Our Local Group of galaxies

Look upward at the night sky and you’re viewing the stars of the Milky Way galaxy as they were hundreds and even thousands of light-years in the past. The time it takes the starlight from these celestial bodies to travel the distance between these stars and Earth is very long in human terms, despite the speed of light. If astronomers indicate that a particular galaxy is sixty-million light-years away from Earth, this means it takes light sixty-million light-years to travel the distance to Earth from this galaxy. The true environments existing in distant galaxies remains a mystery for the moment. We’ll board our time-machine-to-the-stars tonight and “Journey to the Beginning of Space and Time’ to take a look a look at the local group of galaxies within the gigantic wheel of the Virgo Supercluster. The physical reality existing in these distant galaxies is likely to be unlike anything imaginable by humankind and things out among distant galaxies doesn’t work as you have been taught things work on Earth. Travelers unfamiliar with Einstein’s relativity need to bone-up on special and general relativity, before getting on board, this will help you deal with the realities of your “Journey to the Beginning of Space and Time”.

Astronomers looking upward into the night sky realised centuries ago that deep-sky objects are distributed unevenly about the night sky. French comet hunter Charles Messier (1730-1817) looking upward into the night sky through his time-machine-to-the-stars compiled a popular catalog of deep-sky objects. His catalogue contains high concentrations of deep-sky objects within the Milky Way above you, where open star clusters and star-forming areas that form them congregate.

Messier’s catalogue also contains entries on 16 objects he located near the border between the constellations Virgo and Coma Berenices. Star gazer William Herschel (1738-1822) and his son, John Herschel (1792-1871), recorded more than 200 celestial objects in this same region of the night sky. It would be in the 1920s and 1930s that astronomers would determine that these nebulous objects are in fact galaxies as big, or larger than, the Milky Way galaxy that constitute a cluster of galaxies far beyond the Milky Way.

Two decades later, French-born astronomer Gerard de Vaucouleurs (1918-1995) noted that the halo of galaxies surrounding what astronomers referred too as the Virgo cluster actually extends all the way to our Local Group of galaxies, which the Milky Way calls home. Today astronomers refer to this Local Group of galaxies as our Local Supercluster of galaxies.

Presently, astronomers believe our Local Supercluster extends 50 million light-years, from the center of the Virgo cluster. We’ll journey from the center of our Local Group to slightly beyond the Virgo cluster. Along the way we’ll stop at all of the galaxy groups and clusters containing at least three reasonably large galaxies and see what astronomers have determined about these distant celestial bodies in the night sky above you.

The first celestial object in the night sky we’ll journey to see is called the Ursa Major North Group, next we’ll travel to Ursa Major South Group, and then make our way to each of the galaxy groups and clusters in the Milky Way’s Local Group of neighbors.