Streaks of Light in the Sky
What are those points of light moving across the sky? If they blink or glow red, they are probably on an airplane. A white, continuous, slowly moving light is probably an artificial satellite. The bright streaking white light is a "shooting star," which is actually a meteor. In this project, you will determine why meteor showers occur by modeling the plane of Earth's orbit in relation to that of a comet. You will discover the two types of meteoroid streams and learn how to represent them. You will also compare the number of meteors in "showers" with the numbers of meteors that fall to Earth sporadically.
Purpose: To model Earth's orbit passing through a comet's orbit.
- 1-by-3-inch (2.5-by-7.5 cm) strip of poster board
- one-hole paper punch
- three 12-inch (30-cm) pipe cleaners—2 yellow, 1 green
- Draw the Sun in the center of the strip of poster board.
- Punch four holes in the strip, centering them near the edges of the four ends.
- Thread the green pipe cleaner through the holes on the short ends of the strip. Twist its ends together, and form it into an elliptical shape. This is a model of Earth's orbit.
- Twist the ends of the yellow pipe cleaners together to form one long piece. Thread it through the remaining holes. Twist the ends together and form it into an ellipse. This is a model of a comet's orbit.
- Position the two orbits at angles so that Earth's orbit touches the comet's orbit at only one point (see Figure 12.1).
The comet's orbit is at an angle nearly perpendicular to Earth's orbit, so they only touch at one point.
Comets are celestial bodies made of dust, rock, sand, gases, and ices (mainly water and carbon dioxide) that move in an extremely elongated orbit about the Sun. They are often called dirty snowballs. When they get near the inner planets, the Sun's heat vaporizes surface ice, freeing some of the rock, sand, and dust. These pieces become meteoroids (solid particles that have broken off a celestial body and that orbit the Sun) scattered along the comet's path. Meteoroids from comets are generally the size of dust specks, while those from asteroids (irregularly shaped rocky chunks of matter that rotate as they orbit the Sun, generally between Mars and Jupiter; also called minor planets) can be very large.
When a meteoroid enters Earth's atmosphere, it is called a meteor. Meteors move so fast that friction with the air causes them to heat up and vaporize (change to a gas). The hot vapor is incandescent (glowing because of heat). This incandescence is the light of a "shooting star." Any meteor large enough to survive its fall through Earth's atmosphere and actually make it to Earth's surface is called a meteorite.
The orbit of Earth and the orbits of most comets never meet. But some comets have orbital paths that do intersect with Earth's orbit. Thus, in its annual trip around the Sun, Earth passes through the orbital paths of several comets at different times throughout the year. Each time this happens, Earth passes through debris the comet left in its path, and a meteor shower (an increase in the rate of meteors) is seen by observers on Earth. On any clear night 3 to 15 meteors are generally seen per hour. But during a meteor shower as many as 60 meteors per hour have been seen.