Radcliffe waveThe Radcliffe wave is the nearest coherent gaseous structure in the Milky Way, dotted with a related high concentration of interconnected stellar nurseries. It stretches about 8,800 light years. This structure runs with the trajectory of the Milky Way arms, and lies at its closest (the Taurus Molecular Cloud) at around 400 light-years and at its farthest about 5,000 light-years (the Cygnus X star complex) from the Sun, always within the Local Arm (Orion Arm) itself, spanning about 40% of its length and on average 20% of its width.
Physical cosmologyPhysical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fundamental questions about its origin, structure, evolution, and ultimate fate. Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed those physical laws to be understood.
Hubble bubble (astronomy)In astronomy, a Hubble bubble would be "a departure of the local value of the Hubble constant from its globally averaged value," or, more technically, "a local monopole in the peculiar velocity field, perhaps caused by a local void in the mass density." The Hubble constant, named for astronomer Edwin Hubble, whose work made clear the expansion of the universe, measures the rate at which expansion occurs. In accordance with the Copernican principle that the Earth is not in a central, specially favored position, one would expect that measuring this constant at any point in the universe would yield the same value.
Orders of magnitude (numbers)This list contains selected positive numbers in increasing order, including counts of things, dimensionless quantities and probabilities. Each number is given a name in the short scale, which is used in English-speaking countries, as well as a name in the long scale, which is used in some of the countries that do not have English as their national language.
Mechanical explanations of gravitationMechanical explanations of gravitation (or kinetic theories of gravitation) are attempts to explain the action of gravity by aid of basic mechanical processes, such as pressure forces caused by pushes, without the use of any action at a distance. These theories were developed from the 16th until the 19th century in connection with the aether. However, such models are no longer regarded as viable theories within the mainstream scientific community and general relativity is now the standard model to describe gravitation without the use of actions at a distance.
Mass-to-light ratioIn astrophysics and physical cosmology the mass-to-light ratio, normally designated with the Greek letter upsilon, Υ, is the quotient between the total mass of a spatial volume (typically on the scales of a galaxy or a cluster) and its luminosity. These ratios are often reported using the value calculated for the Sun as a baseline ratio which is a constant Υ☉ = 5133 kg/W: equal to the solar mass divided by the solar luminosity , /.
Models of scientific inquiryModels of scientific inquiry have two functions: first, to provide a descriptive account of how scientific inquiry is carried out in practice, and second, to provide an explanatory account of why scientific inquiry succeeds as well as it appears to do in arriving at genuine knowledge. The philosopher Wesley C. Salmon described scientific inquiry: The search for scientific knowledge ends far back into antiquity.
