The Planets

Mercury

After its best evening apparition of 2015, elusive Mercury now climbs gradually into the dawn. It should become visible low in the east in mid- to late June.

Mercury from MESSENGER
A crescent Mercury, imaged close up by NASA’s MESSENGER spacecraft in 1998. Colors were created using data recorded through infrared, red, and violet filters. NASA / JPL

Mercury reaches greatest elongation, 22° west of the Sun, on June 24. That morning Mercury is almost 7° high a half-hour before sunrise, and shows up easily through binoculars if you have an unobstructed horizon. Just don’t confuse it with slightly dimmer Aldebaran, only 2° to Mercury’s lower right.

As always when Mercury is visible in the morning, its brightness and phase increase throughout the apparition. On the 24th, the planet shines at magnitude +0.6 and telescopes show its 8”-long crescent less than 40-percent lit. As June ends, Mercury has brightened to magnitude -0 and the disk appears exactly half-lit.

Galileo made the first telescopic observations of Mercury in the early 17th century. Although he observed phases when he looked at Venus, his telescope wasn’t powerful enough to see the phases of Mercury.

Thirty years later another Italian, Giovanni Battista Zupi, using a slightly more powerful telescope discovered that Mercury went through phases like the Moon. His observation was more proof that the Copernican theory was correct and the Earth wasn’t the center of the Universe.

Finder map (mid-June) – 30 minutes before sunrise, looking east.
Finder map (late June) – 30 minutes before sunrise, looking east.

Venus

Close Venus-Jupiter Conjunction
Last year, on August 18, Venus and Jupiter gathered close in dawn skies (Venus is above and to the left of Jupiter). The two meet again this month, on the 30th. Stefano De Rosa

For observers at mid-northern latitudes, blazing beacon Venus appears striking as twilight falls. Scan for it a generous 30° high in the west, 30 to 45 minutes after sunset.

On June’s first evening Venus lies among the background stars of Gemini, forming a straight line with the constellation’s brightest stars, Castor and Pollux. The inner world shines at magnitude -4.3, about ten times brighter than Jupiter, 20° to Venus’ upper left.

While Venus gleams a pure white, Jupiter shines a few shades toward pale peach. Watch how their colors deepen toward orange, and even red, as they descend through Earth’s lower atmosphere.

On June 6, Venus reaches a greatest elongation of 45° from the Sun and sets well after 11 P.M. local daylight time. It then slowly approaches M44, the Beehive Cluster in Cancer, and on the evenings of June 13 and 14 slides less than 1° from the cluster’s center.

On June 19, Venus and Jupiter are separated by only 7°. A crescent Moon joins the scene, some 7° below Venus. The next evening, June 20, the Moon lies 5° to Jupiter’s lower left.

In the final week of the month, the separation between Venus and Jupiter shrinks to less than 3°. The two appear closest together on the evening of June 30, when the separation between them is only 0.3° (two-thirds of the Full Moon’s diameter). Both planets will fit in a single field of view through a telescope at fairly high power.

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

Mars

Mars remains out of sight all month. It passes through conjunction with the Sun on June 14, and won’t return to view in the predawn twilight until late July.

Jupiter

Throughout the month, Jupiter can be seen clearly in the evening sky starting at sunset. The giant planet appears some 40° above the western horizon and shines at magnitude -1.9. Its high altitude distinguishes it from Venus, which is the only other point of light that glows so brightly. Jupiter is within 0.3° of Venus on June 30, and the two make a spectacular pair. Both planets are still relatively close on the week surrounding that date.

Jupiter shows off its spectacularly detailed atmosphere to anyone who points a telescope at it. Although the planet’s diameter shrinks from 35″ to 32″ during June, even at its smallest, Jupiter appears more than twice as big as any other planet. It’s plenty large enough to reveal the major belts and zones that run parallel to the Jovian equator. On nights with steady seeing, look for finer details within these surface features. The best views will come in the early evening, when the planet lies higher in the sky.

Any telescope will show as many as four moons near Jupiter. Io, Europa, and Ganymede – the innermost of these so-called Galilean moons – disappear whenever they pass behind the planet or into its shadow. When these three cross in front of Jupiter, observers can see their disks and their ink-black shadows against the bright Jovian cloud tops. The fourth moon, Callisto, lies far enough from the planet that it passes above and below both the disk and shadow, so it’s always on view.

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

Saturn

Saturn from Cassini
The Cassini spacecraft acquired this natural color mosaic in 2007, as it soared 39° above the unilluminated side of Saturn’s rings. NASA / JPL

As Jupiter sinks westward in the late evening, Saturn comes up in the southeast. Although it reached opposition and peak visibility in late May, the ringed planet remains essentially at its closest, biggest, and brightest for 2015.

Saturn lies against the stellar backdrop of eastern Libra, some 10° northwest of 1st-magnitude Antares, the Scorpion’s brightest star. It appears stunning through any telescope once it reaches a respectable altitude shortly before midnight. The planet’s disk measures 18″ across while the rings span 42″ and tilt 24° to our line of sight.

