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Astronomy Picture Of the Day (APOD)
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...
A Magellanic Starfield
13.12.1999
Stars of many types and colors are visible in this Hubble Space Telescope vista of the Large Magellanic Cloud (LMC). Over 10,000 stars are visible -- the brightest of which are giant stars. Were our Sun 170,000 light-years distant and among these stars, it would hardly be discernable.
NGC 4314: A Nuclear Starburst Ring
12.12.1999
Is this old galaxy up to new tricks? The barred spiral galaxy NGC 4314 is billions of years old, but its appearance has changed markedly over just the past few millions of years. During that time, a nuclear ring of bright young stars has been evolving.
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