A constellation is a collection of stars that seem to form a pattern when observed from the earth. To date, there are 88 known constellations that cover the night sky with 36 of them located in the northern hemisphere and the bulk of them (52 constellations) located in the southern hemisphere.
The Ursa Major is one of the 88 constellations and is located in the second quadrant of the northern hemisphere. It can be easily spotted between the latitudes of -30o and +90o. Ursa Major is the largest constellation in the northern hemisphere (occupying 3.102% of the northern sky) and the third biggest constellation in the night sky after Virgo and hydra. Due to the fact that Ursa Major never sets below the horizon, it visible in the night sky all year (Ursa Major Constellation, n.d.).
Between the months of January to march the constellation can be viewed in the north-eastern sky at around 6 pm and disappears to the north-west as daybreak approaches around 7a.m.It appears overhead at around 9 p.m and moves in the north-west horizon before dawn at around 6 a.m in the months of April to June. In July to September, it appears at around 10 pm in the north-west and lowers to the northern horizon as dawn approaches at around 6 am.Finally, in the months of October to December, it appears lower in the north-west horizon from 6 pm to 6 is as the day breaks (Rey, 2017)
The name Ursa major was coined from Latin meaning the big bear and was well known in most ancient cultures and mythologies because aside from being one of the largest, it is also one of the oldest constellations to be identified. Ptolemy, a Greek astronomer cataloged it in the 2nd century. According to Greek mythology, the constellation is associated with a beautiful nymph called Calisto who had sworn chastity to Artemis but ended up breaking her vow when she got pregnant with Zeus son.
Once Hera discovered Zeus betrayal of falling in love and siring a son with Calisto, in a feat of anger she turned her into a bear. Calisto roamed in the forest, running from hunters for almost 15 years until one day when arcas, her son saw the bear and drew a spear in defense but Zeus who was watching from Olympus intervened by sending a whirlwind that carried arcas and Calisto into the sky and turned them into the constellation Bootes and Ursa major respectively. Hera was mad after realizing this and she persuaded Oceanus and Tethys (her foster parents) not to let the bear bathe in the northern waters and thats why Ursa Major does not set the horizons (Ursa Major Constellation, n.d.).
Ursa Major is composed of up to 209 stars with its seven brightest stars forming the big dipper asterism. The seven stars are Alkaid, Mizar-Alcor, Megrez, Alioth, Phecda, Merak and Dubhe. Alioth is a white star and the brightest star of the constellation with a magnitude of 1.77.it is estimated to be located over 81 light years from earth. The surface temperatures at Alioth is 10500k on average which is twice as much to that of the sun at 5500k averaging .it is also larger than our own sun with its radius being 4 times bigger than that of the sun which is at 696,000 km. Alioths mass is approximately 3 times that of our sun with the suns mass being around 1.989 x 1030 kilograms (Christoforou, 2017)
The sun is a yellow dwarf while Alioth is a white dwarf nearing the end of its lifespan. Yellow dwarfs are stars at the hydrogen fusion stage. This stage may take billions of years before depletion. Once fusion is done, the star expands its size and eventually sheds all its outer layers while the core cools and shrinks into a white dwarf where the is no hydrogen - fusion and therefore the remaining mass is slowly converted to energy as the star continues to contract. Putting the facts into context, Alioth is currently aging while the sun which is said to be middle-aged at approximately 4.5 billion years still has over 5 billion years before it starts collapsing (Aguilar, 2007)
Figure 1: Ursa Major constellation [Pattern formed by the stars].
Aguilar, D. A. (2007). Planets, stars, and galaxies: a visual encyclopedia of our universe. Washington, D.C.: National Geographic
Christoforou, P. (2017, July 02). Star Facts: Alioth. Retrieved November 24, 2017, from https://www.astronomytrek.com/star-facts-alioth/
Rey, H. A. (2017). Find the constellations. Boston: Houghton Mifflin Harcourt.
Ursa Major Constellation. (n.d.). Retrieved November 24, 2017, from http://www.constellation-guide.com/constellation-list/ursa-major-constellation/
Ursa Major constellation [Pattern formed by the stars]. (n.d.). Retrieved November 24, 2017, from https://www.solarsystemquick.com/universe/ursa-major-constellation.htm
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