As you may expect, most of our detailed knowledge of Saturn has been drawn from space probes. Four spacecraft have passed by the planet. The first encounter, by Pioneer 11 in September 1979, was just a brief preliminary reconnaissance. Voyager 1 was the next mission to arrive at Saturn, about a year later, followed by Voyager 2 a year after that. The Voyagers sent back the first high-resolution images of the planet, rings, and moons.

The main results, however, have come from Cassini-Huygens, which arrived and went into orbit around Saturn in 2004. The spacecraft found evidence of liquid water reservoirs on the moon Enceladus, revealed a previously undiscovered planetary ring, and saw the first proof of lakes of hydrocarbons on Titan.

Saturn lies almost 800 million miles (1300 million kilometers) from Earth. At that distance, its light takes more than an hour to reach us.

Finder map (early June) – two hours after sunset, looking southeast.
Finder map (mid-June) – two hours after sunset, looking south.
Finder map (late June) – two hours 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 30° when it lies due east shortly before dawn. Glowing at magnitude +5.9, 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 doesn’t 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 isn’t known. It’s often thought that at an early stage in its evolution Uranus was hit by an Earth-sized protoplanet, and literally knocked sideways. This doesn’t sound very likely, but it’s 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 +7.9 and lies in the southeastern sky among the background stars of Aquarius the Water-Bearer, not very high at dawn’s first glow. It remains 2° southwest of 4th-magnitude Lambda Aquarii all month.

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

Pluto from New Horizons
This image of Pluto and its largest moon, Charon, was taken by the Ralph color imager aboard NASA’s New Horizons spacecraft on April 9, 2015. NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute

Throughout June, the dwarf planet Pluto lurks in a region about 1° 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’ll 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 will reach opposition and best visibility next month, on July 6. 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’ll 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

Globular Star Cluster M80
M80, also known as NGC 6093, is one of the densest globular star clusters in our Milky Way galaxy. Hubble Heritage Team (AURA / STScI / NASA)

The southern summer Milky Way is rich in globular clusters. Several are within about a binocular field-width of bright, orange-red Antares. M80 isn’t so prominent, but can be located easily halfway between Graffias (Beta Scorpii) and Antares.

The discovery of M80 has been credited to both Messier and Mechain, both of whom recorded the cluster in January 1781; Messier’s observation seems to have preceded that of his friendly rival by about three weeks. Messier describes it as “A nebula without a star in the Scorpion, between the stars g [now Rho Ophiuchi] and Delta. It was compared with g to determine its position. The nebula is round, its centre brilliant and it resembles the nucleus of a small comet, surrounded by nebulosity.”

At magnitude +7.3 you’ll easily sweep up M80 through a 3-inch telescope. Its stars appear tightly packed, so at 70x it looks more like a tiny, glowing cloud with a bright core. Under excellent conditions (and fairly high power), one can begin to resolve delicate dark rifts in the central core, but even then there’s no real resolution of the cluster into individual stars.

When observing M80, you’ll notice the magnitude +8.5 star SAO 184288. It sits only 4’ northeast of the cluster’s center, but has nothing to do with M80.

M80 has a mass of nearly five hundred thousand Suns and a diameter of about 50 light years. It’s a bulge cluster (meaning it orbits inside the central bulge of our Galaxy) and takes about 70 million years to complete one revolution about the Milky Way. The cluster is home to the largest known concentration of “blue stragglers”, hot stars that have remained in their hydrogen-burning stage longer than they should because stellar mergers have boosted their fuel supplies.

M80 is also the first globular cluster to have a nova discovered in it. The new star (known as T Scorpii) appeared in 1860 and for a few days outshone the globular itself. It soon faded away, but in case it’s a recurrent nova, M80 is worth monitoring.

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

Asteroids

Olbers' Primary Instruments
Olbers’ primary instruments: two five feet (1.5 meters) focal length telescopes, two “comet seekers” and a refractor on the right, and a pendulum clock in the background for the measurement of time. Wilhelm Olbers – “Sein Leben und Seine Werke”

Since the first night of the 19th century, when Father Giuseppe Piazzi discovered Ceres, we’ve noted and cataloged more than 625,000 asteroids with regular orbits, most of them concentrated in the main-belt between the orbits of Mars and Jupiter.

Most main-belt asteroids have reasonably circular orbits and revolve around the Sun in roughly the same plane as the planets. As a result, they never stray far from the ecliptic – the dotted curved line on the circular all-sky map. However, some are highly inclined by 35° in the case of 2 Pallas, for example. It’s likely that this asteroid suffered a big collision during the solar system’s early days, which modified a more typical orbit.

German amateur astronomer Heinrich Wilhelm Olbers discovered Pallas in 1802 while looking for the first asteroid, Ceres. Olbers – best known for posing Olbers’ paradox: “Why’s the sky dark at night?” – also discovered the brightest asteroid (4 Vesta) and several comets. Pallas turned out to be a bit more than 330 miles (530 kilometers) in diameter, making it the second-largest object in the asteroid belt.

