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
CIE chromaticity diagram. This diagram (developed in 1931) shows all the colours that can be perceived by the normal human eye, and is the international standard for defining colours. The colours are defined as a weighted sum of 3 primary colours, although in reality no 3 primary colours can combine to give all possible colours, so virtual primary colours are used. The curved edge of the plot corresponds to the colours of the visible spectrum (wavelengths are shown in nanometres), while the straight edge corresponds to non-spectral shades of purple. Pure colours are at the edges; as colours move towards the centre they become less saturated. White is at the centre of the diagram.
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Powder Plot Cellar
The crypt under the old Palace of Westminster where Roman Catholic conspirators stored 36 barrels of gunpowder in an attempt to blow up Parliament on 5th November 1605. Engraved after a drawing by William Capon, 1799. (Photo by Hulton Archive/Getty Images)
© 2005 Getty Images
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