The Brightest Planets in July's Night Sky: How to See Them (and When)

There is only one planet that is completely out of the visibility loop this month: Mars , which is now on the far side of the sun and lost in the solar glare. Interestingly, exactly one year from now, all eyes will be on Mars as the Red Planet makes its closest approach to Earth since the summer of 2003. In the summer of 2018, Mars will glow as a spectacularly brilliant fiery light in the east-southeast sky as darkness falls.

In the meantime, we can be content with views of Jupiter , low in the west-southwest sky at dusk; and Saturn, reaching its highest point in the south at nightfall. For early birds, there’s Venus, which rises 2.5 hours before the sun on July 1, increasing to 3 hours before dawn by month’s end. Finally, there’s Mercury, which is an evening object but is very difficult to see, as it lies very low to the western horizon soon after sunset all month long.

In our schedule, remember that when measuring the angular separation between two celestial objects, your clenched fist held at arm’s length measures roughly 10 degrees. [14 Best Skywatching Events of 2017 ]

Below is a schedule that provides some of the best planet-viewing times in July and tells you where to look.

Mercury — moves steadily east of the sun, reaching greatest elongation (27 degrees) on July 30. Although the size of the elongation is unusually large (because the planet is near aphelion, its farthest point from the sun in its orbit), the geometry is very unfavorable, and Mercury is no more than a scant 1 degree above the western horizon an hour after sunset.

Venus — shines brilliantly, rises just shy of 3 a.m. all month long and is well up in the east just before sunrise. Even though Venus is closer to the sun in angular separation this month compared to June, the ecliptic (the path the sun and planets take through Earth’s sky) is inclined at a steeper angle to the horizon, making Venus appear at a greater altitude. Venus passes 3.1 degrees north of the orange, first-magnitude star Aldebaran in the constellation Taurus on July 13, and the planet forms a triangle with this star and Earth’s moon on the morning of the 20th. Perceptive observers will notice that Venus dims slightly this month, from magnitude minus 4.2 to minus 4.0, an artifact of its pulling away from the Earth: On July 1, Venus is 85.4 million miles (137.4 million kilometers) away, but it will recede to 106 million miles (170.6 million km) out by July 31. Telescopes reveal a dazzling, albeit featureless gibbous disk.

Earth — reaches aphelion on July 3 at 4 p.m. EDT (2000 GMT). Our planet is then 94,505,901 miles (152,092,505 km) from the sun (measured center to center), which is 3,101,579 miles (4,991,508 km), or 3.3 percent, farther from the sun than Earth was at perihelion (the closest point) last Jan. 4 — a change of only 1 part in 30. 

Mars — is in conjunction with the sun on July 27 and is not visible all through July.

Jupiter — beams in the southwest at dusk and is followed not very closely by the bluish first-magnitude star Spica . Jupiter is at eastern quadrature (90 degrees east of the sun) on July 5, so all month it casts its shadow well to the east, permitting good views of eclipses of its four bright moons. On the 28th, Earth’s moon lies just above Jupiter. By month’s end, Jupiter is setting as early as around 11 p.m. daylight saving time. 

Saturn — is probably the first thing most people will turn to when setting up a telescope at dusk in July and August. The ringed planet decorates the constellation of Ophiuchus and is well up in the south by late twilight. Look for it below the moon on the 6th. Saturn’s rings are now wide open, with their north face tilted 26.7 degrees into view; that’s practically at their greatest possible tilt (which ultimately will be attained in October). Saturn sets around 4:30 a.m. local daylight time on July 1, and around 2:20 a.m. by month’s end. 

Joe Rao serves as an instructor and guest lecturer at New York’s Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers’ Almanac and other publications, and he is also an on-camera meteorologist for Fios1 News in Rye Brook, NY. Follow us @Spacedotcom , Facebook or Google+ . Originally published on Space.com .

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