reach for the stars
Zeta ophiuchi
3rd brightest star in its constellation/9 young star 3M yrs old. Just over the line into third magnitude (2.56), and third brightest star within the constellation Ophiuchus (the Serpent Bearer), Zeta Ophiuchi is oddly not graced with a proper name, which is odder still since it is in the middle of the line of stars that make the bottom border of the constellation, the others, from west to east being Yed Prior (Delta Ophiuchi), Yed Posterior (Epsilon), and Sabik (Eta) (though Zeta has been known to share that name with just-barely-brighter Eta). Zeta Oph is a blue-white class O (though at 09.5 just barely) hydrogen-fusing "dwarf" (a strange term for a star with a diameter 8 times that of the Sun). The star (which is very slightly variable), however, does not LOOK so blue- white. Zeta Oph is one of the brighter stars in the sky to be significantly affected by absorption and reddening of its light by passage through interstellar dust (which lies everywhere within the Milky Way). At a distance of 460 light years, the star is deeply involved with dust gas clouds (and even illuminates one of them), and is used as a background light source with which to examine the stuff of interstellar space. If the dust were not in the way, Zeta would shine at almost first magnitude. From its distance and great temperature of 32,500 Kelvin (from which we can account for the star's fierce ultraviolet light), we calculate a magnificent luminosity of 68,000 times that of the Sun, and from that a mass of 20 times solar, the star about in the middle of its short (8 million years) hydrogen-fusing lifetime. Like most luminous stars, Zeta Oph is losing mass through a strong wind that in this case blows at about 1600 kilometers per second at a rate of about a hundredth of a millionth of a solar mass per year. The star's only fate seems to blow up as a supernova. Among Zeta Ophiuchi's most interesting properties is that it is one of the sky's most famed "runaway stars," stars that used to be together and are now fleeing from a once-common point. Zeta Ophiuchi, on the other hand, seems to have been expelled from a double star system when its one-time and clearly more-massive companion exploded and is now a tiny "neutron star" about the size of a small town. The explosions that make supernovae are apparently off-center, so that when one of the stars goes off and is blasted like a bullet to one side, the other one can, if conditions are right, be shot off as well. Zeta Ophiuchi is now single, however, so that the scene cannot repeat itself.
Spica
A B1III-IV star with an apparent magnitude varying between 0.92 and 1.04 over a 4-day period of time. Spica is a binary star system (companion Spica B is a B2V star) about 260 LY away. Its name comes from Latin for "Virgo's ear of grain".
Aldebaran
A K5III star (giant, not main sequence) with an apparent magnitude of 0.87, Aldebaran is the 13th brightest star in the nighttime sky. It is around 65 LY away, and it has a white dwarf companion Aldebaran B, with a classification of M2V. The name Aldebaran is from Arabic for "the follower" (because it follows the Pleiades across the night sky). The nickname "the Bull's eye" comes from its bright orange color and its position in the "Bull's head" asterism
Milky way
A barred spiral galaxy in the Local Group (which, in turn, is in the Virgo Supercluster) about 100,000 LY in diameter and 1,000 LY thick. Of the 200-400 billion stars in this galaxy, most are red dwarfs. The oldest ones are 12.8-14.4 billion years old. The galactic center is in the general direction of the constellation Sagittarius- in fact, Sagittarius A* is a supermassive black hole at the center of the Milky Way. It could collide with the Andromeda Galaxy in 3-4 billion years. The Milky Way can be seen as far north as Cassiopeia and as far south as Crux (the Southern Cross).
Globular cluster m13
A globular cluster (hence the name) about 25,100 LY away and 145 LY across in the constellation Hercules. M13 has several hundred thousand stars, but is barely visible from Earth, with an apparent magnitude of 5.8. Its brightest star is V11, which has an apparent magnitude of 11.95.
Geminga
A neutron star in the constellation Gemini. It is a major gamma ray source. It is the decaying core of a star that exploded about 300,000 years ago.
