Galactic halo in the context of "Galactic corona"

The type-cD galaxy (also cD-type galaxy, cD galaxy) is a galaxy morphology classification, a subtype of type-D giant elliptical galaxy. Characterized by a large halo of stars, they can be found near the centres of some rich galaxy clusters. They are also known as supergiant ellipticals or central dominant galaxies.

Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, form part of the Hubble sequence. Most spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. These are often surrounded by a much fainter halo of stars, many of which reside in globular clusters.

Spiral galaxies are named by their spiral structures that extend from the center into the galactic disk. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disc because of the young, hot OB stars that inhabit them.

Proper motion is the angular speed of a celestial object, such as a star, as it moves across the sky. It is an astrometric measure, giving an object's change in angular position over time relative to the center of mass of the Solar System. This parameter is measured relative to the distant stars or a stable reference such as the International Celestial Reference Frame (ICRF). Patterns in proper motion reveal larger structures like stellar streams, the general rotation of the Milky Way disk, and the random motions of stars in the Galactic halo.

The components for proper motion in the equatorial coordinate system (of a given epoch, often J2000.0) are given in the direction of right ascension (μ_α) and of declination (μ_δ). Their combined value is computed as the total proper motion (μ). It has dimensions of angle per time, typically arcseconds per year or milliarcseconds per year.

Messier 80 (also known as M80 or NGC 6093) is a globular cluster located approximately 32,600 light-years (10,000 pc) from Earth in the constellation Scorpius. Discovered by Charles Messier in 1781, it is one of the densest globular clusters in the Milky Way, containing several hundred thousand stars within a spatial diameter of about 95 light-years.

The cluster is situated in the Galactic halo, more than twice as distant as the Galactic Center, and lies midway between the stars α Scorpii (Antares) and β Scorpii in a region rich with nebulæ. With an apparent angular diameter of 10 arcminutes, it can be observed from locations below the 67th parallel north using modest amateur telescopes, where it appears as a mottled ball of light under low light pollution conditions.

A stellar halo is the component of a galaxy's galactic halo that contains stars. The stellar halo extends far outside a galaxy's brightest regions and typically contains its oldest and most metal-poor stars.