Illustration by NASA/JPL-Caltech
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An illustration shows the Juno spacecraft approaching Jupiter.

Illustration by NASA/JPL-Caltech

This Week’s Night Sky: See Jupiter as a NASA Probe Closes In

Also this week, the moon glides near Leo’s heart and an asteroid slips through Scorpius’s claw.

Juno at Jupiter. As NASA’s Juno spacecraft settles into orbit around Jupiter on July 4, skywatchers will get a chance to see the gas giant for themselves hanging in the western sky.

While the probe is too small to pick out even with the best backyard telescopes, the planet will shine like a creamy-colored star that will be hard to miss. Jupiter’s brightness is due in part to its size but also to the highly reflective clouds that blanket the planet.

Small telescopes with high magnification can reveal extraordinary views of Jupiter’s dynamic and colorful atmosphere, including some of the same cloud structures that Juno will be studying up close. These include two brown cloud belts on either side of the planet’s equator and the Great Red Spot, the largest cyclonic storm in the solar system, which has been raging for at least three centuries.

With just binoculars, viewers can see the gas giant’s four major moons: Callisto, Ganymede, Europa, and Io. These objects appear as tiny pinpoints of light on either side of Jupiter’s disk. Watch them over the course of a few hours and you can even see them move in their orbits around the planet.

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After dusk on July 7, look for the moon parked next to Regulus, the brightest star in the constellation Leo, the lion.

Luna and Leo’s Heart. Just as evening dusk sets in on July 7, a thin waxing crescent moon will appear to sink slowly in the west. Look carefully to its right to find the bright star Regulus. The blue-white giant star marks the heart of Leo, the lion, the mythical king of the cosmic jungle. Regulus will be only three degrees away from the moon, about equal to the width of your two middle fingers held at arm’s length.

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On July 8, the moon and Jupiter will make a spectacular pairing for unaided eyes.

Jupiter and the Lion. By the evening of July 8, the moon will slip just under Jupiter, making for a spectacular naked-eye pairing. While the two objects will look close together in our skies, Jupiter lies nearly 2,000 times farther away from Earth than our moon.

As an added observing challenge, see if you can spot the very faint naked-eye star Sigma Leoins, one of the feet of the great lion, which will be less than one degree to the upper left of the planet. This blue-white giant lies 220 light-years from Earth and is 3.5 times larger than our sun.

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On July 10, the asteroid Iris will be sailing through the constellation Scorpius, between brilliant Saturn and Mars.

Asteroid Iris. As night falls on July 10, the fourth brightest asteroid visible from Earth, 7 Iris, will appear to glide through the constellations Scorpius in the southern sky.

Shining at 10th magnitude, the 124-mile-wide (200-kilometer-wide) Iris is an easy target for small backyard telescopes, and on this night a very faint naked-eye star acts as a convenient guidepost.

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The asteroid Iris will be about half a degree below the faint star Lambda Libr.

Begin your search looking toward the southern sky between the planets Saturn and Mars. Iris sits nearly at the halfway point between the two bright star-like objects. Look for the faint star-like Iris positioned in the scorpion’s claw, about 0.5 degrees south of the 5th magnitude star Lambda Libr. The apparent distance between the two objects will be about equal to the width of the moon’s disk in the sky.

To confirm you have bagged Iris, sketch the positions of a handful of stars around the asteroid as seen through the telescope. Look again at the same field of stars a night or two later—the “star” that has moved is the space rock.

Clear skies!

Andrew Fazekas, the Night Sky Guy, is the author of Star Trek: The Official Guide to Our Universe. Follow him on Twitter, Facebook, and his website.