The Planets

Mercury

Mercury from MESSENGER
Pictured above is the limb of Mercury seen by NASA’s MESSENGER spacecraft upon approach, from about one and a half Earth diameters away. MESSENGER Teams / JHU APL / NASA

During the first two weeks of July, the sun-scorched planet can be glimpsed without any optical aid, low in the eastern sky before sunrise. On the 1st, Mercury glows at magnitude -0.1 and through a telescope shows a disk 7” across, just over half-lit.

One week later, on July 7, Mercury appears 6” in diameter and the Sun illuminates 70-percent of its disk. As the month progresses, the planet falls rapidly sunward and becomes harder to see. It passes behind the Sun from our viewpoint July 23.

Of the five naked eye planets, Mercury, nearest to the Sun, has the most eccentric orbit, and also the orbit most highly inclined to the ecliptic. These peculiarities help explain why the planet is not hard to spot at some apparitions and difficult at others.

Mercury’s disk never appears more than 13” across, and at its elongations it is only half this size. When observing, good, clean optics and high magnifications are important. Red or light-blue filters attached to the eyepiece will also enhance your telescope viewing.

Perhaps the best views of Mercury occur during mid-twilight, when the planet’s pinkish disk stands out brightly against the deep blue. Whenever Mercury can be seen in a darker sky, it is very low. On the other hand, observers who study it in the daytime are often disappointed by air turbulence and washed out contrast.

Finder map (early July) – 30 minutes before sunrise, looking east.
Finder map (mid-July) – 30 minutes before sunrise, looking east.

Venus

Venus and Jupiter on June 28
Venus and Jupiter on the evening of June 28, above Curitiba, Brazil. Although still two days from closest approach, the pair is a striking sight, even with all the light pollution of a large city. Fabiano Diniz

Venus reigns supreme in the evening. The dazzling planet starts the month side by side with Jupiter, some 20° above the western horizon (both worlds set about two and a half hours after the Sun).

On July 1, Venus and Jupiter are separated by only 0.6°, slightly more than a Full Moon’s width. Venus shines at magnitude -4.4 and Jupiter at magnitude -1.8. Only the Full Moon itself – in the southeastern sky this evening – appears brighter.

During the next few days, Venus moves southwest (left as seen from mid-northern latitudes) of Jupiter. By July 10, 4° separate the two. About a week later, on the American evening of July 18, the thin crescent Moon glows only 1.5° from Venus, while the Moon, Venus, Jupiter, and Regulus all fit within a 7° circle.

Venus begins retrograde (westward) motion on July 23; on that evening, both Venus and Jupiter appear 4° from Regulus. The trio is low in the bright twilight, however, setting within an hour of the Sun.

As Venus prepares for its swing between the Earth and Sun in August, the planet’s disk grows dramatically in size but becomes more backlighted and wanes to a thinner crescent. At the start of the month, the 33-percent sunlit crescent is 33” across. By month’s end it is 52” across – much larger than even the disk of Jupiter or the ring system of Saturn – but it thins to only 7-percent illuminated.

Finder map (early July) – 30 minutes after sunset, looking west.
Finder map (mid-July) – 30 minutes after sunset, looking west.
Finder map (late July) – 30 minutes after sunset, looking west.

Mars

Mars, emerging from its travels on the far side of the Sun, will become visible in the last week of July. Binoculars will be essential, since Mars is faint and barely even clears the northeastern horizon by late twilight, half an hour before sunrise.

If you see it, you are one of the select few catching the very start of a nearly two-year apparition, during which the whole world will see Mars lighting the evening skies of mid 2016. Just do not confuse it with orange Pollux to its upper-left.

The orbit of Mars is decidedly eccentric. The distance from the Sun ranges between 155 million and 129 million miles (between 249 million and 207 million kilometers), and this has a definite effect upon Martian climate. As with Earth, perihelion occurs during southern summer, so that on Mars the southern summers are shorter and warmer than those of the north are, while the winters are longer and colder.

At its nearest to us, Mars may come within 36 million miles (59 million kilometers) of the Earth, closer than any other planet apart from Venus. Small telescopes will then show considerable surface detail.

First, there are the polar ice caps, which vary with the seasons. The dark areas are permanent, though minor variations occur. There are also various bright areas, of which the most prominent is Hellas, in the southern part of the planet. At times, it is so bright that it has been mistaken for an extra polar cap.

Finder map (late July) – 30 minutes before sunrise, looking northeast.

