Diagram showing the spectral class and luminosity of stars
Diagram showing the spectral class and luminosity of stars. The diagram was named The Hertzsprung-Russell Diagram, or the H-R diagram for short. At the beginning of the 20th century two astronomers found that if stars were plotted on a diagram with their luminosity (brightness) on one axis, and their spectral class on the other, that stars formed three distinct groups. The largest group, the Main Sequence Stars, is where 90% of the stars are found. These stars are fusing hydrogen into helium in their cores. This group propagates diagonally from the upper left corner, down to the right corner. The group below the main sequence is the White Dwarfs, which is a group of small, earth-sized stellar remnants. The third group, which is found above the main sequence is that of the giants.
Stars appear on a specific place on the main sequence depending on their mass and age. The mass determines when it will leave the main sequence.The H-R diagram is a significant tool for astronomers, when it comes to understanding stellar evolution.
© Fahad Sulehria/Stocktrek Images
WW1 - Catholic Mass in the Trenches at Bienvillers-aux-Bois
WW1 - French troops partake in Catholic Mass in the Trenches at Bienvillers-aux-Bois - August 1915. It was estimated that over 20, 000 priests served in the French army in some capacity. Services were often carried out in the trenches, and the priest would wear his surplice over his uniform where possible. Date: 1915
© Mary Evans / Grenville Collins Postcard Collection
Higgs Boson particle, artwork
Higgs Boson particle. Computer artwork of a yellow sphere in a circular chamber with light emanating from behind it. This could represent the Higgs Boson particle being discovered in a particle accelerator. The Higgs Boson is an elementary particle predicted by the Standard Model of particle physics. It is the only particle of the Standard Model which is yet to be detected (as of 2009). Particle accelerators are enormous circular tunnels built underground. They are used to accelerate particles towards each other at massive speeds. When the particles collide they break up into smaller particles, revealing their component parts. It is hoped that this process will enable the detection of the Higgs Boson.
© LAGUNA DESIGN/SCIENCE PHOTO LIBRARY