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Man must rise above the Earth, to the top of the atmosphere and beyond, for only then will he fully understand the world in which he lives.
Socrates, 469 - 399 BC

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URSA MINOR

The Little Bear

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Ursa Minor - Celestial Atlas by Alexander Jamieson - 1822

The constellation Ursa Minor was once Arcas, son of the nymph, Callisto. When Zeus (Jupiter) seduced Callisto, his jealous wife Hera turned her into a bear. When Arcas was about to unknowingly kill his mother in this form, Zeus turned him into a bear as well, and grabbing them both by their tails, flung them into the sky to escape Hera, stretching their tails in the process.

Callisto the nymph became Ursa Major, the big bear, and her son Arcas became Ursa Minor, the little bear. Ursa Minor is also widely recognized as The Little Dipper, (albeit with an awkwardly curved handle), a smaller version of "The Big Dipper" asterism inside the constellation representing his mother. Ursa Minor is a circumpolar constellation that never sets below the horizon for viewers above 15 degrees north latitude, according to myth a final spiteful act by Hera, condemning Arcas and his mother to an eternity of circling the pole star with no rest.

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Ursa Minor - February 15, 10:00 PM - Latitude 45° North, Longitude 95° West

Stars of Ursa Minor

Polaris (RA: 02h31m52.536s DE:+8915'50.61")

Alpha Ursae Minoris is one of the most important stars in the heavens, named "Stella Polaris", the Pole Star, or simply Polaris. Commonly known as the North Star, it is found at the end of the backwards handle of the Little Dipper - the tail of the Little Bear. Novice observers can use the two stars known as "the pointers" on the front of the Big Dipper to show them the way. Polaris is positioned almost exactly where our planet's northern axis points off into space, so as Earth turns, Polaris appears to stand still, with all the other stars rotating around it, making it a steadfast beacon that has guided travelers throughout the ages.

In 1780, Astronomer William Herschel discovered that Polaris had a small companion star revolving around it, named Polaris B, making it a binary, or two-star system, as seen in the Hubble photo below left. In January, 2006, the Hubble Space Telescope found a third star, named Polaris Ab, orbiting much nearer Polaris A, shown in the close-up image below right. This new star makes Polaris now a triple star system.

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Polaris Triple Star System - Hubble Space Telescope - January, 2006

Polaris A is an F7I yellow supergiant, shining brightly at magnitude 1.97, even though it is quite far away at a distance of 430 light years. Polaris B is a much smaller and dimmer F3V yellow main sequence star with a magnitude of 8.7, orbiting Polaris A at a distance of 240 billion miles. Polaris Ab is an even dimmer little F6V yellow main sequence star with a magnitude of 9.2, orbiting only 1.8 billion miles from Polaris A.

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Precession

Polaris has not always been the North Star in the past, and will not always be the North Star in the future. Because of a slight wobble in Earth's rotation called precession, its axis traces a counter-clockwise circular path through the stars that takes 28,000 years to complete, and gradually moves from one North Star to the other. As the image below shows, around the time of the pyramids, the North Star was Thuban, in the constellation Draco. In the year 4500 the star Alrai in Cepheus will point the way north. And if there are still Humans on Earth in the year 14000, they will call the bright star Vega, in Lyra the North Star.

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Kochab - with a planet (RA: 14h50m42.203s DE:+7409'19.98")

Beta Ursae Minoris is named Kochab (also spelled Kocab), an Arabic name of unclear origins. It is a K4III orange giant, with a magnitude of 2.07, about 131 light years away. Kochab is one of two stars that form the front of the Little Dipper, and are known as the "Guardians of the Pole", as referenced by the Bard:

The wind-shak'd surge, with high and monstrous mane
Seems to cast water on the burning Bear,
and quench the guards of th' ever fixed pole.

Shakespeare - Othello - Act 2, Scene 1

In 2014 a gas giant planet six times the size of Jupiter was confirmed in orbit around Kochab. The planet is large enough to have small planet/moons of its own, and it's a pretty safe bet that it does. It's always a thrill to be able to look up at a big, bright star that you know has at least one confirmed planet, and who knows how many more, and wonder if there might be some sort of life up there, growing, evolving, maybe even looking back at us.