Orion nebula
A part of a larger nebula (the Orion Molecular Cloud Complex), the Orion nebula is about 1270 LY away and 24 LY across. It's the middle star in Orion's sword, with large O-class stars in the center. M42 has protoplanetary disks, brown dwarfs, and large supersonic "bullets" of gas. The Orion Nebula is quite prominent on infrared because of all the stars that are being formed. In 100,000 years, it will be wisps of gas around hot, new stars, like the Pleiades. Pleiades- Another open cluster in the constellation Taurus; one of the closest to Earth at about 440 LY away. Most of the stars in M45 are hot, blue stars formed in the last 100 million years or so, but there are also some brown dwarfs. The cluster will survive for about another 250 million years, then be dispersed by gravity. The name Pleiades is from Greek for either "sailing ones", "many", or "flock of doves".
Ring nebula
A planetary nebula about 2300 LY away in the constellation Vega with apparent magnitude 9. The central star is evolving into a white dwarf (right now, it mainly consists of carbon and oxygen).
CoRoT 2a
A planetary system located about 880 light years away, CoRoT-2a consists of a yellow dwarf main sequence star and a planet about 3 times the size of Jupiter. The star, dubbed CoRot-2 or CoRoT 2a, bombards the planet, CoRoT-2b, with X-rays and evaporates about five million tons of matter from the planet every second. CoRoT-2a has very powerful and turbulent magnetic fields, and the high activity is thought to be caused by the nearby planet.
Eta carinae
A stellar system located about 7,500 light years away. A binary system with a star of 120-150 solar masses and another star of 30 solar masses. It is thought to be the largest observable star system, though not observable optically. It is enclosed in the Homunculus Nebula, which is further enclosed in the Carina Nebula. Eta Carinae is famous for its distinctive double-lobed shape, formed by the stars expelling their outer layers. Also, at least one of the stars will probably go supernova soon, in astronomical terms.
Crab nebula
A supernova remnant in the constellation Taurus, M1 is the result of a 1054 supernova where a supergiant star collapsed inwards and subsequently exploded. At the very center is the Crab Pulsar, a rapidly rotating neutron star that emits pulses of x-rays and gamma rays. In fact, the Crab Pulsar is the strongest persistent source of x-rays and gamma rays in the sky.
Vela supernova remnant
A supernova remnant in the constellation Vela. It is about 800 light years away, which makes it one of the closest SNRs to us.
Tycho's star
A supernova remnant, left over from a supernova detected in November 1572 which remained highly visible for 2 years, then faded. The supernova resulted from a white dwarf accumulating too much matter and exploding. It is called Tycho's SNR after the astronomer Tycho Brahe, who was the most accurate observer of the supernova itself.
sn 1993j
A supernova remnant. What makes this one so special is its dramatic change in spectral characteristics over time. Initially, it resembled a Type II supernova, but then changed to resemble a Type Ib supernova.
Cygnus x-1
A system 6100 light years away consisting of a black hole and a blue supergiant with an orbital rate of 5.6 days. X-rays are emitted in large amounts from a disk of gas that is going into the black hole. Cygnus X-1 is dubbed a microquasar.
Algol
A triple star system, with Algol A as a B8V star, Algol B as a K0-2III star, and Algol C as a A5V star. Combined, it has an apparent magnitude of 2.1, which drops to 3.4 every 3 days or so when Algol A is eclipsed by Algol B (called an eclipsing binary). "Algol" is from Arabic for "head of the ghoul"
Ngc 7000
Also called the North America Nebula,this is an emission nebula in the constellation Cygnus, near Deneb. It is called the North America Nebula because of its eerie resemblance to the continent of North America.
Ncg 7293
Also known as the Helix Nebula or God's Eye Nebula. It is a large planetary nebula in the constellation Aquarius. It is very easy to mistake it for the Ring Nebula, so be careful! It is about 700 light years away, while the Ring Nebula is more than 2000 light years away.
