The Night Sky This Month (June 2010)

The Planets Mercury From midnorthern latitudes look for Mercury during the first half of June, very low in the east 30 minutes before sunrise. As the month begins, the innermost planet glows at magnitude +0.1 and reveals a half-lit disk 7" wide. Although Mercury brightens a few tenths of a magnitude, it becomes lost in the Sun's glare by the third week of the month. The first telescopic observations of Mercury were made by Galileo

in 1610, and although he observed phases when he looked at Venus, his telescope was not powerful enough to see the phases of Mercury. Three decades later Giovanni Zupi, an Italian astronomer, mathematician, and Jesuit priest, peered at Mercury through a more powerful telescope than the one used by Galileo and discovered that the planet went through phases like the Moon.

These observations were easily explained by understanding that the two planets orbited between Earth and the Sun, and were profoundly significant because they were proof that the Copernican theory was correct and the Earth was not the center of the Universe.

Except for the discovery of the phases of Mercury, early observations did not contribute much to our understanding of the planet. Most of our detailed knowledge of the planet has been obtained from one probe, Mariner 10. It was launched on November 3, 1973, and during three flybys of Mercury, it photographed more than half of the planet's moonlike surface.

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

Venus

NASA's Pioneer Venus Orbiter captured this ultraviolet image of Venus in 1979. NASA/JPL [larger image]

Venus is often considered the Evening Star or the Morning Star, depending on which time of day it is up and dominating the twilight. For example, until late September 2010, Venus will appear as a brilliant yellow star in the evening sky, right after sunset. Located 15° above the western horizon one hour after sundown, it remains on view until after 10 P.M. local daylight time. At the beginning of June, Venus spans 13" across and shows a gibbous disk 80-percent lit. By late in the month, the disk has grown to 16" and the phase has shrunk to 70-percent illumination. The planet shines at a stunning -4 magnitude, about ten times brighter than the brightest star Sirius, and by far the brightest celestial object after the Sun and Moon. Venus is so bright due to a combination of factors.

Venus is covered with an opaque layer of highly reflective clouds of sulfuric acid. These clouds reflect 70-percent of the sunlight that hits them. For comparison, the Earth reflects 36-percent and Mars and the Moon around 15-percent of the sunlight striking them. Venus is also rather large, being only a bit smaller than the Earth - its radius is 95-percent as large as Earth's. The final piece of Venus' brightness puzzle is its close distance to Earth. Right now, the planet is 1.2 astronomical units (110 million miles) from Earth.

Finder map (early June) - one hour after sunset, looking west.
Finder map (mid-June) - one hour after sunset, looking west.
Finder map (late June) - one hour after sunset, looking west.

Mars

Mars is the fourth planet from the Sun, and is commonly referred to as the Red Planet. NASA/JPL [larger image]

Mars can be found after sunset in the western sky, far upper left of Venus along the ecliptic. It begins June near blue-white Regulus, Leo's brightest star, which lies at the base of the constellation's Sickle asterism. The planet's eastward motion carries it to within 13° of Regulus by the end of the month, when it sets before midnight local daylight time. Mars shines at magnitude +1 and its 6"-diameter disk reveals practically no detail through a telescope. Mars is also known as the Red Planet, although its color varies from rusty orange to gray. Some casual earthbound observers mistake it for a red-giant star, however, because of its significant apparent diameter it does not twinkle as a star does.

In ancient times, the planet's wandering motion and blood-red color were portents of ill tidings, and this led the Romans to name Mars after their war god. Yet the source of the reddish hue is not the bloody spirit of the Roman god, but simple iron ore. The Martian surface contains large amounts of iron oxide, red and rusting. As Viking 1 and Mars Pathfinder images revealed, even the Martian sky takes on a rust- pink tinge during seasonal dust storms.

Finder map (early June) - one hour after sunset, looking west.
Finder map (mid-June) - one hour after sunset, looking west.
Finder map (late June) - one hour after sunset, looking west.

Jupiter

Dawn is the hour when Jupiter is highest in the southeast. It pokes over the horizon by 3 A.M. local daylight time June 1st and is 25° high by this time at month's end. The gas giant spends June in the constellation Pisces the Fish and shining at magnitude -2.4 it dominates this region of sky.

Jupiter makes a great target for your telescope. A small instrument at about 70x readily shows two dusky belts spanning Jupiter's equatorial region. The planet's disk measures 38" at the start of the month, but by late June, as Jupiter gets closer to us, the disk's angular size increases to 42". Notice its polar diameter spans 3" less, which gives Jupiter a distinct flattened appearance. This comes about because of its fast rotation - the planet's gravity cannot hold the bulging equatorial regions as tightly.

