A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust. The word galaxy is derived from the Greek galaxias, literally “milky”, a reference to the Milky Way galaxy. Examples of galaxies range from dwarfs with as few as ten million stars to giants with a hundred trillion stars, each orbiting their galaxy’s own center of mass.

Galaxies contain varying amounts of star systems, star clusters and types of interstellar clouds. In between these objects is a sparse interstellar medium of gas, dust, and cosmic rays. To date it is believed that supermassive black holes may exist at the center of many galaxies (if not all). They are thought to be the primary driver of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy appears to harbor at least one such object.

Galaxies have been historically categorized according to their apparent shape and are broadly based on three types, more can be read about Galaxies here:

  • Elliptical Galaxies – These have an ellipse-shaped profile.
  • Spiral Galaxies – are disk-shaped with dusty, curving arms.
  • Irregular Galaxies – or unusual shapes are known as irregular galaxies

Hubble Sequence Photo

Types of galaxies according to the Hubble classification scheme. E indicates a type of elliptical galaxy; S is a spiral; and SB is a barred-spiral galaxy

There are estimated to be more than 170 billion galaxies in the observable universe.Most are 1,000 to 100,000 parsecs in diameter and usually separated by distances on the order of millions of parsecs. The majority of galaxies are organized into a hierarchy of associations known as groups and clusters, which, in turn usually form larger superclusters.

FYI – The parsec (symbol: pc) is a unit of length used in astronomy. It is about 3.26 light-years, which is equal to just under 31 trillion kilometres or just over 19 trillion miles. A single light year is equal to just under 10 Trillion kilometers.

I hope you enjoy my images of the Galaxies 🙂

Cheers

Anthony

EQ6 Mount Gallery

EQ8 Mount Gallery