from Come Fly With Me – Exploring Science through aviation and aerospace concepts.
GROUP SIZE: Small
TIME: 60 minutes
TYPE OF ACTIVITY: Student Investigation
TEACHING STRATEGY: Expository Guided Discovery
CONCEPTS: Cratering Interpreting Data Modeling
SKILLS: Modeling Experimenting Interpreting Data
Objectives: To simulate the cratering process found on the Moon and planets; to investigate the effects of the angle of the Sun on the viability of craters in photographs; to demonstrate the aging process of craters on the Moon.
Materials: Five petri dishes; fine mesh sand; simulated raindrop maker (fine mesh nylon stocking stretched on an embroidery hoop.); water sprayer (spray bottle type); container for damp sand; old newspapers for table top; camera and film; stop watch.
Teacher Background Information: This experiment is designed to create craters in dry sand by placing filled petri dishes in a light rain or by using simulated raindrops over the dishes. The raindrop craters represent a relatively random process in which each drop has about the same chance of impacting in a given area as in any other area. Given enough time, several impacts may occur by chance in the same spot causing a large crater which may be mistaken for a crater formed by a single event.
Careful observation of large craters may reveal that they were in fact formed by several “hits” in the same area.
As more and more craters are formed, they begin to overlap and destroy one another. The craters will start out small and theoretically “saturate” an area with craters of about the same size. Slowly, as meteorites hit the same areas more than once, the crater size in an area will grow. Generally, the larger the craters in an area the older the area is thought to be.
- Fill the petri dishes with dry sand and smooth the tops off.
- Place a dish in a light rain for about 5 seconds. This should produce only a few craters. How do the craters compare in size? Are they clustered or single? Do they overlap?
- Place a second dish in the rain for about 30 seconds. How do these dishes compare?
- Drop a marble or steel bearing into another dish or make a crater with your finger. Place this dish in the rain for about 30 seconds. What happened to the large crater you made?
- Form craters in two more dishes with the bearings or your finger. Place one dish in the rain for two minutes and the other for about four minutes. What happened to the large craters? Are there any tiny craters in the dishes? These can be formed by the “ejecta” from the other craters. Are there more of the tiny craters in the dish left for 30 seconds? in the dish for 5 seconds?
Turn off all the lights in the room and shine a light on the dishes from different angles. Compare the number of craters you see with the light at several angles. Try photographing the dishes in each of the lighting situations. The identification of craters and other features on the Moon depends greatly on the angle of illumination. This is easily seen by looking at the moon at different stages through a telescope. The tiny details are best seen at the sunset line where the shadows are the greatest. This does exaggerate the features however and may lead to false conclusions about the relative height of the ridges. Compare the photos of your dishes with the real thing.
adapted from material available from the NASA Educational Programs Division.