As we head toward the cusp of a new season, and welcome in spring, the Winter constellations begin to make way for a new regime in the night sky.
The change in season also sees a lengthening of daylight hours. But before the seasonal baton is passed on, there’s a chance to catch ‘The Twins’, ‘The Seven Sisters’, and the much talked about planet Mars…
Stars and Constellations
Featured Constellation: Gemini The Twins
As we head towards spring, a gradual seasonal change in constellations begins, as the Winter stars begin to leave the evening sky. However, with February’s featured constellation of Orion The Hunter slowly sinking in the South West, this is an opportune time to turn our attention during March, to the constellation of Gemini The Twins, which is closely following Orion on its journey across the sky from east to west.
Gemini features two bright stars which will be easily visible to the naked eye, and that acts as a great starting point when trying to locate more stars within this zodiacal constellation. Gemini consists of two roughly parallel lines of stars, capped by the two brightest stars in the constellation, Castor and Pollux.
Castor and Pollux can be found by firstly finding Orion (see image of Orion below). Then, by slowly sweeping upwards and to the left, you should encounter these two bright stars. First, look for the star Rigel in Orion: the bottom right-hand star. Once you’ve located Rigel, look for the star Belelgeuse in Orion: the top left-hand star. Then, draw a mental line from Rigel to Belegeuse; picturing this line as the small hand on a clock pointing to 11 o’clock. Keep going straight until you reach two bright stars. Castor will be to the right, and Pollux to the left.
Gemini is one of the twelve zodiac constellations that follow a distinct path across the heavens, known as the ecliptic. As the Earth rotates, the Sun, the Moon and planets all travel on the ecliptic, a sort of flat plane across our Solar System. The name ‘ecliptic’ is derived from the Greek, meaning ‘animal circle’ and also is related to the word ‘zoo’, coming from the fact that most of the zodiac constellations are named after animals, such as Leo the Lion, and Taurus the Bull.
Gemini in Mythology
Gemini was one of the 48 constellations first described by second century AD astronomer, Ptolemy, (100-170 AD), and remains one of the 88 constellations that are recognized today by the International Astronomical Union (IAU) – an organisation that promotes and safeguards astronomy. The IAU is instrumental in assigning official names to celestial bodies. Of the 88 constellations recognised today, 42 depict animals, 29 depict inanimate objects, and 17 depict human or mythological characters.
Gemini, meaning ‘The Twins’ in Latin, are the children of Leda. Castor was the son of Tyndareus (King of Sparta and Leda’s husband), whilst Pollux was the son of Zeus (Zeus having seduced Leda). The twins are also the mythological twin brothers of Helen of Troy. When Castor died, because he was mortal, Pollux begged his father Zeus to give Castor immortality. Zeus obliged, and united them together in the heavens.
Castor and Pollux are also associated with St. Elmo’s fire in their role as the protectors of sailors. St Elmo’s fire is a weather phenomenon, whereby a blue or violet glow is observed due to electrical disturbance in the atmosphere. Sailors are said to take particular note of this phenomenon, as the glow appears as fire coming from the top of masts. Sailors would sight the fire, and feel reassured that their saints, Castor and Pollux, were close at hand to protect them during the thunderstorms that sometimes created the glowing effect.
Additional myths relating to Gemini The Twins
- The Egyptians identify the twins as a pair of goats, whilst in Arabian culture, the twins are a pair of peacocks.
- In Babylonian astronomy, Castor and Pollux were known as the Great Twins and regarded as minor gods. These gods were called Meshlamtaea and Lugalirra, meaning ‘The One who has arisen from the Underworld’ and the ‘Mighty King’ respectively.
- In China, Castor and Pollux represent the opposing natural forces of yin and yang, whilst cultures in India and North American thought of the two stars as a married couple.
The Main Stars
Castor is the second brightest star in the constellation of Gemini, and the 44th brightest star in the entire sky, sitting 51 light-years away from Earth. Castor, which has an apparent golden glow, is in fact a system comprising six stars, and although to the naked eye it appears as one, a telescope will split the star into two separate groups of luminosity.
In Arabic culture, Castor was known as ‘The Head of the Foremost Twin’ or Al-Ras al-Taum al-Muqadim. Much like the ancient Greek seafarers who used the stars for navigation, the Arabs were skilled astronomers. Their ‘sea’ was the desert, and whenever they found themselves lost, they used the stars as their guide; as the night sky above the desert has very few clouds. They named these stars accordingly, which is why many prominent stars have names that can be traced back to the star catalogue or Arab astronomer, al-Sufi.
Pollux, which appears whiter than Castor, shines as the brightest star in the constellation, and the 18th brightest star in the entire sky. Pollux is around 34 light-years away from Earth, and around nine times larger than our Sun.
