Why the sky changes colour

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Slide 1

Why Does the Sky Change Colour as the Day Progresses?

Chitra Patil Mr. McClure SCH 4U0 18 December 2013

Slide 2

Every colour change in sky is related to light and atmosphere Colour is what the human eye perceives when light is given off

Slide 3

Light

Slide 4

Light

Light waves are electromagnetic energies (electromagnetic spectrum!)

They have different waves and frequencies

Long wavelength = low frequency + energy

Travels at 299,792 km/sec (speed of light)

Slide 5

1. Light (cont’d)

Visible light looks white:

White is made up of different colours (monochromatic light)

Each colour is related to size of wavelength, frequency, and energy

Sun’s colours are arranged from short to long

Light with shorter wavelengths (ie: blue) are more easily absorbed in sky

Rayleigh scattering: process of absorbing light and scatter particles

Slide 6

Atmosphere

Slide 7

Atmosphere

Molecules present:

Carbon dioxide

Ozone

Hydrogen gas

Nitrogen gas

Oxygen gas

When light is shone, N2 gas and O2 gas will absorb the most energy…

Let’s focus on these

Slide 8

Atmosphere (cont’d)

Called fluorescence

Electrons in N2 gas and O2 gas will be excited

Electrons become promoted to higher sublevel

They have a time-frame for which they can stay excited

Once reached, it may fall down energy sublevels or entire energy levels

Photon is released

F L U O R E S C E N C E

Slide 9

Atmosphere – Fluorescence (cont’d)

Oxygen gas and nitrogen gas bright-line emission spectra

This is [half of the reason] why sky is blue!

Slide 10

Atmosphere (cont’d)

Atmosphere is thicker when it’s closer to the Earth (gravitational pull)

This is why horizon is another colour

More atmosphere = more molecules to scatter light

Thickness determined by weather patterns and human factors

Light travels straight until it hits an atmosphere particle

ie: when light hits water molecule, water acts as a mirror and reflects light wavelengths