Moving in line with Jupiter's equator are the four bright Galilean moons: Io, Europa, Ganymede, and Callisto. They appear as bright stars on either side of Jupiter and move relative to every other hour to hour, and night to night.

Telescope owners enjoy watching the moons pass in front of Jupiter, cast their shadows on Jupiter (the shadows are dark and contrast well against the bright white clouds), disappear in eclipse in the planet's shadow, become occulted by the edge of the planet, or even (very rarely) eclipse each other.

Finder map (early June) - 30 minutes before sunrise, looking southeast.
Finder map (mid-June) - 30 minutes before sunrise, looking southeast.
Finder map (late June) - 30 minutes before sunrise, looking southeast.

Saturn

Pictured above, Saturn's famous rings are visible along with two of its largest moons, Dione and Rhea. NASA/JPL/Caltech [larger image]

Saturn will be in excellent position for observation until at least early July. It reached opposition to the Sun on March 21st, when it was closest to Earth and at its largest and brightest. Although Saturn is now slowly receding from our home planet, it remains visible well after midnight and looks stunning through a telescope. Look for Saturn high in the southwest after sunset, in western Virgo, just a couple of degrees below Denebola, the second brightest star in the constellation Leo the Lion. In a telescope Saturn's disk spans 18" across the equator and the rings appear very narrow. They are currently tipped just 1.7° to our line of sight, but they will double their tilt during the next two months. Saturn's rings consist of countless particles of water ice, ranging in size from small grains to irregularly shaped pieces generally a few feet across. It is interesting to note that if all of the material of the

rings of Saturn were formed into a single moon, the moon would be about the mass of Janus (one of the smallest of Saturn's moons) and only 1/20,000 the mass of the Earth's Moon.

Finder map (early June) - one hour after sunset, looking southwest.
Finder map (mid-June) - one hour after sunset, looking southwest.
Finder map (late June) - one hour after sunset, looking southwest.

Uranus

Uranus is in the morning sky, in the same binocular field as Jupiter and about 5° southeast of 4th-magnitude Lambda Piscium (the star that forms the southeast corner of the "Circlet" in Pisces). Some observers may be able to spot the planet with binoculars, although at magnitude +5.8 it will be a difficult object and will require very transparent skies.

Uranus is so inconspicuous that it was mistaken for a star dozens of times before its accidental discovery in 1781 by German-born British astronomer William Herschel, using a primitive 6-inch Newtonian reflector. The planet is never less than 1,600 million miles from the Earth; it qualifies as a giant, with a diameter of over 30,000 miles, but it is much smaller than Jupiter or Saturn and its composition is quite different.

Uranus is made up largely of "ices", but these need not be in a solid form - there is a mixture of water, methane and ammonia, plus a certain amount of solid matter. The outer atmosphere is made predominantly of hydrogen, and also some methane which absorbs red light and gives the planet its distinctive greenish hue.

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

Neptune

An artist's concept of Voyager 2, the only spacecraft to have visited far-off Neptune and its 13 moons. NASA/JPL [larger image]

Seek out Neptune in western Aquarius, 1.5° northwest of the 4th-magnitude star Iota Aquarii. The distant world lies 2.8 billion miles from Earth and glows dimly at magnitude +7.9. Because Neptune is pretty low in the morning sky you will need at least a 4-inch telescope to see it and resolve its disk, only 2.5" in diameter. Neptune is a cold, dark world. With a mean solar distance of 2,798 million miles (30.11 astronomical units), light levels at Neptune are more than 800 times dimmer than they are on Earth. Noon on Neptune would appear no brighter than what a human would experience at dusk on Earth. Even the Sun would take on an appearance more like a star than the bright disk seen from our home planet. Because Neptune is so distant, so far, only one spacecraft, Voyager 2, has visited the planet - a flyby in 1989. The spacecraft observed Neptune almost continuously between June and October of

that year. It measured the planet's radius and interior rotation rate, confirmed that Neptune has rings, and discovered six new moons. Voyager 2 also recorded pulses of radio emission, zonal cloud bands, and large scale storm systems with up to 1,500 miles per hour winds - the strongest measured on any planet.

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

Pluto

The dwarf planet Pluto lies in northwestern Sagittarius and is highest above the horizon in the predawn sky.

Pluto glows at magnitude +14, and as a result, it is a challenge to spot. An 8-inch telescope on a perfect night brings Pluto to the edge of visibility. For a direct view, however, you will want to use at least a 10-inch scope.

Pluto was discovered in 1930 as a result of an extensive search by American astronomer Clyde Tombaugh. Astronomers have argued since the late 1990s that Pluto's small size, less than one-fifth the diameter of Earth, and a weird tilted orbit that takes it inside Neptune's orbital path every couple hundred years make Pluto more like a Kuiper Belt body than a full-fledged planet.

