<P> On average , the visible diameter of the Sun on Mercury is 2.5 times as large as it appears from Earth , and its total brightness is more than 6 times as great . Because of the planet 's eccentric orbit , the Sun 's apparent size in the sky would vary from 2.2 times that from Earth at aphelion ( with total brightness 4.8 times as great ) , to 3.2 times at perihelion ( with total brightness 10.2 times as great ) . </P>
how big is the sun in mercury 's sky
2.5 times as large as it appears from Earth