The Moon has a brilliant companion tonight. Jupiter stands to the lower right of the Moon as night falls. Although it looks like a bright star, it’s actually the largest planet in the solar system — about 11 times Earth’s diameter and more than 300 times Earth’s mass.
Earth and Jupiter were at their closest just six weeks ago — about 410 million miles apart. Now, Earth is pulling away from the giant planet, so the gap between them is getting wider. Jupiter is about 24 million miles farther than it was in early May. And over the coming months, the gap will get wider still.
As that happens, Jupiter will grow a bit fainter. Right now, it’s the third-brightest object in the night sky. It’s outshined only by the Moon and by the planet Venus, the dazzling “evening star.” But Jupiter is already a few percent fainter than it was in early May. And by this time next month, it will have lost the “third-brightest-object” title to Mars — both because Jupiter is fading and because Mars is getting brighter.
A planet is at its best when it’s closest to Earth, which comes as it lines up opposite the Sun in our sky. Jupiter was at opposition six weeks ago. Saturn will be at opposition next week; we’ll have more about that tomorrow. Saturn is smaller and farther than Jupiter, though, so it won’t shine as brightly. And Mars will reach its opposition in about a month — allowing it to briefly outshine the giant planet Jupiter.