Galaxies on Instagram: "A day on each planet is defined by how long it takes the planet to rotate once on its axis, and they vary dramatically across the solar system. Mercury spins slowly, so its day lasts about 59 Earth days. Venus rotates even more slowly and in the opposite direction, giving it the longest day of all—243 Earth days. Earth takes 24 hours. Mars rotates in about 24 hours and 37 minutes, making its day very close to ours. Jupiter spins the fastest, completing a rotation in just