The goal for this lab is for you to understand how the color of light from an object - gas, dust, the Sun, an extrasolar planet - can tell us what it is made out of!

This is the art and science of Spectroscopy - or studying the spectrum of light.

You may know that white light is made of all colors of the rainbow - this is why water creates a rainbow - it splits the rays of the Sun up and shows them to us!


In the same way, we can use a prism or diffraction grating to split light into its components.  The colors in an atom come from the electrons in their atomic orbits - every atom has a unique spectral finger print!  No two atoms are the same color.  This way we can know what elements we are seeing in another object just by studying the light coming from it.

All light is the result of photons being absorbed and emitted by atoms and their electrons - photons have energy and give them to electrons, and electrons spit light back out.  This process is called absorption and emission.  

The thing is, every atom has a different electron configuration, and these electrons can only absorb certain energies.  Then every atom is color-matched to specific wavelengths of light.

Our eyes are tuned to observe only a small window of possible photon energies - called the visible spectrum - and these are ROYGBIV - red, orange, yellow, green, blue, indigo, and violet.

But remember, there are gamma rays, X-rays, ultraviolet, infrared, microwave, radio waves and so on - many many different possible photon energies.

Part 1:  Human Vision


The human eye is made of rods and cones - the rods measure intensity of light independent of color.  The cones are split up into red sensors, blue sensors, and green sensors.

The wavelength of visible light cover 400 nm - 700 nm, from blue to red respectively.

Part 2:  Wien's Law

According to Wien's law, the peak emission spectrum of a very hot object is related to its temperature.

In this way, you can measure the temperature of a star simply by finding the brightest color of its emission.

What this equation says is that the temperature (in units of Kelvin) is given by 0.0029 divided by the peak wavelength in (units of meters).

So make sure you have your units in METERS and in KELVIN, NOT nanometers or Celsius or Fahrenheit.

In the following image, note that you want the X VALUE of the wavelength, where the value of the wavelength is peaked on the Y axis.

Part 3:  The Spectrum of a Quasar

A Quasar is a 'quasi stellar radio source' and we now know them to be supermassive black holes with accretion disks.

When they were first detected, they were observe to be as bright as stars with an unknown origin, so were given the name quasar for the ambiguity.  But by measuring their spectrums, we learned that they exist across the universe - certainly not stars in our own galaxies.

How could something so bright be so far away?

More than 1 million quasars have been discovered to date, with the closest more than 600 million light years away.

Part 4:  Determining the Mystery Element 

When gases are ionized, they emit their colors.  In class, we can use a spectrometer to measure the emission lines of the gas.  Here are the emission lines of some common elements.  Which element is being observed in class?