Sep 16, 2010

False Dawn: The Zodiacal Pyramid of Light

The gorgeous pyramid of light above is called the zodiacal light. Andrew Fazekas of the National Geographic News explains the elusive celestial phenomenon:

"Unlike the stars and gases of the Milky Way, which stretch away from Earth for light-years, the source of the zodiacal light lies between the inner planets of our solar system. There, billions of dust grains orbit the sun in a flattened disk spread out along the ecliptic, the plane of the solar system, which also contains the paths of the 12 constellations of the zodiac."

The dusty disk, also called the zodiacal cloud, radiates from near the sun out beyond the orbit of Mars, toward Jupiter. The dust reflects and scatters sunlight in such a way that it creates a visible glow for observers on Earth.

"Because the dust in the solar system is concentrated along the ecliptic plane, the zodiacal light is likewise concentrated," said Geza Gyuk, an astronomer with the Adler Planetarium in Chicago.

Until recently, astronomers had thought most of the space debris in the zodiacal cloud came from asteroid collisions. But a study released in April suggests that the dust is instead shed by comets that swing close to Jupiter's orbit. The gas giant planet's strong gravitational pull scatters dust off these comets, according to the study. This dust then falls into orbit around the sun, continuously replenishing the zodiacal cloud.

The triangular tower of light is easiest to spot around the spring and fall equinoxes. Look for it over the eastern horizon about an hour before sunrise in the fall, and over the western horizon just after sunset in the spring.

No comments: