Astronomy Picture of the Day
APOD: 1999 August 6 - Hubble Tracks Jupiter's Great Red Spot
Explanation: It is a hurricane twice the size of the Earth. It has been raging at least as long as telescopes could see it, and shows no signs of slowing. It is Jupiter's Great Red Spot, the largest swirling storm system in the Solar System. Like most astronomical phenomena, the Great Red Spot was neither predicted nor immediately understood after its discovery. Still today, details of how and why the Great Red Spot changes its shape, size, and colour remain mysterious. A better understanding of the weather on Jupiter may help contribute to the better understanding of weather here on Earth. In the pictures on the left, the Hubble Space Telescope has captured Jupiter's Great Red Spot in various states over the past several years.
APOD: 2006 May 5 - Jupiter and the Red Spots
Explanation: Jupiter's Great Red Spot is a swirling storm seen for over 300 years, since the beginning of telescopic observations. But in February 2006, planetary imager Christopher Go noticed it had been joined by Red Spot Jr - formed as smaller whitish oval-shaped storms merged and then developed the remarkable reddish hue. This sharp Hubble Space Telescope image showing the two salmon-coloured Jovian storms was recorded in April. About half the size of the original Red Spot, Red Spot Jr. is similar in diameter to planet Earth. Seen here below and left of the ancient storm system, it trails the Great Red Spot by about an hour as the planet rotates from left to right. While astronomers still don't exactly understand why Jupiter's red spots are red, they do think the appearance of Red Spot Jr. provides evidence for climate change on the Solar System's ruling gas giant.
APOD: 2004 May 2 - Io in True Colour
Explanation: The strangest moon in the Solar System is bright yellow. This picture, showing Io's true colours, was taken in 1999 July by the Galileo spacecraft that orbited Jupiter from 1995 to 2003. Io's colours derive from sulphur and molten silicate rock. The unusual surface of Io is kept very young by its system of active volcanoes. The intense tidal gravity of Jupiter stretches Io and damps wobbles caused by Jupiter's other Galilean moons. The resulting friction greatly heats Io's interior, causing molten rock to explode through the surface. Io's volcanoes are so active that they are effectively turning the whole moon inside out. Some of Io's volcanic lava is so hot it glows in the dark.
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