January 26, 2003
On your birthday, photons that left distant stars before humans walked the Earth finally completed their journey. You began yours.
The Lyman Alpha Forest
Birthday · January 26, 2003
A little universe, just for you
Your date.
Ready to give.
Free PNG · 1080 × 1350 · No account needed
Image rights and credit requirements apply when sharing or reusing imagery.
Date & occasion only
Change the year
APOD published January 26, 2003. 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