Reach for the Stars: Revenge of the Event

Serpens

"The Serpent," Greek Ὄφις, is a constellation of the northern hemisphere. One of the 48 constellations listed by Ptolemy, it remains one of the 88 modern constellations defined by the International Astronomical Union. It is unique among the modern constellations in being split into two non-contiguous parts, Serpens Caput (Serpent Head) to the west and Serpens Cauda (Serpent Tail) to the east. Between these two halves lies the constellation of Ophiuchus, the "Serpent-Bearer." In figurative representations, the body of the serpent is represented as passing behind Ophiuchus between Mu Serpentis in Serpens Caput and Nu Serpentis in Serpens Cauda. The brightest star in it is the red giant star Alpha Serpentis, or Unukalhai, in Serpens Caput, with an apparent of 2.63. Also located in Serpens Caput are the naked-eye globular cluster Messier 5 and the naked-eye variables R Serpentis and Tau^4 Serpentis. Notable extragalactic objects include Seyfert's Sextet, one of the densest galaxy clusters known; Arp 220, the prototypical ultarluminous infrared galaxy; and Hoag's Object, the most famous of the very rare class of galaxies known as ring galaxies. Part of the Milky Way's galactic plane passes through Serpens Cauda, which is therefore rich in galactic deep-sky objects, such as the Eagle Nebula (IC 4703) and its associated star cluster Messier 16. The nebula measures 70 light-years by 50 light-years and contains the Pillars of Creation, three dust clouds that became famous for the image taken by the Hubble Space Telescope. Other striking objects include the Red Square Nebula, one of the few objects in astronomy to take on a square shape; and Westerhout 40, a massive nearby star-forming region consisting of a molecular cloud and an H II region.

Cassiopeia

A constellation in the northern sky, named after the vain queen in Greek mythology, who boasted about her unrivaled beauty. One of the 48 constellations listed by Ptolemy, and it remains one of the 88 modern constellations today. It is easily recognizable due to its distinctive "M" shape when in upper culmination but in higher northern locations when near lower culminations in spring and summer it has a "W" shape formed by five bright stars. It is bordered by Andromeda to the south, Perseus to the southeast, and Cepheus to the north. It is opposite the Big Dipper. In northern locations above 34ºN latitude it is visible year-round and in the (sub)tropics it can be seen at its clearest from September to early November in its characteristic "M" shape. Even in low southern latitudes below 25ºS it can be seen low in the North.

Dorado

A constellation in the southern sky. It was named in the late 16th century and is now one of the 88 modern constellation. Its name refers to the dolphinfish (Coryphaena hippurus), which is known as dorado in Portuguese, although it has also been depicted as a swordfish. Contains most of the Large Magellanic Cloud, the remainder being in the constellation Mensa. The South Ecliptic pole also lies within this constellation. Even though the name is not Latin but Portuguese, astronomers give it the Latin genitive form Doradus when naming its stars; it is treated (like the adjacent asterism Argo Navis) as a feminine proper name of Greek origin ending in -ō (like Io or Callisto or Argo), which have a genitive ending -ūs.

Ophiuchus

A large constellation located around the celestial equator. Its name is from the Greek Ὀφιοῦχος "serpent-bearer," and it is commonly represented as a man grasping the snake that is represented by the constellation Serpens. Was one of the 48 constellations listed by Ptolemy, and it remains one of the 88 modern constellations. It was formerly referred to as Serpentarius and Anguietenens.

Cygnus

A northern constellation lying on the plane of the Milky Way, deriving its name from the Latinized Greek word for swan. The swan is one of the most recognizable constellations of the northern summer and autumn, and it features a prominent asterism known as the Northern Cross (in contrast to the Southern Cross). Cygnus was among the 48 constellations listed by Ptolemy, and it remains one of the 88 modern constellations. Contains Deneb, one of the brightest stars in the night sky and one corner of the Summer Triangle, as well as some notable X-ray sources and giant stellar association of Cygnus OB2. One of the stars of this association, NML Cygni, is one of the largest stars currently known. The constellation is also home to Cygnus X-1, a distant X-ray binary containing a supergiant and unseen massive companion that was the first object widely held to be a black hole. Many star systems in Cygnus have known planets as a result of the Kepler Mission observing one patch of the sky, the patch is the area around Cygnus. In addition, most of the eastern part of Cygnus is dominated by the Hercules-Corona Borealis Great Wall, a giant galaxy filament that is the largest known structure in the observable universe; covering most of the northern sky.

