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“Red sky at night, sailor’s delight; red sky in morning, sailors take warning”. Why does the sky appear red at sunset or sunrise, but not during the day? Why is the sky blue during the day and not when the sun is lower in the sky?
The Sunset in a Glass experiment demonstrates how the sun’s rays are scattered as they travel through the atmosphere. When there are more particles in the atmosphere, we see reds and oranges in the sky. When there are fewer particles to pass through, the sky appears blue.
This experiment really packs a punch of knowledge, so be sure to check out the “STEM behind” section to dive into the science!
How to make the Sunset in a Glass STEM experiment
Supplies you will need
For this experiment, you’ll need:
- Milk
- Glass container
- Water
- Flashlight
- Spoon
- Optional: tea, powdered drink mix, flour
Here’s a great book answering lots of questions about sky for curious minds.
Before you start
This goes without saying, but never shine a flashlight in someone’s eyes.
Instructions
Here is how to do this experiment with your child:
Step 1: Place the flashlight on the side or behind the glass container
Place your flashlight on table behind or on the side of the glass container.
Pour water into the container and observe the color you can see. It should look bluish if there is no milk inside.
Step 2: Pour milk into the container with water in it
Pour in a little bit of milk at a time, stirring with a spoon to completely mix it with the water.
Make an observation again: is the light changing from blue to a different color? What does the light look like when you observe it through the milky water?
Keep pouring in a little bit of milk at a time and continue making observations.
Step 3: Make observations and, if possible, compare
We wanted to have a side-by-side comparison to see the difference between the two glass containers, one with only water and the other with the milky water. Having that side-by-side comparison really helped to see the difference in color between the two!
So what exactly is going on here?
When the sun is directly overhead, around midday, its light passes through less atmosphere than when it is lower on the horizon. Since it has less atmosphere to pass through, there aren’t as many atmospheric particles causing the light to refract (and therefore we see the orange/red).
The STEM behind the Sunset in a Glass experiment
This experiment teaches:
- Why the sunset/sunrise is red and orange
- Pollution/particles in the atmosphere
- Light and color
How it works
The Sunset in a Glass experiment demonstrates how the sun’s rays go through the atmosphere when there are fewer particles to pass through (so no milk, just water in the glass) and more particles to pass through (milky water).
When the sun is directly overhead, around midday, its light passes through less atmosphere than when it is lower on the horizon. Since it has less atmosphere to pass through, there aren’t as many atmospheric particles causing the light to refract (and therefore we see the orange/red).
That’s why you are more liable to get a sunburn midday than in the morning or the evening: the sun has much less atmosphere to get to your skin than in the evening and morning!
Why the sunset/sunrise is red and orange
This experiment is great for teaching kids why the sky is a different color during sunrise and sunset than in the middle of the day.
At sunrise and sunset, the sunlight has to travel through more of the atmosphere. At those times of day, the blue light is scattered away and we are left with the reds and oranges that fill the sky.
When we see a red sky, that typically means that the air contains more dust and moisture (aka, more particles). The sun’s rays have to pass through more particles, and the longer wavelengths of the color red get through while the shorter wavelengths of the color blue get scattered.
Ever heard the phrase “red sky at night, sailor’s delight; red sky in morning, sailors take warning”?
That saying has to do with weather patterns. High and low-pressure systems typically move from left to right in the atmosphere. High-pressure systems are associated with mild and normally calm weather. Low-pressure systems are typically associated with more turbulent weather and storms.
Particles in the atmosphere are of the highest value when there is more sinking air, which is a high-pressure system. So, we see the reddest sunrise or sunset when high pressure surrounds us.
Knowing that, along with the fact that these systems typically move from left to right, what type of pressure system could we expect after the high-pressure system passes?
A low-pressure system!
Now, let’s put all of that knowledge together: the sun sets in the west. If there are red skies from light coming from the west, that means a high-pressure system is on its way (calm weather; sailor’s delight). Since the sun rises in the east, if we see red skies from light coming from the east, that means a low-pressure system (turbulent sky) is on its way.
Pollution/particles in the atmosphere
The experiment can also be used to discuss how pollution can affect sunsets, making them more intense or changing their color.
Remember: the color of the sky has to do with how the sun’s rays are being scattered. If there is less atmosphere and less particles to travel through, the sunlight appears more blue. If there is more atmosphere to travel through and more particles, the sun’s rays will appear more orange and red.
The particles in the atmosphere can be anything from water droplets to dust to pollutants.
Light and color
This experiment is also a great opportunity to talk about light as waves and how different colors of light have different wavelengths. You could even show your child an electromagnetic spectrum chart to not only show the different color wavelengths but also that the visible spectrum makes up just a portion of the total spectrum!
You can also discuss light scattering, which is when light passes through something (like the atmosphere and everything in it). The light can scatter in different directions when passing through the atmosphere, which is why the sky is blue during the day and red and orange when the sun is lower in the sky.
More experiments about optics to try out with your child
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