Wednesday, February 29, 2012

The Rare Triple Eclipse of Jupiter

Written by Matthew Winter 

On March 28, 2004, The Hubble Space Telescope snapped an amazing picture of the transit of two of Jupiter’s confirmed sixty-six moons, and the shadows of three of them, resulting in an image of which shows the spontaneous phenomena capable of this planet’s lunar bodies. At first glances, Jupiter appears to be a brightly colored orb, with hues parallel to a pastel or neon painting, with five different spots placed randomly about its northern hemisphere; its altered coloring was result of being taken by Hubble’s Near Infrared Camera and Multi-Object Spectrometer, instead of photographing in the visible spectrum. The image is comprised of three of these near-infrared photographs, producing the different shades of color visible—yellow indicates high cloud cover, red indicates low, and blue, even lower cloud cover. 

 Although phenomena such as the event captured in the image, finding Jupiter in the night sky is no hard task and can be especially bight when at opposition. But, there are no definite set of celestial coordinates in locating this planet, because of its ever-changing position in the night sky. According to ephemerides however, computers have been able to plot the course of Jupiter on timescales greater than one millennium, so locating and charting the planet’s position will never be tedious work. For the end of February 2012, Jupiter will be visible in the south-southwestern sky just after sunset, at the averaged Right Ascension of 2h 19m and the Declination of + 12° 53’. Again, phenomena seen in the image are rare and do not occur often.

Upon looking at the image, you might inquire of when such an event will occur on Jupiter. Although it might seem very rare that three moons cast their shadow while two transit, rather it is not. This event is called a Jovian Dual-Transit, as it incorporates two different moons, in this case Io and Ganymede, simultaneously transit the surface. But because of the two shadows also cast by these two moons, it is more appropriately named A Jovian Dual-Shadow Transit where two moons transit and cast shadows. The third shadow, consequently given by Callisto, not pictured in the image, makes this event even more complex—and it is quite spectacular that Hubble was in the right place at the right time to photograph such a spectacle. In describing it, however, it is not troublesome to locate the three, distinct shadows of the three moons notwithstanding Io and Ganymede, which seem to be camouflaged in with Jupiter’s pallid colors. Io sits nearly in the center of the image, in white, opposed to its visible color of hazy yellow or golden. Ganymede is to the upper right of Io, and is pale blue; Ganymede is visibly the color of our Moon, a flushed grey.

Whereas a beautiful image of Jupiter with three shadows and two moons cresting its upper hemisphere is rather somber and dreamy, to astronomers, this image allowed them to attempt a new technique of imaging, which succeeded in the end. Attempting to capture images of Jupiter and its moon is rather difficult, especially when completely focused on an object. Because Jupiter moves quickly across Hubble’s telescope view, it was necessary to take a rapid succession of images, before Jupiter moved out of the telescope’s lenses.

Of course, Hubble has the equipment to track an object far away and hold for hours; Jupiter is much closer to earth than distant galaxies, so things tend to move quicker than you would think—and when locked onto it, the sharpness of the image was distorted, creating a blurry picture, not fit to be called a Hubble image. So, astronomers tried, for the purpose of creating a sharper, neater image, to speed up Hubble’s tracking system, resulting in the ‘slower’ movement of Jupiter through the telescope, which in return allowed Hubble to take such a fine image of its moon in such phenomena.

In conclusion, it is important to see that not only did this image of Jupiter’s rare triple ‘eclipse’ phenomena helped astronomers for the better of planetary images (in that, the slowing down of Hubble’s tracking system made clearer photographs of planets from earth), but also to record a rare event for the wonder and mystery of extraplanetary phenomena—other planets do indeed experience eclipses and transits!

With Information from (Accessed February 24 & 27 2012):

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Credit: NASA