The diagram below shows the possible axes for an H-R diagram. Of course, all three quantities are essentially showing the same thing. Hertzsprung-Russell Diagram The vertical position represents the stars luminosity. On the H-R diagram, plot the star with a surface temperature of 20 000 K and a. Figure 10.12 plots luminosity versus temperature for a few well-known stars. A third alternative along the horizontal axis is to use spectral class. The Hertzsprung-Russell Diagram depicts the luminosity of stars against. If colour index (B-V) rather than effective temperature is used then it goes from negative (blue) on the left to positive (red) on the right. Unlike the height/mass plot earlier in this section, the effective temperature does not increase as it goes from left to right, it actually decreases, that is the highest temperature is on the left-hand side. This points to an interesting and sometimes confusing feature of the H-R diagram - the scales on the axes.

Given that they have the same total power output Procyon B must therefore have less surface area than Barnard's Star, that is its radius is smaller. The H-R diagram is a graph that shows the effects that both temperature and surface area have on a star. Procyon B however is much hotter than Barnard's Star thus emits much more energy per second per unit surface area. Procyon B and Barnard's Star share the same low luminosity with an absolute magnitude of about +13. The following diagram shows the lower region of the H-R diagram. If we compare the dimmest stars on the H-R diagram we can also make some inferences. Simple calculations provide a size for white dwarfs roughly that of our Earth, less than 1/100 that of the Sun. Technically they have a luminosity class of wd. Last week, we took a first look at the Hertzsprung-Russell diagram (HR diagram), which is how astronomers discovered that stars have life cycles. White dwarfs are very different objects to main sequence stars as we shall see in a later page. In this video, the stars in globular cluster Omega Centauri are rearranged according to their intrinsic. The terminology of white dwarf must not be confused with the old-fashioned term of dwarf stars that was applied to main sequence stars. A Hertzsprung-Russell diagram (H-R diagram) is a graphical. The fact that they are so dim however, means that they must be extremely small and have a very low surface area. Two of the fundamental quantities which describe a star are luminosity and temperature.

They are very hot (about 10,000 K or hotter) therefore emit a lot of energy per second for each square metre of their surface.

If you follow the pink band for hot stars down to the bottom of the H-R diagram you will notice that it intersects another group of stars that includes Procyon B. Sirius is a main sequence star but because it is hotter than the red main sequence Barnard's Star it is much more luminous than it. They have large radii than Sirius hence greater surface areas and higher luminosities. In this case the supergiants Rigel and Deneb have the same effective temperature as Sirius but have extremely high luminosities.

Hr diagram