Mercury's orbit has a semimajor axis of 0.387 au. How large would the Sun appear to be in the sky (in angular diameter) as seen by someone on Mercury, compared with its angular diameter from Earth?

Question

Quizplus · Accepted Answer

The angular diameter of an object is inversely proportional to the distance from the observer. Since Mercury is 0.387 au from the Sun, compared to Earth's 1 au, the Sun would appear larger by a factor of 1/0.387, which is approximately 2.58 times larger.

Mercury's Orbit Has a Semimajor Axis of 0