February 24, 1998
Light takes eight minutes to travel from the Sun to the Earth. It took the universe 13.8 billion years to make you.
The Lyman Alpha Forest
Birthday · February 24, 1998
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APOD published February 24, 1998. Credit: J. Shalf, Y. Zhang (UIUC) et al., GCCC. A publication-date match, not a photo taken on your date. Independent of NASA.
We live in a forest. Strewn throughout the universe are "trees" of hydrogen gas that absorb light from distant objects. These gas clouds leave numerous absorption lines in a distant quasar's spectra, together called the Lyman-alpha forest. Distant quasars appear to be absorbed by many more Lyman-alpha clouds than nearby quasars, indicating a Lyman-alpha thicket early in our universe. The above image depicts one possible computer realization of how Lyman-alpha clouds were distributed at a redshift of 3. Each side of the box measures 30 million light-years across. Much remains unknown about the Lyman-alpha forest, including the real geometry and extent of the clouds, and why there are so many fewer clouds today.
Image credit: J. Shalf, Y. Zhang (UIUC) et al., GCCC