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03-04-09 Desperately Seeking Mercury

After dominating the western evening sky for more than half a year,the planet Venus has now transitioned into the morning sky.But during April another planet will take its place in the western evening twilight.Mercury is often cited as the most difficult of the five brightest naked-eye planets to see.It's also called an "inferior planet" because its orbit is nearer to the sun than the Earth's.Therefore,it always appears from our vantage point to be in the same general direction as the sun.Since it's the planet closest to the sun,Mercury never strays too far from the sun's vicinity in our sky.Hubert J. Bernhard,who for many years was a lecturer at San Francisco's Morrison Planetarium, noted that Mercury "stays close to the sun like a child clinging to its mother's apron strings." Relatively few people have set eyes on Mercury (there is even a rumor that Copernicus never saw it).While that is certainly true most times of the year,there are other intervals – and we're about to enter one of them – where making a sighting of Mercury requires almost no effort.You simply must know when and where to look,and find a clear west-northwest horizon