Star Trak: July 2017

BLOOMINGTON, Ind. -- If you have a clear sky to the southwest after sunset at the start of July, you may notice Jupiter. The giant planet is now well above the horizon an hour after sunset, near the bright white star Spica in the constellation Virgo the Maiden. Jupiter will set by 1 a.m. local daylight time at the start of the month and two hours earlier by month's end.

The first few nights of the month will be the best time to view Jupiter through a telescope, since its altitude will drop during July. By the end of the month it will be just 20 degrees high an hour after sundown. Its four brightest moons will all be visible, though occasionally one or more will be passing in front of or behind the planet.

As Jupiter sinks low in the west, Saturn will shine almost as brightly in the southern sky. Saturn's rings will be tilted more than 26 degrees to our line of sight this month, nearly their greatest possible tilt. The planet's largest moon, Titan, will be visible with any telescope.

Venus will rise more than two hours before the sun as July begins and three hours before the sun by month's end. An hour before sunrise it will already be almost 20 degrees high in the east, near the bright orange star Aldebaran in the constellation Taurus the Bull.

Mercury will come into view low in the west during evening twilight all month, but it will be inconspicuous for observers at mid-northern latitudes. At its highest it will be only about 8 degrees above the west-northwestern horizon a half hour after sunset.

Mars will be in conjunction with the sun July 26 and will be out of sight in the solar glare all month.

Meteor shower

The Delta Aquarid meteor shower will peak before dawn July 30, when moonlight will not interfere. Observers can expect to see about 25 meteors per hour in a dark sky. The meteors will appear several nights before and after the peak as well, so the show may be just as good during the hour or two before the start of morning twilight July 29 and 31. The long bright streaks will seem to come from a point in the constellation Aquarius in the southern sky.

Aphelion

On July 3, Earth will reach its greatest distance from the sun for the year, called aphelion. Those sweltering in summer heat in the Northern Hemisphere may find it hard to believe they are about 3 percent farther from the sun than they were in January. But the actual cause of the high temperatures is the tilt of Earth's axis. The part of the planet tilted toward the sun (in this case the Northern Hemisphere) is much warmer than the part tilted away, because more sunlight reaches the ground instead of being absorbed by the atmosphere.

Moon phases

The moon will be full on July 9, at third quarter on July 16, new on July 23 and at first quarter on July 30.

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Hal Kibbey

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