Great Bear

The Ursa Major (in Latin, Ursa Maior; abbreviated, UMa), also known as the Greater Car, is a visible constellation throughout the year in the northern hemisphere. Among fans it is known by the name of "the car" or "the saucepan", due to the way its seven main stars draw, although it has received other names.

Notable features

Constellation Osa Mayor, AlltheSky.com

The main stars of "the dipper", except Dubhe and Alkaid, have a common proper motion towards a point in the constellation Sagittarius, forming part of the so-called Ursa Major stellar association. The brightest among them is Alioth (ε Ursae Majoris), located in the tail of the bear, distant 81 light years from Earth. It is a white star of spectral type A1III-IVpkB9 108 times more luminous than the Sun and a chemically peculiar Ap star, the brightest of its class. Its light spectrum is atypical, showing certain chemical elements enhanced or diminished, which also change with great regularity with the rotation of the star.

The second brightest star in the constellation is Dubhe (α Ursae Majoris), a stellar system where the binary formed by a yellow-orange giant of type G9III and a white-yellow main sequence star of type A7.5 stands out. with an orbital period of 44 years. Much further away, at 8,000 AU, is a yellow dwarf that is itself a spectroscopic binary. Next in brightness is η Ursae Majoris, officially named Alkaid and also known as Benetnasch, a bluish-white main sequence star of spectral type B3V with an effective temperature of about 20,000 K.

Mizar (ζ Ursae Majoris) and Alcor (80 Ursae Majoris) form one of the best-known double stars in the night sky. On the one hand, Mizar is a quadruple stellar system formed by two binaries separated by at least 500 au; additionally, each of them is a spectroscopic binary. All four components are white main sequence stars. Alcor, on the other hand, is a type A5V star that does appear to be physically linked to the Mizar system. Two other of the constellation's brightest stars, Merak (β Ursae Majoris) and Phecda (γ Ursae Majoris), are also white main sequence stars, of type A1V and A0V respectively.

Several bright red giants can also be seen in the Big Dipper. μ Ursae Majoris, named Tania Australis, has spectral type M0III and is a spectroscopic binary. For its part, ρ Ursae Majoris is a star of the giant asymptotic branch of type M3III; It has a surface temperature of 3279 K and a radius 59 times that of the Sun.

Among the variables of the Big Dipper, W Ursae Majoris stands out, whose variability was first detected by Muller and Kempf in 1903. It is a contact eclipsing binary whose components share a common outer shell, so both stars have the same spectral type, G2Vn. The system's orbit is circular with an orbital period of only 0.3336 days, or 8 hours and 23 seconds. It is the prototype of this class of variables, known as W Ursae Majoris variables. Another variable of this type in the constellation is AW Ursae Majoris, its period being slightly longer, 0.4387 days. On the other hand, the variable Z Ursae Majoris is a red giant whose semiregular periodicity is the result of several different pulsation periods within the star. SU Ursae Majoris, a dwarf nova within the group of cataclysmic variables, has very different characteristics..

Planet orbits around 47 Ursae Majoris

In this constellation there are several yellow dwarfs analogous to the Sun. 61 Ursae Majoris is a G8V-type star, cooler and smaller than the Sun, located 31.1 light-years away. Somewhat further away—41.9 light-years—36 Ursae Majoris is an F8V-type star with an effective temperature of 6110 K; the possible presence of a faint red dwarf or brown dwarf around it in a highly eccentric orbit (ε = 0.8) has been reported. 47 Ursae Majoris —called Chalawan by the IAU— is a G1V-type star where three extrasolar planets have been discovered at 2.1, 7.7 and 11.6 AU from the star. Of spectral type G0V, 16 Ursae Majoris is a star older than the Sun with a stellar companion that has an orbital period of 16.23 days. Finally, HD 98618 is a solar twin whose temperature, metallicity, and age parameters are almost indistinguishable from solar ones. Its luminosity is slightly higher than solar luminosity, approximately 6% higher.

