Interesting Facts About Ursa Major

Interesting Facts About Ursa Major
The Big Dipper by Bob King

The Great Bear

In Latin, “ursus” means bear, while in Greek the word is “arktos”, hence the name Arctic (“bearish”) which describes the far northern region of the Earth where the constellation of Ursa Major (“greater she-bear”) dominates. The constellation can be seen by observers located between +90° and -30° of latitude, and together with the adjoining constellation of Ursa Minor (“the smaller she-bear”), these two conspicuous northern constellations are circumpolar are therefore visible throughout the year from the northern hemisphere.

Contains The Dipper Star Asterism

Ursa Major is the 3rd largest constellation, taking up 3.102% of the night sky, and is readily distinguished by means of a remarkable cluster of seven bright stars in the northern heavens, forming what is familiarly termed “The Dipper”. It is also referred to as the “Plough” or “Frying Pan”, with four of its stars forming a pan shape, and the other three a handle. However, this beautiful arrangement of stars forms less than half of the entire constellation known as Ursa Major.

Seven Brightest Stars

Ursa Major’s seven brightest stars in order of visual magnitude are as follows:

– Alioth (Epsilon Ursae Majoris) is a blue-white subdwarf star located 81 light-years distant with a visual magnitude of 1.75. It is 4 times more massive than our sun, and shines around 127 times brighter.

– Dubhe (Alpha Ursae Majoris) is an orange giant found 124 light-years from our solar system with a magnitude of 1.81. It is 415 times brighter than our sun, but is actually a binary system whose stars orbit each other once every 44.4 years.

– Alkaid (Eta Ursae Majoris) is a blue-white main sequence star situated 101 light-years away with a visual magnitude of 1.85. It is about six times more massive than the Sun, and 700 times more luminous.

– Mizar and Alcor are perhaps the most famous naked eye double star in the night sky, and together are known as the “Horse and Rider.” They are both white stars approximately 80 light years away, with Mizar shining with a magnitude of 2.23, and Alcor at 4.01.

– Merak (Beta Ursae Majoris) is a blue-white star 79 light-years distant of magnitude 2.34. It is has around 3 times the radius and mass of our sun, and shines 70 times brighter.

– Phecda (Gamma Ursae Majoris) is a white main sequence star 84 light-years distant that shines with a magnitude of 2.43. It is about 71 times brighter than our sun.

Megrez (Delta Ursae Majoris) is a blue-white star 58.4 light years from Earth with a magnitude of 3.312. It is 63% more massive than our sun, and is 14 times more luminous.

ursa major star guideInteresting Objects

Ursa Major is a remarkable constellation containing seven Messier objects, including the following galaxies: Bode’s Galaxy (M81), a dense spiral galaxy with an incredible 250 billion suns; the Cigar Galaxy (M82); the Pinwheel Galaxy (M101); as well as the Barred Spiral Galaxies of M108 and M109, both of which are 12 million light years away. The other Messier Objects in Ursa Major includes the planetary Owl Nebula (M97) situated 1,630 light-years from Earth; and Winnecke 4 (M40), a faint double star found 510 light years away.

Ursa Major As A Star Clock

From the Northern hemisphere, Ursa Major is  circumpolar and never sets below the horizon, making it visible the whole year round. Moreover, the constellation is seen to complete a whole counterclockwise rotation every 24 hours around the ‘North Star’ (Polaris) located in neighboring Ursa Minor, with this motion having made it an excellent star clock throughout history.

Ursa Major As A Directional Compass

Polaris is located very close to the north celestial pole and has also been extremely useful as a directional compass, as well as determining latitude, as the North Star is always elevated as many degrees above the horizon as the observer is north of the equator. The stars Merak and Dubhe in ‘The Dipper’ are called the pointers, because they always point northwards toward Polaris. Note the second star from the end of the Dipper’s handle actually consists of Mizar and its fainter companion Alcor. These stars appear close together and being able to distinguish one from the other was used by many ancient armies as a test for those wishing to become an archer, including the Persian and Romans. The Arabs also used them as a test of good eyesight.

Mythology of Ursa Major

One version of the legend goes that Callisto, a nymph devoted to the goddess Artemis, caught the eye of Zeus, king of the gods, who subsequently deceived and impregnated her. After later giving birth to a son called Arcas, the queen of the gods, Hera was so infuriated that she turned Callisto into a bear. Years later, Arcas was out hunting and was about to kill the bear unwittingly when Zeus intervened and swung both Callisto and Arcas, now transformed into a bear, up into the sky as Ursa Major and Ursa Minor respectively. Hera was annoyed the pair were given so much honor and so convinced Poseidon to forbid them from bathing. It is for this reason that these constellations are circumpolar and never dip below the horizon when viewed from Northern latitudes.

Three Meteor Showers

The three meteor showers associated with the constellation of Ursa Major are as follows:

Alpha Ursa Majorids, which is active from August 9th to 30th, and peaks on the 13/14th with around 4 meteors per hour.

Kappa Ursae Majorids, which can be viewed from November 2nd to 9th, and peak on the 5th when a mere 1 meteor per hour can be seen.

– Ursids, which runs from between December 17th to 24th, and peaks on the 23rd with up to 10 meteors per hour.

Next Step: Mapping the night sky using Ursa Major