Who invented the hr diagram

Module Stellar Properties. Search for:. The Hertzsprung-Russell Diagram The Hertzsprung-Russell diagram , also referred to as the H-R Diagram, is a graph of stellar absolute magnitude or luminosity versus their spectral type or photosphere temperature. A main sequence star of the same brightness would have only 40 Sun diameters.

The reason for that is that giants are in the right half of the HR diagram, the cooler half, and cooler stars need a much larger surface to reach the same brightness. This is another law of black body radiation, the Stefan-Boltzmann 5 law. In the realm of giants you find many variable stars, ie stars with variable brightness. There are different types, the two most famous being Mira stars in the M-region varying in brightness by a factor and the Cepheides between classes F and G with a very regular light change.

The biggest stars are not part of the main sequence, they are really giants. However, there are hints that even larger stars exist. Dwarfs of luminosity class VI play only a minor role in stellar astronomy.

But very interesting are the white dwarfs , tiny hot suns in the lower left of the HR diagram. Some of them are only 20,km in diameter - twice the Earth! Sometimes they form the minor partner in a twin star system, eg Sirius or Procyon.

This makes it possible to determine their mass quite accurately by measuring the rotational period of the pair. As already mentioned, the HR diagram is spanned by spectral class and absolute brightness. The absolute brightness is directly correlated with luminosity. Although most HR diagram suggest that, the link between spectral class and temperature is not that strong.

But for all practical purposes, one certain spectral class yields a certain surface temperature. The core temperature of the star is something completely different! It lies in the millions of Kelvins region.

Due to the laws of black body radiation, a certain temperature and luminosity means a certain star surface, and with it a certain radius. So you can add lines of constant radius to the HR diagram. They decrease slightly from left to right. As a rule of thumb, the mass increases from right to left, but it's impossible to determine it accurately from the position of the star in the HR diagram alone.

The heaviest stars have the mass of about 70 Suns, the lightest one fifth of our Sun's mass. The exact appearance of the H-R diagram will be slightly different when these alternative axes are used e. Also, spectral type depends weakly on luminosity. Making the decision to study can be a big step, which is why you'll want a trusted University.

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CREDIT: Stuart This isn't in any way supposed to be accurate - it is qualitative - and most of the "Main Career Sequence" is invented based on expectations of an evolutionary sequence assuming little use of the internet before becoming an astronomer.

Mega-stars such as Dr Brian May may follow a totally different path.