Light, Stars, and the Solar System Lab

Follow the instructions to construct a spectrometer and answer the corresponding questions.

The instructions below describe how to build a spectroscope. Here is a link to the site where the instructions are taken from: Spectroscope

Part 1: How to Make a Spectroscope

What you will need:

A CD or DVD that can be sacrificed to this project. We won't damage it, but getting it back will involve destroying our spectroscope. Old software CDROMs work great, and some can be had for free from internet service providers like AOL.

A cardboard box. An 8-inch cube works fine, but any size that can hold a CD or DVD disk will do.

Two single-edged razor blades. These can be found in paint or hardware stores.

A small cardboard tube; the kind used as a core on which to wrap paper.

Some cellophane tape.

Some aluminum tape (found in hardware stores), or some aluminum foil and glue.

Our spectroscope has three main parts: there is a slit made from two razor blades; a diffraction grating made from a CD; and a viewing port made from a paper tube.

To make sure that all three parts are lined up properly, we will use the CD as a measuring device, and mark the spots where the slit and the viewing port will go.

Set the CD on top of the box, about a half-inch from the left edge and close to the box's bottom, as shown in the photo. Use a pen to trace the circle inside the CD onto the box. This mark shows us where the paper tube will go.

Now place the paper tube on the box, centered over the circle we just drew. Draw another circle on the box by tracing the outline of the paper tube.

Move the paper tube over a little bit. A half-inch is probably fine; in the photo, I placed it much farther to the right than necessary, but the aluminum tape covered up the mistake nicely. Trace another circle around the paper tube. These circles will tell us where to cut the box.

Now cut an oval out of the box with a sharp knife. The oval will allow the paper tube to enter the box at an angle.

The next step is to make the slit. Turn the box one quarter turn, so the oval we just cut is to the right. Using the CD again, draw another small circle close to the left side of the box.

The slit will be on the far left of the box. Cut a small rectangle out of the box at the height marked by the small circle we made with the CD.

The rectangle should be about a half-inch wide and two inches high.

Carefully unwrap the two razor blades and set them over the rectangular hole. Make their sharp edges almost touch. Tape the razor blades to the box, being careful to leave a gap between the sharp edges that is nice and even, and not wider at the top or bottom.

Next, set the box right-side-up, with the slit towards you. Now tape the CD onto the back wall of the box. The rainbow side should face you, with the printed side touching the cardboard. The photo shows the disk a little too far to the left. The left edge of the disk should be the same distance from the left of the box as is the slit.

Now seal up any places on the box where light might leak in. Use the aluminum tape for this. You can also use aluminum foil for this purpose if you don't have any aluminum tape.

The last step is to use the aluminum tape to attach the paper tube. The aluminum tape will make a light-tight seal around the tube. To make sure the angle is correct, hold the slit up to a light and look through the paper tube, adjusting it until you can see the full spectrum from red to purple.

Once you have assembled your spectrometer using the instructions in the lecture and above, use it to examine the spectra of three different light sources. Make sure that at least one of them is the sun or moon, but the others can be, for example, incandescent lights, compact fluorescent bulbs, LED lights, halogen or xenon bulbs, televisions, computer screens, candles, or fireplaces.

Answer the following questions:

Describe the differences in appearance among the three spectra.

What feature of the light source do the spectra represent? In other words, what is it that you are actually analyzing?

Why do you think spectrometers are so valuable for studying celestial objects?

Part 2: Estimating the Number of Visible Stars in the Night Sky

For this, you will need an empty toilet paper roll and a clear, dark night. Before you start, jot down the number of stars that you think you can see in the night sky.

Aim your toilet paper roll at a part of the sky well above the horizon to avoid any haze pollution. Hold your roll steady, and allow your eyes to get used to the light for a few seconds.

Count the number of stars that you can see through the roll. Do this four more times in other parts of the sky, and average the five counts.

The viewing diameter of a toilet paper roll is about 1/135th of the entire sky, at least for a relatively flat area. Mountains, buildings, or large trees will obscure some of the sky. To determine the number of visible stars, multiply your average by 135.

Answer the following questions:

What is the average number of stars that you observed through the toilet paper roll?

How similar is this number to your original estimation?

What percentage of our galaxy do you think we can see with the naked eye from Earth?

Part 3: The Solar System

Answer the following questions:

Why do you think that the inner planets are relatively close together, but the outer planets are spaced so widely apart?

Why do you think that the gaseous planets are gaseous, but the inner planets are not?

Submit a lab report file (Microsoft Word or Excel is preferred) including answers to the eight questions in this exercise. Your paper should conform to Writing and APA Requirements.