Lalande 21185, the fourth closest star to the solar system —at 8.31 light years—, is found in this constellation. It is a faint red dwarf of type M2.0V with a luminosity equal to 2% of solar luminosity and a metallicity—relative abundance of elements heavier than helium—equal to 52% of solar. At 0.079 AU it orbits an extrasolar planet whose mass is at least 2.69 times that of Earth. Likewise, two planets have been discovered around the red dwarf HIP 57050, orbiting at 0.17 and 0.91 AU. Another stellar system close to us is Gliese 412, composed of two red dwarfs of unequal mass separated from each other by approximately 140 au; the faintest is a flaring star which is variable-named WX Ursae Majoris. Groombridge 1618, 3 light years distant from Gliese 412 and 15.9 light years from the solar system, is an orange dwarf of type K7V and a temperature of 3947 K whose luminosity corresponds to 4.6% of that of the Sun. On the other On the other hand, in the Big Dipper is the third star with the greatest proper movement, Groombridge 1830. It is a subdwarf star in the galactic halo whose metallicity is equivalent to 9% of that of the Sun.

M82 mosaic image obtained with Hubble space telescope

Another object of interest in the constellation is the M97 nebula or Owl Nebula, a planetary nebula located at an uncertain distance of 2600 light-years. It is a very complex nebula whose estimated age is approximately 6000 years. The mass of the nebula is estimated to be 0.15 solar masses, while the central star is approximately 0.7 solar masses.

On the other hand, several notable galaxies are found in the Big Dipper. M81, known as the Bode Galaxy, is a distant spiral galaxy 11.8 million light-years away, one of the closest beyond the Local Group. It is possibly the most important galaxy in the M81 galactic grouping. On the contrary, M82, called Cigar Galaxy, is an irregular galaxy prototype of a starburst galaxy, characterized by a high rate of star formation in its center, whose origin seems to be due to the gravitational interaction with the Bode Galaxy between 200 years ago. and 500 million years. Another prominent galaxy is M101, one of the largest galaxies in the vicinity of the Local Group with a diameter more than twice that of the Milky Way; It is characterized both by its richness in gas to form new stars and by its high number of H II regions. M108 and M109 are also more distant spiral galaxies, the second of which is classified as a theta-type barred spiral, and is observed as a hazy point.

Image of the Hubble of NGC 3079

NGC 2787 is a lenticular galaxy 24 million light years distant that has a nuclear region with low ionization emission lines (LINER). Likewise, NGC 3079 and NGC 3310 are starburst galaxies whose star formation rate is much higher than that of a normal galaxy. The Hubble Space Telescope has allowed us to observe how in the nucleus of NGC 3079 there is a lumpy bubble of hot gas that rises from a cauldron of incandescent matter. For its part, NGC 3310 contains several hundred stellar clusters, each of which can give rise to the birth of up to a million stars.

Lastly, the galaxy I Zwicky 18 is also interesting, which was initially thought to be the youngest galaxy in our environment with an age of 500 million years; however, later observations with the telescope Hubble suggest that its star formation began at least a billion years ago and even ten billion years ago. Therefore, it seems to have formed at the same time as the rest of the galaxies.

