SPECTROSCOPY Tahoma Jr. High 8 th Grade Science Maple Valley, WA

Remember, the Electro-Magnetic Spectrum is an expanded “rainbow” of frequencies.

Some of those frequencies when combined make visible white light, but we’ve shown that white light is made of separate frequencies creating a real rainbow of colors.

Excited gases (either produced by the source or a gas charged by light going through it) give off energy when the excited electron drops to a lower energy level (more stable). The extra energy has to go somewhere – so it becomes a photon (light particle). This is how fluorescent and neon lights work. photon excited e - e - drops and photon created photon released

You learned in the 6 th Grade Plant Unit that plants absorb red and blue, but of course reflect green – that’s why they LOOK green!

There are three types of spectrums: Incandescent light gives off all colors. A cloud of hot gas gives off its own frequencies (like fireworks) depending on the chemicals. If full light passes through a gas, certain wavelengths are absorbed.

Here are different emission spectra for different chemicals. (each chemical has its own “signature” pattern)

EMISSION (what comes out or is “emitted”)

Things work opposite with ABSORPTION (what does NOT get through)

Notice how the lines for hydrogen are the same on both emission and absorption, but: absorption REMOVES them emission MAKES the lines

The Sun is made of many chemicals (it is actually making them from hydrogen). As the Sun loses hydrogen, the amount of other chemicals will increase (up to iron, where the Sun is not big enough to make bigger atoms).

How do we know what the Sun (and other stars) are made of ?? By looking at the emission and absorption spectra and this can also help tell us how much of each: Hydrogen = 73.5 %Helium = 25%

By the way, it was a lady physicist in 1925 (very rare for those days) who first figured the Sun’s composition out – and unfortunately (as has happened too often in history) men took credit for her work. Her name was Cecilia Payne Gaposchkin we should give credit where credit is due

Look at these carefully: sunlight is well balanced white light, incandescent bulb gives off lots of heat (towards red wavelengths) and fluorescent light is more white, but there’s spikes from the certain chemicals that are excited to make the light as well (their “signature”!). fluorescent incandescent sunlight

SPECTROSCOPY We can also tell of what an atmosphere is made of if we can catch light passing through it.

Or different clouds of gas (or nebula) when the light passes through more than one.

Here’s a picture showing different satellites / telescopes humans have made to observe certain parts of the E-M Spectrum (they are above / below their wavelengths of study)

Emission and absorption spectra are important tools in many areas of science. By combining knowledge of light (the E-M spectrum) and chemistry (the Periodic Table) we can learn much about Nature! end show