A shame. While it never blazes against a truly dark sky like the here-I-am beacon of Jupiter now lighting up the pre-dawn heavens, nor possesses the riveting fire of Venus currently hiding behind the sun, Mercury's zero-magnitude brightness makes it rank among the night's top five stars. Were it not for its incurable addiction to twilight, it would quickly grab attention.
Each year, Mercury briefly rises like a phoenix from the ruddy embers of dusk and plays peekaboo with anyone who cares to look. In 2008 that time is now alone, when it swings to the edge of its orbit, slanting favorably above the western horizon.
From now until next weekend - the first ten days of May - you've got a fabulous chance to carve a Mercury notch on your belt. You'll need a fairly unobstructed western horizon. If you live on the east side of the River, or anywhere you can see the sun an hour before it sets, or find yourself at any of the Kingston malls soon after sunset, you're in luck.
Start looking at 8:30. You'll have a nice "window" until 8:45 as twilight darkens but Mercury sinks lower. It's the second-brightest "star" in the sky, bested only by the low blue Dog Star Sirius to the left of Orion. (Mercury floats to the right of the setting Hunter.) It's the only bright star above the point of sunset - and you might notice that it's a bit reddish. If you spot any star at one fist held at arm's length above the western horizon, you've found it. It all reaches a peak Tuesday evening, May 6, when things get stone-simple: Mercury will hover just beneath the crescent moon.
Binoculars snap Mercury right out of the twilight. But you don't need a telescope: Higher power doesn't greatly improve the experience. The tiny charbroiled world displays moonlike phases when viewed telescopically, but rarely any additional detail as it shimmers in the turbulent horizon air.
Yet, over the centuries, occasional drawings recorded at the eyepieces of amateur instruments have depicted Mercury with bright white poles: ice caps. Such sightings were always dismissed as illusions akin to the spurious canals of Mars. Mercury's fiery, airless surface - hot enough to melt lead during its ferocious 88-day stretch of daily sunshine - would surely be the last place to host an arctic panorama. Or so we thought: Astronomers were as amazed as anyone else when new radio pulses were bounced off that cratered world in 1991. The best interpretation of those signals spells i-c-e.
We didn't think that Mercury had any water at all, in any form. Moreover, Mariner 10 had passed by three times in 1974 and 1975, and no caps were seen. But its cameras had just missed the exact poles. Apparently the shallow polar depressions permanently shield those regions from both the low sun and the snooping optics of passing spacecraft. Mercury's unique talent as the only planet to travel through space without any tilt to its axis has prevented the poles from ever tipping toward the raging nearby sun.
What a splendid reward for curious earthly eyes: that this tiny world of fire and ice could not hide forever. See it for yourself the next clear evening. It may look like a common star, but the mercurial vagabond grants an odd satisfaction to those who catch it as it hovers in spring's ambrosial twilight.
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