Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2002 December 15
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A Network of Microlensing Caustics
Credit & Copyright: Joachim Wambsganss (Ap. Inst. Potsdam)

Explanation: 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 twenty 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.

Tomorrow's picture: Martian Canyon

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
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