You see, Beer's Law states that the absorbance of a chemical in solution is proportional to it's (molar) concentration. So the more concentrated, the darker to solution appears.
A colorimeter measures the intensity of a particular color of light. So to use it in chemistry, you need to aim light of the opposite color through a colored solution. So for,example, measure the color of red light shining through a green-colored solution. If you measure the brightness of at least two known solutions (one being zero concentration), you can determine the concentration of other solutions of the same chemical.
Let's now turn this in a new direction. I wanted to measure the color/intensity of lunar maria and highlands. Maria are young lava flood plains (rich in basalt and dense) and highlands are older feldsic-rich scum that floated to the surface of the once molten moon.
Maria are darker than highlands. This is in fact very apparent when you look at the moon even with just your eyes. But could I actually make a measurement of this?
I pointed my new 16" dobsonian telescope at the moon on the 18th and focused it while wearing my glasses. Then I started the colorimeter app and pointed the cellphone at the moon. I also had a screen capture app running so I could record the results.
In the two pictures below, you can see that indeed the colorimeter app did detect the difference between lunar maria and highlands and quantify that difference. But I don't know how consistent this will be. I really need a bracket to hold the cellphone to the eyepiece while I record data.
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| Interesting color description. You'll notice the RGB values for the lunar highlands are higher than those for Lunar maria. |
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| Maria is darker than highlands, according to the colorimeter app. The screen capture app was set to vibrate when it captured an image, hence the blurriness of this capture. |
By the way, the app is from Research Lab Tools and costs $0.99.
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