Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

January 23, 1998

Explanation: These two recently released Hubble Space Telescope close-ups show the Northern and Southern lights ... on Jupiter. Like aurora on Earth, these Jovian aurora are caused by charged particles funneled into the atmosphere above the planet's North (right) and South poles by magnetic fields. But Jupiter's magnetic field is extremely large and ionized material expelled from the volcanic moon Io is trapped in it creating light shows 1,000 times more intense than Earth's auroral storms. Charged particles released by Io are also funneled along magnetic flux tubes which form a direct "bridge" to the Jovian atmosphere. The result is auroral hot spots - magnetic footprints 600 or more miles across which race over Jupiter's cloud tops. A hot spot is visible in both images as a comet-like feature just outside the polar auroral rings. In these false color ultraviolet images, Jupiter's limb (edge) appears dull brown while the auroral displays are shades of white and blue.