Testudo

Testudo is a caelregio located in the first quadrant of the at its midpoint, but it extends into the fourth and second quadrants. The northernmost border is just 80 s away from the, making this a near- caelregio. Testudo is divided into nine s (listed in the infobox).

Testudo contains many examples of prototype variables and eclipsing binaries such as and, as well as many notable galaxies, nebulae, and star clusters such as the  and the. This caelregio contains the famous asterism "." Testudo also contains the first exoplanet discovered around a sun-like star, the first sun-like star discovered to have multi-planet system , and two most studied transiting exoplanets (Osiris and Teumesia ).

Name and symbolism
is directly named after the where it is now part of  in the neighboring caelregio Hippocampus. Testudo is originally named after the Latin word for. It can be imagined that turtles are domesticated by the King (Cepheus) and the Queen (Andromeda), who ride s (Equuleus) or even s (Pegasus).

Bright stars
An   is the Testudo's brightest star at a  is 1.82, located in. Perseus also contains a   (2.12$th$) in addition to Mirfak.

is a located in. Its magnitude is 2.06 and it is 197 light-years from Earth. is a B-type also located in Andromeda. Its magnitude is 2.07 and it is 97 light-years from Earth.

is a  located in. Its magnitude is 2.25 and it is 228 light-years from Earth. is a B-type subgiant also located in Cassiopeia. Its magnitude is 2.39 and it is 549 light-years from Earth. is a subgiant located in. Its magnitude is 2.44 and it is 49 light-years from Earth.

is a K-type supergiant located in. Its magnitude is 2.40 and it is 689 light-years from Earth. is a red giant also located in Pegasus. Its magnitude is 2.42 and it is 196 light-years from Earth. is a B-type giant again located in Pegasus. Its magnitude is 2.50 and it is 133 light-years from Earth. is a B-type subgiant yet again located in Pegasus. Its magnitude is 2.83 and it is 391 light-years from Earth.

Alpheratz, Scheat, Markab, and Algenib make up the "," which is the most prominent autumn.

Nearby stars
The red dwarf is the Testudo's nearest star at a  of 10.30 s (3.16 s), located in Andromeda.

Variable stars
The   can be found. Cepheids are used as s to measure distance of stars in star clusters. The variability period of Cepheids depend on luminosities. When variability period is determined, then its luminosities can be assumed. Using luminosities and magnitudes seen by observer, then distances can be determined. Using this can even measure accurate distances where the distances are too great for current astrometric research to calculate, such as in other galaxies.

Another variable star is, also known as the Herschel's Garnet Star because of the  red color of the star. This star is a and is one of the largest stars known. The star varies between magnitudes 3.62 to 5 over a period of 2 to 2.5 years.

Yet another variable is, also properly named Alfirk. The magnitude of this star varies between 3.15 and 3.21 with a period of 4.57163 hours. This star is also a comprising a  with a 8th magnitude optical companion.

Algol, which is a, is one of the best known  and the second (non-) variable star discovered after. Every 2 days, 20 hours and 49 minutes, the magnitude drops from 2.1 to 3.4 as the fainter star partially eclipses the brighter star, which lasts about 10 hours. To make it more precise, Algol is actually a.

is another variable star that is also called "shell star." It is an eruptive variable star that varies irregularly in brightness from 2.20$th$ to 3.40$undefined$. This star varies in average brightness by 40% every 50 years.

Another eclipsing binary is, located in the open cluster. SS Lacertae orbits around the every 14.4 days. This eclipsing binary is unique because it turns on and off caused by inclination changes by the gravity of a tertiary star.

(19 Piscium) is another variable star. This star varies brightness irregularly from magnitudes 5 to 6 in about 18 months.

Mulitple stars
Alpheratz is a comprising of B-type subgiant and A-type main sequence stars. The orbital period around the center of mass is 96.7 days at an about 24 s, which is only resolvable in large  s. It also contains an optical companion ADS 94 B, which is a 10.8$m$  main sequence star. This companion is 89.3 s away from component A, which can be resolvable using the low-power s but the star is too faint to be seen using this equipment.

An example of a in Testudo is. The primary star 85 Pegasi A has a binary secondary companion 85 Pegasi B. It is speculated that a pair of super-Jupiter planets with masses of 5.4 and 9.1 M$m$ orbit the center of mass at an of 18 and 29  respectively.

Planetary systems
As of 2015, there are more than five dozen s identified orbiting around more than 50 stars in Testudo. On October 6, 1995, astronomers found the first ever confirmed exoplanet around a, named Bellerophon (, P13) around (P1 Tes); this was also the first  known.

