The Hubble Space Telescope, one of the biggest and most versatile space telescopes that astronomers use, has been sending home important scientific data since it was launched into low-Earth orbit in 1990. Sometimes, it also takes some remarkable pictures that unravel the natural beauty of the cosmos such as the image dubbed the Pillars of Creation.
The recent image the flagship of the world's orbiting telescopes has taken is captured with some stroke of luck. Hubble has captured three of the moons of Jupiter transiting across its face, a phenomenon that rarely occurs.
"Hubble has been important for science, but we felt that there are images that have aesthetic value above and beyond their scientific value," said Zolt Levay, from the Space Telescope Science Institute.
Although Jupiter has more than 60 known moons, its four largest moons are Europa, Io, Ganymede and Callisto. Also known as the Galilean moons after Galileo Galiei, the 17th century scientist who discovered them, these moons complete their orbit around the Solar System's largest planet for a duration ranging from two to 17 days.
While these Galilean moons can be commonly seen transiting Jupiter's face, the sight of three of these moons doing this at the same time is a rare opportunity. Europa, Callisto and Io were captured in a triple-moon conjunction on Jupiter on Jan. 24, an occurrence that happens only once or twice every 10 years.
Mike Wong, from UC Berkeley likened the phenomenon with the eclipses on Earth. Each planetary system has its own eclipse season that depends on how the moons' orbits are inclined relative to the sun. In the case of Jupiter, the alignment of the three Galilean moons has only occurred two times in the last 15 years and the phenomenon is not expected to occur again until the year 2035.
Scientists were also initially concerned if the Hubble would be in the position to capture the event. The Hubble orbits the earth every 96 minutes so it is not clear whether or not it would have the view. Wong said that it is just luck that the telescope was on the right side of the Earth when three of Jupiter's moons were transiting.
The moons in the photos taken by Hubble's Wide Field Camera 3 in visible light are marked by their distinctive colors. Callisto appeared brownish. lo is marked by its orange color while Europa appeared yellow-white.