Why the Sky Changes Colour
Written by Studio AM.
Your result
- Words per minute
- Score
- Pace
Words per minute mean something only with the score beside them. They describe this passage on this read. With fewer than 3 right, try the next slower pace.
Choose a pace and select Start. The passage is paced and timed, then the questions check what you understood. How pace mode works
Reading time 0:00
On a clear day, the sky overhead looks blue. Near sunset, the light around the sun can look orange or red. Both colours are linked to scattering: air molecules redirect some of the sunlight passing through the atmosphere.
Sunlight contains different wavelengths. Nitrogen and oxygen molecules are much smaller than these light waves, and they scatter shorter wavelengths more strongly than longer ones. The process is biased toward the shorter wavelengths. Blue light is therefore scattered more strongly than red light. Some of that scattered blue light reaches our eyes from across the sky.
At sunset, sunlight travels through a longer path in the atmosphere. More blue light is scattered out of the direct beam before it reaches us. Longer wavelengths make up a greater share of the remaining light, so orange and red become more noticeable near the sun. These colours were already in the sunlight; the longer path changes their relative share of the visible spectrum.
Clouds and particles can also affect the colours. Scattering by air molecules explains the basic clear-sky pattern, not every detail of every sunset.
The passage is hidden while you answer. It comes back with your result.
Questions
Choose an answer. The explanation appears after you answer.
-
Question 1 of 4
What does the passage set out to explain?
The answer is A: How a blue sky and an orange sunset arise from the same scattering of light.
The passage uses the same process, scattering, to explain blue light across the daytime sky and orange or red light near sunset.
-
Question 2 of 4
Why can light near sunset look less blue?
The answer is C: The longer path through the atmosphere scatters more blue light out of the direct beam.
With a longer path through air, more blue light is redirected away from the direct beam. The sun has not stopped producing blue light.
-
Question 3 of 4
If far fewer air molecules scattered sunlight, how would a clear daytime sky look?
The answer is B: Darker, because less air means less scattered light to see.
Fewer molecules would redirect less sunlight toward an observer. The clear sky would look darker, not more brightly blue.
-
Question 4 of 4
The passage calls scattering 'biased'. Here that means the process:
The answer is D: affects some wavelengths far more than others
The passage says shorter wavelengths are scattered more strongly. 'Biased' describes an unequal effect, not an unfair decision.
Score: none answered yet.