May stargazing: Here’s what to see

During May, the chilly evening air is replaced with some late warmth. Then gazing skyward, the first stars twinkle in the fading light as the heavens reveal some early gems of summer.

This month we turn our attention to a roaring lion in the night sky, a glorious supermoon, some shooting stars, and the planets Mercury and Venus leading us a merry dance…

Stars and Constellations

Featured Constellation: Leo the Lion

May offers a whole host of treats when it comes to the stars and constellations. The outgoing constellations of spring are met with the prospect of summer’s newly emerging wonders in the night sky.

April’s featured constellation was Cancer the Crab, and it’s Cancer we need to seek out first before we can locate the Lion. During May, Cancer is positioned in the South West portion of the sky, and to locate Leo the Lion, all we need to do is seek out Asellus Australis (pictured below), the second brightest star in Cancer. From Asellus Asutralis, you can slowly sweep eastwards until you arrive at the brightest star in Leo the Lion, known as Regulus.

Leo is a highly recognizable constellation, as it is one of the few constellations that actually resembles its namesake. The entire lion can be visualised once you detect Regulus. Once you’ve spotted Regulus, you can pan upwards in the night sky and attempt to make out what appears to be a back to front question mark. This portion of the constellation represents the Lion’s head and is known as ‘the Sickle of Leo’.

Six bright stars form the Sickle of Leo, with Regulus (Alpha Leonis) marking the beast’s heart. Another bright star, Denebola (Beta Leonis) marks the tip of the Lion’s tail. Algieba (Gamma Leonis) lies on the Lion’s neck – even though its name means ‘the forehead’ – and Zosma (Delta Leonis) marks the Lion’s rump.

Leo is one of the twelve zodiac constellations that follow a distinct path (known as the ecliptic) across the heavens. As the Earth rotates, the Sun, the Moon and planets all travel on the ecliptic, which is a sort of flat plane across our Solar System. The name ‘ecliptic’ is derived from the Greek for ‘animal circle’ – meaning Leo the Lion is in good company with the likes of Taurus the Bull, Cancer the Crab, and Scorpius the Scorpion.

Leo in Mythology

Leo is one of the oldest recorded constellations. It was perceived as a lion by ancient civilizations as far back as 6,000 years ago.

The Greeks associated Leo with the Nemean lion – the beast killed by Heracles during the first of his twelve labours. As the story goes, the Lion lived in a cave in Nemea, a town located to the South-West of Corinth in Greece. the Lion is said to have been sired by the dog Orthrus and the monster Typhon – or to be the offspring of Selene, the Moon goddess.

This fearsome beast terrorised the land, killing all who dare venture near him. Not only was he fiercer, larger and stronger than other lions, but he also had the added advantage of possessing a skin which was impervious to metal, stone and wood.

Heracles could not kill the Lion with arrows, so he trapped the Lion in its cave, grappled with the beast, and eventually choked it to death. He used the Lion’s claws to cut off its pelt, and then wore the pelt as a cloak, complete with the Lion’s head. The cloak protected Heracles, and made him appear even more fearsome.

Additional myths and cultural perceptions of Leo the Lion

  • Babylonians knew the star Regulus as ‘the star that stands at the Lion’s breast,’ or ‘the King Star’.

  • Archaeological evidence suggests that Mesopotamians had a constellation similar to that of Leo as early as 4000 BCE.

  • The Turks knew the constellation as Artan; the Syrians as Aryo; the Jewish as Arye, and the Indians as Simha – all of which translate as ‘lion’.

  • In Egypt, the Lion is represented as an important animal in the livelihood of the Egyptians. The Egyptians relied on the flooding of the Nile river every year to nurture the land for the harvest. During the summer months, the heat in the desert would bring the Lions from the plains to the Nile where they could cool down. Their movement to the Nile coincided with the river’s yearly flooding. The event was so crucial to the survival of the Egyptians that festivals were held regularly, where people would pray to the Gods, in the hopes that the flooding would be a success. Today, statues depicting lion heads can be found alongside the Nile to symbolise the importance of the Lion’s movements, and of the flooding that came with them to the livelihood of the Egyptian people.