30 doradus
Also known as the Tarantula Nebula, 30 Doradus is 160,000 light years away in the LMC and is extremely luminous. It is one of the largest star forming regions in the Local Group with a diameter of 200 parsecs, as well as the most active. It was called 30 Doradus because it was so bright that it was initially thought to be a star. However, it's home to one of the largest stars known - R136a1. R136a1 has more than 250 solar masses, far surpassing what was thought to be the physical limit for a star's mass
Ss433
An eclipsing x-ray binary system. It is the first microquasar ever discovered. The primary is most likely a black hole, possibly a neutron star, and secondary seems to be an A-type star.
Antares
Antares is a M1.51 star (a supergiant), with an apparent magnitude ranging from 0.9 to 1.8 (it's a variable star). The ancient Greek for "against Mars" (roughly, anti-Ares) became the modern day name of Antares. About 600 LY away, it is also the 16th brightest star in the sky, even though a large portion of its emitted energy is in the infrared wavelengths. Its companion Antares B is a B2.5V star
Regulus
Around 77.5 LY away, Regulus is a quadruple star system- Regulus A is a B7V star with a white dwarf companion, while Regulus B and C are dim main sequence stars (a K1-2V star and a M5V star, respectively). Regulus A is a young star that spins very rapidly and it has a magnitude of 1.35. The name comes from Latin for "little king" or "prince".
Proxima centauri
At only 4 light years, Proxima centauri is the nearest star to the sun. It is a type-M red dwarf star, and despite its distance, it is too dim to see with the naked eye, at magnitude 11.05. Proxima Centauri is part of a triple star system with its brighter neighbor Alpha Centauri A and B. It is a flare star, a variable type that changes brightness drastically.
Betelgeuse
Betelgeuse (yes, pronounced beetle-juice) is a M2I red supergiant about 600 LY away. It is most likely a young star evolving quite rapidly. Betelgeuse is usually the second brightest star in Orion with an apparent magnitude of around 0.58, but since it's a variable star, Betelgeuse is sometimes brighter than Rigel. Also, it is one of the vertices of the Winter Triangle, along with Sirius and Procyon. "Betelgeuse" comes from a mistranslation of the Arabic phrase for "hand of the central one". Betelgeuse is considered very likely to go supernova after its red giant phase.
Cassiopeia a
Cassiopeia A is a supernova remnant about 11,000 LY away. The supernova itself happened around 1667 (the most recent supernova in the Milky Way visible to the naked eye), and resulted from the collapse and explosion of a large star. Cassiopeia A emits lots of radio waves, but is very hard to see with the naked eye at the present day.
Castor and pollux
Castor is the second brightest star in the constellation Gemini, named after one of the twin sons of the Greek god Zeus. Castor is actually a sextuple star system, with two pairs of A-class stars (1V and 2V) and M-class stars orbited by two more M-class dwarfs. The apparent magnitude can be either 1.96 or 2.91, depending on which of the A-class stars is measured. Pollux is the brightest star in Gemini, with an apparent magnitude of 1.14. It's 34 light-years from Earth and it's also a K0 III star, meaning that it is one of the hotter orange giants. Pollux is also one of the only giant stars with a planet. This planet has a mass at least 2.9 times that of Jupiter and orbits 1.69 AUs from its host star
Y velorum
Far in the southern sky lies a very interesting star - Gamma Velorum. It is an extremely luminous Wolf-Rayet star, which is a type of massive star that is losing mass due to a stellar wind at a violent rate. Currently, Gamma Velorum is about 10 times the mass of the sun, it was initially over 20 times heavier than the sun, but has been losing mass rapidly. It orbits another highly-luminous blue supergiant. From Earth, it appears at apparent magnitude 1.27.
Gliese
Gliese 581 is a red dwarf, M3V star about 20 LY away. The star has an apparent magnitude between 10.56 and 10.58 and is located in the constellation Libra. The star is well known for its planet Gliese 581 g, thought to be in the habitable zone of its star, but the planet's existence is disputed.
G359.23-0.82
Located in Sagittarius, this is an energetic radio pulsar. Radio images show a small head, bulbous body, and a trailing tail which give it its nickname, the Mouse.
