In May, as the spring peepers begin their mating call at nightfall, two very bright planets draw our eyes in opposite directions and compete for our attention.
Venus, the dazzling Evening Sky, is the first to make its presence known. In the minutes following sunset, you can readily spot it over 20 degrees above the west-northwestern horizon. Venus is the brightest celestial object after the Sun and Moon and easily shines through the twilight. Once the sky gets darker, there’s no missing the planet. On May 17 at twilight, a thin crescent Moon less than three days old is 6 degrees to the left of the Evening Star, creating an even more captivating scene. One hour after sunset, the sky is a deep blue and the part of the lunar disc beyond the crescent is bathed in a faint ashen glow. This earthshine is beautiful to the naked eye and especially stunning through binoculars.
In principle, Venus moves away from the Sun for a few months still, but as of June the imaginary line connecting the planet to the Sun starts to be slanted more toward the horizon. Rather than continue to rise higher in the sky at twilight, Venus reaches a sort of plateau before gradually descending. As a result, Venus appears at its highest point in the sky after sunset during the last days of May and first days of June. At this time, the Evening Star sets over two and a half hours after the Sun. Through a telescope, its disc is 12 arc seconds in diameter and resembles a gibbous Moon lit at about 85%.
Jupiter in opposition
Around 9 p.m., as Venus descends slowly toward the west-northwestern horizon, look in the almost diametrically opposite direction. Your eyes will be immediately drawn toward another remarkably bright object: Jupiter rising in the southeast. The planet appears a bit dimmer than Venus because of its distance: Jupiter is over seven times farther from the Sun than Venus is and almost three and a half times farther from Earth than Venus is at present. But thanks to its impressive diameter, almost 12 times larger than the beautiful Evening Star, Jupiter reflects more sunlight and therefore manages to greatly compensate for its distance. Jupiter is truly the giant of the solar system!
Jupiter, which shines now in the constellation Libra, is in opposition on the evening of May 8 and found directly opposite the Sun in the sky. The planet rises at sunset, sets at dawn and culminates in the middle of the night (around 1 a.m. during daylight saving time) at 28 degrees above the southern horizon. But it rises, culminates and sets earlier and earlier as the weeks pass. By late May, Jupiter reaches its optimal position for observation just after 11 p.m. On the evening of May 27, the waxing gibbous Moon lies less than 5 degrees from Jupiter.
When a planet is at opposition, its distance from Earth is shortest and its apparent diameter greatest. That’s why this period is so important for observers. Through a small telescope, Jupiter’s disc now appears 45 arc seconds in diameter. You can easily make out its main bands of light and dark clouds. Look carefully and you can also see that Jupiter’s disc isn’t perfectly circular. Indeed, the planet looks flattened at its poles because the gas giant rotates so rapidly on its axis. Its four main moons change position within a few hours and are also fascinating to observe.
Another duo of planets at dawn
After Venus sets, Jupiter doesn’t remain alone very long. Two other planets show up in the south-southeast. Saturn, which is in opposition next month, appears first. Mars, whose eagerly awaited opposition occurs in July, then emerges about one hour later in early May (the length of time increases somewhat during the month). Around 3:30 a.m., just before the first light of dawn, you can see the two planets about 20 degrees above the southern horizon. The planet on the right is Saturn, which shines in the constellation Sagittarius above the Teapot asterism. Mars, recognizable by its orange hue, is found several degrees to the left of Saturn and is moving toward the constellation Capricornus.
On the morning of May 4, the waning gibbous Moon lies a few degrees to the right of Saturn. The next day, on May 5, our celestial neighbour slips between Saturn and Mars. On the morning of May 6, the gibbous Moon shines less than 2 degrees from the red planet. Almost a lunar month later, the Moon is nearly back where it started: the waning gibbous Moon lies only 2 degrees to the left of Saturn on the evening of May 31 and the night of June 1.