Cygnus X-1

Abbreviated Cyg X-1, it is a galactic X-ray source in the constellation Cygnus, and the first such source widely accepted to be a black hole. It was discovered in 1964 during a rocket flight and is one of the strongest X-ray sources seen from Earth, producing a peak X-ray flux density of 2.3*10^-23 Wm^-2 Hz^-1 (2.3*10^3 Jansky). It remains among the most studied astronomical objects in its class. The compact object is now estimated to have a mass about 14.8 times the mass of the Sun and has been shown to be too small to be any known kind of normal star, or other likely object besides a black hole. If so, the radius of its even horizon is about 44 km. It belongs to a high-mass X-ray binary system, located about 6070 light years from the Sun, that includes a blue supergiant variable star designated HDE 226868, which it orbits at about 0.2 AU, or 20% of the distance from the Earth to the Sun. A stellar wind from the star provides material for an accretion disk around the X-ray source. Matter in the inner disk is heated to millions of degrees, generating the observed X-rays. A pair of jets, arranged perpendicular to the disk, are carrying part of the energy of the infalling material away into interstellar space. This system may belong to a stellar association called Cygnus OB3, which would mean that this is about five million years old and formed from a progenitor star that had more than 40 solar masses. The majority of the star's mass was shed, most likely as a stellar wind. If this star had then exploded as a supernova, the resulting force would most likely have ejected the remnant from the system. Hence the star may have instead collapsed directly into a black hole. It was the subject of a friendly scientific wager between Stephen Hawking and Kip Thorne in 1975, with Hawking betting that it was not a black hole. He conceded the bet in 1990 after observational data had strengthened the case that there was indeed a black hole in the system. This hypothesis has not been confirmed due to a lack of direct observation but has generally been accepted from indirect evidence.

Altair

Also designated Alpha Aquilae (α Aquilae, abbreviated Alpha Aql, α Aql), is the brightest star in the constellation of Aquila and the twelfth brightest star in the night sky. It is currently in the G-cloud-- a nearby accumulation of gas and dust known as an interstellar cloud. It is an A-type main sequence star with an apparent visual magnitude of 0.77 and is one of the vertices of the asterism known as the Summer Triangle (the other two vertices are marked by Deneb and Vega). It is 16.7 light-years (5.13 parsecs) from the Sun and is one of the closest stars visible to the naked eye. It rotates rapidly, with a velocity at the equator of approximately 286 km/s. This is a significant fraction of the star's estimated breakup speed of 400 km/s. A study with the Palomar Testbed Interferometer revealed that it is not spherical, but is flattened at the poles due to its high rate of rotation. Other interferometric studies with multiple telescopes, operating in the infrared, have imaged and confirmed this phenomenon.

Capella

Also designated Alpha Aurigae (α Aurigae, abbreviated Alpha Aur, α Aur), is the brightest star in the constellation of Auriga; the sixth-brightest in the night sky and the third-brightest in the northern celestial hemisphere, after Arcturus and Vega. Although it appears to be a single star to the naked eye, it is actually a star system of four stars in two binary pairs. The first pair consists of two bright, type-G giant stars, designated Capella Aa and Capella Ab, in a very tight circular orbit some 0.76 AU apart and a derived orbital period of 104 days. Capella Aa is the brighter of the two at spectral class G8III (G8 Giant) whereas Ab is slightly smaller and of spectral class G0III (G0 Giant). Aa has a calculated mass of 3.05 times that of the Sun and Ab some 2.57 times that of the Sun. These two stars have both exhausted their core hydrogen fuel and become giant stars, though it is unclear exactly what stage they are on the stellar evolutionary pathway. The second pair, around 10,000 astronomical units from the first, consists of two faint, small and relatively cool red dwarfs. They designated Capella H and Capella L. The stars labeled Capella C through to G and I through to K are actually unrelated stars in the same visual field. The Capella system is relatively close, at only 42.8 light-years (13.1 pc) from the Sun.

Arcturus

Also designated Alpha Boötis (α Boötis, abbreviated Alpha Boo, α Boo) is a star in the constellation of Boötes. It is relatively close at 36.7 light-years from the Sun. Together with Spica and Denebola (or Regulus, depending on the source), it is part of the Spring Triangle asterism and, by extension, also of the Great Diamond along with the Cor Caroli.

Procyon

Also designated Alpha Canis Minoris (α Canis Minoris, abbreviated Alpha CMi, α CMi), is the brightest star in the constellation of Canis Minor. To the naked eye, it appears to be a single star, the eighth-brightest in the night sky with a visual apparent magnitude of 0.34. It is a binary star system, consisting of a white main-sequence star of spectral type F5 IV-V, named Procyon A, and a faint white dwarf companion of spectral type DQZ, named Procyon B. The reason for its brightness is not its intrinsic luminosity but its relative closeness to the Sun. As determined by the European Space Agency Hipparcos astrometry satellite, it lies at a distance of just 11.46 light-years (3.51 parsecs), and is therefore one of Earth's nearest stellar neighbours. Its closest neighboring star is Luyten's Star, about 1.12 ly (0.34 pc) away, and the latter would appeal as a visual magnitude 2.7 star in the night sky of a hypothetical planet orbiting Procyon.

Ursa Major

Also known as the Great Bear, is a constellation in the northern celestial hemisphere. One of the 48 constellations listed by Ptolemy, it remains one of the 88 modern constellations. It can be visible throughout the year in most of the northern hemisphere. Its name, Latin for "the greater (or larger) she-bear," stands as a reference to and in direct contrast with Ursa Minor, "the smaller she-bear," with which it is frequently associated in mythology and amateur astronomy. The constellation's most recognizable asterism, a group of seven relatively bright stars commonly known as the "Big Dipper," "the Wagon," or "the Plough" (among others), both mimics the shape of the lesser bear (the "Little Dipper") and is commonly used as a navigational pointer towards the current northern pole star, Polaris in Ursa Minor. The Big Dipper and the constellation as a whole have mythological significance in numerous world cultures, usually as a symbol of the north. The third largest constellation in the sky, Ursa Major is home to many deep-sky objects including seven Messier objects, four other NGC objects, and I Zwicky 18, which is potentially the youngest-known galaxy in the visible universe.

