December 20, 1995
Somewhere above you, light is arriving from places so distant their names feel like poetry.
A Galaxy Gravitational Lens
Birthday · December 20, 1995
A little universe, just for you
Your date.
Ready to give.
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APOD published December 20, 1995. Full image credits are on the original APOD entry below. A publication-date match, not a photo taken on your date. Independent of NASA.
Sometimes it takes a keen eye to see a good mirage. Around the center of the red galaxy image in the above photograph lie four blue "smudges." Each smudge is actually a different image of the same background quasar. The central galaxy happens to fall directly in the light path of the quasar. Consequently, the huge mass of the galaxy is able to pull separate images of the quasar around it - an effect called gravitational lensing. Hence we see a gravitational mirage! Astronomers have hopes of using light differences between these quasar images to not only "weigh" the central galaxy but even provide clues about the expansion rate and composition of the universe.