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
Solar coronal loops, TRACE image
Solar coronal loops. Coloured ultraviolet TRACE image of coronal loops on the Sun following a solar flare event observed in November 2000. The bases of the loops are the hottest areas (white). These areas raise the temperature of the solar corona (atmosphere) thousands of times above that of the Sun's surface (dark, lower frame). The loops comprise electrically charged gases (plasma) at millions of degrees Celsius. Gas is heated as it is ejected from the surface, and follows the path of magnetic field lines before crashing back down on the Sun's surface at over 100 kilometres per second. TRACE (Transition Region and Coronal Explorer) is a space observatory launched in 1998 to study the Sun at ultraviolet wavelengths.
© Lmsal/Stanford Univ/Nasa/Science Photo Library
An incubator nursery
Nurses attending to sick babies kept alive in a ward of incubators. The incubators pictured are from a design by Paul Altmann and distributed by Messrs Coney and Schenkhein. The machine was automatic with the temperature maintained by a thermostat. A chimney was positioned on top of the incubator, acting as an outlet for impure air.
© Mary Evans Picture Library 2015 - https://copyrighthub.org/s0/hub1/creation/maryevans/MaryEvansPictureID/10218178