Observing Leo

The Main Stars

Regulus  – α Leonis (Alpha Leonis)

Regulus (Alpha Leonis) is the 21st brightest star in the sky. The star is 77 light years away from Earth, with a surface temperature more than twice that of the Sun. Regulus is around four times the mass and radius of the Sun. While all stars spin, Regulus is a particularly fast-spinner, spinning at a velocity of 318 km/197.5 miles per second. It spins so fast it has become oblate in shape (flattened at the poles).

When observing Regulus with the naked-eye, it appears as one star, but it’s actually a four-star system composed of two pairs of stars. Regulus, means ‘little king’ or ‘prince’ in Latin. The star’s Greek name, Basiliscos, has the same meaning. While, the Arabic name for the star is Qalb al-Asad, which means ‘the heart of the Lion.’

Denebola – β Leonis (Beta Leonis)

Denebola is the second brightest star in Leo and the 61st brightest star in the sky. The star is only 75% larger in mass and radius than our Sun, but is fifteen times brighter. Denebola is 35.9 light years away from Earth, and is a relatively young star – with an estimated age of less than 400 million years. The name Denebola comes from the Arabic ðanab al-asad, which means ‘the Lion’s tail’.

Other Stars in Leo

Algieba – γ Leonis (Gamma Leonis) 

Algieba (Gamma Leonis) is composed of two stars. The brighter and larger of the two is 320 times more luminous than the Sun. The second star is 50 times brighter than the Sun, and has 10 times the solar diameter. The two stars have an orbital period of 500 years, and sit at a distance of 130 light years away from Earth. A planet was discovered within the orbit of the stars in November 2009.

Its traditional name, Algieba or Al Gieba, comes from the Arabic, Al-Jabhah, which means ‘the forehead’. The star is sometimes also known by its Latin name, Juba.

Zosma – δ Leonis (Delta Leonis)  

Zosma (Delta Leonis) is slightly larger and hotter than the Sun, and is about 15.5 times more luminous. The star is 58.4 light years away from Earth, and like Regulus, is a fast spinner – with a rotational velocity of around 180 km/111.8 mi per second. The star’s traditional name, Zosma, comes from ancient Greek and means ‘the girdle’. Zosma is located on the Lion’s hip.

Chort – θ Leonis (Theta Leonis)

Chort (Theta Leonis) is the sixth brightest star in Leo, and has an estimated age of 550 million years, which means that it is much younger than the Sun. The star is 165 light years away from Earth. The star is sometimes known by its traditional names Chort (from the Arabic al-kharāt or al-khurt, which means ‘small rib’), Coxa (Latin for ‘hip’), and Chertan (from the Arabic al-kharātān, meaning ‘two small ribs’).

Al Minliar – κ Leonis (Kappa Leonis)

Al Minliar (Kappa Leonis) consists of two stars, that lie 210 light years away from Earth. Its traditional name, Al Minliar, comes from the Arabic Minkhir al-Asad, which means ‘the muzzle of the Lion’.

Alterf – λ Leonis (Lambda Leonis)

Alterf (Lambda Leonis)  lies 336 light years from the Sun. The star’s traditional name, Alterf, comes from the Arabic aṭ-ṭarf, which means ‘the view (of the Lion)’.

Subra – ο Leonis (Omicron Leonis)

Subrea (Omicron Leonis) consists of two stars that sit 135 light years away from Earth. It is sometimes known by its traditional name, Subra.

Al Jabbah – η Leonis (Eta Leonis)

Al Jabbah (Eta Leonis) is 2,000 light years away from Earth. The star is 5,600 times more luminous than the Sun.

Adhafera – ζ Leonis (Zeta Leonis)

Adhafera (Zeta Leonis) lies 274 light years away from Earth, and is six times larger in diameter than the Sun, around three times its mass, and 85 times brighter. Its traditional name, Adhafera, comes from the Arabic al-ðafīrah, which means ‘the curl’ or ‘the braid’.