In 2006, a planet was discovered orbiting Pollux. Named Thestias, the body of the planet is of considerable size, and makes one complete trip around Pollux every 590 days. Pollux is also known as ‘The Head of the Second Twin’, from the Arabic Al-Ras al-Tau’am al-Mu’akhar.
Other Stars in Gemini
Wasat, meaning ‘middle’ in Arabic, is a three-star system around 60 light-years away from Earth. The star is estimated to be about 1.6 billion years old, with the position of Wasat in the constellation layout indicating the middle part of Pollux’s body.
As the Earth and Wasat travel through space, it is estimated that in 1.1 million years, Wasat will come within 6.7 light-years of our Sun. Both the Earth within our own Milky Way galaxy and all surrounding stars and galaxies are moving through space, meaning that some objects are getting nearer to us, while some are moving further away. The Solar System which contains the Sun and eight orbiting planets is moving collectively through space at 515,000 mph on one of the arms of the Milky Way.
When Pluto was discovered by American astronomer Clyde Tombaugh, (1906–1997) in 1930, Wasat was positioned just a fraction to the East of the planet.
Mekbuda is around 27 times the radius of our Sun and is about 2,900 times more luminous. The star’s name comes from ancient Arabic, and means ‘The Lion’s Folded Paw’. The zodiac in the Arab world is viewed very much differently from the European and Indian perspectives, hence the different meanings.
From the Arabic meaning ‘The Outstretched Paw’, Mebsuta is in fact a double star at around 840 light-years away from Earth. Mebsuta is about 8,500 times more luminous than our Sun, with a radius around 105-175 times greater. The star sits at the right knee of the twin Castor.
Alzirr is a yellow-white star around 59 light-years away from Earth. Alzirr has a radius almost three times greater than our Sun, and is 11 times more luminous. Alzirr, which means ‘The Button’ in Arabic, marks one of the four feet of the Gemini twins.
The star’s traditional name, Alhena, comes from the Arabic Al Han’ah, which means ‘The Brand’ referring to the brand on a camel’s neck. It is also sometimes known as Almeisan, which is derived from the Arabic Al Maisan, which means ‘The Shining One’. The star is the third brightest star in Gemini, and sits 109 light-years away from Earth. Alhena is around four times larger than our Sun and 123 times brighter.
Tejat Posterior means ‘The Back Foot’ and it refers to Castor’s foot. It is also sometimes known by another Latin name, Calx, which means ‘The Heel’. Tejat Posterior is more than 2,500 times more luminous than our own Sun, at a distance of 230 light-years away from Earth.
Propus is in fact made up of three stars, despite appearing as one to the naked eye. At a distance of around 326 light-years from Earth, Propus means ‘The Forefoot’ in Latin.
In last month’s article, the Pleiades or ‘The Seven Sisters’ star cluster was discussed. The Pleiades is a cluster of stars of which there are many, but only a few that are visible to the naked-eye. March gives an excellent opportunity to spot both Mars and the Pleiades apparently close-by to each other.
During the opening week of March, look to the South-West with the naked eye to try and spot a bright, reddish coloured object. This should be Mars. Once you have located Mars, pan slowly upward in the sky until you reach what appears to be a hazy patch of stars. This will be The Seven Sisters.
Right at the end of March, for any early risers, both Jupiter and Saturn can be seen low in the East, just before sunrise. Jupiter will appear as the brighter of the two objects, but sighting them won’t be easy, as there will be less than an hour before the Sun rises to spot them.
The Spring Equinox occurs on Saturday 20th March. This event marks the astronomical first day of spring in the Northern Hemisphere. After this date, the Northern Hemisphere begins to tilt more toward the Sun, resulting in increasing daylight hours.
The word equinox comes from the Latin words for ’equal night’— aequus (equal) and nox (night). During the equinox, the length of day and night is nearly equal.
March’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 phenomena 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 March’s Moon phases:
Third Quarter March 6th; New Moon March 13th; First Quarter March 21st; Full Moon March 28th.
March’s sunrise/sunset times
British Summer Time accounted for: BST commences at 01:00 am on Sunday 28th March when the clocks are put forward by one hour.
Start of March: Sun rises at 7.07 am. Sets at 5.51 pm
End of March: Sun rises at 6.50 am. Sets at 7.53 pm
Start of March: Sun rises at 6.57 am. Sets at 5.53 pm
End of March: Sun rises at 6.50 am. Sets at 7.44 pm
Start of March: Sun rises at 6.45 am. Sets at 5.41 pm
End of March: Sun rises at 6.37 am. Sets at 7.32 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.