- Delta Cephei (stars.astro.illinois.edu)
DELTA CEP (Delta Cephei). Surely among the most famed of all stars, fourth magnitude (4.1 or thereabouts) Delta Cephei, set at the southeastern corner of dim Cepheus (the King), does not even have a proper name. It is, however, the only star that has given its constellation name over to represent a whole class of stars, the “Cepheids.”
- Oxygen (Wikipedia)
Oxygen is a chemical element; it has symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. Oxygen is Earth’s most abundant element, and after hydrogen and helium, it is the third-most abundant element in the universe. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. Diatomic oxygen gas currently constitutes 20.95% of the Earth’s atmosphere, though this has changed considerably over long periods of time. Oxygen makes up almost half of the Earth’s crust in the form of oxides.