Galactic astronomy Galactic astronomy Brightest Cluster Galaxies {BCGs) are the brightest and most massive galaxies in the universe, emitting purely photospheric light. They are generally elliptical galaxies which lie close to the host galaxy cluster kinematic centre, and except for those undergoing major mergers, they lie at the bottom of the cluster potential well and close to the X-ray peak emission. ...more on Wikipedia about "Brightest Cluster Galaxy"
Galactic astronomy is the study of our own Milky Way galaxy and all its contents. This is in contrast to extragalactic astronomy, which is the study of everything outside our galaxy, including all other galaxies. ...more on Wikipedia about "Galactic astronomy"
Astronomers classify galaxies based on their overall shape ( elliptical, spiral or barred spiral) and further by the specific properties of the individual galaxy (for example degree of ellipse, number of spirals or definition of bar). The system of galaxy classification is called the Hubble "tuning fork" diagram, and is the Hubble sequence. ...more on Wikipedia about "Galaxy classification"
Intergalactic space is the physical space between galaxies. Generally free of dust and debris, intergalactic space is very close to a vacuum. The average density of the Universe is less than one atom per cubic meter. The density of the Universe, however, is clearly not uniform; it ranges from relatively high density in galaxies (including very high density in structures within galaxies, such as planets, stars, and black holes) to extremely rarified conditions in vast voids that have lower density than the Universe's average. Surrounding and stretching between galaxies, there is a rarified gas that is thought to possess a cosmic filamentary structure and that is slightly denser than the average density in the Universe. This material is called the intergalactic medium (IGM) and is mostly ionized hydrogen (i.e. a plasma) consisting of equal numbers of electrons and protons. The IGM is thought to exist at a density of 10 to 100 times the average density of the Universe -- which implies the mass of 10 to 100 hydrogen atoms per cubic meter. ...more on Wikipedia about "Intergalactic space"
The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias), sometimes referred to simply as "the Galaxy"), is a barred spiral galaxy which forms part of the Local Group. Although the Milky Way is but one of billions of galaxies in the universe, the Galaxy has special significance to humanity as it is the home of the solar system. Democritus (460 BC - 370 BC) was the first known person to claim that the Milky Way consists of distant stars. ...more on Wikipedia about "Milky Way"
In cosmology, a protogalaxy is a cloud of gas which is forming into a galaxy. It is believed that the rate of star formation, during this period of galactic evolution, will determine whether a galaxy is a spiral or elliptic galaxy; a slower star formation tends to produce a spiral galaxy. ...more on Wikipedia about "Protogalaxy"
In astronomy, the Tully-Fisher relation, published by astronomers R. Brent Tully and J. Richard Fisher in 1977, is a standard candle that measures the distance to rotating spiral galaxies by the width of the galaxy's spectral lines. The empirically-derived relation states that the luminosity of a galaxy is directly proportional to the fourth power of its rotational velocity, which can be calculated from the width of the spectral line, and uses the distance modulus to find distance from luminosity and apparent magnitude. ...more on Wikipedia about "Tully-Fisher relation" This text is made on www.shortopedia.com shortopedia
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