On August 24 2006, the International Astronomical Union (the organization responsible for classifying planets) passed a new definition of planet that excludes Pluto and puts it in a new category of "dwarf planet".

The two finder maps below will help you identify Pluto. First, locate its general position on the coarse finder map and after that, use the fine finder map which shows the position of the dwarf planet on each night of the month.

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

The warm nights of June offer prime conditions for galaxy hunting. The winter Milky Way is lost in the glare of the Sun, while the star clouds of Cygnus and Sagittarius are just rising in the east. It is on these evenings that we have an unobstructed view of what lies beyond our own galaxy. At the center of this view, we find the constellation Virgo. Virgo is a large constellation, second in size to Hydra and spanning more than 1295°. Despite its large size Virgo is not a particularly prominent constellation, with the notable exception of silver-blue Spica, magnitude +1. Spica is over twice as hot as Sirius (the brightest star in the night

Elliptical galaxy M 87 is likely home to a supermassive black hole with a mass of three billion suns. CFHT/J.-C. Cuillandre [larger image]

sky) and 100 times more luminous. However, Spica appears fainter than Sirius because of its considerably greater distance, 270 light-years.

The primary telescopic draw to Virgo is the Virgo Galaxy Cluster, which spills across its northern border in Coma Berenices. A neighbor to our own Local Group, the Virgo Cluster is the richest gathering of galaxies in the Local Supercluster - a large group of associated small galaxy clusters that include the Local Group and therefore our own galaxy, the Milky Way.

The Virgo Galaxy Cluster contains about 3000 galaxies, centered on the giant elliptical galaxy M 87, which is visible as a 9th-magnitude smudge in small telescopes or even binoculars. M 87 has a total mass of nearly 800 billion suns, making it one of the most massive galaxies known. Long-exposure photographs show a jet of luminous gas being shot out of M 87, as though the galaxy has suffered a violent event. Astronomers now believe that the activity in M 87 is due to a black hole with a mass of three billion suns, which lurks in the galaxy's nucleus.

M 87 is easily located in northern Virgo, about 3° northwest of the 5th-magnitude star Rho Virginis. At low power, the 8.6-magnitude galaxy resembles an unresolved globular cluster, about 3' across and perfectly round. A very bright core, one-third of the galaxy's overall size, blazes in the center.

Finder map - field width 15°, stars to magnitude +9.

Asteroids

This 1.4-pound meteorite is thought to have been ejected from the crust of the asteroid Vesta in a collision. NEMS [larger image]

There are countless asteroids in our solar system, of which around 160,000 have names or identifying numbers. However, only Vesta, the fourth of the large asteroids discovered in the first decade of the 19th century, ever becomes close and bright enough for us to spot with the unaided eye. Vesta is a large chunk of rock around 320 miles in diameter, which rotates once about its axis in 5.34 hours. Its surface must consist of a really light- colored soil because it reflects light some six times better than the Moon's darker regolith. Because of this high

surface reflectivity, or albedo, Vesta reflects a whopping 38 percent of the sunlight striking it and currently glows at magnitude +7.7.

From a suburban backyard, it is easy to find the asteroid if you have a good view of the western sky. Mars, the brilliant star-like object in the west during early evening, serves as a good guidepost for locating it; Vesta is about 5° north of the planet. If you return every two or three nights, you will surely notice the asteroid's telltale displacement against the background stars.

Like most asteroids in the belt between Mars and Jupiter, Vesta follows an eccentric orbit. Every 3.63 years it reaches perihelion, the point in its orbit where it is nearest to the Sun. The asteroid was last at perihelion on May 31st, 2007, when it passed a mere 106 million miles from us and reached magnitude +5.4. Vesta will next come to perihelion on January 15th, 2011.

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

Comets

Comet C/2009 R1 McNaught is now rapidly brightening in the morning sky, as it sweeps from Andromeda past Perseus to Auriga during the month.

Astronomers predict C/2009 R1 McNaught should peak at 5th magnitude or a bit brighter in mid-June, making it bright enough to see with the naked eye under a suburban sky. And even if it does not get quite that bright, it will be an easy target for binoculars and small telescopes.

At the start of the month, Comet McNaught can be found in Andromeda, close to the 2nd-magnitude double star Gamma Andromedae. It passes about 1° north of the open star cluster M34 in Perseus on the morning of June 10th and 3° south of Mirfak (Alpha Persei) on the 13th.

As the comet continues to push northward, it skims just 2° above Capella on the 21st and is very low by the 24th, when it passes 2nd-magnitude Beta Aurigae. C/2009 R1 McNaught will be lost to view by the end of the month - just before it reaches perihelion on July 2nd, 38 million miles from the Sun.

