684). In addition, he made very careful measurements of the periods of Jupiter’s large moons. This enabled Olaus C. Rømer (1644–1710) to make the first determination of the velocity of light (Figure 5.1). Rømer noticed that the times at which the four moons disappeared behind Jupiter became systematically later as the Earth moved away from its position of opposition, E1 (Figure 5.2), to the other side of the Sun, E2. As the Earth came back towards opposition, the times became earlier.

On a clear, moonless night, away from city lights, one can see a broad streak of light spanning the heavens. During the northern winter months, it stretches from south to north, eastwards of the well-known constellation Orion. In the summer months, it stretches from the Southern Cross, through the tail of Scorpius, northwards to Cygnus. This faint streak of light is the Milky Way. The Greek word for it, Galaxias, is derived from “galaktos”, like milk. From this the word Galaxy has been derived. The Galaxy includes all the stars, planets, pulsars, nebulae and much more.

The year 1957 was International Geophysical Year, during which scientists of many nations co-operated in research on the Earth and its environs. On 4 October 1957, the world stood amazed when it was announced that the first artificial satellite, Sputnik, had been launched and that it was revolving in a stable orbit with perigee (nearest point to Earth) of 228 km and apogee (furthest from Earth) of 947 km.

From their fairly safe haven among the lakes where the Mediterranean Sea now divides Africa from Europe, our ancestors were able to view the starry sky at night and were enthralled by the brilliant flickering of the stars. They were not entirely safe because their spaceship “Earth” was subject to dangers from storms, lightning, earthquakes, floods and volcanic eruptions — phenomena which unleashed tremendous power.

The first addition to the five planets that were known since antiquity was made by William Herschel (Figure 7.1). On 13 March 1781 he noticed a bluish-green spot in the constellation Gemini. At first, he thought it was a comet, but on subsequent nights he saw that the motion of the body was not like that of a comet. It had to be a planet!

The stars do not appear to be of equal brightness. About 125 BC, Hipparchus made the first classification of stars according to their brightnesses. His predecessor, Aristarchus (310–230 BC), had proved that the Sun, Moon and planets are at varying distances from the Earth, and that they do not move equally far from the Earth against a crystal sphere, as Aristotle had stated.

The next step in deciphering the secrets of the Universe was made by Nicolaus Copernicus (1473–1543). Although a priest in the Roman Catholic Church, he spent many years studying the movements of the Sun, Moon and planets against the background of stars.