Jupiter dominates evening sky
Mercury puts in a brief appearance at dusk this month, low above the WNW horizon about 30 minutes after sunset.
It begins July shining at mag. -1.0, but fades, by the end of the month, to mag. +0.4. On the evenings of July 24 and 25, about 30 minutes after sunset, look for the thin, waxing, crescent moon near Mercury and the +1.0 mag. star Regulus, in the constellation of Leo the Lion.
As the early evening sky darkens, mighty Jupiter comes into its own. The brightest evening planet of the summer, Jupiter shines at mag. -2.0 as July begins, fading only slightly to mag. -1.9 by month’s end.
Jupiter sets around midnight during the first half of July, but disappears below the western horizon about two hours earlier by month’s end. Look for Jupiter’s four largest moons Io, Europa, Ganymede and Callisto - as they whirl around the planet from hour to hour and night to night. On July 28, the crescent moon sits above Jupiter.
After its opposition (and closest approach to Earth for the year) on June 15, Saturn actually transits (reaches its highest point in the sky for the night) higher in the night sky this month than it did in June, reaching between 25 and 30 degrees above the southern horizon shortly before midnight as July begins, and around 9 p.m. at month’s end. Saturn’s magnificent ring system is open to 26.7 degrees (their near-greatest possible tilt) as seen from Earth. On the night of July 6, the waning, gibbous moon sits above Saturn in the SSE sky. Though you will need a telescope to see the rings, binoculars will enhance your view of Saturn’s golden colour.
Venus, our morning star, rises about two and a half hours before the sun as July opens (three hours by month’s end), and dominates the dawn sky. This brilliant planet fades only slightly this month, from mag. -4.2 to mag. -4.0. About one hour before sunrise on the morning of July 14, Venus will sit to the upper left of the bright star Aldebaran (in Taurus - the Bull) in the eastern sky. Look for the waning, crescent moon to the lower right of Venus on the morning of July 20, about 45 minutes before sunrise.
Mars is nearing superior conjunction (passing on the far side of the sun as seen from Earth) on July 27 and is currently lost in the setting sun’s glare. It will reappear in the eastern dawn sky in late September or early October. In exactly one year, July 27, 2018, Mars will pass on the opposite side of the Earth as seen from the sun, at which time, it will be very close to Earth, and become the fourthbrightest celestial object in the night sky after the sun, moon and Venus.
A long-lived shower (July 12 - Aug.23), the Delta Aquarids (radiant in Aquarius - the Water Bearer) have a nominal peak date of July 27-28.
This shower is thought to be debris from Comet 96P Machholz, though not known for certainty. The meteors strike the Earth’s upper atmosphere about 100 km high and, at approximately 150,000 km per hour, often leaving persistent trails of glowing ionized gas for several seconds after the meteor winks out. The waxing, crescent moon sets before midnight on July 27, leaving the pre-dawn sky moon-free for the peak somewhere between 3-4 p.m. on July 28. Expect to see about 20 plus meteors per hour radiating outward from the southern sky under a dark sky away from city lights. The Aquarids may overlap with some early, brighter Perseid meteors. They peak in mid August.
Here’s an interesting celestial fact: On July 3, the Earth reached aphelion, the farthest point from the sun in its annual orbit. Yes, we are actually about 3.3 per cent further from the sun, at this time of the year, than we are in January, when we reach perihelion (closest point to the Sun).
Until next month, clear skies.