August 24, 1999
When you were born, the Sun rose on a world that had never seen you before. Since then, every dawn has arrived in a universe subtly altered...
A Network of Microlensing Caustics
Birthday · August 24, 1999
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APOD published August 24, 1999. Credit: Joachim Wambsganss (Ap. Inst. Potsdam). A publication-date match, not a photo taken on your date. Independent of NASA.
A virtual sky map like this would be of interest to astronomers studying gravitational microlensing. In microlensing, the gravity of stars near the line of sight can act to magnify the light of background objects such as distant stars, or quasars. Nowhere is this magnification greater than near a gravitational lensing caustic. In the above computer simulated map, caustics are discernible as the sharp bright curved lines. When a background quasar moves across a microlensing caustic, it can appear dramatically brighter. Many astronomers thought microlensing events practically immeasurable even ten years ago, but within the past five years now hundreds have been found. Precise measurements of microlensing are now providing unique information about the composition and distribution of matter in galaxies and the universe. Some astronomers now predict that future microlensing searches might even isolate planets orbiting distant stars.
Image credit: Joachim Wambsganss (Ap. Inst. Potsdam)