Ras Elased Borealis – μ Leonis (Mu Leonis)

Ras Elased Borealis (Mu Leonis) is 121.1 light years away from Earth and is 63 brighter than our Sun. In 2014, a planet was confirmed to be orbiting Ras Elased Borealis. The planet is larger than our own Jupiter, and it completes one orbit around its star once every 358 days.

The star’s traditional names, Rasalas (or Ras Elad Borealis) and Alshemali are abbreviated from the Arabic phrase ra’s al-’asad aš-šamālī, which means ‘the Northern (Star) of the Lion’s head’.

Ras Elased Australis – ε Leonis (Epsilon Leonis)

Ras Elased Australis (Epsilon Leonis) is the fifth brightest star in the constellation Leo. The star is 288 times more luminous than the Sun and four times as massive. Its estimated age is 162 million years. The star is 247 light years away from Earth. The stars’ traditional names, Ras Elased (Australis), Asad Australis and Algenubi, are derived from the Arabic phrase rās al-’asad al-janūbī, which means ‘the Southern Star of the Lion’s head’.

May’s planets

May presents an excellent opportunity to spot the innermost planet of our solar system, Mercury. Mercury, because of its size and distance, can be elusive, so actually sighting the planet is quite an achievement. In order to locate Mercury, we will need to enlist the help of the second innermost planet, Venus.

On Saturday May 1st, looking in a west-northwest direction, watch for Venus around half an hour after sunset. Venus will be the first bright object to appear above the horizon. It’s quite unmistakable in appearance, and its high-altitude clouds make for the perfect reflective surface to bounce sunlight off – hence the reference to Venus appearing as ‘the Evening Star’.

Once you’ve located Venus, you can use the planet as a clock face. With an imaginary hour hand, direct your gaze slowly away from Venus and up toward 11 o’clock. It may take several attempts to locate Mercury, which is considerably less bright than Venus – but once found, you’ll have spotted one of the more trickier objects to detect in the night sky.

As a further guide, a thin crescent Moon will be situated near to Mercury on the evening of Friday May 14th. Using the Moon as a clock face, use the imaginary hour hand to point as if it were 2 o’clock, and this will point you in the direction of Mercury. On Sunday May 30th, both Mercury and Venus will appear very close in the evening sky. Locate Venus, and slowly scan a short distance slightly down and to the left, and you will arrive at Mercury.

For early risers, both Jupiter and Saturn are on view too, situated over to the South East. Jupiter will appear the brighter of the two, as it is closer to Earth and larger in size than Saturn. On the morning of Wednesday May 5th, a waning crescent Moon will be positioned just to the South East of Jupiter in the predawn sky. The best dates to locate Saturn fall on the morning of Monday May 3rd and Tuesday May 4th, when a waning gibbous Moon will be positioned close to the ringed planet.

May’s meteor shower

At the start of May we have the Eta Aquarid meteor shower, which on the morning of Thursday May 6th, will reach its height of activity. The shower is associated with debris left in the wake of Halley’s Comet. The Earth will pass through the most concentrated amount of rubble on May 6th, when in the early hours of the morning, we can expect to see up to 55 ‘shooting stars’ per hour. The rate of meteors per hour is referred to as the Zenith Hourly Rate (ZHR).

The radiant of the shower (also known as the point where the debris enters the atmosphere), is located in the constellation of Aquarius the Water Bearer. One of the brightest stars within Aquarius is called Eta Aquarii, and these meteors appear from this area of the constellation. This star and the constellation of Aquarius from which it appears, is where we get the name for this month’s shower: Eta Aquarids.

There is a substantial amount of debris for the Earth to pass through, so the shower can be observed over several nights leading up to the peak, and for some time after. However, the ZHR will not be as high leading up to or past the night of the 6th, as after this, the rubble that the Earth is passing through will be less concentrated.

To observe the shower, it is vital that you have the best view possible of the South Eastern horizon, as the radiant is quite low in the sky. Whereas you do not require any optical instrument to observe the shower, make sure you are in a safe location, have suitable clothing to keep warm, and if possible, have the darkest skies possible – away from house and street lighting.

