In the first half of the year, more specifically near the spring equinox, the geometry of the ecliptic favours evening appearances of the inner planets. This month, Mercury and Venus take centre stage above the western horizon as soon as the Sun goes down. Mercury even graces us with its best apparition of the year!
Spotlight on Mercury
Even though Mercury offers its best showing of the year, knowing what to look for when trying to spot the tiny planet is important. It appears as an elusive coppery dot in the twilight glow about 30 minutes after sunset and moves quickly with each passing evening.
In early April, look for Mercury near the horizon, slightly to the right of a vertical line drawn directly through the very brilliant Venus. Given its magnitude of –1, Mercury’s rosy glow is easier to make out during the first days of the month, after which it dims. Mercury’s orbital path brings it steadily closer to Venus, until it reaches greatest elongation from the Sun on April 11. Mercury then sinks back toward the Sun. The planet’s position in the sky rapidly affects its visibility, making it tricky to observe as of April 15, and impossible after the 21st.
Venus, the beacon in the west
Venus graces us throughout the month with its unmistakeable brightness, very easy to spot in the west. While it, too, is nearing greatest elongation from the Sun, Venus appears to resist the natural movement that invariably results in celestial bodies setting earlier each evening. Night after night, the iconic winter constellations get swallowed up by the horizon, except for Venus; if you look up at the same time each evening, you’ll see it hanging in about the same location above the horizon for much of the month.
Venus crosses a large part of the constellation Taurus in April. At the start of the month, it can be found to the right of the bull’s front legs, after which it rises rapidly along the animal’s chest, sits 2½ degrees to the left of the Pleiades on April 10, and nestles between the Hyades and the Pleiades from the 11th to the 14th. It then makes its way toward Taurus’s horns and ends the month between the two stars (Beta and Zeta) that mark the tips of the horns. On April 22 and 23, a thin lunar crescent passes close to Venus: The Moon shines 5½ degrees below the brilliant celestial body on the evening of the 22nd and hangs 5 degrees above on the 23rd.
Mars becomes inconspicuous
Mars’s brightness has really waned in the months since its last opposition in December 2022. However, given its magnitude of about +1 and relatively high position in the early evening, the Red Planet is still easy to spot in Gemini. It begins the month at the centre of a triangle formed by the bright stars Betelgeuse, Capella and Pollux, then slowly works its way toward the Twins’ heads. Its apparent diameter has also significantly decreased since its opposition, but experienced, well-equipped observers can still make out a few details with a telescope. On the evening of April 25, the crescent Moon moves to within 2½ degrees of Mars as the two celestial bodies sink toward the west-northwestern horizon around 1 a.m.
Saturn, a treat for early risers
Of the two naked-eye giant planets, only Saturn will be visible in the morning sky in April. At the start of the month, it can be spotted some 30 minutes before sunrise, a short viewing window during which Saturn’s brightness will have to compete with the glow of dawn in the background.
On April 15, a thin crescent Moon hangs 4½ degrees from the planet, elegantly ushering in the second half of the month, during which the gap between the planet and the Sun widens. Saturn is therefore more clearly visible in the hour before sunrise, low above the eastern horizon. Located at the centre of the constellation Aquarius, its magnitude of +1 means it’s much brighter than the surrounding stars.