All About The Big Dipper
As the most recognizable asterism in the sky, the Big Dipper is formed out of the seven brightest stars in the constellation Ursa Major or ‘Greater Bear’. It’s appearance is that of a bowl comprised of four stars – Megrez, Phecda, Dubhe, and Merak – and a handle made out of three stars: Alkaid, Mizar and Alioth.
As a result of its infamy and instant recognizability, the Big Dipper is often used by amateur astrologers to locate other significant astrological landmarks – most notably, the North Star, or Polaris, which is located in Ursa Minor ‘Little Bear’. Polaris is indicated by certain ‘pointer stars’ Merak and Dubhe within the Big Dipper asterism – the next bright star along the same line is the North Star.
Big Dipper Mythology
According to the Ancient Greek mythology, Ursa Major – the constellation that the Big Dipper resides within – was created by Zeus when he sent his former lover, in bear form, to the heavens, along with their son: Arcas.
The myth recalls that Zeus – already married to the goddess Hera – fell in love with a beautiful maiden named Callisto, and subsequently impregnated her. However, when Callisto and Zeus’ child was born, the goddess Hera vengefully turned Callisto into a bear.
After wandering the forest for many years, Callisto (in bear-form) chanced upon her spear-carrying son, Arcas, who made to strike her with the sharpened weapon. Before the spear could meet its mark, however, Zeus intervened and sent them both up to the heavens, turning them into constellations in the sky, making Callisto the Great Bear and Arcas the Little Bear.
Moreover, it is said that Hera didn’t want the bear to be able to go into the sea, and that is why the constellation never falls below the horizon.
As a circumpolar constellation, Ursa Major – and therefore the Big Dipper – is visible all year round, never falling below the horizon, though it lies close to it in the autumn and winter months. Contrastingly, in spring and summer the asterism can be seen high in the sky, hence the rule ‘spring up, fall down’: a saying commonly used to remember the position of the Big Dipper during the different seasons.
This isn’t the only version of the myth behind the Ursa Major constellation – likewise, in Roman mythology, a very similar story about the god Jupiter and the nymph Callisto explains the origin of the constellation that bears the Big Dipper.
By Till Credner - Own work: AlltheSky.com
The Big Dipper Throughout the World.
Likewise, the Big Dipper itself has been commented on by different cultures throughout history: some Native American communities consider the bowl to be a bear, and the handle as three hunters stalking the bear – or, in a less sinister explanation of the asterism, three cubs following the mother bear.
Moreover, in Arabic folklore, the Big Dipper is a funeral symbol, and the bowl of the dipper is considered to be a coffin, while the three stars forming the handle represent three mourners following behind it.
The Big Dipper is called by many different names all over the world. Traditionally, in the UK and Ireland, the asterism was called The Plough, while many European countries – such as Italy, Germany, Romania and Scandinavia – describe it as some sort of wagon: the Great Wagon, Charles’ Wagon, among other variations.
The name of each of the seven individual stars, however, remains the same across the world.
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Stars of the Big Dipper
Meaning ‘the leader’, Alkaid marks the end of the Big Dipper’s handle – or the end of Ursa Major’s tail – and is a blue main sequence star: one of two stars which aren’t part of the Ursa Major Moving Group. This particular star is the 3rd brightest star in the Ursa Major constellation, and is one of the hottest stars we’re able to see from earth without the use of a telescope, and is approximately 103.9 light years away from Earth.
Meaning ‘girdle’, Mizar is the next star along, marking the middle of the Big Dipper’s handle. Mizar is a white sequence star, with a mass over 2000 times that of our sun and is part of a multiple star system which provides the illusion to the naked eye of being a ‘double star’. Furthermore, Mizar is a member of the Ursa Major Moving Group – a group of stars which share common origin, proper motion, and velocities in space.
Meaning ‘fat tail of a sheep’, Alioth is the star which is closest to the bowl as the final star in the handle, and is the Big Dipper’s brightest star. Likewise, it’s also a member of the Ursa Major Moving Group – also known as Collinder 285 – and is a white sequence star, though it’s thought to be coming to the end of its main sequence life.
Meaning ‘the base’, Megrez is the star that appears to connect the bowl of the Big Dipper to the handle, and is also the dimmest of all the stars present in this asterism. However, the star is unique, as it rotates very quickly, turning at a rotational velocity of over 230 km/s. Megrez is also a member of the Ursa Major Moving Group.
Meaning ‘the thigh of the bear’, Phecda is a white main sequence dwarf star, and part of the Ursa Major Moving Group. As the star underneath Megrez, it is positioned at the bottom of the Big Dipper’s bowl. Interestingly, Phecda has an astrometric binary companion in the form of an orange dwarf, which disturbs it and causes it to wobble around the mass.
Meaning ‘the loins’, Merak is a white subgiant star which sits across from Phecda at the bottom of the bowl of the Big Dipper. Merak is the last star to belong to the Ursa Major Moving Group, and is estimated to be 500 million years old.
Meaning ‘bear’, Dubhe is the second brightest star in the Big Dipper, and sits across from Megrez at the top of the Big Dipper’s bowl. Dubhe is an orange giant – though more recent research has suggested that it’s actually a yellow giant – and is a spectroscopic binary star, with a companion of a white main sequence star.
It’s predicted that in roughly 50,000 years the Big Dipper will face the opposite way and even change shape – in particular, the configuration of the end of the handle (marked by Alkaid) and the end of the bowl (represented by Dubhe).
However, because most of these stars are part of the Ursa Major Moving Group – and share common motion through space – the Big Dipper shouldn’t look all that different, even in the distant future.
So, the Big Dipper – and it’s parent constellation Ursa Major – will most likely continue to be spotted and wondered at by those on Earth for tens to hundreds of thousands of years to come, the constellation’s rich history and bright configuration of stars delighting each who comes to learn of them, as they do today, and as they have since Ancient times.