Main Stars

Image of the Biggest Bear captured in Celestia

Double star Alcor and Mizar

From the position of Merak (β) and Dubhe (α) you can find the polar star

• α Ursae Majoris (Dubhe), the second brightest constellation star with magnitude 1.81, a multiple star system 124 light years away.
• β Ursae Majoris (Merak), of magnitude 2,34, is only the fifth star in brightness, and, along with Dubhe, points out the direction of Polaris (α Ursae Minoris), the polar star.
• γ Ursae Majoris (Phecda, Phekda or Phad), a white star of magnitude 2,41, at 84 light years.
• δ Ursae Majoris (Megrez), white star of magnitude 3.32.
• ε Ursae Majoris (Alioth), the brightest constellation with magnitude 1,76, is a chemically peculiar Ap star, the most brilliant of this class. It is an Alpha2 Canum Venaticorum variable whose shine fluctuates 0.02 magnitudes.
• ج Ursae Majoris (Mizar), with magnitude 2,23, is a famous double optic star next to Alcor, separated both 12 minutes of arc. However, Mizar is a real binary star, with its components separated 14 seconds of arc.
• MIL Ursae Majoris (Benetnasch or Alkaid), the third most brilliant constellation with magnitude 1.85, a white-smoiled star.
• θ Ursae Majoris, double star whose components are separated 4.1 seconds of arc. The main star is a spectroscopic binary.
• . Ursae Majoris (Talitha Borealis), multiple star system of magnitude 3,12, 48 light years away.
• κ Ursae Majoris (Talitha Australis), 3.6 magnitude binary star composed of two separate white stars 0.3 seconds of arc.
• λ Ursae Majors (Tania Borealis), a white sub Giant star of magnitude 3.45 with a possible circum-stellar disk around it.
• μ Ursae Majoris (Tania Australis), red giant and semi-regular variable of magnitude 3.06.
• . Ursae Majoris (Alula Borealis), binary star composed of an orange giant of magnitude 3,49 and a yellow dwarf of magnitude 10,1, separated 7,4 seconds of arc.
• roga Ursae Majoris (Alula Australis), of magnitude 3,79, multiple star with four or five components at 27.3 light years.
• ο Ursae Majoris (Muscida), yellow giant and variable star between magnitude 3.36 and 3.6.
• π Ursae Majoris, denomination used for two different stars: π1 Ursae Majoris, yellow dwarf at 46.8 light years, and π2 Ursae Majoris, giant star with an extrasolar planet.
• ρ Ursae Majoris, red giant of magnitude 4,78.
• υ Ursae Majoris, variable Delta Scuti of average magnitude +3.80.
• φ Ursae Majoris, binaria composed of two white subgiants.
• χ Ursae Majoris (Al Kaphrah), orange giant of magnitude 3.71.
• /25070/ Ursae Majoris, also orange giant of magnitude 3.01.
• W Ursae Majoris, contact binary where both stars share the outer layers. Name a type of variables (variables W Ursae Majoris).
• AW Ursae Majoris, also contact binary, where the primary component is 10 times more massive than secondary.
• IQ Ursae Majoris (83 Ursae Majoris), red giant and semi-regular variable.
• 2 Ursae Majoris, white Am star of magnitude 5.46.
• 15 Leonis Minoris, is a yellow dwarf that, despite its Flamsteed denomination, is within the limits of the Greater Wave.
• 16 Ursae Majoris (c Ursae Majoris), binary system of magnitude 5,20 whose main component is a yellow dwarf.
• 23 Ursae Majoris, a 3,65 magnitude binary star composed of a white-yellow star and an orange dwarf.
• 24 Ursae Majoris (DK Ursae Majoris), a giant or slightly variable yellow subgigant.
• 47 Ursae Majoris, solar analogue with three extra-solar planets (47 Ursae Majoris b, c and d).
• 36 Ursae Majoris and 61 Ursae Majoris, yellow dwarfs at 41.9 and 31.1 light years respectively.
• 55 Ursae Majoris, triple system whose three components are white stars.
• 78 Ursae Majoris, a binary system that is also part of the Star Association of the Greater Wave.
• 80 Ursae Majoris (Alcor), of magnitude 3,99; the power to solve it in plain view of Mizar is a regular exercise of visual acuity.
• HD 98618, star with almost identical features to the Sun, considered a solar twin.
• HD 89744, white-yellow star with a planet in an eccentric orbit.
• Lalande 21185, dark-gloss red dwarf, the fourth star closest to the solar system at 8.29 light years.
• Groombridge 1830, yellow Underwater Star with a high movement of its own.
• Groombridge 1618, orange dwarf and shining star at 15,89 light years.
• HR 5256 (HD 122064), solitary orange dwarf distant 33 light years.
• Gliese 412 (WX Ursae Majoris) is a nearby binary star composed of two red dwarfs.
• Gliese 450 e HIP 57050, red dwarfs at 28 and 36 light years respectively; the second of them has two extra-solar planets.
• G 196-3, binary system consisting of a red dwarf and a brown dwarf.
• Sidus Ludoviciana (HD 116798) is an octave star visible in the Mizar-Alcor ocular field that once was confused with a new planet, is located 393 light years.