Canis Major

Constellation in the southern celestial hemisphere. Was included in Ptolemy's 48 constellations, and is counted among the 88 modern constellations. Name in Latin for "greater dog" in contrast to Canis Minor, "lesser dog;" both figures are commonly represented as following constellation of Orion, the hunter, through the sky. Milky Way passes through it and several open clusters lie within its borders, notably M41. Contains Sirius, brightest star in night sky, known as "dog star." Bright because of its proximity to the Solar System. Other bright stars of the constellation are stars of great distance and high luminosity. Epsilon Canis Majoris (Adhara), magnitude 1.5, is the second brightest star of the constellation and the brightest source of extreme ultra violet radiation in the night sky. Next in brightness are the yellow-white supergiant Delta (Wezen) at 1.8, the blue-white giant Beta (Mirzam) at 2.0, blue-white supergiants Eta (Aludra) and 2.4 and Omicron at 3.0, and white spectroscopic binary Zeta (Furud), also at 3.0. Red hypergiant VY Canis Majoris is one of the largest stars known, while the neutron star RX JO720.4-3125 has a radius of a mere 5 km.

Carina

Constellation in the southern sky. Its name is Latin for the keel of a ship, and it was formerly part of the larger constellation of Argo Navis (the ship Argo) until that constellation was divided into three pieces, the other two being Puppis (the poop deck), and Vela (the sails of the ship).

Castor

Designated Alpha Geminorum (α Geminorum, abbreviated Alpha Gem, α Gem), it is the second-brightest star in the constellation Gemini and one of the brightest stars in the night sky. Although it has the identifier 'alpha,' it is actually fainter than Beta Geminorum (Pollux.)

Regulus

Designated Alpha Leonis (α Leonis, abbreviated Alpha Leo, α Leo), is the brightest star in the constellation of Leo and one of the brightest stars in the night sky, lying approximately 79 light years from the Sun. It is a multiple star system composed of four stars that are organized into two pairs. The spectroscopic binary A consists of a blue-white main-sequence star and its companion, which has not yet been directly observed, but is probably a white dwarf. Located farther away are B, C, and D, which are dim main-sequence stars.

Vega

Designated Alpha Lyrae (α Lyrae, abbreviated Alpha Lyr, α Lyr), it is the brightest star in the constellation of Lyra, the fifth-brightest star in the night sky and the second-brightest star in the northern celestial hemisphere, after Arcturus. It is relatively close at only 25 light-years from the Sun, and, together with Arcturus and Sirius, one of the most luminous stars in the Sun's neighborhood. It has been extensively studied by astronomers, leading it to be termed "arguably the next most important star in the sky after the Sun." It was the northern pole star around 12,000 BC and will be so again around the year 13,727 when the declination will be +86°14'. It was the first star other than the Sun to be photographed and the first to have its spectrum recorded. It was one of the first stars whose distance was estimated through parallax measurements. It has served as the baseline for calibrating the photometric brightness scale, and was one of the stars used to define the mean values for the UBV photometric system. It is only about a tenth of the age of the Sun, but since it is 2.1 times as massive its expected lifetime is also one tenth of that of the Sun; both stars are at present approaching the midpoint of their life expectancies. It has an unusually low abundance of the elements with a higher atomic number than that of helium. It is also a variable star that varies slightly in brightness. It is rotating rapidly with a velocity of 274 km/s at the equator. This is causing the equator to bulge outward because of centrifugal effects, and, as a result, there is a variation of temperature across the star's photosphere that reaches a maximum at the poles. From Earth, it is being observed from the direction of one of these poles. Based on an observed excess emission of infrared radiation, it appears to have a circumstellar disk of dust. This dust is likely to be the result of collisions between objects in an orbiting debris disk, which is analogous to the Kuiper belt in the Solar System. Stars that display an infrared excess because of dust emission are termed Vega-like stars.

Betelgeuse

Designated Alpha Orionis (α Orionis, abbreviated Alpha Ori, α Ori), it is the ninth-brightest star in the night sky and second-brightest in the constellation of Orion. Distinctly reddish, it is a semiregular variable star whose apparent magnitude varies between 0.0 and 1.3, the widest range of any first-magnitude star. Betelgeuse is one of three stars that make up the Winter Triangle asterism, and it marks the center of the Winter Hexagon. It would be the brightest star in the night sky if the human eye could view all wavelengths of radiation. The star is classified as a red supergiant of spectral type M1-2 and is one of the largest and most luminous stars visible to the naked eye. If it were at the center of the Solar System, its surface would extend past the asteroid belt, wholly engulfing the orbits of Mercury, Venus, Earth and Mars. Calculations of its mass range from slightly under ten to a little over twenty times that of the Sun. It is calculated to be 640 light-years away, yielding an absolute magnitude of about −6. Less than 10 million years old, it has evolved rapidly because of its high mass. Having been ejected from its birthplace in the Orion OB1 Association—which includes the stars in Orion's Belt—this crimson runaway has been observed moving through the interstellar medium at a supersonic speed of 30 km/s, creating a bow shock over 4 light-years wide. Currently in a late stage of stellar evolution, the supergiant is expected to explode as a supernova within the next million years. In 1920, it became the second star (after the Sun) to have the angular size of its photosphere measured. Subsequent studies have reported an angular diameter (apparent size) ranging from 0.042 to 0.056 arcseconds, with the differences ascribed to the non-sphericity, limb darkening, pulsations, and varying appearance at different wavelengths. It is also surrounded by a complex, asymmetric envelope roughly 250 times the size of the star, caused by mass loss from the star itself. The angular diameter of it is only exceeded by R Doradus (and the Sun).

