A totally transparent piece of glass transmits all wavelengths of light. An opaque object will transmit no light at all. A red filter will transmit red light, a blue filter transmits blue and a yellow filter transmits yellow. All other colors are either absorbed or subtracted. Some man made sources of light, such as fluorescent bulbs, cause objects to appear to be different colors because they do not generate all wavelengths of white light.

In the Hidden Messages activity, you will have the chance to construct your own unique space-themed design and experiment with hiding messages which will be revealed when you view your drawing through different colored filters.

After completing the activity, ask yourself the following questions:

1. When you looked at your design without a filter, what did you see?

2. What did you see when you looked at the design using each colored filter?

3. What did you see when you put two of the filters together at the same time?

4. Why do you think you saw different things with each filter?

The circular features so obvious on the Moon’s surface are impact craters formed when meteorites smashed into the surface. The explosion and excavation of materials at the impacted site created piles of rock (called ejecta) around the circular hole as well as bright streaks of target material (called rays) thrown for great distances.

Two basic methods forming craters in nature are: 1) impact of a projectile on the surface and 2) collapse of the top of a volcano creating a crater termed caldera.

By studying all types of craters on Earth and by creating impact craters in experimental laboratories geologists concluded that the Moon's craters are impact in origin. The factors affecting the appearance of impact craters and ejecta are the size and velocity of the meteorite that struck the surface, and the geology of the target site. By recording the number, size, and extent of erosion of craters, lunar geologists can determine the ages of different surface units on the Moon and can piece together its geologic history. This technique works because older surfaces are exposed to impacting meteorites for a longer period of time than are younger surfaces.

Impact craters are not unique to the Moon. They are found on all the terrestrial planets and on many moons of the outer planets. On Earth, impact craters are not as easily recognized because of weathering and erosion. Famous impact craters on Earth are Meteor Crater in Arizona, U.S.A.; Manicouagan in Quebec, Canada; Sudbury in Ontario, Canada; Ries Crater in Germany, and Chicxulub on the Yucatan coast in Mexico.

Chicxulub is considered by most scientists as the source crater of the catastrophe that led to the extinction of the dinosaurs at the end of the Cretaceous period. An interesting fact about the Chicxulub crater is that you cannot see it. Its circular structure is nearly a kilometer below the surface and was originally identified from magnetic and gravity data.