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Astronomy Picture Of the Day (APOD)
Unusual Aurora During Solar Wind Dropout
23.12.1999
On May 10, for some unknown reason, the Solar Wind virtually stopped. Normally our Sun emits a wind of between five and ten energetic particles per cubic centimeter moving outward at about 500 kilometers per second.
Perigee Moon, Apogee Moon
22.12.1999
Tonight, those blessed with clear skies can enjoy a glorious full moon, the last full moon of the "Y1.9K"s. In fact, tonight's moon will be a full-perigee-solstice moon, reaching its full phase and perigee (the closest point in its orbit) on the solstice, the first day of northern hemisphere winter.
XMM Launched
21.12.1999
X-ray astronomy entered a golden age earlier this month with the successful launch of the X-ray Multi-Mirror (XMM) satellite. XMM's three huge telescope barrels each hold 58 concentric cylindrical mirrors, together totaling a surface area rivaling a tennis court.
Lava Fountain on Jupiter's Io
20.12.1999
A lava fountain shooting over a kilometer high has been discovered on Jupiter's moon Io. The robot Galileo spacecraft orbiting Jupiter photographed the volcanic eruption during its close flyby of the moon late last month. The fountain is visible in the above mosaic of images from the flyby.
Accretion Disk Binary System
19.12.1999
Our Sun is unusual in that it is alone - most stars occur in multiple or binary systems. In a binary system, the higher mass star will evolve faster and will eventually become a compact object - either a white dwarf star, a neutron star, or black hole.
Irregular Galaxy Sextans A
18.12.1999
Grand spiral galaxies often seem to get all the glory. Their newly formed, bright, blue star clusters found along beautiful, symmetric spiral arms are guaranteed to attract attention. But small irregular galaxies form stars too, like this lovely, gumdrop-shaped galaxy, Sextans A.
Hot Gas In Hydra A
17.12.1999
The Hydra A galaxy cluster is really big. In fact, such clusters of galaxies are the largest gravitationally bound objects in the Universe. But individual galaxies are too cool to be recorded in this false-color Chandra Observatory X-ray image which shows only the 40 million degree gas that permeates the Hydra A cluster.
Supernova Remnant In M82
16.12.1999
This false-color radio wavelength picture of an expanding stellar debris cloud is the product of one of the largest radio astronomy experiments ever. Combining the output of 20 radio telescopes scattered around planet Earth...
A Nova In Aquila
15.12.1999
On December 1st, experienced observers patroling the night sky with binoculars noticed what seemed to be a new star in the constellation of Aquila (The Eagle). It wasn't really a new star though.
High Velocity Clouds and the Milky Way
14.12.1999
Where are these gas clouds going so quickly? High velocity clouds (HVCs) of gas have been seen for decades but their origins and destinations have remained mysterious. Recent measurements have now placed at least...
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