Skywatchers are gearing up Monday night for an unusually close alignment of Jupiter and Saturn, the solar system’s two largest planets. The rare spectacle, which coincidentally falls on the winter solstice, can be observed across Canada without a telescope or other special equipment.
Anyone looking toward the southwestern horizon soon after sunset will see the brilliant duo side by side, apparently separated by a visual angle of only one-tenth of a degree – approximately the width of a single tine of a dinner fork when held at arm’s length.
The apparent close proximity of two such bright objects in the sky will be a sight to remember, and one that hasn’t been witnessed by human beings for centuries.
Astronomers refer to such planetary encounters as conjunctions. In reality, the two planets will be nowhere near each other. Saturn is currently a cool 1.6 billion kilometres from Earth, while Jupiter is only half as far, at roughly 885 million kilometres. Yet the position of the two heavenly bodies has temporarily placed them on nearly the same line of sight, as viewed from Earth.
Conjunctions occur fairly often as Earth and its planetary neighbours wheel around the sun at different rates, forming an ever-shifting pattern of moving lights around the night sky. It is because of this celestial ballet that Jupiter and Saturn appear to meet up about once every 20 years, for example.
But what makes this conjunction more special than most is how near to each other the planets will seem to approach. The last time Jupiter and Saturn had such a close meetup was 1623, nine years before Galileo published his ground-shaking manuscript defending the idea that Earth was just one planet among many and that all planets orbit the sun.
But that conjunction would have been difficult for Galileo and his contemporaries to observe because it took place so much closer to the sun’s position in the sky. To find a time when Jupiter and Saturn last appeared as they do now, one would have to rewind the clock back to March 5, 1226.
The planets can been seen easily by the unaided eye, low in the southwest as soon as the sky is dark enough for them to appear. Binoculars will enhance the effect.
A typical cellphone camera will not be able to separate the planets for those hoping to capture an image of the event. For better equipped photographers, Calgary-based astrophotographer and author Alan Dyer said that an 85-millimetre to 200-millimetre telephoto lens with an exposure of no more than three to four seconds at ISO 400 to 1600 should provide best results, “with the lens wide open to keep exposures as short as possible.”
He added that the planets will start to separate again in the lead-up to Christmas when they will be easier for small cameras to capture and frame against the twilight sky.
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