Mars steals the show this month as it rapidly approaches Earth at an average rate of 210,000 miles (338,000 km) per day and nearly doubles in brightness through July. By month’s end it will be at its biggest and brightest for the next 17 years.
But not even Mars' exceptional brilliance can outdo Venus, shining like a sequined showgirl low in the western twilight sky. And well to Venus' lower right, you might even get a glimpse early in the month of Mercury. Jupiter shines brilliantly in the south as darkness falls, while bright Saturn glimmers low in the southeast at dusk fades. Finally, toward month's end, Mars calls attention to itself, low above the southeast horizon during evening twilight. No doubt many who have not yet seen it this year will do a double take and no doubt remark: "What the heck is that?!"
This all sets the stage for August, when four of the five brightest naked-eye planets will be stretched across the early evening sky from west to east. [How to See the Planets in the 2018 Night Sky]
In our schedule for July's night sky, remember that when measuring the angular separation between two celestial objects, your clenched fist held at arm's length measures roughly 10 degrees. Here, we present a schedule below which provides some of the best planet viewing times as well directing you as to where to look to see them.
Mercury is at magnitude +0.5 and easy to observe as July begins. It sets a few degrees south of where the sun sets, but 1½ hours later. On July 11th, this speedy world stands at greatest elongation, 26-degrees from the sun; look for it 12-degrees to the lower right of Venus. Nine days later it sets only an hour after the sun, at a dimmer magnitude +1.1 and will be more difficult to see. After sunset on July 14th, look low toward the western horizon about 45 minutes after sunset and try to catch a glimpse a slender crescent moon hovering about 2-degrees above Mercury. Binoculars will help.
Venus is conspicuous as July's long evening twilights fade. If you live at mid-northern latitudes and look to the west about ¾ hour after sunset, you'll find Venus shining brightly about 15-degrees high this month. This is noticeably lower than it was in June. The planet starts July setting more than two hours after the sun and follows the sun down somewhat sooner by month's end.
Venus is still rather small in a telescope this month, but there's no doubt that it has a gibbous phase. It will be larger in apparent diameter but smaller in phase – down to about half lit – when it reaches greatest elongation from the sun in mid-August. On the evening of July 9th, you will notice a much dimmer but still reasonably prominent point of light near Venus: the bluish 1st magnitude star Regulus. Venus burns only 1-degree to the upper right of Regulus which is 150 times fainter. They're within 3-degrees of each other from July 7th through 12th. Then, on July 15th, the 3½-day old crescent moon will sit 2 to 3-degrees to the right of Venus. Related: Best Telescopes for the Money
Earth reaches aphelion, its farthest point from the sun in its orbit on July 6th, at 1 p.m. EDT. Our planet is then 94,507,803 miles from the Sun (measured center to center), which is 3.3 percent farther from the sun than we were at perihelion last January 3rd; a change of only one part in 30.
Mars owns the summer sky of 2018! Without a question of doubt, this is indeed the "Summer of Mars."
Mars at Opposition 2018: How to See It and What to Expect
This planet is approaching its closest opposition since 2003 and rises two hours after sunset tonight, but only one hour after by the 15th. As its distance during this interval decreases from 41 to 37 million miles, the red planet brightens noticeably from magnitude -2.2 to -2.6, even outshining Jupiter by July 7th. Mars is moving rapidly to the west against the background stars of southern Capricornus, rising about 4 minutes earlier each day. Mars comes to opposition during the overnight hours of July 26-27. This busy little planet is then halfway around the sky from the sun, coming up just about when the sun goes down. A small telescope magnifying only 75-power will readily show its disk, dark surface features and its shrinking polar cap tipped about 15-degrees toward Earth. This month is the best time in the last 15 years for observing the red planet, even though it doesn't get very high in the sky. So don't pass up the opportunity! It's highest around 1 a.m. local daylight time. Even to the naked eye Mars seems to press close, shining as bright as magnitude -2.8. It's now nearly twice as bright as Jupiter and brighter than anything else up there except the sun, moon, Venus, and an occasional fiery summer meteor. Mars is closest to the Earth on July 31st at 3:50 a.m. EDT at a distance of 35.78 million miles; five days after opposition (the difference is due to the ellipticity of the planets' orbits). The next time it approaches Earth as closely as this will be on September 11, 2035.
Jupiter at magnitude -2.2, shines brightly all evening in the south to southwest. After July 11th, careful observers will notice Jupiter start to creep eastward relative to background stars. Its distance from the 3rd magnitude double star Zubenelgenubi, Alpha (α) Librae, shrinks slightly from 2° to 1½-degrees by month's end. On the evening of July 20th, "Big Jupe," is prominently placed about 3½-degrees below the moon, just past first quarter phase.
Saturn is probably the first thing most people will turn to when setting up a telescope at dusk this month. The ringed planet, just past its June 27th opposition, decorates the constellation of Sagittarius. It is well up in the south-southeast by late twilight and transits the meridian (is due south) during evening hours: at midnight local daylight time around the beginning of the month, and at dusk by month's end. Any telescope that shows Saturn's rings (whose face is now tilted 26-degrees into view) will also show its largest moon, Titan, an 8.5-magnitude orange point that is always within 4 ring lengths of the planet. Watch Titan from night to night as it circles the planet every 16 days. Several other Saturnian moons may be visible too. On the evening of July 24th, as the waxing gibbous moon ascends the south-southeast sky, take note of Saturn shining below it. During the course of the night, take note of how the gap between the two shrinks as the moon slowly draws closer, moving at roughly its own diameter each hour.
Joe Rao serves an Associate at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers’ Almanac and other publications, and he is also a meteorologist for Verizon FiOS1 News in the Lower Hudson Valley.
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https://www.space.com/33619-visible-planets-guide.html The Brightest Planets in July’s Night Sky: How to See them (and When)
[bestandroiddoubledinheadunit950.blogspot.com]The Brightest Planets in July’s Night Sky: How to See them (and When)
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