Late summer and early autumn present the best time of year to see the false dawn, also known as the zodiacal light. With the moon out of the morning sky for the next two weeks, this is your chance to catch the zodiacal light before dawn.
This light can be noticeable and easy to see from latitudes like those in the southern U.S. I’ve seen it many times from the latitude of southern Texas, sometimes while driving a lonely highway far from city lights, in the hour or so before true dawn begins to light the sky. In that case, the zodiacal light can resemble the lights of a city or town just over the horizon. Meanwhile, skywatchers in the northern U.S. or Canada sometimes say, wistfully, that they’ve never seen it.
Zodiacal light seenfrom Paranal. Image Credit: Wikipedia Commons
You need a dark sky location to see the zodiacal light, someplace where city lights aren’t obscuring the natural lights in the sky. The zodiacal light is a pyramid-shaped glow in the east before dawn. It’s even “milkier” in appearance than the starlit trail of the summer Milky Way. It’s most visible before dawn at this time of year because (as seen from the northern hemisphere) the ecliptic – or path of the sun, moon and planets – stands nearly straight up with respect to the eastern horizon before dawn now.
The zodiacal light can be seen for up to an hour before true dawn begins to break. Look for it about 120 to 80 minutes before sunrise. Unlike true dawn, though, there’s no rosy color to the zodiacal light. The reddish skies at dawn and dusk are caused by Earth’s atmosphere, and the zodiacal light originates far outside our atmosphere. When you see the zodiacal light, you are looking edgewise into our own solar system. The zodiacal light is actually sunlight reflecting off dust particles that move in the same plane as Earth and the other planets orbiting our sun.