December 21, 1999
Galaxies were colliding long before you were born, and they will keep colliding long after us all.
XMM Launched
Birthday · December 21, 1999
A little universe, just for you
Your date.
Ready to give.
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APOD published December 21, 1999. Full image credits are on the original APOD entry below. A publication-date match, not a photo taken on your date. Independent of NASA.
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. Each mirror has been gold plated to less than one-millimeter thickness to reflect normally penetrating X-rays. ESA's XMM joins NASA's Chandra X-ray Observatory as leading observatories in X-ray astronomy. The XMM satellite also carries a small optical and ultraviolet telescope. XMM's unusually elliptical orbit around the Earth peaks nearly one-third of the way to the Moon. XMM's observing program during its planned two-year mission includes monitoring the hot surroundings of black holes, the fiery regions surrounding the centers of galaxies, the mysterious X-ray background light that appears to come from all directions, and the hot gas that glows between galaxies and stars.