| Constellations (6) | |
|---|---|
| Camelopardalis, Cygnus, Draco, Lyra, Ursa Major, Ursa Minor | |
| Nomenclature | |
| Abbreviation | Avi |
| Genitive | Avis |
| Pronunciation | Name: /'ā•vis/ Genitive: /'ā•vis/ |
| Symbolism | the bird |
| Geometry | |
| Midpoint right ascension | 12h 00.00m |
| Midpoint declination | +58° 51.97' |
| Northernmost border | +90° 00.00' |
| Southernmost border | +27° 43.94' |
| Westernmost border | 00h 00.00m |
| Easternmost border | 24h 00.00m |
| Quadrant | NQ3 |
| Crossed by | North pole Spring meridian Summer meridian Autumn meridian Winter meridian |
| Bordering caelregios | Araneus (S (WW)) Felis (S (W)) Noctua (S (E)) Tarandus (S (EE)) Testudo (E/S/W) |
| Segments | 78 |
| Area | 4465.763 sq. deg. (3rd) |
| Proportion of the sky | 108.253‰ |
| Average constellation area | 744.294 sq. deg. (1st) |
| Stars | |
| Named stars | 47 |
| Stars in the figure | 12 |
| Naked eye stars (m < 6.50) |
331 |
| BF stars | 366 |
| Bright stars (m < 3.00) |
16 |
| Brightest star | Vega (0.03m) |
| Nearby stars (D < 10.00 pc, 32.62 ly) |
22 |
| Nearest star | Lalande 21185 (2.55 pc, 8.31 ly) |
| Messier objects | 12 |
| Visibility | |
| Full visibility range | 90°N–0° |
| Partial visibility range | 0°N–62°S |
| Midnight culmination date | March 20 |
Avis is a circumpolar caelregio located in the third quadrant of the northern hemisphere at its midpoint, but it occupies every quadrant and crossed by every meridian. Avis is the third largest caelregio after Hippocampus and Noctua with an area of 4466 square degrees, covering about 108‰ of the celestial sphere. Avis is divided into six constellations (listed in the infobox).
Avis contains two famous asterisms: the Big Dipper and the Little Dipper. This caelregio also contains the bright north star Polaris at the handle of the Little Dipper.
Symbolism[]
Avis is named after the Latin word for bird. Since Avis is plotted above every other caelregios on the celestial map hence it is the northernmost caelregio, it is analogous to birds flying high above habitats on the ground. Also its shape on the celestial map appears like a wingspan.
Despite its symbolism, Avis contains just one constellation named after a bird: Cygnus the swan. However it is imagined that birds land on giraffe (Camelopardalis), and bear (Ursa Major & Ursa Minor), as well as using harp (Lyra) for singing.
Notable stars[]
Bright stars[]
Avis contains the current bright north pole star, Polaris, located in Ursa Minor. Polaris is an F-type giant star of magnitude 1.97. However, Polaris is not the brightest star in Avis. An A-type main sequence Vega is the Avis' brightest star and is also the fifth brightest overall at a magnitude of 0.03, located in Lyra. At around 14000 AD due to the precession of the equinoxes, Vega will be the north pole star even brighter than the present north pole star.
Besides Polaris and Vega, Deneb, located in Cygnus (a 1.25m A-type hypergiant), is also notably bright. Deneb is one of the stars that make up the Summer Triangle, the other two are Vega (just mentioned above) and Altair, which is located in the neighboring caelregio Tarandus. Deneb is the sky's northernmost first magnitude star.
Nearby stars[]
A red dwarf Lalande 21185 is the Avis' nearest star and is also the fifth nearest star system overall at a distance of 8.31 light-years (2.55 parsecs), located in Ursa Major. Lalande 21185 had two planets that were now regarded doubtful.
Another notable nearby star in Avis is Groombridge 1830 in Ursa Major, which is a rare subdwarf which can produce superflares hundreds to millions of times more powerful than the largest flares ever observed on the Sun. This star is only about 3–10% as enriched with elements heavier than helium as the Sun, making this a halo population II star.
