Hobbies And Interests
Distance Measurements
The sheer magnitude of the sizes, distances and time periods which are needed to quantify the universe on the largest scales is mind boggling. Distances are measured in light years. A light year is how far light can travel in a year at the speed of nearly 300 million meters per second. A light year is approximately 9.5 trillion kilometers. On the grandest scale, the farthest known object astronomers have discovered is about 13.7 billion light years away. The Milky Way Galaxy is about 100,000 light years in diameter.
Grouping of Matter
At every level, matter has a tendency to group into larger collections of matter. This is due to the gravitational force which all matter exudes. It's how stars and planets form, and in turn how stars form into galaxies. However, the large scale structure of the universe does not end with galaxies.
Clusters
A galaxy cluster is a group of galaxies that are all drawn together by mutual gravitational force. Even as the universe expands, these galaxies stay bound together, expanding as a unit but interacting with one another in their own way. The Milky Way is in what is known as the Local Group, containing about 50 galaxies, however larger clusters can contain galaxies in the thousands.
Superclusters
Superclusters are even larger agglomerations of galaxies and galaxy clusters. The different clusters are not necessarily bound together by gravity and the structure is very irregular. Superclusters contain tens of thousands of galaxies. The Milky Way is a part of the Local Supercluster which is also known as the Virgo Supercluster.
Walls and Voids
On an even larger scale, the largest structures known in the universe are known as walls. Superclusters and clusters tend to group together throughout the universe, displaying a structure best described as filamentary, with large empty voids interspersed between thick filaments and walls. The Sloan Great Wall is a massive structure measuring hundreds of millions of light years long and wide.
Dark Matter
The interactions of clusters and superclusters reveal that there must be far more mass in those areas than is visible from the galaxies and interstellar dust and gas alone. This is known as dark matter, which is invisible to astronomers throughout every segment of the electromagnetic radiation spectrum. It is extremely important to the large scale-structure of the universe, and in fact all calculations of the universe's size, scope, past and future depend on dark matter. However, without being able to directly observe it -- it can only be implied -- much about dark matter, including what exactly it is, is still unknown.