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Astronomy Picture Of the Day (APOD)
Cas A Supernova Remnant in X Rays
3.01.2000
The complex shell of a star seen to explode 300 years ago is helping astronomers to understand how that star exploded. The above recently released image of supernova remnant Cassiopeia A (Cas A) shows unprecedented detail in three X-ray colors.
The Largest Rock Known
2.01.2000
There, that faint dot in the center - that's the largest rock known. It is larger than every known asteroid, moon, and comet nucleus. It is larger than any other rocky planet. (Nobody knows...
The Millennium that Defines Universe
1.01.2000
Welcome to the millennial year at the threshold of millennium three. During millennium two, humanity continually redefined its concept of "Universe": first as spheres centered on the Earth, in mid-millennium as the Solar System, a few centuries ago as the Galaxy, and within the last century as the matter emanating from the Big Bang.
The Millennium that Defined Earth
31.12.1999
When the second millennium began, people generally knew that the Earth was round, but few saw much of it beyond their local village. As the millennium progressed, humans mapped the continents, circumnavigated the globe, and determined the composition of the Earth.
The Century that Defined Galaxy
30.12.1999
As the twentieth century dawned a debate raged over whether the Milky Way was the entire universe. The 1920s brought observations of spiral-nebulae that housed familiar but faint variable stars, and hence placed these nebulae much farther than anything else ever found. The Milky Way, apparently, is itself a spiral nebula seen from the inside.
The Decade that Defined Star System
29.12.1999
As the 1990s began, the only planetary star system known was our own Solar System. The first extra-solar star system was discovered orbiting a pulsar in 1991. Slight changes in the precise arrival times of the pulses from the central small dense neutron star gave evidence of orbiting planets.
A Year of New Perspectives
28.12.1999
Fittingly, 1999 saw a decade of astronomical discoveries to an end with portents of things to come - embodied in new spacecraft, telescopes, and perspectives to explore the distant Universe across the electromagnetic spectrum. X-ray astronomy in particular will likely flourish in coming
Solar Moss
27.12.1999
Discovered in recent close-up pictures of the Sun from NASA's Transition Region And Coronal Explorer (TRACE) spacecraft, this spongy-looking stuff has a temperature of 2 million degrees Fahrenheit ... and has been dubbed "Solar Moss". The false-color TRACE image above was recorded in extreme ultraviolet light on October 18.
West Of The Great Red Spot
26.12.1999
The turbulent region West of Jupiter's Great Red Spot is highlighted in this picture constructed from data recorded by the Galileo spacecraft. The image is color coded to show cloud height and thickness; white clouds are high and thick, light blue clouds are high and thin, and reddish clouds are low.
An Earth Ornament
25.12.1999
The Apollo 8 astronauts spent the 1968 Christmas Season orbiting the Moon, returning with striking images of both Moon and Earth from space - pictures which inspired the world. While in lunar orbit...
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