The five naked-eye planets—the same ones our ancestors gazed upon—are all visible this month. But you’ll need to rise early or stay up very late (whatever you prefer) to see four of them...
In early April, at around 5:30 a.m., or about one hour before sunrise, your gaze will be drawn to a highly luminous object in the southeast. It’s the beautiful Morning Star Venus, beaming brightly in the first glimmer of dawn. Look a few degrees to the right of Venus and you’ll notice two other dots of light standing out among the neighbouring stars. The first is Saturn, which shines with a soft, cream-white glow. And slightly to the right is Mars, recognizable by its distinct orange-red colour. The famous Red Planet is still far from Earth and rather faint, but it will steadily get closer to us in the coming months.
From one morning to another, these planets move relative to each other and to the background constellations. Saturn, farther away from the Sun, is the slowest of the naked-eye planets, and its movement is almost imperceptible. The much-closer Mars is significantly faster and dashes eastward (to the left). On the morning of April 5, the Red Planet passes a mere ⅓ of a degree below the ringed planet before resuming its trek. The gap between Mars and Saturn continues to widen, but both planets can be seen increasingly earlier before dawn.
Venus revolves around the Sun even more rapidly. And since its orbit is smaller than that of Earth—from our earthly viewpoint—it never strays more than 47 degrees from our star. This April, Venus also travels eastward, zooming past Mars and Saturn, neither of which can keep up; track how the gap widens as the days go by. On its journey, Venus draws close to another bright object that slowly emerges in the dawn sky after mid-April, very low on the eastern horizon: It’s brilliant Jupiter, which slipped behind the Sun on March 5 and is gradually pulling away.
On the morning of April 30, Venus moves to within ½ a degree of Jupiter: The two brightest planets form a striking duo above the eastern horizon at first dawn, about one hour before sunrise, appearing like a pair of eyes staring intensely at us in the night!
By the end of the month, the waning Moon visits each one of them. On the morning of March 25, it forms a large triangle with Mars and Saturn; then on the 26th, it forms another triangle with Venus and Mars. On the 27th, the lunar crescent lies below the Venus-Jupiter duo: Admire the pair around 5:15 a.m., a half-hour before sunrise.
Four of the five planets in the dawn sky—not a bad sight. The only one missing is Mercury, which is travelling solo in the early evening.
A fine appearance by Mercury in the evening
As the planet closest to the Sun, Mercury never moves too far away from our star. That means Mercury is only ever visible for a few weeks every year, and only in the minutes just before sunrise or right after sunset. At this time of the year, Mercury’s orbit is sharply inclined relative to the horizon at nightfall, making spring the best time for viewing it in the evening.
So, this is your chance to catch a glimpse of this fleeting planet. In fact, Mercury makes an excellent appearance in the evening sky from April 13 to May 10, reaching its greatest elongation on April 29, 20.6 degrees east of the Sun. The tiny planet is much brighter at the start of this window of visibility, but it is too low on the horizon before April 12 and simply becomes too dim after May 10. The prime viewing period extends from April 13 to May 3. Thirty minutes after the Sun sets, look for a small dot of light in the glow of twilight, low on the west-northwestern horizon; Mercury will be visible for up to one hour after sunset. The planet also passes very close to the Pleiades star cluster from April 27 to May 2; the thin crescent Moon then enters the scene on the evening of May 2.
An occultation for night owls
Sometimes the Moon passes in front of certain stars that shine more or less brightly. The event is called an occultation—a sort of mini-eclipse. But unlike the Sun, the eclipsed star is so far away that it appears as a mere dot: When the moon covers and then uncovers it, the star’s disappearance and reappearance lasts only a tiny fraction of a second. On the night of April 18 to 19, the waning gibbous Moon (92% illuminated) occults Dschubba (Delta Scorpii), a relatively bright star (magnitude +2.3) that forms part of the head of Scorpius. As seen from Montreal, Dschubba disappears at 2:12:51 a.m. (EDT) behind the Moon’s illuminated edge (21 degrees high in the south-southeast); less than one hour later, at 3:07:55 a.m., the star reappears at our satellite’s dark limb (22 degrees high in the south). The occultation of a relatively bright star such as this one is easily visible in a small telescope. Note, however, that the times mentioned are approximate and may vary by several seconds depending on your exact geographic location: So, look through the eyepiece at least one minute before to ensure you don’t miss a thing!