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Morning planet spectacular

May 2011: The stage is set for the finest planetary conjunction of the year.
The two brightest planets met in the predawn sky November 4, 2004. Venus (top) and Jupiter will be similarly close May 11. Rick Stankiewicz
The stage is set for the finest planetary conjunction of the year. Mercury, Venus, Mars, and Jupiter cluster near one another before dawn during May’s first 3 weeks. But the highlight comes on the 11th when the two brightest — Venus and Jupiter — lie 1 Moon-width apart. Uranus and Neptune also lurk in the east before sunrise, although you’ll need binoculars or a telescope to spot them.

Among the solar system’s major planets, only Saturn plays on the evening stage. This magnificent actor will command the attention of the observing audience from dusk until well past midnight. To spot the minor character Pluto, you’ll have to look ­carefully and use an 8-inch or larger scope. It rises in late evening and appears best before dawn.

Let’s begin our tour of the planets in the evening sky as twilight starts to fade. Saturn reached opposition and peak visibility in early April, and May finds it only a bit smaller and dimmer. Yet it makes up for this slight decline by appearing much higher in the evening sky. You can find it in the southeast about halfway to the zenith as darkness falls, and it doesn’t set until dawn starts to paint the sky.

Saturn shines at magnitude 0.6, which makes it the brightest point of light in the constellation Virgo. Its nearest rival is Spica, which lies about 15° southeast of the planet. Note the color contrast between the blue-white star and the golden-hued planet.

Although Saturn lies near Spica, it’s almost on top of 3rd-magnitude Gamma (γ) Virginis. At the beginning of May, the ringed world stands 1.6° southeast of this star. But the gap closes quickly. By the 31st, the two lie within 20' of each other, just two-thirds of the Moon’s apparent diameter.

If you swing your scope toward Saturn, you’ll be rewarded with a stunning view. The planet’s disk measures 19" across the equator and 17" through the poles, a difference that’s obvious even at low power. Although features on the globe are subtle, the dusky equatorial belt and dark polar hood show up under good sky conditions.
Venus joins Jupiter in the morning sky May 11. The brilliant pair will lie 1 Full Moon-width apart in the twilight glow. Astronomy: Roen Kelly
Of course, no one who views Saturn through a scope spends much time on the disk — the rings look too spectacular. In May, they span 43" and tip 8° to our line of sight. This tilt gives observers a nice view of the Cassini Division, the dark gap that separates the two brightest rings.

If you look carefully at the rings where they pass behind Saturn, you should notice that they don’t quite touch the planet’s eastern limb. That’s because Saturn’s shadow prevents sunlight from reaching the rings. The shadow eats up more of the ring system as May progresses because the Sun-Saturn-Earth angle grows throughout the month.

You should also take the time to locate Saturn’s brightest moons. Any scope will reveal 8th-magnitude Titan, the planet’s biggest moon and the second largest in the solar system. Titan takes 16 days to circle Saturn, so it completes approximately two orbits every Earth month. It is easiest to pick out when it passes north or south of the planet and thus appears closest. The moon lies due south of Saturn May 3 and 19 and due north May 11 and 27.

A trio of 10th-magnitude moons — Tethys, Dione, and Rhea — require more than the quick glance it takes to reveal Titan. All three orbit closer to Saturn, so they move more rapidly. The changing satellite positions offer different alignments each night. Watch several evenings in a row and you’ll soon become an expert at identifying the moons.

A good time to view the four brightest comes the night of May 22/23, when they all string out in a line that passes through Saturn. Titan is close to its greatest western elongation, so it lies about 4.5 ring diameters from the planet’s center. Rhea appears a bit less than half this distance from Saturn, and Tethys lies half as close as Rhea.

Cross to the eastern side of Saturn and Dione will greet your gaze. If you look closely between Dione and the edge of the rings, you might spot Enceladus. You’ll likely need a 10-inch or larger scope to see this 12th-magnitude satellite.

Iapetus also lies near Saturn the night of May 22/23. Look for it due south of the imaginary line joining Rhea and Tethys. Iapetus glows around 11th magnitude, but it brightens later this month as it moves toward greatest western elongation.
Saturn’s four brightest moons line up the night of May 22/23, when they can help point you to fainter Enceladus. Astronomy: Roen Kelly
Although it’s never easy to find Pluto, late spring and early summer provide the best opportunities of 2011. It rises around 11 p.m. local daylight time in mid-May and appears highest in the south before dawn. You’ll need a dark sky and a 10-inch scope to have any hope of visually spotting this planet’s 14th-magnitude glow. That said, astroimagers can record the faint dot through smaller instruments.

