Light Dispersion and Refraction

Newton's Discovery About Light

• Isaac Newton demonstrated in 1666 that white light could be split into different colors using a glass block shaped like a triangle.
• The colors produced make up white light.

Spectrum

• The range of colors within white light is known as a spectrum.
• The colors in a spectrum appear to merge into each other.
• The seven colors in the spectrum are red, orange, yellow, green, blue, indigo, and violet.
• The acronym "ROY G BIV" can be used to memorize the order of the spectrum colors.

Dispersion

• Dispersion is splitting light into its constituent colors.
• Dispersion occurs due to refraction, with each color being refracted at a slightly different angle.
• A triangular prism can be used to observe dispersion. Prisms are solid shapes.
• Passing white light through a prism results in refraction.
• Violet light is refracted at the largest angle.
• Red light is refracted at the smallest angle.

Rainbows

• Rainbows form through the dispersion of light by water droplets in the air and reflection from inside the drops.
• Requirements to see a rainbow: sunlight, rain (or small water droplets in the air), and the sun behind the observer.

Primary Colours of Light

• All other colors of light are derived from three primary colors, which are the ones that cannot be created by mixing other colors.
• The primary colors of light are red, green, and blue; different from the primary colors in paints.
• Red + green light makes yellow light.
• Red + blue light makes magenta light.
• Blue + green light makes cyan light.
• Red + green + blue light makes white light.
• Combinations of the three primary colors of light produce the colors on mobile phones, computers, and televisions.

Subtracting Colours of Light

• Colored filters can remove colors from light, allowing only light of a specific color to pass through which is called transmission.
• Other colors that don't pass through are absorbed.
• Traffic lights are one example of subtraction.
• Each traffic light uses three identical white lamps with a colored filter for red, yellow, or green in front of them.

Seeing Colours

• Non-luminous objects don't produce their own light.
• The color of a non-luminous object is determined by which light it reflects.
• Reflecting only yellow light will cause a flower to be seen yellow when under white light.
• A white object reflects all colors in white light equally.
• A black object absorbs all colors in white light.

The Milky Way

• The Milky Way is the galaxy containing our solar system that appears as a milky band across the night sky.
• The term "galaxy" originates from the Greek word for "milky."
• Our galaxy looks like a band because the Milky Way is classified as a spiral galaxy.
• Most of the stars visible at night are located within the Milky Way, which contains an estimated 250 billion stars, inclusive of our Sun.
• The Universe encompasses all of space and its contents, containing other galaxies with different shapes.
• Galaxies can be classified as elliptical or irregular based on their shapes.

What Are Galaxies Made Of?

• Galaxies are composed of stellar dust, gas, stars, and solar systems, held together by gravity. Stellar dust: dust found in space. The gravity maintaining a galaxy is strong, due to galaxies possessing large mass.
• The Milky Way's mass, which is estimated to be 1,500,000,000,000 times the mass of the Sun, would take more than 100,000 years to cross even at the speed of light (300,000 km/s).

How many galaxies are there?

• Scientists have estimated the number of galaxies in the Universe by counting the galaxies in a part of space.
• It is estimated that there are 100 billion galaxies in the Universe.
• Estimates may not be accurate because the volume of the Universe is unknown. The closest known galaxy to the Milky Way is called the Canis Major Dwarf Galaxy. The Canis Major Dwarf Galaxy is elliptical in shape and a distance of 240,000 million million km away.