This paper demonstrates how the H-R diagram, when viewed with temperature increasing from left to right on the graph, can better reflect certain stages of stellar evolution.
The year 2003 marks one hundred years since Professors Hertzsprung and Russell created a diagram for stellar classification, the now famous H-R diagram that every astronomy student must learn. The H-R diagram is a two-dimensional graph that demonstrates the correlation between temperature (or spectral star type) and luminosity. For about 90 percent of all stars, as temperature decreases, luminosity diminishes.
Hertzsprung and Russell created this graph based on optical data. Today we view the universe through the entire window of the electromagnetic spectrum, from lower-energy radio waves through the highest-energy gamma rays. We now better understand how the temperature of cosmic objects increases when a protocloud contracts as a whole under its own gravity to form a star. An increase in temperature, therefore, marks the transition from one stage of stellar evolution into another, as shown in figure 1.
Fig.1. HR- diagram that reflects stars evolution.
This is the H-R diagram, but with temperature increasing from left to right on the X-axis, as opposed to the "classic" H-R diagram with temperature decreasing left to right. The diagram displays a variety of star types. It shows the line of main sequence stars in the optical band, much like the classic H-R diagram.
Suppose the track of the evolution of a star with mass equal to the Sun's mass is described by the drop curve above. One can see that the Sun was a variable star in an earlier stage of its evolution. This version of the H-R diagram, therefore, can demonstrate the manner in which many of the stars that we observe in the cosmos today were protostars before the came to rest along the main sequence -- where they live for very long time but ultimately evolve into a white dwarf. One can also see that the Sun's luminosity was once greater than at present during an earlier stage of its evolution.
This is correct if a star evolves by the contraction of a protocloud as a whole. The luminosity of any star has a maximum during some definite stage of its evolution, as we can see on this version of the HR-diagram.