Pollux

Designated Beta Geminorum (β Geminorum, abbreviated Beta Gem, β Gem), is an orange-hued evolved giant star approximately 34 light-years from the Sun in the northern constellation of Gemini. It is the closest giant star to the Sun. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. In 2006, an extrasolar planet, later named Thestias, was confirmed to be orbiting it.

Rigel

Designated Beta Orionis (β Orionis, abbreviated Beta Ori, β Ori), is generally the seventh-brightest star in the night sky and the brightest star in the constellation of Orion—though there are times where it is outshone in the constellation by the variable Betelgeuse. With a visual magnitude of 0.13, it is a remote and luminous star some 863 light-years distant from Earth. The star as seen from Earth is actually a triple or quadruple star system, with the primary star (A) a blue-white supergiant that is estimated to be anywhere from 120,000 to 279,000 times as luminous as the Sun, depending on method used to calculate its properties. It has exhausted its core hydrogen and swollen out to between 79 and 115 times the Sun's radius. It pulsates quasi-periodically and is classified as an Alpha Cygni variable. A companion, B, is 500 times fainter than the supergiant A and visible only with a telescope. B is itself a spectroscopic binary system, consisting of two main sequence blue-white stars of spectral type B9V that are estimated to be respectively 3.9 and 2.9 times as massive as the Sun. B also appears to have a very close visual companion C of almost identical appearance.

Algol

Designated Beta Persei (β Persei, abbreviated Beta Per, β Per), known colloquially as the Demon Star, is a bright multiple star in the constellation of Perseus. The first and best known eclipsing binary and also one of the first (non-nova) variable stars to be discovered. A three-star system - Beta Persei Aa1, Aa2, and Ab - in which the large and bright primary β Persei Aa1 is regularly eclipsed by the dimmer β Persei Aa2. Thus, Its magnitude is usually near-constant at 2.1, but regularly dips to 3.4 every 2.86 days (2 days, 20 hours and 49 minutes) during the roughly 10-hour-long partial eclipses. There is also a secondary eclipse (the "second minimum") when the brighter star occults the fainter secondary. This secondary eclipse can only be detected photoelectrically.

Bootes

Is a constellation in the northern sky, located between 0° and +60° declination, and 13 and 16 hours of right ascension on the celestial sphere. The name comes from the Greek Βοώτης, meaning herdsman or plowman (literally, ox-driver; from βοῦς bous "cow"). One of the 48 constellations described by Ptolemy, now one of the 88 modern constellations. Contains fourth-brightest star in night sky, orange hued Arcturus. Home to many other bright stars, including eight above the fourth magnitude and an additional 21 above the fifth magnitude, making a total of 29 stars easily visible to the naked eye.

Aquarius

Is a constellation of the zodiac Its name is Latin for "water-carrier," one of the oldest of the recognized constellations. Has no particularly bright stars, with its 4 brightest stars less than magnitude 2. α Aquarii, also known as Sadalmelik, is a G2 spectral type star (yellow supergiant) It is the second brightest star in Aquarius with a magnitude of 2.94 (an absolute magnitude of -4.5) and is 523 light-years from Earth. It has a luminosity of 5250 L☉. β Aquarii, sometimes called Sadalsuud, is a G0 spectral type star (yellow supergiant). It is the brightest star in Aquarius with an apparent magnitude of 2.89 and an absolute magnitude of -4.5. Sadalsuud is 537 light-years from Earth and has a luminosity of 5250 L☉, the same as α Aquarii. γ Aquarii, also called Sadachbia, is a blue-white A0 spectral type star of magnitude 3.84 and a luminosity of 50 L☉ that is 163 light years away. It has a luminosity of 50 L☉. δ Aquarii, also known as Scheat or Skat, is a blue-white A2 spectral type star of magnitude 3.27 and luminosity of 105 L☉. ε Aquarii, also known as Albali, is a blue-white A1 spectral type star with an apparent magnitude of 3.77, an absolute magnitude of 1.2, and a luminosity of 28 L☉.Is a constellation in the northern sky.

Orion

Is a prominent constellation located on the celestial equator and visible throughout the world. It is one of the most conspicuous and recognizable constellations in the night sky. It was named after a hunter in Greek mythology. Its brightest stars are Rigel (Beta Orionis) and Betelgeuse (Alpha Orionis), a blue-white and a red supergiant respectively.

