Okay, so you know how when you use a crayon on paper, it leaves a mark and you can see the color of the crayon on the paper? Well, stars also give off colors, but we can't always see them with our eyes. Scientists use a special tool called a spectroscope to help us see the colors of stars.
The tool breaks the light into colors like a rainbow, and each color tells us something about the star. One thing it tells us is what kind of gas the star is made of.
Now, there are some specific colors that stars give off that help us know what kind of gas it is. These colors appear as lines on the spectrum, and they're like a fingerprint for each gas. So if we look at the spectrum of a star, we can see these lines and figure out what gases it's made of.
The k-w line specifically refers to the lines in the spectrum that tell us about the gas called calcium. These lines are important because they help us study the calcium in stars and understand how stars work. So the k-w line is just a special part of the spectrum that tells us about calcium in stars.