The characteristics measured by semen analysis are only some of the factors in semen quality. One source states that 30% of men with a normal semen analysis actually have abnormal sperm function.
Wisps of dust and gas from the nebula which formed the star can also be seen. Credit: Atlas Image courtesy of 2MASS/UMass/IPAC-Caltech/NASA/NSF. Named for the first of their type observed, T Tauri stars are variable stars which show both periodic and random fluctuations in their brightnesses. They are newly-formed (< 10 million years old) low to intermediate mass stars (< 3 solar masses) with central temperatures too low for nuclear fusion to have started.
Alpha Centauri. The closest star to the Sun, Proxima Centauri is marked with a red circle, close to the bright stars Alpha Centauri A and B. Courtesy Skatebiker/Wikimedia Commons. The Alpha Centauri system actually contains three stars all doing a complex orbital dance together.