February 1, 1996
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...
Lensing through Baade's Window
Birthday · February 1, 1996
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APOD published February 1, 1996. Credit: Anglo-Australian Telescope Board. A publication-date match, not a photo taken on your date. Independent of NASA.
What is the shape and composition of our Milky Way Galaxy? This question would be easier to answer if there wasn't so much obscuring dust! In the 1940s, however, astronomer Walter Baade identified a "window" near the center of our Galaxy where there is comparatively little opaque dust. Now called "Baade's Window", this sky region contains millions of stars and is used for many studies of the distant Milky Way. One clever use, devised by Bohdan Paczynski, is to monitor millions of stars in our Galactic Bulge - many through Baade's window - for sudden brightening due to gravitational lensing. Current observations by the OGLE and MACHO collaborations have now identified dozens of gravitational amplification events. This unexpectedly large number supports previous claims that our Galaxy has a "bar" of stars across the central nucleus, pointed nearly at the Sun.
Image credit: Anglo-Australian Telescope Board