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The Glow of Unformed Planets

Countless specks form the Zodiacal Light

The waning crescent moon ends the week low in the southeast before dawn. Sunday marks the new moon, the second in March. But it’s not gone long, reappearing as a thin sliver above the western horizon at sunset on the 31st.
    With the moon out of sight much of the night, this week provides one of the best chances to see the zodiacal light, a hazy glow that extends like a cone from the western horizon pointing heavenward also called false dawn. It appears an hour or two after sunset, and you’ll only see it with clear, dark skies.
    If you see the zodiacal light, you might first think you’re looking at a wispy cloud, back-lit by starlight. Or maybe the Milky Way. But its opaque, pyramid-shaped glow extending up from the horizon is unique.
    What you’re seeing are tiny bits of matter floating between the sun and earth. Left over from the formation of the solar system 4.5 billion years ago, they range in size from meters to millimeters. Like everything else in the solar system, these micro-worlds orbit the sun, following the same path along the ecliptic as the other planets. And like the planets, they are not themselves luminous. What we see is sunlight reflected back to our eyes. None of these pieces of solar system detritus are large enough to reflect enough light to be seen from earth, but collectively they create this distinct glow that we see after sunset in late winter and early spring.
    While you’ll have to hunt for the zodiacal light, Jupiter is not nearly so elusive. In fact, the king of the planets rules the heavens from sunset, when he is almost directly overhead, until 2:30am, when he sets in the west-northwest. In that time, there is no brighter object visible.
    Mars rises around 9:30 and is easily spotted well above the horizon an hour later. Normally Mars shines about as bright as the average star. Not so right now, when the red planet easily outshines blue-white Spica five degrees to its lower-right. Mars glows a distinct orange-red and is almost as bright as it ever gets — almost. Watch over the next coming nights as the red planet climbs higher and glows brighter on its way to opposition April 8.
    Saturn rises before midnight, but your best view of the ringed planet is before dawn, when it is high in the south. It’s far to the left of Mars and not near so bright. The nearest bright star to Saturn is Antares, the red heart of Scorpius to the south.
    Venus rises an hour ahead of the sun. While this Morning Star doesn’t climb high above the horizon, it blazes at –4.5, exponentially brighter than any star.
    The pre-dawn window to see Mercury is closing fast. It trails Venus by about 20 degrees and is tight against the east-southeast horizon a half hour before sunrise.
    As if preparing for a final bow before leaving the stage, Orion stands over the southwestern horizon at sunset. This week is your last chance to observe the great hunter in the Globe At Night campaign. Come the end of April, Leo will become the focus in this effort to plot light pollution around the planet. For more information go to www.globeatnight.org.