Hydrus

Is a small constellation in the deep southern sky. It was first depicted on a celestial atlas by Johann Bayer in his 1603 Uranometria. The French explorer and astronomer Nicolas Louis de Lacaille charted the brighter stars and gave their Bayer designations in 1756. Its name means "male water snake," as opposed to Hydra, a much larger constellation that represents a female water snake. It remains below the horizon for most Northern Hemisphere observers. The brightest star is the 2.8 magnitude Beta Hydri, also the closest reasonably bright star to the south celestial pole. Pulsating between magnitude 3.26 and 3.33, Gamma Hydri is a variable red giant some 60 times the diameter of our Sun. Lying near it is VW Hydri, one of the brightest dwarf novae in the heavens. Four star systems have been found to have exoplanets to date, most notably HD 10180, which could bear up to nine planetary companions.

Sirius

Is a star system and the brightest star in the Earth's night sky. With a visual apparent magnitude of -1.46, it is almost twice as bright as Canopus, the next brightest star. The name is derived from the Ancient Greek Σείριος (Seirios), meaning "glowing" or "scorcher." The system has the Bayer designation Alpha Canis Majoris (α CMa). What the naked eye perceives as a single star is actually a binary star system, consisting of a white main-sequence star of spectral type A1V, termed Sirius A, and a faint white dwarf companion of spectral type DA2, called Sirius B. The distance separating Sirius A from its companion varies between 8.2 and 31.5 AU. It appears bright because of both its intrinsic luminosity and its proximity to Earth. At a distance of 2.6 parsecs (8.6 ly), as determined by the Hipparcos astrometry satellite, the Sirius system is one of Earth's near neighbors. It is gradually moving closer to the Solar System, so it will slightly increase in brightness over the next 60,000 years. After that time its distance will begin to increase and it will become fainter, but it will continue to be the brightest star in the Earth's night sky for the next 210,000 years. Sirius A is about twice as massive as the Sun and has an absolute visual magnitude of 1.42. It is 25 times more luminous than the Sun but has a significantly lower luminosity than other bright stars such as Canopus or Rigel. The system is between 200 and 300 million years old. It was originally composed of two bright bluish stars. The more massive of these, Sirius B, consumed its resources and became a red giant before shedding its outer layers and collapsing into its current state as a white dwarf around 120 million years ago. It is also known colloquially as the "Dog Star," reflecting its prominence in its constellation, Canis Major (Greater Dog). The heliacal rising of it marked the flooding of the Nile in ancient Egypt and the "dog days" of summer for the ancient Greeks, while to the Polynesians in the Southern Hemisphere the star marked winter and was an important reference to their navigation around the Pacific Ocean.

Sagittarius

Is one of the constellations of the Zodiac. It is one of the 48 constellations listed by Ptolemy and remains one of the 88 modern constellations. Its name is Latin for the archer, and its symbol is ♐, a stylized arrow. It is commonly represented as a centaur pulling back a bow. It lies between Scorpius and Ophiuchus to the west and Capricornus to the east. The center of the Milky Way lies in the westernmost part of it.

Virgo

Is one of the constellations of the zodiac. Its name is Latin for virgin, and its symbol is ♍. Lying between Leo to the west and Libra to the east, it is the second largest constellation in the sky (after Hydra). It can be easily found through its brightest star, Spica.

Zeta Ophiuchi

It (ζ Oph, ζ Ophiuchi) is a star located in the constellation of Ophiuchus. It has an apparent visual magnitude of 2.57, making it the third-brightest star in the constellation. Parallax measurements give an estimated distance of roughly 366 light-years (112 parsecs) from the Earth.

Tucana

It is a constellation of stars in the southern sky, named after the toucan, a South American bird. It is one of twelve constellations conceived in the late sixteenth century by Petrus Plancius from observations of Pieter Dirkszoon Keyser and Frederick de Houtman. It first appeared on a 35-centimeter-diameter (14 in) celestial globe published in 1598 in Amsterdam by Plancius and Jodocus Hondius and was depicted in Johann Bayer's star atlas Uranometria of 1603. French explorer and astronomer Nicolas Louis de Lacaille gave its Bayer designations in 1756. This constellation, Grus, Phoenix, and Pavo are collectively known as the "Southern Birds." It is not a prominent constellation as all of its stars are third magnitude or fainter; the brightest is Alpha Tucanae with an apparent visual magnitude of 2.87. Beta Tucanae is a star system with six member stars, while Kappa is a quadruple system. Five star systems have been found to have exoplanets to date. The constellation contains 47 Tucanae, one of the brightest globular clusters in the sky, and most of the Small Magellanic Cloud.

NGC 3603

It is a nebula situated in the Carina spiral arm of the Milky Way around 20,000 light-years away from the Solar System. It is a massive HII region containing a very compact open cluster (probably a super star cluster) HD 97950.

