Sunlight loses some of its blue and red light as it crosses the air…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Sunlight loses some of its blue and red light as it crosses the air. The table shows how much of each is left when the Sun is at different heights above the horizon. What do the numbers say about the colour of the Sun, and why?
| Height of the Sun | Blue light left () | Red light left () |
|---|---|---|
Need a reminder? The key ideaShow
The sky is blue because air scatters blue toward us from every direction. Near the horizon sunlight crosses much more air, about times as much for a Sun degrees high, so most of the blue is scattered away and the Sun looks red.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Overhead (). About of the blue and of the red are left: a ratio of . The Sun looks white or pale yellow.
Step 2. At . About of the blue and of the red: a ratio of . The Sun looks orange.
Step 3. At . Only of the blue, against of the red: a ratio of . The Sun looks deep red.
Answer: as the Sun sinks, its light crosses more air, and blue is lost much faster than red: white, then orange, then red.
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