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Tonight, at mid-northern latitudes, Jupiter lights up the western sky as dusk ends and zodiacal light begins. Look for this mysterious cone of light to jut upward from the western horizon about 80 to 120 minutes after sunset.
• The zodiacal light runs along the ecliptic - the imaginary semi-circle that crosses the sky from west to east, marking the sun's annual path in front of the backdrop stars. The ecliptic is actually Earth's orbital plane projected onto the stellar sphere. Roughly speaking, we can also call the ecliptic the plane of the solar system, for the sun, moon and planets are always found on or the near the ecliptic. Zodiacal light is composed of interplanetary dust reflecting the light of the sun. It lies in the same flat plane as the planets orbiting our sun. That's why we see it gathered along the ecliptic.
• The zodiacal light is elusive. You won't see it unless your sky is completely dark. You need a sky free of light pollution to spot the zodiacal light after all traces of twilight have left the western sky. Once again, remember to refer to the brilliant planet Jupiter - the brightest star-like object in the April evening sky. This brilliant world shines in the west at dusk. It's in this same part of the sky - in the west, more than an hour after sunset - that you'll see the zodiacal light.
• Zodiacal light looks like a large but faint milky-colored pyramid of light with its apex reaching perhaps halfway up the sky. It is caused by sunlight reflecting off interplanetary dust particles that orbit the sun within the inner solar system. People at mid-northern latitudes can see the zodiacal light after dusk at this time of year because the ecliptic - the plane of the solar system - hits the horizon at a particularly steep angle on early spring evenings. The farther south you live within the Northern (Continued on page 18)
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