Report Abuse. The Milky Way, BY FAR! To give you an idea of size: Our sun, the next biggest celestial object on your list, is about 870,000 miles in diameter. The Milky Way's diameter is about 600,000, 000, 000,000 ,000 miles in diameter!Or in more practical terms: If the sun were the size of a large pin-head, the Milky Way would extend from the Earth to nearly twice the distance to the moon. screaming monk · 8 years ago.he Milky Way's diameter is about 600,000, 000, 000,000 ,000 miles in diameter! Or in more practical terms: If the sun were the size of a large pin-head, the Milky Way would extend from the Earth to nearly twice the distance to the moon. screaming monk · 8 years ago.