It’s been more than two decades since a mission of exploration has entered Jovian orbit. The Galileo spacecraft began that encounter December 7, 1995, initiating a venture that provided eight years of close-up observations of Jupiter and parts of its satellite system.
Since then, the most recent proximate glimpse of Jupiter was via the New Horizons flyby of the giant planet February 28, 2007, while the mission received a gravity induced velocity boost on its way toward the historic July 2015 rendezvous with Pluto.
Currently Jupiter remains a vivid feature of our evening sky, and over these weeks a new spacecraft—NASA’s Juno mission—races toward the giant planet with orbital insertion expected on the Fourth of July.
The night of Saturday, June 11, the Moon appears less than five degrees of arc southeast of Jupiter. That span is equivalent to about half a fist-length viewed with your arm fully extended. Personal enjoyment of Jupiter in the western evening sky these weeks provides a fine visual complement to current news updates about the Juno mission.
Named after the wife of Jupiter, chief god in Roman mythology, the Juno mission was launched August 5, 2011. It’s planned to be in an orbit that passes over the Jovian poles, thereby providing full coverage of the planet. Juno's primary goal is to help us better understand the origin and evolution of the Solar System’s largest world. Aims include study of Jupiter’s atmosphere and internal composition, as well as observations of its magnetic and gravitational fields. Answers are sought regarding the planet’s structure, such as the nature of its core. Most astronomy textbooks show cut-away drawings of Jupiter with an extremely hot, dense rocky/metallic core several times the size of Earth. But does such a core actually exist? Juno is expected to provide the definitive answer.
Thursday and Friday, June 16 and 17, the waxing gibbous Moon may be seen about eight degrees north of Mars. If you haven’t spotted the red planet this season, these nights are good times to have a look with the Moon as your guide. That weekend Mars is about 77% as bright as it was May 30, when it was closest to Earth this year.
Saturn’s turn for a June lunar passage is the night June 18, when the Moon, two days before Full, appears during early evening less than 3° from the magnificent ringed planet.
June’s Full Moon, this year on Monday, June 20, is sometimes called the “Strawberry Moon”, a name ascribed to northeast Woodlands Native Americans (and resonant with anyone who grows, picks, and/or eats local strawberries this month).
Also on June 20, at 6:34 p.m. EDT, the Sun will be directly overhead a point in the Pacific Ocean about 148 miles north of Honolulu, Hawaii. At that time summer officially begins in the Northern Hemisphere.