Variable stars[]
The variability of the prototype variable star, RR Lyrae, lasts 13 hours and varies between magnitudes 7.06 to 8.12. RR Lyraes are often used as standard candles to measure galactic distances.
Another prototype variable star is Beta Lyrae. Beta Lyrae variable is a type of eclipsing binary which the stars have ellipsoidal shape and undergoing mass transfer. Its magnitude varies from 3.25 to 4.36 over its 12.9 day period.
The prototype variable star, BY Draconis, averages about 3.8285 days but the brightness varies over several years depending on its stellar activity. This variability is caused by movements of starspots due to its rapid rotation. Unlike the Sun where the sunspots originate from the equator, the group of starspots on BY Dra variables originate from the poles.
There is the prototype variable star W Ursae Majoris. Like Algol and β Lyr types, W UMa variable is a type of eclipsing binary. W UMa variables including the prototype star are contact binaries whose both component stars share a common outer layer. Its magnitude varies from 7.75 to 8.48 over the period of 8 hours.
There is a rare prototype variable star, AN Ursae Majoris. With AM Herculis variable, this type is the polar-class cataclysmic variable. AN UMa has the strongest known magnetic field of any cataclysmic variables at 230 million gauss or 23 kT. The magnitude of this star varies between 14.9 and 20.2. Extopically, AN UMa is a carbon star, that means that this red dwarf abnormally contains more carbon than oxygen.
Polaris is interestingly a Cepheid variable. Around 1900, Polaris' luminosity varied ±8% from its average (0.15 magnitude in total) with a 3.97 day period. Today, the variability period is now 3.98 days, which is 15 minutes longer than it was around the turn of the 20th century. Researchers suggest that Polaris is 2.5 times (about 1 magnitude) brighter today than it was during the time of Ptolemy in the 2nd century.
Multiple stars[]
Cygnus contains four interesting binary stars: Albireo, 61 Cygni, Beta Lyrae, Epsilon Lyrae, and Alcor; plus the quadruple star system Mizar.
Albireo is composed of K-type and B-type stars that takes 214 years to orbit each other. 61 Cygni is an interesting star because it was the first star other than our Sun to have its distance measured in 1838 by Friedrich Wilhelm Bessel. He measured it as 10.4 light-years, very close to the modern value of 11.4 light-years. Both stars in 61 Cygni system are K-type and take 659 years to orbit around the center of mass. 61 Cygni is speculated to have seven planets, three orbit component A and four orbit component B.
Beta Lyrae is another interesting binary star. It is a semi-detached spectroscopic binary which the less massive star is undergoing mass transfer to its more massive companion.
Epsilon Lyrae is a famous 'double-double' star. Using the binoculars, Epsilon Lyrae just appears to be composed of just two stars but a telescope shows that each star is itself double.
Mizar contains two binary stars. Located 0.5–1.5 light-years from Mizar lies another binary star system Alcor. The proper motions show that Alcor and Mizar share a common motion through space and they are physically bound. These two star systems comprise the Ursa Major moving group. The Mizar-Alcor system comprises a total of six stars and three binary stars. The Mizar-Alcor system can sometimes be referred as "Horse and Rider." Mizar was observed to be double by Giovanni Battista Riccioli in 1650 (and probably earlier by Benedetto Castelli and Galileo in the early 1600s).
Polaris is in fact a multiple star containing five stars, even though it just appears as a single star to the naked eye.
Double stars[]
Winnecke 4 in Ursa Major is an optically double star that was formerly thought to be a nebula. The two stars are separated by 51.7', easily separable using the naked eye.
Planetary systems[]
Kepler found its first habitable planet, Kepler-22b (Gayatri, P679)
Avis contains more known planets and planetary systems than any other caelregio, because Kepler is finding numerous planets but only in this caelregio (in the constellations Cygnus, Lyra, and Draco). As of 2015, there are more than a thousand exoplanets orbiting more than 500 planetary systems in Avis.