Despite its large size, Pallas looks like an ordinary field star glowing at 9th magnitude. The asteroid reaches opposition on June 11 and spends the month among the background stars of Hercules, a region already halfway to the zenith in the eastern sky around midnight. Between June 12 – 14 Pallas passes just 0.5° (one Full Moon diameter) south of 4th-magnitude Lambda Herculis. It continues to move due west from there, and by June 30 it pulls within 0.5° of Delta Herculis.

Finder map – field width 10°, stars to magnitude +10.

Comets

Comet Lovejoy on January 12, 2015
Q2 Lovejoy on January 12, 2015. Although the comet has faded significantly, it remains an easy telescope target. Damian Peach

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, 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 +8.5. It clips through the constellation Ursa Minor and, as the month begins, it lies less than 3° south of Polaris. 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 doesn’t set as seen from mid-northern latitudes. It hovers directly above the north celestial pole in the evening above the northern horizon, and dips west of Polaris after midnight.

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

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 +10.5.

88P/Howell treks steadily toward the northeast across Cetus and Pisces. This region appears about 20° high in the east as morning twilight begins, so you’ll 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’ll need a scope 6 inches or bigger. If you own a “Swan band” filter, don’t forget to attach it to the eyepiece. These filters emphasize the cyanogen (CN) spectral line from comets producing some gaseous emissions. They’ll 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 30°, stars to magnitude +7.5.

Meteors

1921 Illustration of Comet Pons-Winnecke
Contemporary 1921 illustration of Comet Pons-Winnecke, parent body of the June Bootids. Popular Science Monthly, Volume 99 – No. 1

The June Bootids (also known as the Pons–Winneckids) are produced by debris from comet 7P/Pons-Winnecke. Activity is usually indistinguishable from that of the sporadic background, but outbursts were seen in 1916 (100 meteors per hour), 1921 and 1927. All three occurred close to perihelion returns of the parent comet.

Gravitational perturbations thereafter pulled the meteor stream orbit away from Earth, and the shower was presumed to be essentially extinct. However, the June Bootids awoke with a vengeance in 1998, when observed rates of a meteor per minute were seen for over 12 hours.

It’s fair to say there may be little or no activity this year, but you won’t know if you don’t look. Observers should be on the lookout for Bootid “shooting-stars” from June 22 to July 2. Any potential outburst, however, will occur Saturday morning, June 27.

The shower’s radiant – the point in the sky from which meteors appear to originate from – is located in northern Bootes near the border with Draco, and will be excellently positioned as darkness falls. It’ll appear nearly overhead and will remain in view through the whole night.

Keep in mind that Bootid meteors are extremely slow, with a speed of “only” 11 miles (18 kilometers) per second. Meteors coming from the same radiant in Bootes, but not traveling more slowly than most other meteors visible at that time, aren’t June Bootids.

Map – June Bootids radiant position.

Some meteors don’t 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 four sporadics per hour during the morning hours and two 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 June and 10 P.M. in late June.

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

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 June.

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

Sky Events

June 1 – 4 P.M. EDT: The Moon is 1.9° north of Saturn.

June 2 – 12:19 P.M. EDT: Full Moon.

June 6 – 2 P.M. EDT: Venus is at greatest eastern elongation, 45° east of the Sun in the evening sky. 6 P.M. EDT: Dwarf planet Ceres is stationary.

June 8 – 11 P.M. EDT: The Moon is 3° north of Neptune.

June 9 – 11:42 A.M. EDT: Last Quarter Moon.

June 10 – 12:44 A.M. EDT: The Moon is at perigee, the point in its orbit when it’s nearest to Earth.

June 11 – 4 P.M. EDT: Mercury is stationary. 4 P.M. EDT: The Moon is 0.5° south of Uranus. 9 P.M. EDT: Asteroid 2 Pallas is at opposition.

June 12 – 4 P.M. EDT: Neptune is stationary.

June 14 – 11 A.M. EDT: Mars is in conjunction with the Sun. 10 P.M. EDT: The Moon is 0.5° south of Mercury.

June 15 – 8 A.M. EDT: The Moon is 1° north of Aldebaran (Alpha Tauri).

June 16 – 10:05 A.M. EDT: New Moon.

June 20 – 8 P.M. EDT: The Moon is 5° south of Jupiter.

June 21 – 12:38 P.M. EDT: The June solstice occurs.

June 23 – 1:00 P.M. EDT: The Moon is at apogee, the point in its orbit when it’s farthest from Earth.

June 24 – 4 A.M. EDT: Mercury is 2° north of Aldebaran (Alpha Tauri). 7:03 A.M. EDT: First Quarter Moon. 1 P.M. EDT: Mercury is at greatest western elongation, 22° west of the Sun in the morning sky.

June 28 – 9 P.M. EDT: The Moon is 2° north of Saturn.

June 30 – 10 P.M. EDT: Venus and Jupiter are only 0.3° apart.

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.