Cas A

It is a supernova remnant in the constellation Cassiopeia and the brightest extrasolar radio source in the sky at frequencies above 1 GHz. The supernova occurred approximately 11,000 light-years (3.4 kpc) away within the Milky Way. The expanding cloud of material left over from the supernova now appears approximately 10 light-years (3 pc) across from the Earth's perspective. In wavelengths of visible light, it has been seen with amateur telescopes down to 234 mm (9.25 in) with filters. It is believed that first light from the stellar explosion reached Earth approximately 300 years ago but there are no historical records of any sighting of the supernova that created the remnant, probably due to interstellar dust absorbing optical wavelength radiation before it reached Earth (although it is possible that if it was recorded as a sixth magnitude star 3 Cassiopeiae by John Flamsteed on August 16, 1680). Possible explanations lean toward the idea that the source star was unusually massive and had previously ejected much of its outer layers. These outer layers would have cloaked the star and re-absorbed much of the light released as the inner star collapsed. It was among the first discrete astronomical radio sources found. Its discovery was reported in 1948 by Martin Ryle and Francis Graham-Smith, astronomers at Cambridge, based on observations with the Long Michelson Interferometer. The optical component was first identified in 1950. It is 3C461 in the Third Cambridge Catalogue of Radio Sources and G111.7-2.1 in the Green Catalog of Supernova Remnants.

NGC 602

It is a young, bright open cluster of stars located in the Small Magellanic Cloud, a satellite galaxy to the Milky Way. Radiation and shock waves from the stars have pushed away much of the lighter surrounding gas and dust that compose the nebula known as N90, and this in turn has triggered new star formation in the ridges (or "elephant trunks") of the nebula. These even younger, pre-main sequence stars are still enshrouded in dust but are visible to the Spitzer Space Telescope at infrared wavelengths. The cluster is of particular interest because it is located in the wing of the SMC leading to the Magellanic Bridge. Hence, while its chemical properties should be similar to those of the rest of the galaxy, it is relatively isolated and so easier to study. It contains three main condensations of stars. The central core is NGC 602a, with the compact NGC 602b 100 arc-seconds to the NNW. NGC 602c is a looser grouping 11 arc-minutes to the NE, which includes the WO star AB8. It includes many young O and B stars and young stellar objects, with few evolved stars. Ionisation in the nebula is dominated by Sk 183, an extremely hot O3 main sequence star visible as the bright isolated star at the centre of the Hubble image.

Scorpius

It is one of the constellations of the zodiac. Its name is Latin for scorpion, and its symbol is ♏. It lies between Libra to the west and Sagittarius to the east. It is a large constellation located in the southern hemisphere near the center of the Milky Way.

Ursa Minor

Latin for "lesser-Bear," contrasting with Uras Major; also known as the Little Bear, is a constellation in the Northern Sky. Like the Great Bear, the tail of the Little Bear may also be seen as the handle of a ladle, hence the North American name, Little Dipper: seven stars with four in it bowl like its partner the Big Dipper. It was one of the 48 constellations listed by Ptolemy, and remains one of the 88 modern constellations. Ursa Minor has traditionally been important for navigation, particularly by mariners, because of Polaris being the North Star. Polaris, the brightest star in the constellation, is a yellow-white supergiant and the brightest Cepheid variable star in the night sky, ranging from an apparent magnitude of 1.97 to 2.00. Beta Ursae Minoris, also know as Kochab, is an aging star that has swollen and cooled to become an orange giant with an apparent magnitude of 2.08, only slightly fainter than Polaris. Kochab and magnitude 3 Gamma Ursae Minoris have been called the "guardians of the pole star." Planets have been detecting orbiting four of the stars, including Kochab. The constellation also contains an isolated neutron star-- Calvera-- and H1504+65, the hottest white dwarf yet discovered, with a surface temperature of 200,000 K.

Lyra

Latin for "lyre," is a small constellation. It is one of 48 listed by Ptolemy, and is one of the 88 constellations recognized by the International Astronomical Union. Was often represented on star maps as a vulture or an eagle carrying a lyre, and hence sometimes referred to as Aquila Cadens or Vultur Cadens. Beginning at the north, it is bordered by Draco, Hercules, Vulpecula, and Cygnus. It is visible from the northern hemisphere from spring through autumn, and nearly overhead, in temperature latitudes during the summer months. From the southern hemisphere, it is visible in the northern sky during the winter months. Vega, the brightest star is one of the brightest star in the night sky, and forms a corner of the famed Summer Triangle asterism. Beta Lyrae is the prototype of a class of stars known as Beta Lyrae variables. These binary stars are so close to each other that they become egg-shaped and material flows from one to the other. Epsilon Lyrae, known informally as the Double Double, is a complex multiple star system. Lyra also hosts the Ring Nebula, the second-discovered and best-known planetary nebula.

Taurus

Latin for "the Bull;" symbol is ♉; is one of the constellations of the zodiac, which means it is crossed by the plane of the ecliptic. It is a large and prominent constellation in the northern hemisphere's winter sky. It is one of the oldest constellations, dating back to at least the Early Bronze Age when it marked the location of the Sun during the spring equinox. Its importance to the agricultural calendar influenced various bull figures in the mythologies of ancient Sumer, Akkad, Assyria, Babylon, Egypt, Greece, and Rome. A number of features exist that are of interest to astronomers. It hosts two of the nearest open clusters to Earth, the Pleiades and the Hyades, both of which are visible to the naked eye. At first magnitude, the red giant Aldebaran is the brightest star in the constellation. In the northwest part of Taurus is the supernova remnant Messier 1, more commonly known as the Crab Nebula. One of the closest regions of active star formation, the Taurus-Auriga complex, crosses into the northern part of the constellation. The variable star T Tauri is the prototype of a class of pre-main-sequence stars.

Aquila

Latin for 'eagle'. Lies astride the celestial equator. β Aql (Alshain) is a yellow-hued star of magnitude 3.7, 45 light-years from Earth. γ Aql (Tarazed) is an orange-hued giant star of magnitude 2.7, 460 light-years from Earth.

Perseus

Named after a Greek mythological hero, is a constellation in the northern sky. It is one of the 48 listed by Ptolemy, and among the 88 modern constellations defined by the International Astronomical Union (IAU). It is located in the northern celestial hemisphere near several other constellations named after ancient Greek legends surrounding the hero, including Andromeda to the west and Cassiopeia to the north. It is also bordered by Aries and Taurus to the south, Auriga to the east, Camelopardalis to the north, and Triangulum to the west. Some star atlases during the early 19th century also depicted the hero holding onto the head of the Medusa, whose asterism was named together as Perseus et Caput Medusae, however, this never came into popular usage. The galactic plane of the Milky Way passes through it but is mostly obscured by molecular clouds. The constellation's brightest star is the yellow-white supergiant Alpha Persei (Also Mirfak or Mirphak), which shines at magnitude 1.79. It and many of the surrounding stars are members of an open cluster known as the Alpha Persei Cluster. The best known star, however, is Algol (Beta Persei), linked with ominous legends because of its variability, which is noticeable to the naked eye. Rather than being an intrinsically variable star, it is an eclipsing binary. Other notable star systems in it include X Persei, a binary system containing a neutron star, and GK Persei, a nova that peaked at magnitude 0.2 in 1901. The Double Cluster, compromising two open clusters quite near each other in the sky, was known to the ancient Chinese. The constellation gives its name to the Perseus cluster (Abell 426), a massive galaxy cluster located 250 million light-years from Earth. It hosts the radiant of the annual Perseids meteor shower-- one of the most prominent meteor showers in the sky.

Leo

One of the constellations of the zodiac, lying between Cancer to the west and Virgo to the east. Its name is Latin for lion, and to the ancient Greeks represented the Nemean Lion killed by the mythical Greek hero Heracles (known to the ancient Romans as Hercules) as one of his twelve labors. Its symbol is ♌. One of the 48 constellations described by Ptolemy. Remains one of the 88 modern constellations, and one of the most easily recognizable due to its many bright stars and a distinctive shape that is reminiscent of the crouching lion it depicts. The lion's mane and shoulders also form an asterism known as "the Sickle," which to modern observers may resemble a backwards question mark.

Gemini

One of the constellations of the zodiac. It was one of the 48 constellations described by Ptolemy and it remains one of the 88 modern constellations today. Its name is Latin for "twins," and it is associated with the twins Castor and Pollux in Greek mythology. Its symbol is ♊.

Canis Minor

Small constellation in the northern celestial hemisphere. Included as an asterism, or pattern, of two stars in Ptolemy's 48 constellations, and is counted among the 88 modern constellations. Name is Latin for "lesser dog," in contrast to Canis Major, the "greater dog;" both figures are commonly represented as following the constellation of Orion, the hunter. Contains only two stars brighter than the fourth magnitude, Procyon (Alpha Canis Minoris), wiht a magnitude of 0.34, and Gomeisa (Beta Canis Minoris), with a magnitude of 2.9. Dimmer stars were noted by Johann Bayer, who named eight stars including Alpha and Beta, and John Flamsteed, who numbered fourteen. Procyon is the seventh-brightest star in the night sky, as well as one of the closest. A yellow-white main sequence star, it has a white dwarf companion. Gomeisa is a blue-white main sequence star. Luyten's Star is a ninth magnitude red dwarf and the Solar System's next closest stellar neighbor in the constellation after Procyon. Fourth-magnitude HD 66141, which has evolved into an orange giant towards the end of its life cycle, was discovered to have a planet in 2012. Two faint deep sky objects within the constellation's borderes. The 11 Canis-Minorids are a meteor shower that can be seen in early December.

Kepler's SNR

Supernova 1604 was a supernova of Type Ia that occurred in the Milky Way, in the constellation Ophiuchus. Appearing in 1604, it is the most recent supernova in our own galaxy to have been unquestionably observed by the naked eye, occurring no farther than 6 kiloparsecs or about 20,000 light-years from Earth. Visible to the naked eye, Kepler's Star was brighter at its peak than any other star in the night sky, with an apparent magnitude of −2.5. It was visible during the day for over three weeks. The first recorded observation was in northern Italy on October 9, 1604. Johannes Kepler began observing the luminous display on October 17 while working at the imperial court in Prague for Emperor Rudolf II. It was subsequently named after him, even though he was not its first observer, as his observations tracked the object for an entire year and because of his book on the subject, entitled De Stella nova in pede Serpentarii ("On the new star in Ophiuchus's foot", Prague 1606). The supernova was also recorded in Chinese and Korean sources. It was the second supernova to be observed in a generation (after SN 1572 seen by Tycho Brahe in Cassiopeia). No further supernovae have since been observed with certainty in the Milky Way, though many others outside our galaxy have been seen since S Andromedae in 1885. SN 1987A in the Large Magellanic Cloud was easily visible to the naked eye. Strong present day astronomical evidence exists for a Milky Way supernova whose signal would have reached Earth ca. 1680 (Cassiopeia A), and another (G1.9+0.3) whose light should have arrived ca. 1870. There is no historical record of either having been detected at the time, probably because absorption by interstellar dust made them fainter than they would otherwise have been. The supernova remnant resulting from this supernova is considered to be one of the prototypical objects of its kind, and is still an object of much study in astronomy.