Jupiter

Jupiter and its Moons
Jupiter and its four bright moons, as seen through a backyard telescope. In this image, from left to right: Ganymede, Io, Jupiter, Europa and Callisto. Jan Sandberg

Jupiter spends July among the background stars of Leo the Lion – the fifth constellation of the zodiac. The gas giant dims from magnitude -1.8 to -1.7 during the month, and its equatorial diameter appears little more than 30” wide. To make matters worse, details in the atmosphere become harder to see, as the planet sinks closer to the horizon.

You can easily locate Jupiter low in the west after sunset, within just a Full Moon’s width of Venus on July 1 (both planets are still relatively close to each other for one week after that date). The best views will come in late twilight, roughly 45 minutes after sundown, in the first half of the month.

Even though Jupiter’s low altitude means our turbulent atmosphere will prevent sharp views of the planet’s cloud features through a telescope, you will have no trouble spying its four bright moons. Io, Europa, Ganymede, and Callisto always lie along a line passing through Jupiter’s equator, so any bright object away from this line must be a field star and not a jovian satellite.

Each night, the moons’ relative positions change. Io orbits Jupiter in 1.8 days, while Europa takes twice as long. Ganymede’s orbital period, 7.2 days, doubles Europa’s, and Callisto takes 16.8 days. We see their orbits edge-on at all times, so they appear to wander either east or west of the planet.

Finder map (early July) – 30 minutes after sunset, looking west.
Finder map (mid-July) – 30 minutes after sunset, looking west.
Finder map (late July) – 30 minutes after sunset, looking west.

Saturn

Saturn, Dione and Rhea
Pictured above, Saturn’s famous rings are visible along with two of its largest moons, Dione and Rhea. NASA’s Voyager 2 took this “true color” photograph on July 21, 1981. NASA / JPL

Saturn is the bright yellow “star” in the south during early evening. The ringed planet shines at magnitude +0.3 at midmonth, twice as bright as 1st-magnitude Antares, 12° to the southeast. Despite its proximity to the luminary of Scorpius, Saturn actually lies among the background stars of eastern Libra the Balance.

Saturn’s disk, which measures 18” across this month, tends to be bland. Yet careful scrutiny with a 6-inch or larger telescope reveals subtle atmospheric details. The most obvious are a couple of dusky bands and the darker polar regions.

Saturn’s rings currently span 40” and can never be described as bland or subtle. The rings tilt 24° to our line of sight, which affords excellent views. You should have no trouble seeing the dark Cassini Division, which separates the outer A ring from the brighter B ring. On nights with low atmospheric turbulence, the innermost, dusky C ring also comes into view.

Any telescope will show Saturn’s brightest moon, Titan, throughout its 16-day orbit of the planet. Glowing at 8th-magnitude, it passes due north of Saturn on July 6 and 22 and due south on July 13 and 29. 4-inch or larger instruments will also reveal 10th-magnitude Tethys, Dione, and Rhea, all heavily cratered worlds that orbit Saturn in periods between 2 and 5 days.

Finder map (early July) – one hour after sunset, looking south.
Finder map (mid-July) – one hour after sunset, looking south.
Finder map (late July) – one hour after sunset, looking south.

Uranus

Uranus from the Keck II Telescope
The two sides of tilted gas giant Uranus, as viewed by the Keck II Telescope at near infrared wavelengths. Lawrence Sromovsky / Keck Observatory

Uranus trails Neptune across the night sky. It reaches a peak altitude of about 45° when it lies due southeast shortly before dawn. Glowing at magnitude +5.8, Uranus is easy to see through binoculars and even shows up to naked eye under a dark sky.

Uranus is a slow mover; it takes 84 years to orbit the Sun. The rotation period is 17 hours 14 minutes, though, as with the other gas giants, the planet does not spin in the way that a rigid body would do. The extraordinary feature is the tilt of the axis, which amounts to 98°; this is more than a right angle, so that the rotation is technically retrograde.

The Uranian calendar is very curious. Sometimes one of the poles is turned towards the Sun, and has a “day” lasting for 21 Earth years, with a corresponding period of darkness at the opposite pole; sometimes the equator is presented. In total, the poles receive more heat from the Sun than does the equator.

The reason for this unusual tilt is not known. It is often thought that at an early stage in its evolution Uranus was hit by an Earth-sized protoplanet, and literally knocked sideways. This does not sound very likely, but it is hard to think of anything better. Significantly, the satellites and the ring system lie virtually in the plane of Uranus’ equator.

Finder map – field width 15°, stars to magnitude +8.