The first planetary system found in Avis is 47 Ursae Majoris (P1 Avi) in Ursa Major, which contains three giant planets as well as three speculated terrestrial planets. The names (designations, planet numbers) are Clio (47 Ursae Majoris b, P14), Euterpe (47 Ursae Majoris c, P62), and Mnemosyne (47 Ursae Majoris d, P402). They have semimajor axes of 2.08, 3.53, and 11.44 AU respectively. The masses are 2.84, 0.60, and 1.76 MJ respectively.
16 Cygni (P2 Avi) has a giant planet Althaea (16 Cygni Bb, P18) in binary system. Althaea orbits the component 16 Cygni B. Althaea has mass 1.70 MJ and orbits at a distance of 1.69 AU with an eccentricity of 0.69.
In Ursa Major, HD 80606 (P5 Avi) has a transiting exoplanet Niobe (HD 80606 b, P60) with the most elliptical orbit (e=0.93366) of any known exoplanets. Astronomers found that the shocking winds on Niobe can reach up to 3 miles per second as gases rush from the hot day side to the cool night side.
TrES-2 (P19 Avi) in Draco contains the lowest measured albedo of all known planets, reflecting less than 1% of its light, making it blacker than coal. That darkness of the planet Chrysothemis (TrES-2b, P191) is believably caused by the lack of reflective clouds or by the presence of light-absorbing chemicals such as vaporized sodium, potassium, or gaseous titanium/vanadium oxide.
An example of a planetary system detected by Kepler is Kepler-10 (P43 Avi) in Draco, which contains the first rocky planet detected by Kepler — Kepler-10b (Decima, P496). Kepler-10 also contains the midplanet Kepler-10c, (Hutena, P524). Another example of a planetary system detected by Kepler is Kepler-11 (P44 Avi) in Cygnus, which contains six planets: five super-Earths and one midplanet. All six orbit within 0.5 AU, making it the most compact planetary system known.
Kepler-16b (Cigfa, P657) is the first circumbinary planet found, that is, the planet orbiting around two stars instead of one. Cigfa is a Tatooine-like planet but much bigger. This planet is located in Cygnus.
Kepler found its first habitable planet in Cygnus, Kepler-22b (Gayatri, P679), with a radius 2.4 R⊕, orbital period 290 days, and an equilibrium temperature 262 K. Gayatri is speculated to be an ocean planet. Kepler also found two Earth-sized planets: Kepler-20e (Tvashtri, P685) and Kepler-20f (Shantadurga, P686) in the five-planet system in Lyra. Tvashtri has a radius 0.87 R⊕ and Shantadurga is 1.03 R⊕. Tvashtri is the first planet found smaller than Earth orbiting around a normal star.
In Cygnus, Kepler-70 (P74 Avi) contains two mid-Earths that survived the red giant stage of parent star's evolution. Both planets orbit extraordinarily close to the star. The innermost planet, Yami (Kepler-70b, P687), orbits at 0.0060 AU taking 5¾ hours to orbit while the outermost planet, Hari (Kepler-70c, P688), orbits at 0.0076 AU taking 8¼ hours to revolve. Also in Cygnus, Kepler-42 (P77 Avi) contains three sub-Earths. Moritasgus (Kepler-42b, P695) has mass 0.498 M⊕, Tiresias (Kepler-42c, P696) has mass 0.385 M⊕, and Idunn (Kepler-42d, P697) has mass 0.224 M⊕. All three orbit merely within 0.015 AU with periods less than two days, making this the most compact and closest orbiting three-planet system known. Again in Cygnus, Kepler-33 (P90 Avi) contains five planets with a super-Earth in the innermost orbit and the rest are midplanets. Yet another planet-hosting star in Cygnus is Kepler-80 (P122 Avi), which contains five planets, all orbiting within 0.1 AU, making it the most compact planetary system known.
