The Hertzsprung-Russell (H-R) Diagram

• The Hertzsprung-Russell (H-R) Diagram is a crucial astronomical tool mapping out the life cycle of stars, displaying temperature against luminosity.
• Stars in the H-R Diagram are differentiated by their colour, temperature, size, and stage in stellar evolution.
• The x-axis of the diagram represents the temperature of stars, which decreases from left to right (opposite to what you might expect). The hottest stars are found on the left, while the coolest are on the right.
• The y-axis of the diagram represents the luminosity, or the brightness of the stars. Higher luminosity stars are found towards the top of the diagram, while lower luminosity stars are positioned at the bottom.
• The diagram is divided into sections, each representative of a specific stage in a star’s life. These sections are the main sequence, giants, supergiants, and white dwarfs.
• Main sequence stars, making up a majority of stars including our Sun, are in a stage where hydrogen is being converted to helium in their cores. On the H-R diagram, they lie in a band that stretches from the top left (hot, bright stars) to the bottom right (cool, dim stars).
• As the stars exhaust their hydrogen fuel, they leave the main sequence and evolve into giants or supergiants. These stars are cooler but much brighter due to their larger size, and are found in the upper-right section of the diagram.
• White dwarfs represent the final stage of medium-sized based stars like our Sun. These are very hot but dim stars because of their small size, hence they are located at the bottom left corner of the H-R Diagram.
• Observations via the H-R diagram aid in understanding the stages of stellar evolution, and comparing characteristics of different stars.