Chakra

History

The constellation of Small Ourse, although it is of ancient origin (Ptolémée catalogued it in its Almageste ), did not have the interest at that time only it presents now since it did not indicate the celestial north pole at all. Probably forming part in the beginning of a constellation disappeared for a long time named the Wing from the Dragon , one says that it was created by the Greek Philosophe Thalès with the VI {{E}} front century J. - C.

The Greek Mythologie was attached there: the nymph Callisto was liked by Zeus. When his jealous wife Héra discovered their relation, Zeus converts Callisto and its small son, Arcas, in the Large one and Small Ourse. Héra, outragée by this offense with its honor, required justice of the Ocean, and the ourses were then condemned to turn perpetually around the North pole, ever authorized to rest under the sea.

This constellation gave several words. The “Arctic” word comes from the Greek word arktos , “bear”, and the word “north” indicates seven stars of this constellation. A myth according to which the constellation would not be a ourse but a dog, led pole star to be sometimes named cynosure , “tail of the dog”, term also meaning “object of interest” in English.

Observation of stars

; Localization of Small Ourse Small Ourse is generally located compared to the Grande Ourse. A very known method makes it possible to determine the site of α Ursae Minoris: by tracing a line of Merak with Dubhe (two stars of the edge external of the pan), and while following it on five times the distance between these two stars, after having passed the tail of the Dragon if it is visible, and one falls on the pole star, which is the only brilliant star of this sector. Arrived on pole star by this alignment, the " small chariot" is with right angle towards the left, drawing a small arc of circle directed towards the Grande Ourse. An alternative method to find Polaris consists starting from the constellation of Cassiopée.

; Form constellation The constellation of Small Ourse is rather poor and not very luminous. One initially does not see (Mag 2) only two extreme stars, (α Ursae Minoris, the pole star) and Kochab (β UMi). When the conditions are a little better (Mag 4), one distinguishes the chain binding both: α UMi, δ UMi, ε UMi, ζ UMi and Kochab (β UMi).

Traditionally, one sees Small Ourse in the form of a " small chariot" , the chain being supplemented after Kochab while turning right, by γ UMi and η UMi. In fact, the symmetrical star of γ UMi compared to Kochab, 5 UMi, is more luminous than η UMi, and this alignment of three stars is more easily visible than the form of " casserole".

The stars which surround Kochab at longer distance form the constellation of the Dragon.

Principal stars

α Ursae Minoris (the pole star)

α Ursae Minoris (the pole star) - also named “Polaris” - is the the most brilliant star of the constellation of Small Ourse, moreover only the relatively interesting one. It is about star visible with the naked eye nearest of the celestial north pole, from which it is distant from 44 ' 9". Because of the phenomenon of Precession of the equinoxes, that was not always the case: there is more than 4 millenia, towards 2700 before our era, it was α Draconis (Thuban) which was in its situation. And in a future distance, this honor will pass to Véga (α Lyrae). The pole star approaches besides in this moment the pole and will be with closest into 2102, with 27 ' 31".

The Pole star is a yellow Supergéante, of a Magnitude connect of 1,97. It is the 52 {{E}} the most brilliant star of the vault of heaven. It is rather distant, distant of 430 light-years of the Solar system.

It is a variable star céphéide, evolving/moving of a hundredth magnitude over one 4 days period. This amplitude strongly decreased in two centuries to become almost null nowadays, without one knowing the reason of it.

The Pole star also has small a companion which Orbite around it in 29,6 years.

It is easy to find Pole star while following a line traced starting from Merak (β Ursae Majoris), passing by Dubhe (α Ursae Majoris), two stars at the end of the bowl of the pan of Large Ourse. One can also follow the central point of “W” of Cassiopée.

Other stars

Two other notable stars of the constellation, Kochab (β UMi) and Pherkad (γ UMi) are located respectively to 130 and 500 light-years. First is apparent magnitude 2,07 and shines like 190 suns (absolute magnitude: -0,87), second is apparent magnitude 3,00 and absolute magnitude -2,84 (thousand suns).

Seven principal stars of Small Ourse (the pole star, Kochab, Pherkad, Alifa Al Farkadain (ζ UMi), Anwar Al Farkadain (η UMi), Yildun (δ UMi) and ε UMi) form a Astérisme comparable with that of the Grande Ourse, in form of “carriage” or “pan”. Contrary to that of Large Ourse, it is not very luminous, the pole star put aside, and it is difficult to locate it since one is in a zone so much is not very enlightened.

HD 150706 has a planet of a mass about equal to that of Jupiter, orbiting on average with 0,82 ua of distance in 264 days.

Summary table

N.B. : The numerical values come from the data measured by the satellite Hipparcos

Celestial objects

The constellation of Small Ourse contains several Galaxie S: NGC 3172, NGC 5034, NGC 5144, NGC 5939, NGC 6071, NGC 6324 and NGC 6331.

The Spiral galaxy barred NGC 6217 (16h 32mn 29s of Right ascension, 78° 11 ' 48" of variation) is most brilliant, although it is rather not very luminous (magnitude 12,10). It appears leaning three-quarter to us.

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