INTRODUCTION

The late astronomer Carl Sagan once said, "Somewhere, something incredible is waiting to be known."

That’s never been easier to believe than now, arguably the golden age of astronomy.

Perhaps not since Galileo trained the first telescope on the heavens in 1610 — and discovered the four large moons of Jupiter — has the study of the heavens so shaken our assumptions.

Of course, the summit of Mauna Kea reigns as one of the premier perches for ground-based observations, and of the telescopes there the twin domes of the W.M. Keck Observatory have been in the thick of the action.

The Keck, which celebrates its 20th anniversary in grand style this week, has been at the forefront of extraordinary discoveries from our stellar backyard to the far reaches of the universe, a time known as the cosmic dawn.

Keck also has contributed profoundly to the search for Earth-like planets around other stars.

The telescope continues to offer new clues to the massive black hole at the center of the Milky Way.

And studies of the accelerating expansion of the universe have shown that very little of what we see — planets, stars, galaxies — is typical. By far the predominant building blocks of the cosmos are dark.

Let’s take a moment to marvel as we wish the Keck a happy birthday.

AS THOUGH presenting an early Christmas gift, a team of astronomers using the Keck Observatory announced in mid-December that it had found the closest thing yet to an Earth around another star.

Tau Ceti, a sunlike star only 12 light-years away, may have five planets, but one of them is in the so-called "Goldilocks zone." This is a not-too-hot, not-too-cold niche where any water would be liquid.

Where life as we know it could exist.

Finding an Earth-like planet around another star is the "holy grail" of astronomy, says Gūnther Hasinger, director of the Institute for Astronomy at the University of Hawaii.

"Extrasolar planets is really one of the hot topics nowadays, and Keck has played a crucial role in discovering the first extrasolar planets," Hasinger said in a recent interview at his office in Manoa. "For a very few cases we are actually able to see the planet directly with the Keck telescope. You need very, very special conditions, but sometimes you are lucky and you can directly image a planet.

"The holy grail is to find an Earth-like planet where we could, in principle, then fly to and have a second place to live if we destroy our own planet."

The search for exoplanets — and ultimately a spectral analysis of their atmospheres for clues to life — is one of a host of groundbreaking topics under discussion this week as the Keck Observatory celebrates its 20th anniversary. The Keck, which began science operations on March 16, 1993, has played a key role in many areas of astronomy, from our planetary neighbors to the far reaches of the cosmos and everything in between.

As part of the anniversary observance, scientists will meet Thursday and Friday at the Fairmont Orchid hotel in South Kohala to mark Keck’s milestones.

The two dozen speakers include three who will describe Keck’s adaptive optics, an innovative technique that uses a laser guide star to counter the blur of the atmosphere.

Mike Brown of Caltech, known as the "planet killer" for his observations that led to the demotion of Pluto, will talk about Keck’s views of the outer solar system.

Michael Liu of UH-Manoa will introduce the "cool neighbors" — brown dwarfs. And Andrea Ghez of UCLA will detail the dizzying carousel of stars around the black hole at the center of the Milky Way.

As if to add an exclamation point on the events, a comet will appear in the evening sky. The best viewing may be tonight, when Comet Pan-STARRS appears below a thin crescent moon.

Since the first exoplanet was detected in 1995 around the star 51 Pegasi, 51 light-years away, the confirmed list has grown to more than 700, with thousands more candidates.

Most cannot be seen directly, so astronomers watch the host star wobble from the gravitation interaction. The movement can be detected by the Doppler effect, the same phenomenon that accounts for the different tones of a train whistle as the train swiftly approaches, then speeds away.

"When the planet is circling the star, the star actually makes a little counteraction because in reality both are circling around a common center of mass, which is inside the star," Hasinger said. "The star is actually moving as fast as the fastest runners on Earth, about 10 meters per second. And for stellar measures this is really small, so you have to have very accurate spectrographs and you see this, the spectral light shifting back and forth in the spectrum."

The other technique to detecting exoplanets is a transit, like the transit of Venus across the face of the sun last June.

"When we are looking at some other planetary system and one of the planets is moving in front of its star, we don’t see that, but we see it as a little dip in the light curve," Hasinger said.

Using that approach, a team of astronomers from California and Hawaii estimated in January that 17 percent of sunlike stars have planets up to twice the diameter of Earth in close orbits. The scientists used NASA’s Kepler space telescope to repeatedly image 150,000 stars in a small region of the sky, looking for a dip in brightness. The stars then were analyzed further with the Keck, fitted with a high-resolution spectrograph, which turns a light wave into a frequency spectrum, similar to a rainbow.

The galaxy’s central black hole is another area where Keck has played a crucial role, Hasinger said.

"When you look at the galaxy with the naked eye, you see this as a bright, white light," he said. "But in between are gas and dust clouds that are actually blocking our view of the center of the galaxy. But when you have infrared eyes, you can actually look through these gas and dust clouds."

There resides an intriguing cluster of stars, 100 or so, all very young, on the order of 2 million years old — the same age as the island of Maui, he said.

"These stars are moving around in regular patterns, they move in ellipsis and they move around an empty spot, which is basically the black hole," Hasinger said. "And from these movements you can determine there must be a very massive heavy object, which is 3.5 million solar masses, which slings around the stars with very fast motions — about 10,000 kilometers a second or so (22.4 million mph), so it’s really a very powerful thing that can sling around a whole star."

While the black hole is not directly observable — its intense gravity keeps even light from escaping its grip — every now and then it offers up an X-ray burst.

"It seems to take a small snack of some material, maybe a gas cloud or maybe an asteroid, something that is falling on it, and it flares up for a short period of time," said Hasinger. "It is usually starving, but every once in a while it gets a snack and does a hiccup."

Astronomers agree that the key to success for any observatory, Keck included, is instrumentation, which can give even an old dog a set of new tricks.

"The growth of technology gives telescopes a new life on decade time scales — expanding the parts of the spectrum they can observe, multiplying the number of objects we can target at once, correcting for atmospheric blurring over bigger and bigger areas," said UH astronomer Roy Gal.

One can only wonder how Keck will celebrate 40.