Darkness shades the Full Moon

Early May offers evening skygazers only one planet, and it’s not the most spectacular. Mercury lies just 5° high in the northwest 30 minutes after sunset. At its best on the 1st, the inner planet glows at magnitude 0.5 and will be hard to spot against the bright twilight. A telescope reveals Mercury’s 8"-diameter disk and one-third-lit phase.

Several hours elapse before the next planet emerges, but the wait will be worth it. Saturn rises near 1 a.m. local time

May 1 and about two hours earlier by month’s end. The ringed planet shines at magnitude 0.7 against the backdrop of eastern Capricornus, 2° north of magnitude 2.8 Delta (δ) Capricorni. Although Delta ranks as the Sea Goat’s luminary, Saturn appears seven times brighter.

Saturn’s appearance through a telescope improves as it climbs during the predawn hours. As with any planet, Saturn looks better when it’s high in the sky because we then see it through less of Earth’s turbulent atmosphere. The ringed world will reward your patience with stunning views. In mid-May, its beautiful ring system spans 38" and surrounds a slightly flattened disk that measures 17" across. The rings tilt 12° to our line of sight and show modest structure through small scopes.

The autumn sky gains a touch of color when Mars rises a couple of hours after Saturn.

The Red Planet paints Aquarius with its ruddy hue until May 19 when it crosses into Pisces. Mars brightens from magnitude 0.9 to 0.6 during May, a brightening that will continue as it approaches opposition in December. Unfortunately, the planet’s 6"-diameter disk won’t show any detail through most amateur instruments.

Mars stands 16° west of Jupiter as May begins, but the gap narrows by about 0.5° a day. That sets up a close conjunction between the two worlds late this month. On

May 29, the Red Planet passes 0.6° south of the gas giant.

As splendid as this encounter may be, Jupiter has a far more striking embrace in early May. On the 1st, brilliant

Venus stands 0.2° to Jupiter’s upper right. Although this conjunction officially took place at 19h UT on April 30, the two planets appear closest on the

1st for observers in Australasia.

A telescope always delivers striking views of Jupiter. In mid-May, the giant world spans 36" and shows a wealth of detail in its colorful cloud tops. Look for two parallel dark belts, one on either side of a zone that coincides with the planet’s equator. Jupiter’s four bright moons — Io, Europa, Ganymede, and Callisto — also show up through small amateur scopes.

Venus draws away from Jupiter as May progresses. The magnitude –4.0 planet begins the month in Pisces, makes a four-day sojourn through

Cetus the Whale during May’s second week, then returns to the Fish before crossing into Aries the Ram on the 31st. A telescope shows Venus’ disk, which spans 15" and appears 73 percent lit at midmonth.

A waning crescent Moon occults Venus on May 27. Observers in southern Madagascar can witness this event in a dark sky. From Tiliara, Venus disappears at 0h50m UT and reappears at 1h27m UT. The Moon takes nearly a minute to hide and later reveal the planet’s disk.

A total lunar eclipse occurs the night of May 15/16. Viewers in South America are ideally placed because the whole eclipse takes place with the Moon high in a dark sky.

The umbral phase runs from 2h28m UT to 5h55m UT with totality lasting from 3h29m UT to 4h54m UT. The Moon should turn a beautiful orange color during the 85 minutes of totality.

The starry sky

Midevenings in May provide gorgeous views of Crux the Cross at its peak altitude in the south. Musca the Fly borders Crux to the south while Centaurus the Centaur surrounds the Cross on its other three sides. Crux and Centaurus hold plenty of striking deep-sky objects, including the Coal Sack dark nebula, the Jewel Box Cluster (NGC 4755), and Alpha (α) Centauri. With this wealth of wonders, it’s not surprising other deep-sky standouts get overshadowed.

But you shouldn’t pass on the chance to view the Blue Planetary Nebula (NGC 3918). Like other planetaries, this nebula represents the death throes of a Sun-like star. As such a star nears the end of its life, it puffs off its outer layers, which glow from high-energy ultraviolet radiation released by the dying star’s core. Some early observers thought their disks looked like those of the planet Uranus, hence the name.

NGC 3918 lies in Centaurus, near the northwestern corner of Crux. Although it’s tough to star-hop to the nebula, you can find it easily through a small telescope with the help of a detailed star chart. If you have a go-to mount, dial in a right ascension of 11h50.3m and a declination –57°11' (2000.0 coordinates).

English astronomer John Herschel discovered this planetary in 1834 while observing from the Cape of Good Hope. He called it a perfect planetary disk and was clearly struck by its color, writing “It is of a most decided independent blue color.” He also noted an 8thmagnitude orange star 10' to its north, which made the nebula’s blue color even more obvious.

Through amateur instruments, NGC 3918 appears as a round disk about 8" to 10" across. Appropriately, it looks remarkably like a larger and bluer version of Uranus.