- August 17, 2016 - Planétarium Rio Tinto Alcan : Astronomical News
Two spectacular planetary appulses are set to take place near the end of the month: On the evening of August 24, Mars will appear about four degrees below Saturn; and at twilight on the 27th, Venus and Jupiter will be just one-tenth of a degree apart — their closest approach in over 25 years!
The term appulse refers to the closest approach of two celestial objects to each other, seen along the same line of sight from a third object (usually the Earth). Strictly speaking, conjunctions occur when two or more astronomical objects appear on the same line of celestial longitude, no matter how far apart they are. So in fact, the two planetary appulses happening this month are also spectacular conjunctions.
Mars and Saturn
Saturn takes nearly 30 years to orbit the Sun, thereby completing one lap of the zodiac constellations. For many months, the magnificent ringed planet has been a fixture in the southern sky above the stars of Scorpius; it currently shines about six degrees north of the bright supergiant star Antares. Mars, on the other hand, takes less than two years to complete its solar orbit, so it travels quickly among the constellations.
For the past month and a half, Mars has been moving steadily toward Saturn, and from August 23 to 24 it will cross an imaginary line connecting the ringed planet to Antares. At that point, Mars will appear less than four and a half degrees below Saturn and just one and three-quarter degrees above Antares — an excellent opportunity to compare the colour of the Red Planet with the red supergiant star whose name, incidentally, means “rival of Ares” (ancient Greek for “rival of Mars”).
Venus and Jupiter
The same situation applies with Venus and Jupiter. Venus occupies a small orbit and takes 225 days to circle the Sun, while Jupiter takes 12 years. For the past several months, the giant gaseous planet has shone in the western evening sky, beneath the stars of Leo. However, it has also been steadily sinking into the twilight, while Venus, which emerged above the western horizon early in July, has been moving rapidly toward Jupiter ever since. On August 27, the two planets will converge, appearing less than one-tenth of a degree apart—so close that to the naked eye they will almost seem to merge!
This challenging observation is possible because Venus and Jupiter are the two brightest planets. Although they will be just five degrees above the horizon, their combined brilliance should be enough to pierce the glow of twilight. Using binoculars, scan the horizon, due west, immediately after sunset: Dazzling Venus will appear first, and as twilight deepens, Jupiter will emerge just below it. Then see if you can resolve them without optical aid. Of course, a clear sky, an unobstructed horizon and a bit of luck will be absolutely essential.
For more information about these and other current celestial events consult: