Looming large in the night sky and readily identifiable, the Big Dipper has been an old friend to most of us since childhood. Its shape is mutating and will appear different in just a few thousand years, but it hasn't changed a bit since we were kids.

Poetically, it is spring itself, the season of renewal, when the Dipper reaches its annual apex. These nights it hovers high in the north, almost overhead - a far cry from the horizon-hugging stance that it adopts in the autumn.

While the southwest regales us with a diamond display of dazzling stars, it's a different story when we look to the north, where the Dipper floats forlornly in a dark and desolate region of the sky. This realm lies far from the Milky Way, far from the plane of our own galaxy. Hence, the Dipper guides our eyes away from own celestial neighborhood and toward the empty richness of the rest of the Cosmos.

Because no foreground Milky Way material obscures the view, the Dipper's direction in space offers a crystal-clear window to distant galaxies. That's why the Hubble Space Telescope's famous 1995 "ultra-deep-field" photo stared at this place for 100 unblinking hours to capture galaxies at the edge of the observable universe. Their ancient light, flushed like an old sepia print and altered by the expansion of the universe, brings us the latest news from an era that no longer exists. (Note: I say "observable universe" because at best only 1.6 percent of the universe's galaxies will ever be visible to us, since the light from at least 98.4 percent of the universe will never arrive here.)

Curiously, the Big Dipper is not even a constellation but an asterism: a segment of Ursa Major, the Big Bear. "Big" is the correct adjective, for it's the third-largest constellation in the heavens - and, indeed, it's nearly a three-way tie for first. Virgo promiscuously occupies a few more degrees of sky, as does Hydra the serpent. The Southern Cross could fit within the Dipper's boundaries nearly 20 times over.

The second star of the Dipper's handle is the sky's most famous double star: bright Mizar and little Alcor. The ability to discern this "horse and rider" was reputedly an old Arabic test of keen eyesight. Either Alcor has brightened over the centuries or else the Arabs had vision problems, because these days any inability to see the pair should qualify as legal blindness. Point a telescope and even a third star pops into view, all physically related.

Indeed, most of the Dipper's stars are gravitationally linked. Not simply random line-of-sight alignments like nearly all other constellations, they're family members forming a large, sparse cluster or association. Of the many thousands of star groups known, the Dipper is the very nearest to Earth. That's why it looks so large.

But its greatest claim to fame remains its ability to guide the celestial tyro to the North Star. These nights, the "Pointers" - the two stars at the end of its bowl - lie at the leftmost edge of the Dipper, pointing downward to a solitary star of their same brightness: Polaris, the Pole Star for the next millennium.

Beyond all this, it's a pleasure merely to gaze at the Dipper the way you did that night long ago when some farsighted adult first pointed it out. Such a dependable friend is worthy of a springtime salute.