Megalodon shark and great white
Megalodon shark (Carcharodon megalodon), computer artwork. A great white shark (Carcharodon carcharias) is shown below it at the same scale. This enormous shark lived between around 20 and 1.2 million years ago, and is known from fossils. It was related to the modern great white shark, and is thought to have fed on whales, as this is the only source of food that could have provided it with enough meat. Megalodon was thought to attain lengths exceeding 20 metres, and possibly significantly larger. It is thought that it died out after the seas cooled, allowing warm-blooded whales to escape the sharks for much of the year by swimming to waters too cold for them to survive in.
© CHRISTIAN DARKIN/SCIENCE PHOTO LIBRARY
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
Japans Expo '70 - British Hostess Uniform - London
Lydia Parry, of Shaw Hill, near Chorley, Lancashire, a 20-year-old student at Sheffield University's Centre of Japanese Studies, is in London to model the uniform to be worn by the six British and 14 Japanese hostesses employed on guide and escort duties in the British Pavilion at Japan's Expo '70 to be held in Osaka.
© PA/Press Association Images