Noctua

Noctua is a two-part caelregio located in the third quadrant of the at its midpoint, but it extends into the southern hemisphere, fourth quadrant, and into the second quadrant. Noctua is the second largest caelregio after Hippocampus with an area of 4590 square degrees, covering about 111‰ of the. Noctua is divided into eight s (listed in the infobox), including, which is the second largest constellation after in Felis.

Noctua is the only caelregio with two separated parts with smaller part being Serpens Cauda, which is one of the two parts of the constellation. The two parts of Noctua are separated by Tarandus while the two parts of Serpens are separated by the serpent-holder.

Noctua contains the as well as many other notable deep sky objects. This caelregio contains the only interesting binary or multiple star system, but there are five interesting planetary systems.

Name and symbolism
is directly named after the where it was located between the end of the 's tail and.

Noctua is originally named after the Latin word for (little). It can be imagined that Noctua influence two component constellations. Owls eat s (Serpens), and are domesticated by s (Boötes). It is also imagined that hunting dogs (Canes Venatici) chase owls, but owls can easily get away since owls can fly while dogs cannot.

Bright stars
A   is the Noctua's brightest star at a  of −0.04, located in. It is also the third brightest overall after in Araneus and  in Malus. Arcturus, along with Spica, Cor Caroli, and, make up the with three stars (excluding Cor Caroli) making up the.

The other notable bright stars in Noctua are
 * –– a 0.98$nd$ giant located in Virgo. Spica is one of the four brightest stars within 5° of the, the others are  in Simianus,  in Felis, and  in Araneus;
 * –– a 2.21$th$  located in ;
 * –– a 2.61$undefined$ B-type main sequence located in Libra;
 * –– a 2.63$m$ K-type giant located in Serpens; and
 * –– a 2.90$m$ A-type main sequence located in.

Nearby stars
A  is the Noctua's nearest star at a  of 10.94 s (3.35 s), located in Libra.

Variable stars
is a. Its brightness fluctuates from 2.84 to 2.98 with a period of 5.47 days.

is an of  plus a. The magnitude varies from 5.80 to 6.40 with a 6.43-hour period. The components of the eclipsing binary are separated by just 0.008 AU, which is three times the Earth–Moon separation.

Multiple stars
One notable is  in Ophiuchus, which comprises of a K-type star, a binary pair of s, and a.

Planetary systems
As of 2015, there are nearly a hundred s orbiting around approximately 75 stars in Noctua. A notable example is (P1 Noc) in Virgo, which has three s. The two most massive planets are the first confirmed s discovered on January 22, 1992.

Another example is (P10 Noc) in Libra which has four confirmed planets, including three super-Earths. Themis (, P220) orbits in the outer region of the, while Eirene (, P209) orbits in the inner region. Themis is speculated to be an with an  of 203  while Eirene is speculated to be a  with a temperature 350 K.

Also in Virgo, (P29 Noc) has three planets: one super-Earth and two midplanets; and likely more. 61 Virginis is speculated to have nine planets.

Another planetary system of interest is (P30 Noc) in Serpens. COROT-9 has a temperate that lies in the Mercury-like distance from the star. The planet Typhoeus (, P404) has a period of 95 days, slightly longer than an 88-day period for. The mass of this planet is the mass of  but slightly larger in size, yielding a mean density slightly lower than water.

In Serpens, there is the pulsar (P53 Noc), which contains a  Tapio (, P576) that was formerly a  before it lost more than 99.9% of its original mass to parent pulsar via  because it orbits so close to its pulsar at a distance of 0.666  (0.957 solar radii) that it takes only 2.177 hours to orbit the star, which is the shortest orbital period of any known planet. Tapio has a density of 23 g/cm$m$, which is the densest planet ever measured, about the same as two densest known ( and ).

Notable deep sky objects
Noctua contains the famous containing many individual galaxies. The examples of galaxies outside the Virgo Cluster are the (51a,  5194),  (NGC 4631),  (NGC 4258),  (M63, NGC 5055), and  (NGC 4736), which are all  located in Canes Venatici. The Whirlpool Galaxy is a interacting with its smaller companion,  (M51b). Virgo Cluster contains, an arrangement of galaxies.

