The fourth chapter “The Origin of Modern Astronomy” discusses the development of astronomy as scientific field. The author embraces the history from the very beginning, when humans showed curiosity about the lights in the sky, and comes up with modern innovations. From the very first stages of development astronomers tended to understand the movements of the Sun and the Moon, planets and other events, whereas others tended to make precise measurements and to describe the motions of heavenly bodies.
Actually, the author distinguishes the following periods in historical development of astronomy: classical astronomy, Copernicus’ times, planetary motion, Galileo Galileo’s times and Isaac Newton’s ideas.
Ancient philosophers believed that our Earth was centre of the universe, but they assume the Earth remained unmoving. Heavens were perfect and, therefore, the circle was assumed to be the only perfect geometrical form. The key idea was that heavens were moving in uniform circular motion.
Further, Aristotle argued that the starts, the moon and the sun were carried around the Earth.
It was Copernicus who had revised ancient theory of the Earth and its motion. Copernicus devised a heliocentric model with the sun in the centre and stressing that the Earth was rotating on its axis. The Earth was believed the circle the sun within the year. Tycho Brahe offered his own views on the motion of our planet. According his model, the sun and the moon circled the Earth, whereas others planets circled the sun.
Tychos’ observations were inherited by Kepler who discovered three laws of planetary motion.
Further, Galileo is known to have discovered the telescope, but he was condemned by Inquisition. He discovered the phases of Venus, the mountains of the moon, the satellites of Jupiter, etc. Finally, Isaac Newton also changed humanity’s views on nature as he discovered three laws of motion and, what is more important, the law of gravity.
The fifth chapter provides definition of light and discusses visual-wavelength telescopes, special instruments, radio telescopes and astronomy from satellites. Light is defined as “the visible form of electromagnetic radiation, an electric and magnetic disturbance that transports energy at the speed of light”. (ch. 4) Electromagnetic spectrum is know to include X rays, gamma rays, visible light, ultraviolet radiation, radio waves and infrared radiation. A photon is a particle of the light and it is defined as a bundle of waves.
Photon may act as a particle and often as a wave. Actually, photon carries energy to the wave, but everything depends on the wavelengths. The length of the wave is ranging from 400nm to 700nm. Infrared and radio photons have longer wavelength, whereas ultraviolet and x rays have shorter wavelengths and carry, therefore, more energy. In astronomy telescopes are used for gathering light, seeing the tiny details and magnifying the necessary image. Discovery of telescope has significantly contributed the field of astronomy.
Astronomers are interested in building telescopes with larger diameters as it offers new opportunities and possibilities for observations. There are many types of telescopes and each of the serves particular functions. For example, refracting telescopes are equipped with a lens that bends the light focusing it on the necessary image. Reflecting telescopes are equipped with mirror that focuses the light – such telescopes are less expensive than refracting and radio telescopes.
Observations are built on high mountains because the air is steady and you see well. Radio telescopes are the most popular among astronomers because they are able to detect cool hydrogen in the space. Moreover, they it is possible to see through the dusk and to analyze invisible processes. Radio telescopes consist of an antenna, disk reflector, data recorder and amplifier. However, radio telescopes have poor resolution because of the wavelength. Atmosphere of the Earth is transparent only in the two wavelengths and, therefore, telescopes must go into space.
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