The Backyard Astronomer: Big, bright Jupiter visits moon

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      On any clear night, look to the southern portion of the sky after sunset and you will come across a bright object. This is not a star but the planet Jupiter.

      Of the eight major planets in our solar system, Jupiter is, literally, the “king”. This fifth planet from the sun is so large; 11 Earths can line up across its equator, and it can hold a thousand more inside.

      Jupiter—along with Saturn, Mars, Venus, and Mercury—can be seen with the unaided eye, while Uranus and Neptune are telescopic objects. In fact, these five planets have been seen for thousands of years and, along with the sun and moon, were named after gods. These seven celestial objects give us our seven days of the week.

      Gary Boyle

      Jupiter has more than 70 moons that are small in size compared to its four giant Galilean moons named Io, Europa, Ganymede, and Callisto. At 5,268 kilometres in width, Ganymede is the largest. Any telescope will show these very distinct worlds as they orbit its mammoth planet. Io is an extremely active moon, with dozens of volcanoes that blast plumes of sulfurous material as high as 500 kilometres. These have been imaged by spacecraft orbiting or passing by the Jovian system.

      At various points in the moons' orbits, they transit—or cross in front of—Jupiter and cast a small, inky-black dot on Jupiter’s cloud tops. At times, there could be two or three shadows at the same time. These four objects were first observed by Galileo in 1609 with his newly built telescope. He also went on to observe the rings of Saturn, the crescent phases of Venus, and the heavily cratered moon.

      Volcanic plume on horizon of Jovian moon Io.

      The moon will be located near Jupiter on July 13 and Saturn two nights later, on the 15th. With orbits of 11.8 and 29.5 Earth years, respectively, around the sun, the two planets' nightly motion against the background stars is extremely slow. For those living in dark skies away from light pollution, the Milky Way is wedged between the two, thus making a striking view.

      Meanwhile, July 20 will be the 50th anniversary of humans landing on the surface of the moon. The last half-century has seen tremendous advancement in technology and space exploration. We have sent Voyagers 1 and 2 to give us a closeup look in the gas giants and sent an array of orbiting satellites and rovers to Mars. For almost 30 years the Hubble Space Telescope has imaged the far depths of the universe. Gravity waves have been detected during the past few years, stemming from Einstein’s prediction in 1916. And, finally, we have imaged a black hole located 55 million light years away. This is a wonderful age to follow amazing discoveries and enjoy the night sky with today’s state-of-the-art telescopes and cameras.

      Till next time, clear skies.

      Gary Boyle is an astronomy educator, guest speaker, and monthly columnist for the Royal Astronomical Society of Canada. He has been interviewed on more than 50 Canadian radio stations and local Ottawa TV. In recognition of his public outreach in astronomy, the International Astronomical Union has honoured him with the naming of Asteroid (22406) Garyboyle. Follow him on Twitter: @astroeducator or his website: