<u>The sun is a star, which is about billion times brighter as the reflected light from any planet orbiting around it. </u>
The brightness is based on its composition and its position from the planet. The sun happens to be the brightest star on the Earth's sky which is about 13 billion times brighter than the next brightest star.
The origin is represented on the graph by the position (y-value) being 0. The portion of the graph that shows position being non-zero and ending at 0 is the portion marked <em>segment D</em>.
