J. E. van Zyl’s scientific contributions

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.

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.

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.

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 In one of the unpublished manuscripts of Thomas Harriot, mention is made of the fact that he saw Jupiter’s four large moons before Galileo mentioned his discovery in 1610.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.

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.

The Universe, as revealed by the various instruments at the disposal of astronomers, is in the first instance a panorama of space. The speed of light and other electro-magnetic radiations is not infinitely great — it requires definite amounts of time to reach the Earth: 4.3 years from the nearest star; 2.2 million years from the nearest large galaxy, M31 in Andromeda; 5 to 18 thousand million years from the quasars. We therefore see these objects as they were, 4.3 or 2.2 million or 5 to 18 thousand million years ago. The greater the distance of an object, the further back in time we have to look in order to see it. The Universe is thus also a time panorama.

Situated about 150 million km from the Earth, the Sun occupies the centre of its planetary system. The mean distance of the Sun has been computed — by sending radar waves to certain planets and monitoring the reflected waves — as 149 597 870 km.

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.