Lab: Refractometer

Please follow the instructions to construct a refractometer and answer the corresponding questions.

The instructions below describe how to build a spectrometer. Here is a link if you wish to view the site where the instructions are from:

 (Links to an external site.)

to an external site.)

Part 1. How to Make a Spectroscope

What you will need:

1. A CD or DVD that can be sacrificed to this project. Old software CDROMs work great.
2. A cereal box. Any size that can hold a CD or DVD disk will do.
3. A sharp knife or razor blade to cut into the cereal box.

Our spectroscope has three main parts. There is a slit made from a razor blade to make a path for the light, a diffraction grating made from a CD disk, and a viewing port.

To construct your spectroscope, you need to put a slice in one side of the box at roughly a 30-degree angle. This will hold the CD. Place the CD in the slot to determine where to place the other two cuts. On the top of the box, cut a hole about half an inch to an inch square above the CD. On the side opposite the CD, make a very narrow slit opposite the CD. Alternatively, you can cut a larger slit and cover it with 2 pieces of foil to control the size of the slit. Spectroscope complete.

Once you have assembled your spectroscope with 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 incandescent lights, compact fluorescent bulbs, LED lights, halogen or xenon bulbs, televisions, computer screens, candles, fireplaces, for example. Aim the slit towards the light source you are investigating, then look through the viewing hole to see the spectrum on the disk.

Answer the following questions:

1. Describe the differences in appearance among the three spectra, including colors, if they are blended together or separated, and fuzzy or distinct.
2. What feature of the light source do the spectra represent? In other words, what is it that you are actually analyzing?
3. 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 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 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 within 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 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:

1. What is the average number of stars you observed through the toilet paper roll?
2. How similar is this number to your original estimation?
3. What percentage of our galaxy do you think we can see with the naked eye from Earth? 

Part 3. Solar System

Review Chapter 15 on Atmospheres of the Planets.

Answer the following questions:

1. Why do you think that the inner planets are relatively close together, but the outer planets are spaced so widely apart?
2. Why do you think that the gaseous planets are gaseous, but the inner planets are not?

Your paper should meet the following requirements:

• 3-4 pages in length
• 1-2 outside sources
• Formatted according to the CSU-Global Guide to Writing and APA Requirements