For us, light is an extraordinary phenomenon that illuminates our world and makes it visible. What would we do without it? Since we first opened our eyes, humans have worshipped the Sun as a god of light and a source of life and security. The emergence of rational thought brought with it a need to question the nature of this phenomenon. So what exactly is light?

Light is a form of energy produced by matter. To understand how light is created, we must first take a look at atoms, the building blocks of matter.

An atom somewhat resembles a beehive with a swarm of bees buzzing around it. The beehive represents the nucleus of the atom and the bee swarm represents the clouds of electrons that circle the nucleus.

An atom’s nucleus and electrons share the distinctive property of being electrically charged, but with opposite charges: the nucleus has what is known as a “positive” charge whereas electrons have “negative” charges. In the world of atomic particles, the adage holds true that opposites attract and thus the nucleus and electrons are mutually attracted to each other within the atom.

There is an important dif Read More
For us, light is an extraordinary phenomenon that illuminates our world and makes it visible. What would we do without it? Since we first opened our eyes, humans have worshipped the Sun as a god of light and a source of life and security. The emergence of rational thought brought with it a need to question the nature of this phenomenon. So what exactly is light?

Light is a form of energy produced by matter. To understand how light is created, we must first take a look at atoms, the building blocks of matter.

An atom somewhat resembles a beehive with a swarm of bees buzzing around it. The beehive represents the nucleus of the atom and the bee swarm represents the clouds of electrons that circle the nucleus.

An atom’s nucleus and electrons share the distinctive property of being electrically charged, but with opposite charges: the nucleus has what is known as a “positive” charge whereas electrons have “negative” charges. In the world of atomic particles, the adage holds true that opposites attract and thus the nucleus and electrons are mutually attracted to each other within the atom.

There is an important difference between bees and electrons: bees can fly wherever they want around a beehive but electrons cannot roam freely around the nucleus of an atom. In fact, despite their electrical attraction to the nucleus, electrons are restricted to specific orbits (scientists call them “orbitals”) that lie at fixed distances from the centre of the atom.

Although an electron cannot randomly occupy positions within an atom, it can nonetheless change its distance from the nucleus by changing its energy level. To do this, its energy content must be modified to match the energy level of the new orbit that it will enter.

In a manner of speaking, photons and electromagnetic waves are synonyms, and in everyday terms they are simply referred to as “light”. In fact, a photon can be thought of as a “particle of light” and an electromagnetic wave as a “lightwave”.
For example, to move from a distant orbit into a closer orbit, the electron must eliminate some of its energy. The energy released is partly electrical in nature and – as with all negatively charged bodies – partly magnetic. This excess energy is released by the electron in the form of an energy packet known as a “photon”.

© 2006 An original idea and a realization of the ASTROLab of Mont-Mégantic National Park

Colour diagram showing the parts of an atom, the nucleus, electrons and the orbits of electrons

An atom.

ASTROLab of Mont-Mégantic National Park

© 2006 An original idea and a realization of the ASTROLab of Mont-Mégantic National Park


Photon

A photon is an energy particle that has no mass and moves at high speed. When a moving photon interacts with matter, it does so as a wave, like a wave moving across the surface of water. These waves are known as “electromagnetic waves” because they display both electrical and magnetic components.

ASTROLab of Mont-Mégantic National Park

© ASTROLab/Mont-Mégantic National Park


Colour video of Hubert Reeves in front of images of space

Hubert Reeves talks about light.

Light is about seeing things. When I see you, it’s because there is light. I cannot see light itself, but thanks to the light you emit, I can see you. If we discuss light in physics terms, we have known since Maxwell’s time that light is a wave, an electromagnetic wave. In other words, light represents variations in a magnetic field. To this, quantum physics has added the notion of a photon: light is also particles, tiny particles that leave a source and move towards you. The question of how light can be both a wave and particles at the same time is answered by quantum physics, but I won’t give you the answer right now because we would be here for a very long time! What we usually tell people (and I quite like this way of putting it) is that light behaves as particles when you’re looking at it, and as a wave when you’re not!