Pluto lies in northern ­Sagittarius, not far from the exquisite open star cluster M25. Aim your scope 30' northwest of the cluster and you’ll spot SAO 161540, a naked-eye star under dark skies that shines at magnitude 5.6. Pluto passes just north of this star May 5. If you target this area on two mornings around the 5th, you easily will detect the motion that confirms Pluto’s identity. After May 5, Pluto heads due west at a rate of about 0.9' per day.

Neptune rises around 3 a.m. local daylight time in early May and 2 hours earlier by month’s end. It lies among the background stars of Aquarius, where it glows at magnitude 7.9. It remains less than a Moon-width southeast of 5th-magnitude 38 Aquarii all month. The star’s proximity makes Neptune relatively easy to find through binoculars or a telescope at low magnification. A scope reveals the planet’s disk, which spans 2.3" and has a blue-gray color.

This year marks the 164th anniversary of Neptune’s discovery, and, because it takes about that long to circle the Sun, the planet is completing its initial orbit since German astronomer Johann Galle first spotted it. The distant world also has returned to the vicinity of its discovery location.

In mid-May, Uranus rises with dawn’s first light. It appears in a darker sky by month’s close, when its position in southern Pisces stands about 15° above the eastern horizon as twilight begins. Uranus glows at magnitude 5.9 and shows up easily through binoculars. Unfortunately, it lies in a fairly sparse region of sky with no nearby bright stars.

Here’s how to find the right area. First, draw a line from Alpheratz to Algenib, the two stars that form the eastern side of the Great Square of Pegasus. Then, extend this line an equal distance to the south (lower right) of Algenib. Once you zero in on Uranus through your telescope, you’ll see the planet’s 3.4"-diameter disk and distinct blue-green color.
Distant Pluto glows at 14th magnitude as it slides past the magnitude 5.6 star SAO 161540 in northern Sagittarius. Astronomy: Roen Kelly
The dawn sky brings several bright planets into view. Venus rises with a slender crescent Moon in the eastern sky May 1. Shining brilliantly at magnitude –3.9, the planet is unmistakable. That same morning, Mercury stands 3° east (lower left) of Venus but appears much fainter at magnitude 0.8. The pair stands about 5° above the horizon 30 minutes before sunrise.

You also might spy Jupiter May 1, when it lies 5° directly below the Moon. At magnitude –2.1, the planet shines bright enough to pierce the twilight glow. Of academic interest only for Northern Hemisphere observers, Mars lies 0.4° north of Jupiter that morning. But, at magnitude 1.3, it’s lost against the bright sky. (From the Southern Hemisphere, however, the Jupiter-Mars pair is easy to see 10° above the horizon half an hour before sunrise.)

All four planets show up in different positions with the arrival of each new morning. During May’s first 10 days, Mercury and Venus remain roughly the same distance apart and at the same approx­imate altitude while Jupiter climbs to meet them. Jupiter and Venus reach conjunction May 11, when the significantly brighter Venus lies 0.6° due south of Jupiter. Binoculars will show this spectacular pairing best, and also reveal Mercury 1.5° to Venus’ south. Mercury has brightened to magnitude 0.2, a small difference but enough to make it easier to spot.

Mercury grows brighter, reaching magnitude 0.0 by May 18. Venus remains 1.5° away, now to Mercury’s northwest. The pair rises 1 hour before the Sun. Seen through a telescope, Venus appears 11" across and nearly full. Mercury spans a bit more than half Venus’ size and shows a slightly gibbous phase.

On May 22, Venus passes 1.1° south of Mars (still invisible to the unaided eye) and lies less than 2° above Mercury. Venus lingers in the morning sky through the end of May, but Mercury drops out of sight by then. Meanwhile, the Red Planet becomes a bit easier to see.

That leaves Jupiter, which continues to rise earlier and become more prominent with each passing day. By May 31, the planet rises 2 hours before the Sun and stands 15° high in the east 30 minutes before sunrise. Through a telescope, Jupiter’s disk spans 35".
The Eta Aquarid meteor shower peaks under moonless skies May 6, when observers could see up to 25 meteors per hour. Astronomy: Roen Kelly
Halley’s debris rains from the Water-bearer
One of the year’s best meteor showers peaks before dawn May 6. The Eta Aquarid shower receives no competition from the crescent Moon, which sets before midnight. Observers under optimal conditions — when the radiant lies overhead and an observer can view stars down to magnitude 6.5 — can expect to see about 70 meteors per hour at the peak.

Unfortunately, Northern Hemisphere observers never get such conditions. The shower’s radiant lies in Aquarius the Water-bearer, which climbs only 20° high by the time twilight begins. So, the best northerners can expect is a still-decent 25 meteors per hour.

