On July 4, NASA's Deep Impact spacecraft will attempt an extraordinarily daring encounter with the far-flung comet Tempel 1 hurtling through space at tens of thousands of miles per hour. As if that is not challenging enough, the comet's size, shape and other characteristics are not entirely known.

Two of NASA's eyes in the sky, the Spitzer and Hubble Space Telescopes, helped scientists prepare for the comet encounter. From their orbits high above Earth, the telescopes watched Tempel 1 in early 2004. Together they came up with the best estimates of the comet's size, shape, reflectivity and rotation... Read more

During the 15 years NASA's Hubble Space Telescope has orbited the Earth, it has taken more than 700,000 photos of the cosmos; images that have awed, astounded and even confounded astronomers and the public.

NASA released new views today of two of the most well-known objects Hubble has ever observed: the Whirlpool Galaxy (spiral galaxy M51) [left] and the Eagle Nebula [right]. These new images are among the largest and sharpest Hubble has ever taken. They were made with Hubble's newest camera, the Advanced Camera for Surveys (ACS). The images are so incredibly sharp, they could be enlarged to... Read more

The dancing light of the auroras on Saturn behaves in ways different from how scientists have thought possible for the last 25 years. New research by a team of astronomers led by John Clarke of Boston University has overturned theories about how Saturn's magnetic field behaves and how its auroras are generated.

While analyzing NASA Hubble Space Telescope images of the Sagittarius dwarf irregular galaxy (SagDIG), an international team of astronomers led by Simone Marchi, Yazan Momany, and Luigi Bedin discovered 13 sucessive faint trails left by a tiny asteroid. The trails are seen as a series of reddish arcs on the right in this August 2003 Advanced Camera for Surveys image.

At first glance, Jupiter looks like it has a mild case of the measles. Five spots - one colored white, one blue, and three black - are scattered across the upper half of the planet. Closer inspection by NASA's Hubble Space Telescope reveals that these spots are actually a rare alignment of three of Jupiter's largest moons - Io, Ganymede, and Callisto - across the planet's face. In this image, the telltale signatures of this alignment are the shadows [the three black circles] cast by the moons. Io's shadow is located just above center and to the left; Ganymede's on the planet's left edge; and... Read more

This image of comet C/2001 Q4 (NEAT) was taken at the WIYN 0.9-meter telescope at Kitt Peak National Observatory near Tucson, Ariz., on May 7, 2004.

The image was captured with the Mosaic I camera, which has a one-square degree field of view, or about five times the size of the Moon. Even with this large field, only the comet's coma and the inner portion of its tail are visible. A small star cluster (C0736-105, or Melotte 72) is visible in the lower right of the image, between the head of the comet and the bright red star in the lower-right corner.

As Saturn grows closer through the eyes of the Cassini spacecraft, which is hurtling toward a rendezvous with the ringed world on June 30 (July 1, Universal Time), both Cassini and the Earth-orbiting Hubble Space Telescope snapped spectacular pictures of the planet and its magnificent rings. Cassini is approaching Saturn at an oblique angle to the Sun and from below the ecliptic plane. Cassini has a very diferent view of Saturn than Hubble's Earth-centered view. For the first time, astronomers can compare views of equal-sharpness of Saturn from two very different perspectives.

Resembling a diamond-encrusted bracelet, a ring of brilliant blue star clusters wraps around the yellowish nucleus of what was once a normal spiral galaxy in this new image from NASA's Hubble Space Telescope (HST). This image is being released to commemorate the 14th anniversary of Hubble's launch on April 24, 1990 and its deployment from the space shuttle Discovery on April 25, 1990. The galaxy, cataloged as AM 0644-741, is a member of the class of so-called "ring galaxies." It lies 300 million light-years away in the direction of the southern constellation Volans.

Astronomers poring over 35 NASA Hubble Space Telescope images of the solar system's farthest known object, unofficially named Sedna, are surprised that the object does not appear to have a companion moon of any substantial size. This unexpected result might offer new clues to the origin and evolution of objects on the far edge of the solar system.

At a distance of over 8 billion miles, Sedna is so far away it is reduced to one picture element (pixel) in the image [at lower right] taken in high-resolution mode with Hubble's Advanced Camera for Surveys. This image sets an upper limit on Sedna's size of 1,000 miles in diameter.

Atmospheric features on Uranus and Neptune are revealed in images taken with the Space Telescope Imaging Spectrograph and the Advanced Camera for Surveys aboard NASA's Hubble Space Telescope. A wider view of Uranus, taken with the Advanced Camera for Surveys, reveals the planet's faint rings and several of its satellites. The observations were taken in August 2003.