Pherkad (RA: 15h20m43.657s DE:+7150'02.73")

The second "Guardian of the Pole" is Gamma Ursae Minoris, named Pherkad, from the Arabic "Farkadain", meaning the two calves, referring to an ancient Arabic vision in which the stars around the pole represented a group of young animals collectively called "The Fold". It is an A2III white giant with a magnitude of 3.00, about 486 light years away.

Pherkad Minor - with a planet (RA: 15h17m05.902s DE:+7149'26.20")

11 Ursae Minoris is named Pherkad Minor. It is a K4III orange giant with a magnitude of 5.02. In August, 2009, a planet was discovered in orbit around Pherkad Minor. It is a massive planet, over ten times the size of Jupiter. The Pherkad solar system is very far away though, at a distance of 397 light years.

Yildun (RA: 17h32m13.165s DE:+8635'12.10")

Delta Ursae Minoris is Yildun, the last of the named stars in Ursa Minor. It is an A0V white main sequence star with a magnitude of 4.35, about 173 light years away.


Planets of Ursa Minor

HD 120084 (RA: 13h42m38.883s DE:+7803'52.67")

So far, there have only been four confirmed planets found in Ursa Minor. As well as the bright star Kochab and nearby Pherkad Minor mentioned above, a third naked eye star, HD 120084, also has a gas giant planet in orbit around it, about 4.5 times the size of Jupiter. The star is a G7III yellow giant at the very limit of naked eye visibilty with a magnitude of 5.91, and very far away at a distance of 318 light years.

HD 150706 (RA: 16h31m18.125s DE:+7947'21.83")

Very much closer, although not exactly next door is HD 150706, at a distance of 88.7 light years. It is a G0 yellow main sequence star similar to our Sun, just beyond visual range at magnitude 7.01. So far it has one confirmed planet 2.7 times the mass of Jupiter that orbits the star at about seven times the Earth-Sun distance (6.7 AU), and takes 16 years to complete one orbit. For more information on these and other extrasolar planets, visit NASA's New Worlds Atlas, and The Open Exoplanets Catalogue.


Deep Skies of Ursa Minor

NGC 6217 (RA: 16h32m 36.0s DE:+7812'00")

Ursa Minor does not have much to offer in the way of deep sky objects, but it is home to a very handsome barred spiral galaxy NGC 6217. It is a "starburst galaxy" displaying an unusually high degree of star formation. The galaxy is less than half the size of our Milky Way galaxy, and lies about 60 million light years away. With a magnitude of 11.2, it is beyond the reach of smaller telescopes, but quite a sight through the eyes of Hubble.

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NGC 6217 - Barred Spiral Sunburst Galaxy - Hubble Space Telescope - September, 2009

NGC 6251 (RA: 16h32m 30.0s DE:+8232'00")

Much farther away, at a distance of 300 million light-years and a magnitude of 14.3 is NGC 6251. It is a giant elliptical galaxy which typically show little form, but a combined visible/ultraviolet exposure by Hubble reveals the effects of a supermassive black hole at the galaxy's core. The event horizon around the black hole blazes with light, illuminating a warped accretion disc, the first of its kind ever seen. Perpendicular to this disc is a powerful 3 million light-year-long jet of radiation producing one of the most powerful radio sources in the sky.

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NGC 6251 - Elliptical Galaxy - Hubble Space Telescope - September, 1997







Winter: Orion   Canis Major   Canis Minor   Monoceros   Lepus   Eridanus   Taurus   Auriga   Camelopardalis   Lynx   Gemini   Cancer  
Spring: Hydra   Sextans   Crater   Corvus   Leo   Leo Minor   Ursa Major   Ursa Minor   Canes Venatici   Coma Berenices   Virgo   Bootes  
Summer: Draco   Corona Borealis   Hercules   Ophiuchus   Serpens   Libra   Scorpius   Sagittarius   Scutum   Aquila   Sagitta   Vulpecula   Lyra   Cygnus  
Autumn: Andromeda   Perseus   Pegasus   Cassiopeia   Cepheus   Cetus   Lacerta   Delphinus   Equuleus   Capricornus   Aquarius   Pisces   Aries   Triangulum  
Southern Skies: Centaurus   Crux   Lupus   Corona Australis   Piscis Australis   Sculptor   Tucana   Fornax   Dorado   Columba   Puppis   Carina   Vela  

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