NGC 3372

The Carina Nebula, also known as the Grand Nebula, Great Nebula in Carina, or Eta Carinae Nebula, is a large, complex area of bright and dark nebulosity in the constellation Carina, and is located in the Carina-Sagittarius Arm. The nebula lies at an estimated distance between 6,500 and 10,000 light-years (2,000 and 3,100 pc) from Earth. The nebula has within its boundaries the large Carina OB1 association and several related open clusters, including O-type stars and several Wolf-Rayet stars. Carina OB1 encompasses the star clusters Trumpler 14 and Trumpler 16. Trumpler 14 is one of the youngest known star clusters at half a million years old. Trumpler 16 is the home of WR 25, currently the most luminous star known in our Milky Way galaxy, together with the less luminous but more massive and famous Eta Carinae star system and the O2 supergiant HD 93129A. Trumpler 15, Collinder 228, Collinder 232, NGC 3324, and NGC 3293 are also considered members of the association. NGC 3293 is the oldest and farthest from Trumpler 14, indicating sequential and ongoing star formation. The nebula is one of the largest diffuse nebulae in our skies. Although it is some four times as large and even brighter than the famous Orion Nebula, the Carina Nebula is much less well known due to its location in the southern sky. It was discovered by Nicolas-Louis de Lacaille in 1752 from the Cape of Good Hope.

NGC 7293

The Helix Nebula, also known as The Helix, is a large planetary nebula located in the constellation Aquarius. Discovered by Karl Ludwig Harding, probably before 1824, this object is one of the closest to the Earth of all the bright planetary nebulae. The estimated distance is about 215 parsecs (700 light-years). It is similar in appearance to the Cat's Eye Nebula and the Ring Nebula, whose size, age, and physical characteristics are similar to the Dumbbell Nebula, varying only in its relative proximity and the appearance from the equatorial viewing angle. It has sometimes been referred to as the "Eye of God" in pop culture, as well as the "Eye of Sauron."

LMC

The Large Magellanic Cloud is a satellite galaxy of the Milky Way. At a distance of 50 kiloparsecs (~163,000 light-years), it is the third closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal (~ 16 kpc) and the putative Canis Major Dwarf Galaxy (~ 12.9 kpc, though its status as a galaxy is under dispute) lying closer to the center of the Milky Way. The LMC has a diameter of about 14,000 light-years (4.3 kpc) and a mass of approximately 10 billion Sun masses (10^10 solar masses), making it roughly 1/100 as massive as the Milky Way. It is the fourth-largest galaxy in the Local Group, after the Andromeda Galaxy (M31), the Milky Way, and the Triangulum Galaxy (M33). In the past, it was often considered an irregular type galaxy. However, it is now recognized as a disrupted barred spiral galaxy. The NASA Extragalactic Database, however, still lists the Hubble sequence type as Irr/SB(s)m. In reality, it contains a very prominent bar in its center, suggesting that it may have been a barred dwarf spiral galaxy before its spiral arms were disrupted, likely by the Milky Way's gravity. Its present irregular appearance is likely the result of tidal interactions with both the Milky Way and the Small Magellanic Cloud. It is visible as a faint "cloud" in the night sky of the southern hemisphere straddling the border between the constellations of Dorado and Mensa, and it appears from Earth more than 20 times the width of the full moon.

M42

The Orion Nebula (also known as NGC 1976) is a diffuse nebula situated in the Milky Way, being south of Orion's Belt in the constellation of Orion. It is one of the brightest nebulae, and is visible to the naked eye in the night sky. It is located at a distance of 1,344 ± 20 light years and is the closest region of massive star formation to Earth. The nebula is estimated to be 24 light years across. It has a mass of about 2000 times the mass of the Sun. Older texts frequently refer to the Orion Nebula as the Great Nebula in Orion or the Great Orion Nebula. The Orion Nebula is one of the most scrutinized and photographed objects in the night sky, and is among the most intensely studied celestial features. The nebula has revealed much about the process of how stars and planetary systems are formed from collapsing clouds of gas and dust. Astronomers have directly observed protoplanetary disks, brown dwarfs, intense and turbulent motions of the gas, and the photo-ionizing effects of massive nearby stars in the nebula.

M57

The Ring Nebula (also catalogued as NGC 6720) is a planetary nebula in the northern constellation of Lyra. Such objects are formed when a shell of ionized gas is expelled into the surrounding interstellar medium by a red giant star, which was passing through the last stage in its evolution before becoming a white dwarf.

30 Doradus

The Tarantula Nebula is an H II region in the Large Magellanic Cloud (LMC).