zodiac light

Sunset, Milky Way and the zodiacal light above the platform of the Very Large Telescope (VLT) on Cerro Paranal.

It is September and it feels like the end of summer in that school is back in session. For almost all of my life, the beginning of the school year as a student or as a teacher meant it was the “fall semester” even if the temperature and nature still looked like summer.

Of course, it is still summer and will be officially until the 2016 autumnal equinox on September 22.

This is the best time to observe the odd “zodiacal light” (AKA the false dawn). For the next two weeks, the Moon is not visible in the morning sky.

Unfortunately, where I live in Paradelle (northern U.S.) and in Canada, it’s not as visible. Right time, wrong place.  Best viewing is in latitudes closer to the equator, as in the southern U.S., which is where I saw it only once.

In a rural area with less light pollution and open spaces, you might see what looks like the lights of a city on the horizon or it might seem that dawn is arriving an hour or two early.

What is zodiacal light? It has been poetically described as looking edgewise into our solar system. At this time of the year, the ecliptic (path of the sun, moon and planets) is nearly straight up with respect to the eastern horizon before dawn. The sunlight is reflecting off space dust particles that move in the same plane as Earth and the other planets orbiting our sun in the zodiacal cloud. After sunset in spring, and just before sunrise in autumn, the zodiac is at this steep angle to the horizon. This light is quite faint and moonlight or light pollution makes it vanish.

Sliding our perspective to the Southern Hemisphere, it’s approaching spring equinox and this strange light will appear in the west, about an hour after the sun goes down, as it will in Paradelle next spring.

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