Summer is in full swing, and though nights are short, there is still plenty to see. Three planets—Mars, Jupiter and Saturn—grace the evening sky. And like many of us, Mercury and Venus are lying low this month, while the summer stars and Milky Way adorn the night.
The inner planets
Mercury rounds the far side of the Sun on July 6 (superior conjunction) and remains masked in evening twilight throughout the current period. After mid-month, try observing the tiny planet with binoculars, but be warned—this is a challenge for experts, and an absolutely clear west-northwest horizon is essential. Start scanning the sky 20 minutes after sunset, looking for a faint point of light emerging in the twilight. On July 16, Mercury will be just above Venus, but it quickly leaves the brilliant planet behind: On the following evenings Mercury moves toward the upper left of Venus, in the direction of Jupiter, which sits some distance off looking out over the scene. On July 30, the furtive planet will be less than half-a-degree above Regulus, the brightest star in Leo. Here’s wishing you success!
Venus was at superior conjunction on June 6, one month before Mercury, and is gradually emerging in the evening sky. Around mid-month, begin scanning for the brilliant planet with binoculars, just above the west-northwest horizon, about 20 minutes after sunset. The shallow angle of the ecliptic on summer evenings constrains Venus close to the horizon in the glare of twilight. But don’t despair: The dazzling planet will be an evening fixture later this fall and throughout the winter.
Earth is a planet we don’t often address in the Monthly Sky, but this month it bears mention. Our beautiful blue world is at aphelion on July 4, farther from the Sun than at any other time of the year! To put things in perspective, at perihelion last January 2, the Earth was about 5 million kilometers closer to the Sun than it is now— a difference of about 16 light seconds. This serves as a perfect illustration that the seasons are not caused by variations in the Earth–Sun distance!
Mars is now well past opposition and resumes its normal eastward movement on July 1, among the stars of Libra, where it will remain throughout the month. The Red Planet is getting farther from Earth and noticeably fainter: it currently shines around magnitude –1 and appears roughly two-and-a-half times fainter than it did at the end of May. Even so, Mars still manages to add an extra splash of colour to the southern part of the evening sky. The waxing gibbous moon will appear above the Red Planet on July 14, forming a flattened triangle together with Saturn.
The outer planets
Jupiter currently shines above the western horizon, during twilight and throughout the evening, beneath Denebola, the star at the tail of Leo, the Lion. Though the giant planet is now too low for detailed telescopic observation, its cloud bands and Galilean moons are still within view. But don’t delay! By month’s end Jupiter sets around 10 p.m., just as astronomical twilight ends. The waxing crescent moon will appear to the lower right of Jupiter on the evening of July 8, and to the lower left on July 9.
Saturn was at opposition on June 3, and continues to shine around magnitude zero, roughly 6 degrees above Antares, the red supergiant star at the heart of Scorpius. This July, the ringed planet continues its retrograde (westward) motion in the constellation of Ophiuchus, where it will remain until the spring. Through a telescope, Saturn’s rings are truly a splendid sight, especially now that they have nearly reached their maximum tilt toward Earth. The waxing gibbous moon will appear less than 3 degrees above Saturn on the evening of July 15.
The summer stars and Milky Way
Altair, Vega and Deneb, the bright stars of the Summer Triangle, have reached their mid-season position: By mid-month, at midnight, they occupy the centre of the sky, stradling our galaxy, the Milky Way, which glows softly in the in the background… Unless you happen to be under a perfectly dark sky, in which case our galaxy doesn’t glow—it blazes overhead! If you scan along the Milky Way with binoculars, from Scorpius and Sagittarius, which dominate the southern horizon, to Cassiopeia and Perseus in the north, you can marvel at all the nebulae and star clusters that inhabit our galactic neighbourhood. Take the time to stop along the way, and try to identify some of them. You’ll find it’s quite an eye-opening experience!