This breathtaking image, taken by Hubble on 28 March 2004, shows a truly fascinating astronomical event: a rare triple eclipse on Jupiter due to an equally rare alignment of three of its largest moons– Io, Ganymede, Callisto – across the planet's face.
At first glance, Jupiter appears to have five distinct spots on its upper surface: one white, one blue, and three black.
In reality, Io is the white circle in the center, and Ganymede is the blue circle. Callisto is out of the image and to the right, and so not visible. The three black circles are the shadows cast by the three moons.
In fact, the shadows of Io, Ganymede, and Callisto are visible because the three moons, lying between Jupiter and the Sun, block sunlight and create an effect similar to a solar eclipse on Earth.
Io's shadow is just above the center and slightly to the left;
Ganymede's shadow is on the left limb of the planet; Callisto's shadow is near the right edge.
The image, taken with Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS), which operates in the near-infrared, explains Jupiter's pastel colors, different from those we see with the naked eye or in visible light.
The image is particularly captivating and significant both visually and scientifically.
A triple eclipse on Jupiter, in which the shadows of three moons simultaneously cross the planet's disk, is a rare phenomenon, occurring only once or twice every ten years, due to the different orbital periods of the moons. Furthermore, in this particular image, Io and Ganymede cross Jupiter's disk at the same time as the three shadows: an even rarer event.
The event, captured in this image, provides a unique opportunity to observe the interactions between Jupiter and its Galilean moons (including Europa, not visible here). The moons' shadows and positions allow scientists to analyze their orbits, sizes, and physical characteristics.
Shadows cast on Jupiter's layers of cloud provide contrast that helps scientists study the structure and composition of its atmosphere. Sunlight, filtered through Jupiter's atmosphere and visible around the shadows, can reveal details about particles and gases in the upper clouds.
The parallel between this type of eclipse on Jupiter and solar eclipses on Earth allows astronomers to delve into the dynamics of eclipses in settings other than our Earth-Moon system.
This event, captured by Hubble, is a testament to the beauty and complexity of our cosmic neighborhood.
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Image Credit: NASA, ESA, and E. Karkoschka (University of Arizona)
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