So far we have explored light. We have learned that sunlight is made of color. We see colors of light in a rainbow and prism. Today we are learning about “elements” and how elements give light color. Elements are the building blocks for all the rest of the matter in the world. Examples of elements include iron, oxygen, hydrogen, gold, and helium. Elements come in different forms; depending on their temperature they can be solid, liquid, or gas. There are currently 118 known elements. Of these, only 94 are thought to naturally exist on Earth. Hydrogen is the most common element found in the universe.
When you use a telescope to view a star, you can break up its light into different colors, like a rainbow. This is known as a star’s spectra, and if you look carefully, you can see black lines, or gaps, which correspond to certain elements. Since they can measure the ratios of different elements, astronomers can just look at a star to see how old it is. They can measure the ratio of uranium-‐238 to lead-‐206, and know how long that star has been around.
Diffracting Grating Mask Activity: See elements as visible through light. Make a mask out of a paper plate and cover the eyeholes with a special plastic called diffraction grating film (more info). Hot glue a popsicle stick on one side. Look through the eyeholes and see “rainbows” – the different colors of gases in lights like the different colors of gases in stars.