The greatest hits of the cosmos

We are living in the midst of a revolution in astronomy, with unprecedented images of the cosmos sent back from outer space. Take a guided tour through some of the best images in the universe, brought to you from Earth orbit and beyond.

Since 1990, the Hubble Space Telescope has looked out to the cosmos from an orbital vantage point more than 350 miles above the earth's surface. After launch, scientists discovered that Hubble's optics were flawed, and it took three years and a dramatic spacewalk to correct its vision.

Since then, the $2 billion, 12.5-ton orbiting observatory has ranked as one of NASA's greatest success stories.

Hubble's best-known images include an iconic look at the starbirth region in the Eagle Nebula, shown above, as well as the Hourglass Nebula, which has been dubbed “the eye of God.” The slide show above takes you through those greatest hits.

Hubble may be the best-known platform for space imagery, but scores of other missions have sent back images that are visually stunning as well as scientifically significant.

Slide show   Jewels of Jupiter See images of Jupiter and its moons.

“Jewels of Jupiter” presents snapshots of Jupiter and its moons, sent back by the Galileo and Cassini spacecraft.

Galileo arrived at Jupiter in 1995 to sample the giant planet's atmosphere and record its cloud patterns, including the Great Red Spot. The mission was extended twice, so that Galileo could focus on the moons of Jupiter. Among the probe’s most intriguing findings were indications that there may be watery oceans beneath the icy crusts of two of those moons, Europa and Callisto. Some scientists believe such alien oceans could harbor life — but this hypothesis will have to be tested by future probes. Galileo was sent on a mission-ending plunge into Jupiter's atmosphere in 2003.

Cassini, meanwhile, snapped pictures of Jupiter on its way to a 2004 rendezvous with Saturn.

Slide show   The greatest hits from Mars See two decades' worth of Red Planet images.

The marvels of Mars have been studied for more than 25 years by space probes including Viking landers and orbiters, the Hubble Space Telescope, Mars Pathfinder and Global Surveyor. The planet is now dry and cold, but scientists believe the Red Planet was once much more like Earth. The images from NASA spacecraft reveal canyons and flood plains where water once flowed. Liquid water may still exist far below the planet’s surface. Could life have developed on Mars billions of years ago? Might microbial life still exist in underground aquifers or beneath polar caps? Such questions will be the focus of future missions.

SLIDE SHOW   Best of Cassini The Cassini spacecraft is sending back unprecedented imagery of Saturn, its rings and its moons. Click "Launch" to see some of the greatest hits from the Cassini mission.

"Starring Saturn" highlights imagery of the ringed planet from the Cassini orbiter, which began its work in 2004. This slideshow highlights Saturn's atmosphere and rings, but we have other views from Cassini as well. You can continue your exploration with a   slideshow focusing on Titan, Saturn's smog-covered moon, which boasts lakes of chilled hydrocarbons and may be following in primeval Earth's footsteps. You can also catch views of   tiger-striped Enceladus, an ice-covered moon that may possess subsurface oceans of liquid water and perhaps life as well.   Yet another slideshow features imagery of Saturn from Cassini plus earlier space missions. And as a bonus, we have a   slideshow featuring Saturn and its moons that celebrates the 10th anniversary of Cassini's launch in 1997.

“The Voyage of the Millennium” is our three-part retelling of America’s early space saga, in audio and historic imagery. Photojournalist Roger Ressmeyer went through stacks of NASA images and selected his favorites to show how Mercury and Gemini led up to the Apollo program and 1969's first moon landing.

Slide show   'We choose to go to the moon’ 1959-1969: Retrace the steps that preceded Apollo 11

Part 1: In the beginning, there were so many questions: Did the success of Sputnik mean the Soviets were taking control of the skies? Could the Americans ever hope to catch up in the space race? Would astronauts survive being sent up on rockets that had an annoying tendency to blow up? In 1962, President John Kennedy addressed those questions dramatically: “We choose to go to the moon,” he said, not because it was easy, but because it was hard. For seven years, hundreds of thousands of people — engineers and explorers — worked to answer the challenge. And some paid a terrible price.

Slide show   ‘One giant leap for mankind’ July 1969: Apollo 11 and the first lunar landing

Part 2: Three men rose into space on July 16, 1969, to begin the world's greatest adventure: Apollo 11. On July 20, while Michael Collins stayed aboard the Apollo command module in lunar orbit, Neil Armstrong and Buzz Aldrin headed for the surface in the lunar lander, known as Eagle. With the fuel supply dwindling, Armstrong realized that the computerized trajectory was sending them toward a field of boulders. He overrode the computer controls, setting the lander down on the lunar shore with 20 seconds’ worth of fuel to spare. The Eagle had landed. The space race was won. The images were icons for a new age: Earth and moon against the blackness of space ... a flag that falsely seemed to flutter in the vacuum ... bootprints in moondust. It was, as Armstrong said, “one giant leap for mankind” — a mental as well as a technological leap.

Slide show   'We leave as we came' 1969 and beyond: Our path in space since Apollo 11

Part 3: Apollo 11 marked the achievement of Kennedy’s goal: America had proven its prowess in space. What else was there to prove?

For scientists, there was still a world of questions to be answered: How was the moon formed? What forces shaped it over billions of years? What could the moon tell us about Earth’s origins, and its fate? New tools, such as a lunar rover, were devised to make the quest more efficient.

But for astronauts, there were the same old risks, the same potential price - as demonstrated by the near-tragedy of Apollo 13. Further giant leaps would have to wait. After Apollo, America would have to take more gradual, safer steps.

When Apollo 17’s Gene Cernan stepped off the lunar soil in 1972, he knew it would be a long time before the next moonwalker arrived - although he never expected that the gap would extend beyond a quarter-century. “We leave as we came,” he said, “and God willing, as we shall return, with peace and hope for all mankind.”

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