StarA star is an astronomical object comprising a luminous spheroid of plasma held together by self-gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night; their immense distances from Earth make them appear as fixed points of light. The most prominent stars have been categorised into constellations and asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations.
Galaxy groups and clustersGalaxy groups and clusters are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation. They form the densest part of the large-scale structure of the Universe. In models for the gravitational formation of structure with cold dark matter, the smallest structures collapse first and eventually build the largest structures, clusters of galaxies. Clusters are then formed relatively recently between 10 billion years ago and now.
Black hole starshipIn astronautics, a black hole starship is the theoretical concept of a starship capable of interstellar travel using a black hole as an energy source for spacecraft propulsion. The concept was first discussed in science fiction, notably in the book Imperial Earth by Arthur C. Clarke, and in the work of Charles Sheffield, in which energy extracted from a Kerr–Newman black hole is described as powering the rocket engines in the story "Killing Vector" (1978).
SubgiantA subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution of a star. The term subgiant was first used in 1930 for class G and early K stars with absolute magnitudes between +2.5 and +4. These were noted as being part of a continuum of stars between obvious main-sequence stars such as the Sun and obvious giant stars such as Aldebaran, although less numerous than either the main sequence or the giant stars.
MegamaserA megamaser is a type of astrophysical maser, which is a naturally occurring source of stimulated spectral line emission. Megamasers are distinguished from other astrophysical masers by their large isotropic luminosity. Megamasers have typical luminosities of 103 solar luminosities (), which is 100 million times brighter than masers in the Milky Way, hence the prefix mega.
Jewish views on evolutionJewish views on evolution includes a continuum of views about the theory of evolution, experimental evolution, the origin of life, age of the universe, evolutionary creationism, and theistic evolution. Today, many Jewish people accept the theory of evolution and do not see it as incompatible with traditional Judaism, reflecting the emphasis of prominent rabbis such as the Vilna Gaon and Maimonides on the ethical rather than factual significance of scripture. Biblical chronology indicates that God completed the creation of the world close to 6,000 years ago.
