Avis

Avis is a circumpolar caelregio located in the third quadrant of the 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. Avis is divided into six s (listed in the infobox).

Avis contains two famous s: the and the. This caelregio also contains the bright north star at the handle of the Little Dipper.

Symbolism
Avis is named after the Latin word for. Since Avis is plotted above every other caelregios on the 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: the. However it is imagined that birds land on giraffe (Camelopardalis), and bear (Ursa Major & Ursa Minor), as well as using harp (Lyra) for singing.

Bright stars
Avis contains the current bright north, Polaris, located in. Polaris is an  of magnitude 1.97. However, Polaris is not the brightest star in Avis. An   is the Avis' brightest star and is also the fifth brightest overall at a  of 0.03, located in. At around 14000 AD due to the, Vega will be the north pole star even brighter than the present north pole star.

Besides Polaris and Vega,, located in Cygnus (a 1.25$rd$ A-type ), is also notably bright. Deneb is one of the stars that make up the, the other two are Vega (just mentioned above) and , which is located in the neighboring caelregio Tarandus. Deneb is the sky's northernmost first magnitude star.

Nearby stars
A  is the Avis' nearest star and is also the fifth nearest star system overall at a  of 8.31 s (2.55 s), located in. Lalande 21185 had two planets that were now regarded doubtful.

Another notable nearby star in Avis is in Ursa Major, which is a rare  which can produce s 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.

Variable stars
The variability of the, , lasts 13 hours and varies between magnitudes 7.06 to 8.12. RR Lyraes are often used as s to measure galactic distances.

Another variable star is. Beta Lyrae variable is a type of which the stars have ellipsoidal shape and undergoing. Its magnitude varies from 3.25 to 4.36 over its 12.9 day period.

The variable star,, averages about 3.8285 days but the brightness varies over several years depending on its stellar activity. This variability is caused by movements of s due to its rapid rotation. Unlike the Sun where the s originate from the equator, the group of starspots on BY Dra variables originate from the poles.

There is the variable star. Like and β Lyr types, W UMa variable is a type of eclipsing binary. W UMa variables including the prototype star are 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 variable star,. With, this type is the. AN UMa has the strongest known of any cataclysmic variables at 230 million  or 23. The magnitude of this star varies between 14.9 and 20.2. Extopically, AN UMa is a, that means that this red dwarf abnormally contains more than.

Polaris is interestingly a. 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 in the 2nd century.

Multiple stars
Cygnus contains four interesting binary stars:, , Beta Lyrae, Epsilon Lyrae, and ; plus the quadruple star system.

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. 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. 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  which the less massive star is undergoing mass transfer to its more massive companion.

Epsilon Lyrae is a famous 'double-double' star. Using the, Epsilon Lyrae just appears to be composed of just two stars but a 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 s show that Alcor and Mizar share a common motion through space and they are physically bound. These two star systems comprise the. The Mizar-Alcor system comprises a total of six stars and three binary stars. The Mizar-Alcor system can sometimes be referred as "." Mizar was observed to be double by in 1650 (and probably earlier by  and  in the early 1600s).

Polaris is in fact a containing five stars, even though it just appears as a single star to the.

Double stars
in Ursa Major is an optically that was formerly thought to be a. The two stars are separated by 51.7, easily separable using the naked eye.

Planetary systems
Avis contains more known planets and planetary systems than any other caelregio, because 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 s orbiting more than 500 s in Avis.

The first planetary system found in Avis is (P1 Avi) in Ursa Major, which contains three s as well as three speculated s. The names (designations, planet numbers) are Clio (, P14), Euterpe (, P62), and Mnemosyne (, P402). They have of 2.08, 3.53, and 11.44  respectively. The masses are 2.84, 0.60, and 1.76 respectively.

(P2 Avi) has a giant planet Althaea (, P18) in. Althaea orbits the component 16 Cygni B. Althaea has mass 1.70 M$st$ and orbits at a distance of 1.69 AU with an of 0.69.

In Ursa Major, (P5 Avi) has a   Niobe (, 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 as gases rush from the hot day side to the cool night side.

(P19 Avi) in Draco contains the lowest measured of all known planets, reflecting less than 1% of its light, making it blacker than coal. That darkness of the planet Chrysothemis (, 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 (P43 Avi) in Draco, which contains the first rocky planet detected by Kepler —  (Decima, P496). Kepler-10 also contains the midplanet, (Hutena, P524). Another example of a planetary system detected by Kepler is (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.

(Cigfa, P657) is the first found, that is, the planet orbiting around two stars instead of one. Cigfa is a -like planet but much bigger. This planet is located in Cygnus.

Kepler found its first in Cygnus,  (Gayatri, P679), with a radius 2.4 R$undefined$, orbital period 290 days, and an equilibrium temperature 262 K. Gayatri is speculated to be an. Kepler also found two Earth-sized planets: (Tvashtri, P685) and  (Shantadurga, P686) in the five-planet system in Lyra. Tvashtri has a radius 0.87 R$m$ and Shantadurga is 1.03 R$J$. Tvashtri is the first planet found smaller than Earth orbiting around a normal star.

In Cygnus, (P74 Avi) contains two mid-Earths that survived the  stage of parent star's evolution. Both planets orbit extraordinarily close to the star. The innermost planet, Yami (, P687), orbits at 0.0060 AU taking 5¾ hours to orbit while the outermost planet, Hari (, P688), orbits at 0.0076 AU taking 8¼ hours to revolve. Also in Cygnus, (P77 Avi) contains three sub-Earths. Moritasgus (, P695) has mass 0.498 M$J$, Tiresias (, P696) has mass 0.385 M$⊕$, and Idunn (, 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, (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 (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 (P126 Avi) in the Lyra constellation. The planet, Maenad (, 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'.

(P129 Avi) contains two super-Earths separated by a factor of seven in distance from the star. (P130 Avi) contains five rocky planets ranging from 0.15 M$⊕$ to 4.5 M$⊕$ in mass and all orbit within the orbit of from the star, although outer two planets lie within the.

(P137 Avi) and (P138 Avi) have close-in planets in the billion-year old open star cluster NGC 6811 in Cygnus. Both planets are smaller than 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, is the first planet discovered in the quadruple star system. The planet is the size and  the mass of Jupiter, orbiting at  the Earth-Sun distance from the eclipsing binary pair. Kepler-86b (Belobog, P958), or, is a Jupiter mass giant gas planet that sits in the. Large moons may have liquid water, and potentially life, on its surface. Both planets discussed in this paragraph are located in Cygnus.

(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.

(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, (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 (101,  5457) is a  located in Ursa Major. The (NGC 7000, 20) is a  located in Cygnus. The ( 5070 and IC 5067) is an  associated with the North America Nebula in Cygnus. Also in this constellation, we find the (also known as the Cirrus Nebula or the Filamentary Nebula) (NGC 6960, C34), which is a  within the. In the same constellation, we find the (also known as the Gamma Cygni Nebula) (NGC 6888, C27), which is an, the  (IC 5146, C19), which is a stellar nursery, and the  (IC 1318), which is a  emission nebula.

There is the (NGC 6946, C12) in Cygnus, where nine supernovae have been observed in this  since 1900. Another galaxy in Cygnus is ( 405), which is an. Cygnus A is the most famous and is among the  radio sources in the sky.

In Ursa Major, there is (M81, NGC 3031), which is a nearby active spiral galaxy located some 12 million light-years from the. This galaxy is with M82 to be mentioned and. Also in this constellation, we find the nearest  (M82, NGC 3034) at 11 million light-years away, which is an. , which is a, can be seen famous in Ursa Major. Another interacting galaxy in Ursa Major is ( 148) appearing as a  with a tail emerging from it as a result of a collision between two galaxies.

In Draco, there is the ( 10214), which is a disrupted, can be seen using a. The Tadpole Galaxy has a tail of s shaped by the gravitational influence of a passing galaxy. Also in this constellation, the (M102, NGC 5866, C53) –– a, and  (C3) –– a barred spiral galaxy, can be seen using a small telescope.

The (NGC 6543, C6) is a  also located in Draco. The (M97) is also a planetary nebula located in Ursa Major. The (CRL 2688) is a   located in Cygnus. The (also known as the Cygnus Star Cloud) (-101) is an emission nebula also located in Cygnus. The (M57, NGC 6720) is a planetary nebula in Lyra. The (NGC 6826, C15) and the  (NGC 7008) are both planetaries in Cygnus. In Cepheus, there is the.

Notable meteor showers
Every year around December 22, the (also called December Avids) peak in the constellation Ursa Minor. This is controversally caused by the. It can produce about 10 meteors per hour.

Another meteor shower in Avis is (also called April Avids), which peak around April 22 every year in the constellation Lyra. This shower is caused by the periodic. It produces an average about 10 meteors per hour, but sometimes during the, 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 in Ursa Major and the  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 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 devices, time of the day and year can still be determined by the orientation of the Little Dipper relative to Polaris.

Zodiac
Since the never crosses Avis, this is not a al caelregio.