labeled with Greek Bayer designation
- Klein bottle (Wikipedia)
In mathematics, the Klein bottle (/ˈklaɪn/) is an example of a non-orientable surface; that is, informally, a one-sided surface which, if traveled upon, could be followed back to the point of origin while flipping the traveler upside down. More formally, the Klein bottle is a two-dimensional manifold on which one cannot define a normal vector at each point that varies continuously over the whole manifold. Other related non-orientable surfaces include the Möbius strip and the real projective plane. While a Möbius strip is a surface with a boundary, a Klein bottle has no boundary. For comparison, a sphere is an orientable surface with no boundary.
- 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.”
- Delta Cephei (Wikipedia)
Delta Cephei (δ Cep, δ Cephei) is a quadruple star system located approximately 887 light-years away in the northern constellation of Cepheus, the King. At this distance, the visual magnitude of the star is diminished by 0.23 as a result of extinction caused by gas and dust along the line of sight. It is the prototype of the Cepheid variable stars that undergo periodic changes in luminosity.