The Eta Aquarids derive from debris ejected by Comet Halley. Each May, Earth passes through this dust and the particles get incinerated in Earth’s atmosphere, giving us the meteor shower.
Sinus Iridum appears as a half bay on the northwestern edge of Mare Imbrium. The rugged Jura Mountains create the northern and western shores of this 160-mile-wide bay. Consolidated Lunar Atlas/UA/LPL
Somewhere over the Bay of Rainbows
One of the Moon’s prettier sights shows up a couple of nights after First Quarter phase. Sinus Iridum (the Bay of Rainbows) then appears prominent in the northwestern quadrant of the lunar face. The dark lava plains stand in stark contrast to the bright Jura Mountains, a semicircular mountain range that forms the bay’s northern and western shores. The region comes into view May 12 when the Sun rises over this impressive landscape.

That evening, Promontorium Laplace (which forms the northeastern tip of the Jura Mountains) casts a long shadow across the bay’s undulating lavas. The shadow shortens noticeably in just a few hours as the Sun climbs higher in the lunar sky and illuminates more peaks along the mountainous rim.

The highest peaks on the dark side of the terminator flicker in and out of view, changing color in the same way Sirius twinkles due to turbulence in Earth’s atmosphere. Perhaps this is why early Moon-watchers called this the Bay of Rainbows.

Several long wrinkle ridges stretch south from the bay. They show up well on the 12th because their shadows define them, but they gradually disappear day by day as the Sun climbs higher. The full arc of the Jura Mountains, out to Promontorium Heraclides at the southwestern end, comes into view on the 13th. (The photo above matches the scene that evening.) Although the bay recedes in prominence by Full Moon (May 17), the surrounding mountains remain a landmark because they separate highland material to the north from the dark lavas of Mare Imbrium to the south.
When to view the planets
Saturn (southeast)
Saturn (southwest)
Mercury (east)

Venus (east)

Mars (east)

Jupiter (east)

Uranus (east)

Neptune (southeast)
Comet C/2009 P1 (Garradd) should glow around 10th magnitude as it slides northward through Aquarius. Astronomy: Roen Kelly
An early taste of this year's finest visitor
The past couple of months haven’t been nice to comet-watchers. None of these visitors to the inner solar system has brightened past 13th magnitude — targets for light buckets, perhaps, but not for those with small telescopes. The famine ends in May, as Comet C/2009 P1 (Garradd) gives us an early taste of better things to come.

This interloper from the Oort Cloud appears to be making its first foray into the inner solar system. Astronomers sometimes have a hard time forecasting how bright such objects will become, but ­early predictions suggest Comet Garradd could reach 6th magnitude by autumn. And if it continues to brighten as expected, we could be looking at a naked-eye comet in early 2012.

This ages-old ball of ice and dust still lies a long way from Earth (about 300 million miles away), so it should glow around 10th magnitude in May. You’ll need a 4-inch or larger scope and a dark sky to see the comet’s soft light and slightly oval shape.

Comet Garradd currently lies among the background stars of Aquarius, so you’ll have to get up early or stay up all night to view it. This region appears about 15° high in the southeast as twilight begins in mid-May. The comet is heading north, so it rises earlier and climbs higher in the predawn sky by late in the month. Although the brightest star in the area is 4th-magnitude Lambda (λ) Aquarii, a pair of 6th-magnitude suns (81 and 82 Aqr) make better guide stars between May 17 and 20.

Garradd’s fuzzy oval shape mimics the appearance of the many elliptical galaxies that dot the background of Aquarius. But at 10th magnitude, the comet appears noticeably brighter.
Iris shines dimly at 10th magnitude, but it passes near a few bright stars and the cluster M67, which makes it easier to find. Astronomy: Roen Kelly
Iris cruises through the Crab's claw
Asteroids rarely shine brightly enough to see with unaided eyes. Of the main-belt objects, only 1 Ceres and 4 Vesta ever get that bright, and then just barely. More often than not, asteroid viewers need to use a telescope and hunt for space rocks glowing closer to 10th magnitude. That’s the case in May, when asteroid 7 Iris offers a nice target.
Iris peaked back in January when it reached 8th magnitude and showed up through binoculars. You’ll need the extra light-gathering power of a telescope to bring this 10th-magnitude asteroid into range in May. Iris currently plies the southern part of Cancer the Crab, where it gets camouflaged by many similarly bright background stars.

The key to identifying Iris is to track its eastward trek against the starry backdrop from one night to the next. But on a few convenient evenings, the 130-mile-wide object passes near a stellar landmark that makes seeing its motion much easier. On May 10, you can watch it separate from the 6th-magnitude star 45 Cancri. On the 17th, you can find it passing just north of the impressive star cluster M67. But perhaps the easiest picking comes May 22, when Iris lies a mere 4' south of 4th-magnitude Alpha (α) Cancri.

Martin Ratcliffe
provides professional planetarium development for Sky-Skan Inc. Alister Ling is a meteorologist for Environment Canada.


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