(P2 Tes) has four giant exoplanets with orbital periods ranging from 4.6 days to about 38 years; the mass ranges from 1.27 to 6.67. Upsilon Andromedae became the first normal star discovered to have a multi-planet system.

Both (P3 Tes, in Pegasus) and  (P6 Tes, in ) contain  s (respectively Osiris (, P30) and Teumesia (, P161)) that were most studied of all exoplanets, especially their evaporating atmospheres. Another star with a transiting planet is (P10 Tes, in Cassiopeia), which has a very eccentric planet Thetis (, P213). This star also has an unconfirmed planet Intercidona (, P257) as well as two hypothetical planets beyond the orbits of known planets.

(P44 Tes) contain a 12.8-Jupiter mass super-Jupiter (named Ligdus (, P841)). It orbits nearly twice the distance between the Sun and.

Notable deep sky objects
Testudo contains the nearest : the (31,  224), located in Andromeda. Andromeda contains two most famous examples of satellite galaxies:  (NGC 221) and  (NGC 205).

The (M33, NGC 598) is the second closest spiral galaxy located in. Perseus contains two s (both s) which is the only constellation to contain double clusters. One double cluster contains (h Persei) and  (χ Persei), which collectively designated 14.

Located in Perseus, there is the  (also known as Perseus A) (C24), which is a member of the  ( 426) which also includes. Located in Cassiopeia, there is Tycho's  (B Cas) after the progenitor star exploded in 1572. This supernova was seen by.

This constellation also contains the (NGC 1499), which is an. Cepheus contains the ( 1396), which is a concentration of interstellar gas and dust where. In Andromeda, there is the (also known as the Blue Snowball Nebula) (NGC 7662, C22), which is an egg-shaped planetary nebula.

Pegasus contains, which is one of the most compact known. Four of the five galaxies in Stephan's Quintet form a physical association that will most likely end with all four galaxies merging together to form a giant. Also in this constellation, there are (C44) and, which are  and spiral galaxies respectively. In Andromeda, we find the edge-on spiral galaxy (also known as the Silver Silver Galaxy) (C23) with HII  and dust lanes, which can prominently be visible to a large telescope. NGC 891 is one of the sky's finest edge-on galaxies.

(NGC 7078), also in Pegasus, is one of the densest s in the. This cluster contains a million old stars within a diameter of just 120 light-years.

Vulpecula contains the (also known as Brocchi's Cluster or Al Sufi's Cluster) ( 399), which is an  clearly seen in binoculars. This constellation also contains the (also known as the Apple Core Nebula, Diablo Nebula, or the Double-Headed Shot) (M27, NGC 6853), which is a famous.

In Cassiopeia, the (NGC 7635, C11), which is an  and emission nebula, can be found using an. Also in the same constellation, the (also known as the Baby Nebula) (IC 1848) and the  are found using a telescope and are collectively known as "Heart and Soul." Both members of the pair are e. Also in this constellation, there is the (NGC 281), which was named after its resemblance to the video game character.

The (NGC 604), which is an  with massive HII region, can be found in the Triangulum Galaxy in Triangulum Boreale. This nebula is 1500 light-years or 460 parsecs across, 40 times the size of the Milky Way's. This nebula is over 6300 times more luminous than the Orion Nebula. If the Garren Nebula is located at a same distance as the Orion Nebula from Earth, it would appear twice the size of the full moon and outshine.

In Cepheus, the (NGC 7023, C4) can be found. This "nebula" is actually a within the nebula LBN 487. The nebula is lit by a seventh magnitude star, making this a. This nebula is located 1300 light-years away and it is 6 light-years across. Another in Cepheus is the  (-155, C9), which is a dim and very   within a larger nebula complex appearing like a deep cave through a telescope. Yet another nebula in this constellation is ( 215), which is a  powered by the variable star  at its center.

In Lacerta, there is the , which was thought to be an irregular variable star in the. This galaxy varies in magnitude just like a variable star, it varies between magnitudes 14 to 17 over a fairly small time periods. Another deep sky object in this constellation is the HII region.

Notable meteor showers
The (also called Testudids) peak between August 9–14 every year. This is caused by the. Up to 142 meteors per hour were visible on August 12, 2010. The most active Perseids in recorded history took place on August 12, 1972 when 292 meteors per hour were visible, roughly twice as active as the 2010 peak.

Visibility
In the northern hemisphere, Testudo is most prominent from mid summer till late fall. At mid-northern latitudes, about half of Testudo is circumpolar, therefore at least half of this caelregio can be visible all-year round. However in the mid-southern latitudes, only half of this caelregio can be visible at once, from mid winter till late spring.

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