Zwicky estimated the cluster's total mass based on the motions of galaxies near its edge and compared that estimate to one based on the number of galaxies and total brightness of the cluster.

One of the main challenges to galaxy formation is the great number of thin disk galaxies in the local universe.

The Lambda-CDM model of galaxy formation underestimates the number of thin disk galaxies in the universe.

Particularly, galaxy surveys in the Zone of Avoidance ( the region of the sky blocked by the Milky Way ) have revealed a number of new galaxies.

In addition to the classifications mentioned above, there are a number of galaxies that can not be readily classified into an elliptical or spiral morphology.

Most galaxies in the universe are gravitationally bound to a number of other galaxies.

If there is insufficient kinetic energy, however, the group may evolve into a smaller number of galaxies through mergers.

Clusters of galaxies have been found in surveys by a number of observational techniques and have been studied in detail using many methods:

By 2003, the number of known Local Group members has increased from his initial twelve to thirty-six, by way of the discovery of almost two dozen low-luminosity galaxies.

Among these, the Book of Fixed Stars ( 964 ) was written by the Persian astronomer Abd al-Rahman al-Sufi, who observed a number of stars, star clusters ( including the Omicron Velorum and Brocchi's Clusters ) and galaxies ( including the Andromeda Galaxy ).

Since galaxies are intrinsically elliptical and the weak gravitational lensing signal is small, a very large number of galaxies must be used in these surveys.

These weak lensing surveys must carefully avoid a number of important sources of systematic error: the intrinsic shape of galaxies, the tendency of a camera's point spread function to distort the shape of a galaxy and the tendency of atmospheric seeing to distort images must be understood and carefully accounted for.

* Arp number, a numbering system for galaxies, designed by Halton Arp

Others, called starburst galaxies, have an extremely high number of newly forming stars heating interstellar dust clouds.

The number density of galaxies in the LS falls off with the square of the distance from its center near the Virgo Cluster, suggesting that this cluster is not randomly located.

Overall, the vast majority of the luminous galaxies ( greater than absolute magnitude − 13 ) are concentrated in a small number of clouds ( groups of galaxy clusters ).

Ninety-eight percent can be found in the following 11 clouds ( given in decreasing order of number of luminous galaxies ): Canes Venatici, Virgo Cluster, Virgo II ( southern extension ), Leo II, Virgo III, Crater ( NGC 3672 ), Leo I, Leo Minor ( NGC 2841 ), Draco ( NGC 5907 ), Antlia ( NGC 2997 ) and NGC 5643.

The luminous galaxies in the halo are also concentrated in a small number of clouds ( 94 % in 7 clouds ).

While some of these may be distant background objects, the total number of galaxies in the cluster is quite large.

Twenty first century observations have shown that a very small number of H II regions exist outside galaxies altogether.

Indeed, with improved observing techniques, a number of host galaxies have been observed around quasars which indicates that those quasars at least really are at cosmological distances and are not the kind of objects Arp proposes.

As with many other rich galaxy clusters, Virgo's intracluster medium is filled with a hot, rarefied plasma at temperatures of 30 million Kelvin that emits X-Rays, and within it can be found a large number of intergalactic stars ( up to 10 % of the stars in the cluster ), including some planetary nebulae, that it's theorized were expelled of their home galaxies on interactions with other galaxies, as well as some globular clusters, possibly stripped of dwarf galaxies, and even at least one star formation region

The number of square arcminutes in a complete sphere is

... the atoms of the elements consist of a number of negatively electrified corpuscles enclosed in a sphere of uniform positive electrification, ...

However, the number of crafts required to obtain, transmit, and maintain a complete Dyson sphere far exceeds our present-day industrial capabilities.

Shown is a sphere in Stokes flow, at very low Reynolds number.

If the surface of concentric sphere shells were considered, the number of stars on each shell would be proportional to the square of the radius of the shell.

It is also the derivative of the formula for the volume with respect to r because the total volume of a sphere of radius r can be thought of as the summation of the surface area of an infinite number of spherical shells of infinitesimal thickness concentrically stacked inside one another from radius 0 to radius r. At infinitesimal thickness the discrepancy between the inner and outer surface area of any given shell is infinitesimal and the elemental volume at radius r is simply the product of the surface area at radius r and the infinitesimal thickness.

At longer ranges, solid shot or the common shell — a hollow cast iron sphere filled with black powder — was used, although with more of a concussive than a fragmentation effect, as the pieces of the shell were very large and sparse in number.

: For Newton number, see also Kissing number in the sphere packing problem

A vajra is also a scepter-like ritual object ( dorje ), which has a sphere ( and sometimes a gankyil ) at its centre, and a variable number of spokes, 3, 5 or 9 at each end ( depending on the sadhana ), enfolding either end of the rod.

The non-orientable genus, demigenus, or Euler genus of a connected, non-orientable closed surface is a positive integer representing the number of cross-caps attached to a sphere.

The number of degrees can be determined via a ratio of marine leagues to degrees applied to the Earth regardless of its assumed size, or via a specific marine league applied to the true size of the Earth, called " our sphere " by Harrisse.

In the former, the cylinder power is a number of diopters more convergent than the sphere power.

In the latter, the cylinder power is a number of diopters more divergent than the sphere component.

There is no difference in these forms of notation and it is easy to convert between them: simply add the sphere and cylinder numbers together to produce the converted sphere — then change the sign of the cylinder number.

Angle excess, also known as spherical excess is the amount by which the sum of the angles of a polygon on a sphere exceeds the sum of the angles of a polygon with the same number of sides in a plane.

Thermal control was planned to be achieved by a large number of small " propeller blade " devices on the surface of the sphere.

The Crusade was prosecuted primarily by the French crown and promptly took on a political flavour, resulting in not only a significant reduction in the number of practicing Cathars but also a realignment of Occitania, bringing it into the sphere of the French crown and diminishing the distinct regional culture and high level of Aragonese influence.

There are a large number of people with connections to the town who have made themselves important in one sphere or another.

Note that for orientable compact surfaces without boundary, the Euler characteristic equals, where is the genus of the surface: Any orientable compact surface without boundary is topologically equivalent to a sphere with some handles attached, and counts the number of handles.

The number of states with energy less than E < sub > f </ sub > is equal to the number of states that lie within a sphere of radius in the region of n-space where n < sub > x </ sub >, n < sub > y </ sub >, n < sub > z </ sub > are positive.

Probably we should connect with this the statement that Xenocrates called unity and duality ( monas and duas ) deities, and characterised the former as the first male existence, ruling in heaven, as father and Zeus, as uneven number and spirit ; the latter as female, as the mother of the gods, and as the soul of the universe which reigns over the mutable world under heaven, or, as others have it, that he named the Zeus who ever remains like himself, governing in the sphere of the immutable, the highest ; the one who rules over the mutable, sublunary world, the last, or outermost.

The physical significance of Biot number can be understood by imagining the heat flow from a small hot metal sphere suddenly immersed in a pool, to the surrounding fluid.