Neptune

New Berlin Observatory
1838 painting of the New Berlin Observatory at Linden Street, where Johann Galle first observed Neptune. Leibniz Institute

Neptune shines at magnitude +7.8 and lies among the background stars of Aquarius, highest in the south as morning twilight begins. The planet starts July 2° southwest of 4th-magnitude Lambda Aquarii; the gap grows to 2.5° by month’s end.

Following the discovery of Uranus, astronomers set about charting its orbit and quickly discovered a small discrepancy between the planet’s predicted position and where they actually observed it. After half a century, the discrepancy had grown to a quarter of an arcminute, far too big to be explained away as observational error. The logical cause was perturbation by an unknown planet at a greater distance from the Sun.

In the 1840s, two mathematicians independently solved the difficult problem of determining the mass and orbit of the new planet. John Couch Adams reached the solution in September 1845; in June of the following year, Urbain Le Verrier came up with essentially the same answer.

The German astronomer Johann Galle at the Berlin Observatory, using calculations by Urbain Le Verrier, found the new planet within one or two degrees of the predicted position. After some wrangling over names and credits, the new planet was named Neptune, and Adams and Le Verrier are now jointly credited with its discovery.

Finder map – field width 15°, stars to magnitude +8.5.

Pluto

Artist’s Concept of New Horizons
Artist’s concept of the New Horizons spacecraft during its planned encounter with Pluto and its moon, Charon. Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute (JHUAPL / SwRI)

Throughout July, the dwarf planet Pluto lurks in a region about 0.5° northeast of Xi2 Sagittarii. In relation to the familiar “Teapot” asterism of Sagittarius, this star is located 5° north of the Teapot’s handle.

At magnitude +14, Pluto is hard to spot visually even under the best conditions. You will likely need at least a 10-inch scope, although a smaller telescope with a CCD camera attached will also work. Take images a few nights apart, and Pluto’s motion relative to the background stars will betray its location.

Pluto reaches opposition on July 6 and is highest in the middle of the night. Eight days later, on July 14, NASA’s New Horizons probe will make a close flyby of the distant world – more than 3 billion miles (4.8 billion kilometers) from home! After completing its tasks at Pluto, New Horizons will fire its engines and change course to make the first of what will hopefully be two flybys of small but ancient Kuiper Belt Objects (KBOs).

The exploration of Pluto and the Kuiper Belt will provide important insights into the architecture of our solar system, the nature of comets, and even the manner in which Earth and Mars may have acquired water and other volatile compounds. Moreover, New Horizons will reveal the nature of a new and populous class of planets – the ice dwarfs. These objects have never been explored despite 50 years of robotic surveys of the solar system.

Coarse finder map – field width 10°, stars to magnitude +8.5.
Fine finder map – field width 1°, stars to magnitude +14.5.

The Deep Sky

Open Cluster IC 4665
A fine cluster for binoculars or a wide-field eyepiece, IC 4665 is wider than the Full Moon, and easily found 1.5° northeast of Beta Ophiuchi. Bob Franke

Standing along the stream of the summer Milky Way is the large constellation Ophiuchus, the Serpent Bearer. According to mythology, Ophiuchus was the physician who accompanied Jason and the Argonauts in their quest for the Golden Fleece. Appropriately, he is depicted in the sky as holding a serpent, a symbol of wisdom and healing.

Aside from his serpent, Ophiuchus bears many fine examples of nearly every type of deep sky object. Some are big and splashy, while others appear as modest enhancements of the background star field. IC 4665 lies somewhere in between.

This large open cluster just northeast of Beta Ophiuchi is a nice binocular sight, consisting of several dozen 7th- and 8th-magnitude stars. Though its stellar density is not very high, IC 4665 stands out well thanks to the sparseness of its environment. On dark, clear nights, and just with the naked eye, the cluster may be seen as a hazy spot measuring nearly two Full Moons across.

IC 4665 is still an attractive star cluster in a telescope, at low magnification – not from any virtue of concentration, which it most certainly lacks, but from the uniform brilliance of its brightest stars, which with larger apertures are really bright. The group appears as a ring with a short “handle” on its northwestern side and a single bright star almost at its center. The “handle” consists of four progressively fainter stars arching northwest and then west away from the ring.

The stars of IC 4665 are scattered over a 1° area; because the cluster is about 1,400 light-years distant, its full diameter must therefore be around 30 light-years. IC 4665 is anywhere from 30 to 40 million years old – relatively young in astronomical terms! This places it somewhere between the age of the Jewel Box cluster in the southern constellation Crux and the Pleiades.

Finder map – field width 15°, stars to magnitude +8.5.

