Venus, the brilliant Evening Star, is visible in the west immediately after the Sun sets. At the beginning of May, it culminates some 30 degrees above the horizon and remains visible more than three-and-a-half hours after sunset.
However, the dazzling planet is gradually closing in on the Sun, and losing altitude from evening to evening, in the twilight sky — slowly at first, and then more rapidly as the gap narrows. By mid-May, at sunset, Venus is roughly 20 degrees above the horizon and sets two-and-a-half hours after the Sun. On the evening of May 22, don’t miss the crescent Moon right next to the brilliant planet, a truly splendid sight against the colours of twilight.
During the last evenings of May, Venus literally plunges toward the horizon and is lost in the glare of the setting Sun. Until what date can you spot the sinking planet with the naked eye? What about binoculars?
If you have access to a small telescope, try to observe Venus on a regular basis. You’ll notice that its appearance changes dramatically over the course of a few weeks: As the evenings progress, its apparent diameter grows as it approaches Earth. At the start of the month, the planet’s disk measures 38 arc-seconds across; by May 10, it grows to 44 arc-seconds; and on May 20, it reaches a whopping 51 seconds of arc. Meanwhile, as the angle formed by Venus, the Sun and Earth gets narrower, so does the sunlit crescent-shaped part of the planet. The illuminated crescent takes up 26 percent of the planet’s disk on May 1, then 17 percent on May 10, and just 8 percent by May 20.
All these changes are a prelude to a very special event. Because Venus has a smaller, faster orbit than Earth, it passes us every 584 days, which it is now on the verge of doing. On June 5, Venus will be at inferior conjunction, which means it will move between the Sun and Earth. Because Venus’s orbit is inclined a few degrees with respect to ours, when viewed from our planet, Venus usually passes either above, or below, the Sun. This time, however, the alignment will be almost perfect: For a few hours, the planet will move directly in front of the Sun’s disk — a rare phenomenon known as a transit.
Though the last transit of Venus occurred in June 2004, the one before that took place in 1882. And if you miss this opportunity, you should know that the next one will not occur until 2117! Visit transitofvenus.ca to learn more about this interesting event, and the various observing sessions organised by astronomy clubs throughout Québec.
Mars gets farther and fainter
At the beginning of May, Mars culminates high in the south around twilight. The Red Planet dominates the stars of Leo with its colour and brightness. But over the coming weeks, Mars will get farther and fainter. As well, the planet will appear progressively lower in the southwest at nightfall, and by month’s end it will resemble Saturn in brightness. You might also notice that Mars is moving away from Regulus, toward Saturn: In fact, the two planets will rendezvous during the month of August. The gibbous Moon will be near Mars on the evenings of May 1 & May 28.
Saturn at its best
For the last few months, off to the left of Mars, the planet Saturn has formed a remarkable duo with the brilliant blue star, Spica, the brightest in the constellation of Virgo. The pair can be seen above the southern horizon at nightfall. This is the best time to observe Saturn and its famous rings: The sight is spectacular, even with a small telescope. The gibbous Moon will be near Saturn and Spica, on May 4 & May 31, which should help you identify the ringed planet.
An eclipse of the Sun
Another astronomical phenomenon of note — an annular eclipse of the Sun — will take place on May 20. In fact, the band of annularity begins on the morning of May 21, in China, and crosses Japan; it then extends out, over the Pacific, across the International Date Line, and ends in the southwest United States, where the solar “ring of fire” will be visible at sunset on May 20. From Québec, the eclipse will only be partial — insignificant even. Since it begins just a few minutes before sunset, the Moon will barely have a chance to move in front of the Sun before the two objects sink below the horizon.