In Virgo, the (M104, NGC 4594), which is an  nearly edge-on, can be seen famous. The most famous  (also called Virgo A) (NGC 4486) can also be seen famous in Virgo. Also in Virgo, the  (NGC 4406) can be seen. M86 is close to another lenticular galaxy (NGC 4374). (NGC 4649) is another elliptical galaxy in Virgo which may be interacting with a nearby spiral companion. All of these galaxies in this paragraph are members of the Virgo Cluster.

, which was the first identified in 1963, is also located in Virgo. , which is a spiral that is the strong, is located in Canes Venatici.

In Serpens, ( 54559) can be found, which is an unusual type of galaxy called the. Also in Serpens, there is, which is the largest [lenticular] galaxy known at 5.5 million light-years across located 1.07 billion light-years from the at the center of the. Again in Serpens, there is ( 10116), a group of six galaxies with  being the brightest member. However because of the gravitational pull of all six members, all six will eventually merge to form one giant elliptical galaxy within the next several hundred million years.

In Serpens, there is the (M16, NGC 6611), which contains a prominent feature called "." There is another nebula in Serpens: the (MWC 922), which is a  recently discovered in April 2007.

In Corvus, the (NGC 4038 and NGC 4039, 60 and 61) can be found, in which a pair of galaxies are merging together to form one supergalaxy. In Coma Berenices, the (NGC 4676) is a merging pair of spiral galaxies in the. Also in this constellation, there are the spiral galaxies and the  (also known as the Sleeping Beauty Galaxy or the Evil Eye Galaxy) (M64, NGC 4826). Coma Berenices also contains the  (C21) similar to the.

This caelregio also contains the ( 111), which is an  containing about 40 stars in Coma Berenices. This cluster lies 288 light-years distant, twice as far as the in Araneus. It covers an area of 5° in the sky.

In Canes Venatici, there is the   with recent and ongoing active s. The motto of this galaxy is "a star-formation labratory" according to an article on astronomy.com. This galaxy is located 10 million light-years away. This constellation also contains the (NGC 4565, C38), which is an edge-on spiral galaxy, and, which is a special type of spiral galaxy called the. This galaxy has the smallest ever measured, its mass is only about 60,000 ± 5,000 solar masses, thus making the core of this galaxy appears absent.

In Boötes, there is the appearing as a "cosmic exclamation point":  ( 302, UGC 9618). Both galaxies are spirals and they are in early stages of collision. A vertical line of an exclamation point is VV 340 North while a dot is VV 340 South. In Canes Venatici, there is the (also known as the Crowbar Galaxy) (NGC 4656-7), which is a. The line of gas and dust looking like a length of a hockey stick is designated NGC 4656 while the bright knot of is designated NGC 4657. The distorted gas and dust looking like a blade of a hockey stick is caused by the interaction with its large neighbor,.

In Virgo, there is the (also known as the Butterfly Galaxies) (NGC 4567 and NGC 4568), a set of spiral galaxies located in the Virgo Cluster. These two galaxies maybe in the process of. Also in Virgo, there is the interacting galaxy in the Virgo Cluster: the (NGC 4435–NGC 4438, Arp 120).

Notable meteor showers
Every year on January 3–4, the (also called Noctids) peak, caused by the. During this, up to 40 meteors per hour would be visible. This meteor shower is named after the  where it is now part of Boötes.

Visibility
In the northern hemisphere, Noctua can be visible during the first two months of fall. Since Noctua is an equatorial caelregio, it can be seen from around the world, but all of it can only be visible from 60°N down to 35°S. The whole caelregio can be seen from most of Americas including the United States, Africa, most of Eurasia, and most of Oceania.

The most prominent constellation in Noctua is Boötes, which contains three bright stars (m<3.00) including a star below zero magnitude. Seven out of eight constellations in this caelregio contain at least one star brighter than 3.00$m$.

Zodiac
The appears to cross Noctua from September 16 till November 22: it crosses the constellations Virgo (September 16 till October 30) and then Libra (October 31 till November 22). This al caelregio is located between Felis to the west and Simianus to the east.

Noctua was formerly in the from August 22 till October 23.