The phenomenon of light has been a subject of investigation for the scientists since the ancient times. Many inquisitive minds devoted time and efforts to learn it and many theories explaining its nature were created. Not all of the theories proved to be true in the course of time, however, all of them contributed to the development of the modern view on this subject and creation of the recent light model recognized by the scientists.

The answers to the questions about the nature of light, the way it is produced, transmitted and at what speed have helped us understand the fundamental principles of our universe and has enabled advances in technology in areas such as lenses, fiber optics, and digital devises (Ackroyd, Anderson, Berg, and Martin 634).

The light is the source of information for astronomers who study light coming from the sun, stars, planets, moons, galaxies and other celestial objects no matter how far they are. The collected data gives the scientists an opportunity to investigate the universe and extract information about the nature of its objects (Seeds and Backman 75).

The phenomenon of light is of dual nature. It can act both like a wave and a particle. Different investigators such as Isaac Newton, Christiaan Huygens, Thomas Young, and others studied the phenomenon of light and its characteristics from different perspectives. The wave model described light as a stream of waves, the particle model – as a stream of particles (Ackroyd, Anderson, Berg, and Martin 639). In the course of history, both wave model and particle model were investigated and supported by much scientific evidences. Though, neither of the models separately could explain all the characteristics and behavior of light. This dilemma was solved by introducing an absolutely new theory. At the beginning of the twenties century, Max Planck proposed a quantum model of light, which was a combination of wave and particle models. The quantum model describes light as packets of energy, called photons. Each photon behaves in two ways – wave-like and particle-like (Ackroyd, Anderson, Berg, and Martin 639-641).

Light as a wave phenomenon is “an electromagnetic disturbance consisting of rapidly varying electric and magnetic effects” (Moche 32). The main characteristics of a light wave are wavelength and frequency, according to which, the types of light are distinguished. The visible spectrum ranges from 400 to 700 nanometers (10-9 m – a unit used to measure the wavelength) (Seeds and Backman 76). The visible spectrum can be accepted by human eyes, which sense the wavelength of light as colors. The short wavelength of the visible spectrum looks violet and long wavelength looks red. The visible spectrum is only a small part of the entire radiation spectrum. Infrared radiation, microwaves, and radio waves have longer wavelength and lie beyond the red end of visible spectrum. The types of radiation with short wavelength lie beyond the violet end of the visible spectrum. These are ultraviolet, X-rays, and gamma rays (Seeds and Backman 76).

Light can also be viewed as a stream of photons that carry energy from the source. “The amount of energy is inversely proportional to the wavelength. In other words, the longer the wavelength is the less energy a photon can carry” (Seeds and Backman 76). Energy is a notion describing light as a particle. The wavelength is a peculiarity of the light being a wave. The relationship between the energy and the wavelength shows and proves the dual nature of the phenomenon of light.

Speed is another peculiarity of light, which makes it a unique phenomenon. In the past, the speed of light was not a major question of consideration for the scientists as it was believed that the speed of light is infinite, and thus cannot be measured. The first person who tried to measure the speed of light was an Italian scientist Galileo. Unfortunately, he failed (Caes 5). The first person who succeeded in measuring the speed of light and proved its finiteness was Ole Roemer. The result of his measurements was the estimation of the speed of light to be approximately 2x108 m/s. The modern measurements are 3x108 m/s. Of course, the Roemer’s measurements in 1675 were not precise due to the lack of devices and technical means of that time, which are available for modern science (Crowell 794). However, this success was a big step to better understanding of the phenomenon of light. The speed of light is an absolute speed of the universe. It means that nothing in the universe can move at speed higher than the speed of light. The speed of light is constant. In nature, when measuring the speed, its velocities are added or subtracted, but the speed of light is an exception. It does not depend on the motion of the source of light or any other objects; it stays the same for all the observers (Grandy 1). This is a well-known and commonly accepted fact that was proved empirically. However, there is no answer to the question about the reasons of such constancy. According to Grandy, “light is a manifestation of cosmic unity”, meaning that light is the very thing that unites the universe and allows the numerous and diverse forms to emerge (2).

To conclude, the unique nature of light is still of a big interest for scientists. Any wave needs a medium like water or air to travel from the source outwards. Light, though having wave characteristics, does not require any medium to be transmitted. It means that light can travel in vacuum. The outer space is a vacuum and in this regard the ability of light to travel in space is of great importance because it is one of the reasons that made the appearance of life on our planet possible. Besides, the astronomers have the ability to explore the universe in all its diversity due to the investigation of light because light is almost the only source of knowledge about the nature of the sun, stars, and other celestial objects.

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