Asteroids

Ceres Viewed by the Dawn Spacecraft
Ceres viewed by the Dawn spacecraft on May 4, 2015, from a distance of 8,400 miles (13,600 kilometers). NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

On January 1, 1801 (the first day of the new century), Father Giuseppe Piazzi was observing the sky from his home in Sicily when he happened upon a faint starlike object in the constellation Taurus. No doubt, he thought it strange that this star did not appear on his charts of the region.

He marked its position relative to the other known stars and made it a point to return to that area on the next clear night. After a few days passed, he found, to both his surprise and delight, that his “star” had moved! The Italian astronomer had just discovered the first object in the asteroid belt between Mars and Jupiter.

Ceres – once the largest asteroid, now the smallest “dwarf planet” – comprises about a third of the estimated total mass of the asteroids in the solar system, or about 4-percent of the mass of the Moon. It rotates once every nine hours, its brightness showing little variation, which is indicative of a fairly uniform surface, thought to be powdery in nature.

Throughout July, Ceres lies at the border between Sagittarius and Microscopium, below the southern tip of the Capricornus star pattern. For Northern Hemisphere observes this region lies highest around 3 A.M. local daylight time, some 20° above the southern horizon from latitudes close to 40° north. If you can see the whole Sagittarius Teapot asterism, you have a low enough southern view for Ceres.

Ceres comes to opposition on July 25, and brightens from magnitude +7.8 at the start of the month to +7.5 on July 31. Binoculars should easily show it on any clear night, but a small (or big) telescope would be the better bet. The dwarf planet will readily identify itself by its movement within the star field, shifting by about 10’ during a twenty-four hour period.

Finder map – field width 15°, stars to magnitude +8.5.

Comets

C/2014 Q2 Lovejoy on June 6, 2015
C/2014 Q2 Lovejoy on June 6, 2015. Although the comet has faded significantly, it remains an easy telescope target throughout July. Norbert Mrozek

Australian amateur astronomer Terry Lovejoy discovered comet C/2014 Q2 Lovejoy last year, on the night of August 17. His name is already familiar to many stargazers around the world, as a pioneer of early digital SLR imaging and discoverer of no less than five comets.

The comet brightened to roughly magnitude +4 in January this year and became one of the brightest comets located high in a dark sky in years. Observers throughout the world managed to spot it with the unaided eye, even from mildly light polluted suburban locations.

Despite receding from both the Earth and Sun, Comet Lovejoy is still hovering around magnitude +9.5. It clips through the northern constellations Ursa Minor and Draco and, as the month begins, it lies less than 1° south of 2nd-magnitude Kocab (Beta Ursae Minoris). A 4-inch telescope under country skies should reveal the comet as a small fuzz ball roughly 5’ across, not unlike a globular cluster.

C/2014 Q2 Lovejoy is a circumpolar object, meaning it does not set as seen from mid-northern latitudes. It hovers to the upper-left of the north celestial pole in the evening above the northwestern horizon, and dips well below Polaris in the wee morning hours.

Finder map – field width 30°, stars to magnitude +7.5.

88P/Howell on April 27, 2015
Comet 88P/Howell imaged on April 27, 2015, three weeks after perihelion. José J. Chambó

The second bright comet gracing Northern Hemisphere skies this month is 88P/Howell. Discovered with the 18-inch (0.46 meter) Schmidt telescope at Palomar Observatory in 1981, this periodic “dirty snowball” is currently about magnitude +11.

88P/Howell treks steadily toward the northeast across Pisces, Cetus and Aries. This region appears about 30° high in the east as morning twilight begins, so you will have to get up early or stay up all night. Observe from well outside the city and wait until midmonth, when moonlight has left the morning sky.

88P/Howell is fainter and smaller than most of the Messier galaxies. Even under a dark sky, you will need a scope 6 inches or bigger. If you own a “Swan band” filter, do not forget to attach it to the eyepiece. These filters emphasize the cyanogen (CN) spectral line from comets producing some gaseous emissions. They will cause such a comet to appear brighter, but will have little or no effect on a comet whose coma and tail is mostly dust.

Finder map – field width 20°, stars to magnitude +8.5.

Meteors

Bright Meteor over Loch Ness
A stunningly bright shooting star over Loch Ness, Scotland on March 15, 2015. John Alasdair Macdonald

Meteors arise when bits of cosmic debris enter Earth’s atmosphere and burn up from friction with the air, producing bright streaks of light. Most meteor showers result from Earth plowing through a stream of such debris, usually left behind by a comet after innumerable trips around the Sun.

Streams of meteors come and go throughout the year, but July tends to be a quiet month. The best-known annual meteor shower, the Perseids, begins about mid-month but activity starts slowly, with peak action reserved for August. Until then, there is a less productive shower that deserves careful scrutiny.