Deep Sky Objects

M81 (Galaxia de Bode). Image obtained by Hubble Space Telescope

M101 (Galaxia del Molinete). Image obtained by the Spitzer space telescope

With small telescopes, up to 50 galaxies can be seen in the Big Dipper. As objects of greatest interest, it is worth highlighting:

• M81 or Bode Galaxy, the most prominent of the M81 Group. In 1993, a type II supernova (SN 1993J) took place in this galaxy, being discovered by the Spanish amateur astronomer Francisco García Díaz.
• M82 (Galaxia del Cigarro), located above the head of the bear; irregular galaxy, is the best example of star outbreak galaxy.
• M97 or Nebula del Búho, one of the most subtle objects in the Messier catalogue. It is a planetary nebula whose central star is 16.
• Molinete Galaxy (M101), visible in front. One of the largest in the Milky Way environment is the brightest of the galactic grouping that bears its name, M101 Group.
• M108 spiral galaxy, 1.5.o southeast of Merak (β Ursae Majoris). From Earth, it appears practically in profile.
• M109 spiral galaxy, located 36 minutes of arc southeast of Phecda (γ Ursae Majoris). It is part of a large group of galaxies (M109 Group) that are part of NGC 3949, NGC 3953, NGC 3982, NGC 4088 among others.
• NGC 2841, NGC 3079, NGC 3184, NGC 3310, NGC 4051 and NGC 4013, all spiral galaxies.
• NGC 3077, elliptical galaxy 47 minutes of arc east of M81.
• NGC 2685, lenticular galaxy with a ring of stars and gas perpendicular to it.
• Enana Galaxy I Zwicky 18, an irregular galaxy composed almost exclusively of hydrogen and helium; initially it was considered the youngest galaxy in our environment.
• Hubble Deep Field, image of a small region in the constellation, based on the results of a series of observations with the Hubble Space Telescope.

Mythology and Fiction

The Greater Wave in the Hevelius catalogue.

The constellation Ursa Major has received different names throughout history based on the images that the human imagination has seen in it. For example, the Arabs saw a caravan, the Native Americans of the North a bucket or the Romans draft oxen.

Many other civilizations have seen a bear in its form. Greek mythology considered Ursa Major to be the bear into which Callisto had been turned by Artemis after being seduced by Zeus. Homer mentions the Bear in Canto V of the Odyssey (circa VIII century B.C..), in which Ulysses tries in vain to be guided by her to return to Ithaca, his land. At that time, this constellation was already known by the nickname of Car, according to the same author, a name that continues today in several languages.

One of the few stars mentioned in the Bible (Job 9:9; 38:32 – Orion and the Pleiades are the others), Ursa Major was also imagined as a bear by the Hebrews and most North Americans. However, since bears do not have long tails, they considered Alioth, Mizar and Alkaid as three cubs following their mother or three hunters. ('The Bear' was mistranslated as 'Arcturus' in the Vulgate and the error persisted in the King James Bible. Later translations have corrected this.)

The Big Dipper is part of the fictional cosmogony created by the British writer J. R. R. Tolkien to set the scene for the stories of his legendarium. In these stories the Chariot takes the name of Valacirca (which in Quenya means 'the sickle of the Valar'). The Silmarillion narrates how she was placed in the firmament by Varda when he remade the stars.