The night sky in May

Want to know what's up in the sky tonight? Our night sky chart will provide you with the information you need to locate the brightest planets, stars and deep-sky objects ...

During early May, the Earth passes through a debris trail left by comet Halley. This results in a meteor shower is called the Eta Aquarids. They are so called because the meteors appear to come from part of the constellation of Aquarius. (In October we pass through another section of Halley’s debris path in a shower called the Orionids.)

At their peak on May 5, the Eta Aquarids may produce up to 30 meteors per hour.

may This month’s chart shows the night sky looking South in mid May at 2300. (click on image for larger view)

The Stars and Constellations

May is a great month to enjoy the night sky because the weather is so much better (hmmm, we’ll see!). Soon after sunset we see a sky that is moving into its ‘Summer phase’. If you stay outside a few hours past sunset you will get a preview of our summer stars and constellations.

Rising from the eastern horizon, about an hour after sunset is the brilliant star Vega. With a magnitude zero (0.0), is a real treat on its very own. It’s 50 times more luminous as the Sun and only 26 light-years away so it’s very bright in our night sky.

In 1983 a cloud of cool material orbiting Vega was detected. This was interpreted as a disk of sub-planetary size materials – like asteroids and comets – orbiting the star. We believe that our Solar System started in this way; as a disk of condensing materials that eventually accumulated by gravity into planets. In the 1990s instruments mapped the shape of the material surrounding Vega (and two other stars, Fomalhaut and Beta Pictoris). The results showed that there are localized concentrations of materials in some places and gaps in other parts. Some astronomers interpret this as evidence of planet formation. So. it’s possible that at this very moment, planets are being created around Vega.

Opposite Vega but still in Lyra is the Ring Nebula (M57). Not so long ago an old star used to sit in this part of Lyra. It eventually ran out of nuclear fuel and underwent a series of pulsations, eventually throwing off its outer layers in a violent explosion. The nebula’s ‘ring’ is actually, in simplistic terms, material ejected from the dying star. Its ring appearance is just a line-of-sight effect. When nebula like these were first discovered, hundreds of years ago, it was thought that the ring was due to condensing, not expanding, material. This is why they were so-called ‘planetary nebula’. Nothing could be further from the truth! A planetary nebula is not the sign of planet formation. It’s the sign of a recently dead star. Indeed, any planets that orbited close to the star, were probably annihilated.

The corpse left behind, in the center of the explosion, is a white dwarf. These stars are very dense. A teaspoon of white dwarf material weighs a ton – literally – that’s about a thousand kilograms per cubic centimeter. It’s impossible to squeeze atoms that tightly without destroying their atomic structure. Every atom in the white dwarf is transformed into an unusual state of matter called degenerate matter – a tight mass of nuclei and electrons with no real atomic structure. There’s nothing on Earth quite like it. The light given off by a white dwarf is the remnant energy leftover from its former life as a proper nuclear-fusing star. White dwarfs no longer undergo nuclear fusion.

The Ring Nebula is too dim for most low-power binoculars but within the range of a good telescope. It’s a great find for amateur astronomers so, if you have a telescope, give it a try.

Bootes, the Herdsman – this month’s sky highlight

Bootes contains the fourth brightest star, orange Arcturus. In Arab mythology, Bootes herded the flock of circumpolar stars.

At 2230 in mid-May the bright star Arcturus is almost due South. If you have trouble finding it use the handle of the Plough to trace an arcing line 30 degrees away from it, taking us on to Arcturus. The star is unmistakable as it is the brightest object in that region of the sky.

Arcturus is the Alpha (meaning the brightest) star of the constellation Bootes. It is a giant star, twice as massive and 215 times as bright as the Sun. It takes 37 years for its light to reach us, so when we gaze at it, we’re seeing the star as it looked 37 years ago. Once you have found it, you will notice that it forms the point of a pattern of stars resembling a kite.

Ancient astronomers had measured the position of Arcturus for nearly 2,000 years, which gave Edmond Halley enough data, in 1718, to discover that it was slowly moving against the background stars of its constellation. Before this discovery of proper motion, the stars were thought to be permanently fixed in the sky. Today we know that all stars move, but Arcturus moves much faster than most—about the width of the full moon every 800 years.

Locate the two middle stars within the kite shape. Using binoculars trace a line in the direction of four o’clock (from the right-hand star) for 11 degrees until you arrive at a smudge of fuzzy light. This is the globular cluster M3. It contains about 500 000 stars. M3 is host to more known variable stars than any other globular cluster. It was Messier’s first original discovery. With the naked eye, it is difficult to separate M3 from a nearby orange sixth magnitude star. With a telescope and moderate power this cluster takes on a 3-dimensional quality with many stars resolved around the edges and across the central halo.

In history …

On the first night of May, 1949 Gerard Kuiper discovered Nereid, Neptune’s second largest Moon. (Until Neptune was visited by the Voyager spacecraft, it was thought that it had only two moons) Subsequent observations of Nereid showed it had a highly eccentric orbit – it’s distance from Neptune varies from 1.3 to 9.7 billion kilometers.

On May 28, 1959 Able and Baker complete a sub-orbital flight to become the first primates in space.

Alan Shepard became the first American in space on May 5, 1961. His 15 minute sub-orbital flight in the Mercury spacecraft Freedom 7 put him in second place to the Russian Yuri Gagarin, who had orbited the Earth (one orbit) three weeks earlier.

Regardless, Shepard’s flight made the space race a two nation race … Sixteen days later, on May 21, President John F. Kennedy, speaking before a joint session of Congress upped the ante by declaring, ‘I believe this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the Earth.’ With that sentence President Kennedy launched the most ambitious and far reaching science and engineering program the world has ever seen.


© Macclesfield Astronomical Society 2017