The Alpha Capricornids produce only about two to five meteors per hour and can be seen from July 3 to August 15. Most Capricornid meteors are bright, flashing streaks, known for leaving ghostly smoke trails in their wake. It appears that they are remnants of debris left by the short-period comet 169P/NEAT, discovered in 2002.

Throughout most of the month, the shower’s radiant is located in northeastern Sagittarius. It shifts by 1° each day, and by July 30 (the date of the maximum), the radiant lies just northeast of the wide naked-eye double star Alpha Capricorni. This region rises to a decent altitude by late evening and climbs still higher in the hours after midnight.

Map – Alpha Capricornids radiant position.

The Southern Delta Aquariids, one of the two distinct meteor showers in the Delta Aquariid stream, produce about 10 to 15 meteors per hour with average speeds of 25 miles (40 kilometers) per second. Best observed after midnight, members of this shower can be seen from July 12 through August 23. Maximum occurs on July 30, just one night before this year’s “Blue Moon” – the second Full Moon in a calendar month.

From mid-northern latitudes, the shower’s radiant rises in the east at around 11 P.M. local daylight time and is highest above the horizon at 4 A.M. Southern Delta Aquariids have an average magnitude of about +3, with very few meteors exhibiting trains.

The Southern Delta Aquariids can be seen over most of the world, but the Southern Hemisphere is favored by long nights this time of year and a higher radiant elevation. The radiant passes directly overhead for anyone located at 16° south latitude; this would be the best location in which to view the display.

Map – Southern Delta Aquariids radiant position.

Some meteors do not belong to any known shower. These are the sporadic meteors, caused by random bits of comet debris spread throughout the inner solar system. They appear randomly across the sky all year long.

In this month’s night sky, careful observers can expect around nine sporadics per hour during the morning hours and three during the dark evening.

Observing Aids

Northern Hemisphere’s Sky – This map portrays the sky as seen near 40° north latitude at 11 P.M. local daylight time in early July and 10 P.M. in late July.

Southern Hemisphere’s Sky – This map is plotted for 35° south latitude. It shows the sky at 8 P.M. local time in early July and 7 P.M. in late July.

Visibility of the Planets – The table provides general information about the visibility of the planets during the current month.

Phases of the Moon – This Moon Phase Calendar shows the Moon’s phase for every day in July.

Jupiter’s Moons – The diagram shows the positions of Galilean satellites on each day in July at midnight.

Sky Events

July 1 – 10 A.M. EDT: Venus is 0.4° south of Jupiter. 10:20 P.M. EDT: Full Moon.

July 5 – 2:52 P.M. EDT: The Moon is at perigee, the point in its orbit when it is nearest to Earth.

July 6 – 4 A.M. EDT: The Moon is 3° north of Neptune. 1 P.M. EDT: Pluto is at opposition. 4 P.M. EDT: Earth is at aphelion, the point in its orbit when it is farthest from the Sun.

July 8 – 4:24 P.M. EDT: Last Quarter Moon. 11 P.M. EDT: The Moon is 0.8° south of Uranus.

July 12 – 2 P.M. EDT: The Moon is 0.9° north of Aldebaran.

July 15 – 9:24 P.M. EDT: New Moon.

July 18 – 2 P.M. EDT: The Moon is 4° south of Jupiter. 9 P.M. EDT: The Moon is 0.4° south of Venus.

July 21 – 7:02 A.M. EDT: The Moon is at apogee, the point in its orbit when it is farthest from Earth.

July 23 – 2 A.M. EDT: Venus is stationary. 3 P.M. EDT: Mercury is in superior conjunction with the Sun.

July 24 – 12:04 A.M. EDT: First Quarter Moon.

July 25 – 4 A.M. EDT: Dwarf planet Ceres is at opposition.

July 26 – 4 A.M. EDT: The Moon is 2° north of Saturn. 1 P.M. EDT: Uranus is stationary.

July 30 – 4 A.M. EDT: The Alpha Capricornid meteor shower is at peak activity. 4 A.M. EDT: The Southern Delta Aquariid meteor shower is at peak activity.

July 31 – 6:43 A.M. EDT: The second Full Moon of the month, also called a Blue Moon. 4 P.M. EDT: Venus is 6° south of Jupiter.

The information provided on this page is accurate for the world’s mid-northern latitudes. Finder maps for the five naked eye planets are plotted for 40° north latitude, but can also be used from other latitudes close to 40° north. Except the two all-sky maps, all other maps can be used no matter the latitude. Local time (local daylight time during summer) represents the time of the reader.