May’s supermoon

The brightest and largest ‘supermoon’ of 2021 will grace our skies on the evening of Wednesday May 26th. So, what is a supermoon, and why does it occur?

The distance between the Moon and the Earth varies, because the Earth is not directly at the centre of the Moon’s orbit, and the Moon’s orbit is not a circle – it’s an ellipse. The moment when the Moon is closest to the Earth is known as a ‘lunar perigee’, and if this coincides with a Full or New Moon, we get what is known as a supermoon. A supermoon appears around 15% larger and around 30% brighter than a micromoon (which we’ll explain in a minute) – or around 7% larger and 15% brighter than an average Full Moon.

The average distance of the Moon from the Earth is 238,855 miles. April’s supermoon (which appeared pink in colour) was just 222,212 miles from Earth making it the second closest supermoon of 2021. May’s ‘flower’ supermoon (called so because it coincides with the blooming of flowers) will be slightly closer to Earth than last month’s Moon at 222,117 miles away. This makes it the closest of this year’s three supermoons, with the final one occurring in June.

In contrast with a supermoon, there’s also a micromoon, which you’ll also be able to spot this month. The points at which the Moon is furthest away from the Earth during its orbit is known as an apogee – or a ‘micromoon’ when combined with a Full or New Moon. A micromoon is classed as a Moon that’s at least 251,655 miles away from Earth. Keep your eyes peeled for a micromoon on Tuesday May 11th!

May’s Moon phases

To understand why we see phases of the Moon, we have to understand the relationship between the Earth, the Moon, and the Sun. The phases result from the changing angles of the Moon and Sun, as viewed from Earth. As the Moon orbits the Earth every month, the angle of it alters, revealing different portions of the Moon’s surface.

During the Moon’s journey around the Earth, the same side of the Moon always presents itself to us – a phenomenon known as ‘tidal locking’. The Moon is tidally locked to the Earth because it rotates in exactly the same time that it takes to orbit the Earth, which is 29.5 days, or one lunar cycle.

There are four main phases of the Moon. Together, these four phases create the outline for a lunar cycle that begins with the New Moon, then the First Quarter Moon, next the Full Moon, and then finally the Third Quarter (or Last Quarter) Moon, before the cycle starts all over again.

To be able to more clearly see and understand the Moon’s phases, it can help to take a note of the dates below; where on a clear night, you should be able to see each phase.

Dates for May’s Moon phases:

  • Third Quarter Moon: May 3rd
  • New Moon: May 11th
  • First Quarter Moon: May 19th
  • Full Moon: May 26th

May’s sunrise/sunset times

Glasgow

Start of May: Sun rises at 5.33 am. Sets at 8.56 pm

End of May: Sun rises at 4.40 am. Sets at 9.49 pm

Cardiff

Start of May: Sun rises at 5.44 am. Sets at 8.36 pm

End of May: Sun rises at 5.02 am. Sets at 9.19 pm

London

Start of May: Sun rises at 5.32 am. Sets at 8.24 pm

End of May: Sun rises at 4.49 am. Sets at 9.07 pm

If you’re new to stargazing or astronomy, and would like a general introduction to the night sky, then you might want to check out our beginner’s guide, here.

Jonathan is a contributor to the BBC Sky at Night magazine. He has written three books on astronomy, Cosmic Debris; Rare Astronomical Sights and Sounds (which was selected by ‘Choice’ magazine as an Outstanding Academic Title for 2019); and From Cave Art to Hubble, all of which are available from Amazon. Jonathan worked at BBC Radio Wales as their astronomy correspondent and is currently a columnist at the South Wales Argus. He has also written a book on castles, ‘Fortress Wales’, and was part of the writing team for the BBC Television show, ‘The Fast Show’, which won a BAFTA.

Are you interested in astronomy? Do you plan to look out for any of the stars, planets or moons above? Join the conversation on the community forum or leave a comment below.

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