1. Luminosity: This refers to the total amount of energy a star emits per second. It's essentially how bright the star is.
2. Temperature: This refers to the surface temperature of the star, which is determined by the color of the light it emits. Hotter stars appear bluer, while cooler stars appear redder.
These two characteristics are plotted on a graph, with luminosity on the vertical axis and temperature on the horizontal axis (often with increasing temperature going from right to left). This allows astronomers to classify stars based on their properties and understand their evolution.