Avis is home to the smallest exoplanet known around a main sequence star, which orbits the star Kepler-37 (P126 Avi) in the Lyra constellation. The planet, Maenad (Kepler-37b, P862) is slightly bigger than our moon and masses over twice that of the Moon, one-half the Mercury's mass, and one-quarter the Mars'.
Kepler-69 (P129 Avi) contains two super-Earths separated by a factor of seven in distance from the star. Kepler-62 (P130 Avi) contains five rocky planets ranging from 0.15 M⊕ to 4.5 M⊕ in mass and all orbit within the orbit of Venus from the star, although outer two planets lie within the habitable zone.
Kepler-66 (P137 Avi) and Kepler-67 (P138 Avi) have close-in planets in the billion-year old open star cluster NGC 6811 in Cygnus. Both planets are smaller than Neptune and learned from those discoveries that planets are just as abundant in star clusters as there are around isolated stars.
Kepler-64b (Vayu, P1009), or PH1, is the first planet discovered in the quadruple star system. The planet is 4⁄7 the size and 1⁄7 the mass of Jupiter, orbiting at 2⁄3 the Earth-Sun distance from the eclipsing binary pair. Kepler-86b (Belobog, P958), or PH2, is a 4⁄7 Jupiter mass giant gas planet that sits in the habitable zone. Large moons may have liquid water, and potentially life, on its surface. Both planets discussed in this paragraph are located in Cygnus.
Kepler-413 (P162 Avi) is a close binary system with the planet Connla orbiting around orbiting pair in Cygnus. A strange property is that planet varies its orbital tilt over a 11-year cycle, as well as its axial tilt. As a result, the planet will not transit every orbit. Its orbital period is about two months, but it can go nearly a decade without transit.
Kepler-90 (P174 Avi) contains seven planets, all orbiting within 1 AU from the star located in the Avis' subdivision Draco. The two innermost planets have oceans of lava, the middle three have deep oceans of water, and the two outermost are gaseous.
In Cygnus, Kepler-138 (P202 Avi) has two planets, both 61% bigger than Earth, but one has the same mass as Earth while the other is nearly four times more massive than Earth. The Earth-mass planet is gaseous while the more massive planet is rocky.
Notable deep sky objects[]
Avis contains a lot of interesting deep sky objects. The Pinwheel Galaxy (M101, NGC 5457) is a spiral galaxy located in Ursa Major. The North America Nebula (NGC 7000, C20) is a stellar nursery located in Cygnus. The Pelican Nebula (IC 5070 and IC 5067) is an HII region associated with the North America Nebula in Cygnus. Also in this constellation, we find the Veil Nebula (also known as the Cirrus Nebula or the Filamentary Nebula) (NGC 6960, C34), which is a supernova remnant within the Cygnus Loop. In the same constellation, we find the Crescent Nebula (also known as the Gamma Cygni Nebula) (NGC 6888, C27), which is an emission nebula, the Cocoon Nebula (IC 5146, C19), which is a stellar nursery, and the Sadr Region (IC 1318), which is a diffuse emission nebula.
There is the Fireworks Galaxy (NGC 6946, C12) in Cygnus, where nine supernovae have been observed in this intermediate spiral galaxy since 1900. Another galaxy in Cygnus is Cygnus A (3C 405), which is an elliptical galaxy. Cygnus A is the most famous radio galaxy and is among the strongest radio sources in the sky.
In Ursa Major, there is Bode's Galaxy (M81, NGC 3031), which is a nearby active spiral galaxy located some 12 million light-years from the Milky Way. This galaxy is gravitationally interacting with M82 to be mentioned and NGC 3077. Also in this constellation, we find the nearest starburst galaxy Northern Cigar Galaxy (M82, NGC 3034) at 11 million light-years away, which is an irregular galaxy. NGC 2787, which is a barred lenticular galaxy, can be seen famous in Ursa Major. Another interacting galaxy in Ursa Major is Mayall's Object (Arp 148) appearing as a ring-shaped galaxy with a tail emerging from it as a result of a collision between two galaxies.