ASTROLab/Mont-Mégantic National Park

© ASTROLab/Mont-Mégantic National Park


In 1665, Francesco Maria Grimaldi, an Italian Jesuit priest, conducted a simple experiment the results of which went on to occupy the minds of several generations of physicists, including Newton and Einstein.

The experiment consisted of light entering a dark room through a small slit and projecting onto a white screen. Grimaldi’s objective was to test if the width of the beam was the size predicted by the light beam’s geometrical path.

To his great surprise, Grimaldi found that the beam of light illuminating the screen was larger than expected. Strangest of all, however, was that the light was no longer white, but became two or three rays of different colours.

Without knowing it, Grimaldi had conducted the first experiment into the splitting of light. He assigned the term “diffraction” to the phenomenon, a term that survives to this day.

Isaac Newton.Grimaldi later realized that diffraction is a phenomenon that does not only occur when light is projected through a slit; instead, it occurs each time light strikes the edges of any object. Several scientists were interested in the effect but none could explain it. Th Read More
In 1665, Francesco Maria Grimaldi, an Italian Jesuit priest, conducted a simple experiment the results of which went on to occupy the minds of several generations of physicists, including Newton and Einstein.

The experiment consisted of light entering a dark room through a small slit and projecting onto a white screen. Grimaldi’s objective was to test if the width of the beam was the size predicted by the light beam’s geometrical path.

To his great surprise, Grimaldi found that the beam of light illuminating the screen was larger than expected. Strangest of all, however, was that the light was no longer white, but became two or three rays of different colours.

Without knowing it, Grimaldi had conducted the first experiment into the splitting of light. He assigned the term “diffraction” to the phenomenon, a term that survives to this day.

Isaac Newton.Grimaldi later realized that diffraction is a phenomenon that does not only occur when light is projected through a slit; instead, it occurs each time light strikes the edges of any object. Several scientists were interested in the effect but none could explain it. The answer was not long in coming, however, and it was Isaac Newton himself who would provide the explanation.

In 1662, Newton began his own optical experiments. One of his first projects was to construct a refracting telescope. He polished lenses and attempted to improve the instrument by getting rid of the coloured fringes that would appear on the margins of his images (he did not succeed and decided instead to develop a mirror-based reflecting telescope).

In 1666, during one of his optical experiments, Newton passed sunlight through a prism and split the light beam into different colours, like what he observed along the edges of his optical lenses. Others before him had conducted similar experiments, but Newton was the first to understand that white light consists of a mix of light rays, each with a different colour.

Newton also understood that white light can be separated into its components because each ray of colour is deviated by the glass of the prism by a different amount. He realized, for example, that red light is consistently less deviated than violet light.

As a result, Newton understood that when white light passes through a transparent medium (like air) into another (like glass), its components are deflected the first time according to their colour, and once again when they reemerge (back into air, for example). This creates a spread of coloured light rays from red to violet, like the colours of the rainbow.

This ordered separation of coloured rays is known as the “spectrum”. The spectrum of white light consists of six basic colours arranged in a specific order: red, orange, yellow, green, blue and violet.

Although Newton understood that a beam of light of a particular colour is always deviated by the same amount, he did not appear to understand why this is so. More than a century would pass before another British scientist by the name of Thomas Young would provide part of the answer.

© 2006 An original idea and a realization of the ASTROLab of Mont-Mégantic National Park

Painting of Francesco Maria Grimaldi

Francesco Maria Grimaldi.

Scienzagiovane - Bologna University web site for Science Communication

© Scienzagiovane - Bologna University web site for Science Communication


Colour painting of Isaac Newton

Isaac Newton.

Web Gallery of Art/http://www.wga.hu/

© Web Gallery of Art/http://www.wga.hu/


Colour image of white light entering a prism and splitting into the colour spectrum

Separation of white light by a prism.

Steve Smith/www.vislab.usyd.edu.au/

© Steve Smith/www.vislab.usyd.edu.au/


Learning Objectives

The learner will:
  • identify recent contributions, including Canada’s, to the development of space exploration technologies;
  • describe in detail the function of Canadian technologies involved in exploration of space;
  • draw a solar system with all its components;
  • establish the link between atoms and light using different instruments.

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