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.
Scientists think that 20 out of the 30 stars nearest to Earth are red dwarfs; however, none of them can be seen with the naked eye. The closest star to the sun, Proxima Centauri, is a red dwarf. Despite its frequent appearance, the term red dwarf does not refer to a single kind of star. It is frequently applied to the coolest objects, including K- and M-dwarfs, which are true stars, and brown dwarfs, often referred to as failed stars because they do not sustain hydrogen fusion in their cores.