In Draco, there is the Tadpole Galaxy (UGC 10214), which is a disrupted barred spiral galaxy, can be seen using a telescope. The Tadpole Galaxy has a tail of star clusters shaped by the gravitational influence of a passing galaxy. Also in this constellation, the Spindle Galaxy (M102, NGC 5866, C53) –– a lenticular galaxy, and NGC 4236 (C3) –– a barred spiral galaxy, can be seen using a small telescope.
The Cat's Eye Nebula (NGC 6543, C6) is a planetary nebula also located in Draco. The Owl Nebula (M97) is also a planetary nebula located in Ursa Major. The Egg Nebula (CRL 2688) is a bipolar protoplanetary nebula located in Cygnus. The Tulip Nebula (also known as the Cygnus Star Cloud) (Sh2-101) is an emission nebula also located in Cygnus. The Ring Nebula (M57, NGC 6720) is a planetary nebula in Lyra. The Blinking Planetary (NGC 6826, C15) and the Fetus Nebula (NGC 7008) are both planetaries in Cygnus. In Cepheus, there is the star formation region NGC 7822.
Gallery[]
 The Pinwheel Galaxy (M101, NGC 5457) |
 The North America Nebula (NGC 7000, C20) |
  The barred lenticular galaxy NGC 2787 |
  The Northern Cigar Galaxy (M82, NGC 3034) |
  The Spindle Galaxy (M102, NGC 5866, C53) |
  The Cocoon Nebula (IC 5146, C19) |
  The Tadpole Galaxy (UGC 10214) |
  The Cat's Eye Nebula (NGC 6543, C6) |
  The Fireworks Galaxy (NGC 6946, C12) |
  The Crescent Nebula (also known as the Gamma Cygni Nebula) (NGC 6888, C27) |
  The Ring Nebula (M57, NGC 6720) |
  Bode's Galaxy (M81, NGC 3031) |
  The Veil Nebula (also known as the Cirrus Nebula or the Filamentary Nebula) (NGC 6960, C34) |
  The Pelican Nebula (IC 5070 and IC 5067) |
  The Tulip Nebula (also known as the Cygnus Star Cloud) (Sh2-101) |
  Mayall's Object (Arp 148) |
  The Blinking Planetary (NGC 6826, C15) |
Notable meteor showers[]
Every year around December 22, the Ursids (also called December Avids) peak in the constellation Ursa Minor. This meteor shower is controversally caused by the Tuttle comet. It can produce about 10 meteors per hour.
Another meteor shower in Avis is Lyrids (also called April Avids), which peak around April 22 every year in the constellation Lyra. This shower is caused by the periodic comet Thatcher. It produces an average about 10 meteors per hour, but sometimes during the meteor storm, up to 90 meteors per hour are visible.
Visibility[]
In the northern hemisphere, Avis can most prominently be visible from mid fall till mid summer. In the north temperate zone such as in the United States' Midwest, Europe, and central Asia, about half of this caelregio would be circumpolar. From north of 62°N in places like Siberia, Scandinavia, Greenland, and Alaska, all of Avis would be circumpolar as it rotates clockwise around the sky once a day and once a year at a given time. From south of 62°S like in Antarctica, Avis would never rise.
Avis contains two prominent asterisms: the Big Dipper in Ursa Major and the Little Dipper in Ursa Minor. Both Dippers contain bowl of fours stars and handle of three stars. The Big Dipper is highest from late winter till early spring while the Little Dipper is highest from mid to late spring. But from north of 40°N, both Dippers can be seen rotating around the north pole and therefore both Dippers can be visible all-year round.
Polaris is a useful pole star for navigation to northern observers because that star is where the direction of north lies since that star virtually stays at a same point of the sky both daily and annually. So all other stars including the Little Dipper appear to rotate around Polaris. Even without timekeeping devices, time of the day and year can still be determined by the orientation of the Little Dipper relative to Polaris.
Zodiac[]
Since the Sun never crosses Avis, this is not a zodiacal caelregio.
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