Australian astronomer Robert H. McNaught discovered this comet on an image taken on September 9th, 2009. It is approaching on a hyperbolic orbit, which means that it is making its first trip from the Oort Cloud.

Finder map - field width 80°, stars to magnitude +5.

Comets are leftovers from the formation of our solar system, sometimes called "dirty snowballs". Pictured above is Comet Hale-Bopp, the Great Comet of 1997. John Gleason [larger image]

As the sky darkens on June evenings, a solar system visitor lies due north and more than one-third of the way from the horizon to the zenith. Comet C/2009 K5 McNaught tracks through the star-barren constellation Camelopardalis during the month and remains circumpolar (meaning it never sets) for most midnorthern observers. Glowing with the combined light of a 10th-magnitude star, the comet will be easily accessible from suburban backyards with a 6-inch scope. Bump up the power past 100x to darken the background sky, and use a dark hood over your head to further cut stray light. The best views will come around mid- month, when moonlight will not interfere with evening observing. Comet C/2009 K5 McNaught, like all other comets, is a chunk of ice and dust only a few miles across. The ice is mostly frozen water and carbon dioxide, and the dust is simple silicates. When far from the Sun, the ice is frozen and the comet is too small and too faint to be seen. But as the comet approaches the

Sun, it warms. Sunlight thaws the ice, which evaporates (it does not melt), carrying with it the dust that was embedded in it.

The gas molecules absorb solar radiation, and then reradiate it at another wavelength while the dust acts to scatter the sunlight. The effect of this is the creation of a coma - a spherical envelope of gas and dust (perhaps 60,000 miles across) surrounding the nucleus - and a long tail consisting of gases and more dust particles.

Finder map - field width 40°, stars to magnitude +7.

Meteors

People spend a lot more leisure time outdoors during the summer months, so it is no wonder they observe more meteors at this time of the year. If you can survive the onslaught of hungry mosquitoes, a June evening can be a great time to view a few shooting stars blazing across the sky. The only equipment you will need is your eyes and a modest amount of patience. The best meteor shower of June, in terms of both sky position and meteor activity, is the June Bootid stream. This well-known annual shower usually produces just a few visible meteors per hour, yet twelve years ago, on June 27th, 1998, northern sky watchers were surprised when dozens of bright meteors suddenly began to stream out of the constellation Bootes the Herdsman. It was not the first time: similar June Bootid outbursts had been recorded many decades ago, in 1916, 1921, and 1927. This year the June Bootids reach a peak on June

Meteors are tiny specks of space dust that burn up during their fatal encounter with the Earth's upper atmosphere. Yuichi Takasaka [larger image]

27th, and can be seen from about June 22nd through until July 2nd. The shower's radiant - the point in the sky from which meteors appear to originate from - is located in northern Bootes, and will be excellently positioned as darkness falls. It will appear nearly overhead and will remain in view through the whole night.

This is great, but will you see a large number of meteors coming from Bootes on Sunday evening, June 27th? Unfortunately, the answer is probably not. No outburst is expected this year, and the bright moonlight will hide all but the brightest meteors. However, it is worth keeping an eye open. No one knows why the June Bootid shower spiked in 1998, or when it might again.

Keep in mind that members of this shower are extremely slow, with a velocity of only 11 miles per second. Meteors coming from the same radiant in Bootes, but not traveling more slowly than most other meteors visible at that time, are not June Bootids.

Map - June Bootids 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 seven 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 3 - The Moon is at apogee, the point in its orbit when it is farthest from Earth.

June 4 - Last Quarter Moon at 6:13 P.M. EDT.

June 6 – Mars is 0.8° north of Regulus (Alpha Leonis) at 8:15 P.M. EDT.

June 8 – Venus is 4.7° south of Pollux (Beta Geminorum) at 10:59 A.M. EDT.

June 10 – The Moon is 0.6° north of the Pleiades at 5:46 P.M. EDT.

June 12 - New Moon at 7:15 A.M. EDT.

June 15 - The Moon is at perigee, the point in its orbit when it is nearest to Earth.

June 19 - First Quarter Moon at 12:29 A.M. EDT.

June 21 - The June solstice occurs at 7:28 A.M. EDT; summer begins in the Northern Hemisphere.

June 24 – The Moon is 1.9° south of Antares (Alpha Scorpii) at 7:41 A.M. EDT. June 25 – The dwarf planet Ceres is 1° south of the Moon at 2:10 P.M. EDT. Pluto is at opposition, directly on the opposite side of the Earth from the Sun. June 26 - Full Moon at 7:30 A.M. EDT. A partial lunar eclipse is visible from much of the Americas, the Pacific and eastern Asia. June 28 - Mercury is at superior conjunction, on the opposite side of the Sun from Earth.

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.

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