Sagittarius a
Most likely the supermassive black hole at the center of the Milky Way about 44 million km in diameter, Sagittarius A* is a source of radio waves. It is about 26,000 LY away.
Rigel
Named in Arabic "left foot of the central one", Rigel is an important star for navigation. Somewhere between 700 and 900 LY away, Rigel is also known as the most luminous star in the nearby Milky Way. Most of the time, it is the brightest star in Orion, but Betelgeuse can be brighter because it is a variable star. Rigel is known to be a triple star system; however, it may in fact be a quadruple star system. The most prominent star is a B8I star with an apparent magnitude of 0.11.
Deneb
One of the vertices of the Summer Triangle, Deneb is an A2I star about 1550 LY away. With an apparent magnitude of 1.25, Deneb is actually the farthest 1st-magnitude star from Earth. It will probably become a supernova in a few million years. Because Deneb is the tail of Cygnus, the swan, its Arabic name is quite fittingly, "tail".
Capella
Part of the Hyades moving group, Capella is the 6th brightest star in the night sky and the 3rd brightest in the northern celestial hemisphere. It is actually a "star system" of 4 stars in 2 pairs. The first pair are G8III and K0III stars (probably previously A-class stars that have now moved off the main sequence and are becoming red giants) while the second pair consists of 2 small, cool, dim red dwarfs. Combined, these stars have an apparent magnitude of 0.08; additionally, they are 42.2 LY from Earth. There are lots of x-rays being emitted from the corona of the largest star. Capella means "she-goat."
Polaris
Polaris is an important star for navigation; however, it is only approximate North - it's not exactly at the celestial pole. Polaris A is a F7I-II star, while companions Polaris B and Ab are a F-class main sequence star and a dwarf, respectively (there are also 2 farther stars, Polaris C and D). Polaris may be part of a loose cluster of A- and F-class stars.
Procyon
Procyon is the 7th brightest star in the nighttime sky with an apparent magnitude of 0.34. Procyon is a binary star system (Procyon A is a F5IV-V star, Procyon B is a white dwarf) and it's also a vertex of the Winter Triangle. Procyon forms a prominent equilateral triangle with Sirius and Betelgeuse. In Greek, Procyon means "preceding the dog", because it rises before Sirius.
Sirius
Sirius is the brightest star in the night sky, with an apparent magnitude of -1.47. The binary star system consists of Sirius A (an A1V star) and Sirius B (which used to be even larger than Sirius A but has evolved into a white dwarf). Sirius can be seen up to 73 degrees north or south of the equator, and it's one of the vertices of the Winter Triangle, along with Procyon and Betelgeuse. The nickname "Dog Star" comes from the constellation Sirius is in: Canis Major, the Big Dog. Sirius is about 8.6 LY away.
W49 b
Stellar evolution; young, massive stars ionise nearby gas clouds with high-energy UV radiation is a large,is a strong galactic thermal radio source characteristic of an HII region Since the supernova shock of W49B is observed to be interacting with the molecular cloud in which the supernova exploded, the detection of W49B at GeV and TeV emission is a strong indication for a hadronic nature of the accelerated particles. In case of W49A, shocks created by the strong winds of numerous massive stars provide a plausible mechanism for particle acceleration. Recently, evidence for the presence of two expanding shells in W49A with an energy in the 10^49 erg range was found by Peng et al. (2010), providing an appropriate source of energy. w49 is obscured by interstellar dust. The W49 region hosts two bright radio sources (Fig. 1): the star forming region W49A and the supernova remnant W49B. The million solar mass Giant Molecular Cloud W49A is one of the most luminous giant radio HII regions in our Galaxy and hosts numerous active, high¬ mass star formation sites embedded a 50 light year region. The supernova remnant W49B (top image) stands out among remnants of this type due to its high radio surface brightness; it is also one of the brightest ejecta-¬dominated remnants in X¬-rays. W49B lies at a distance of about 30000 light years (Brogan & Troland 2001), has an estimated age of a few 1000 years and appears at a size of 4 minutes of arc. W49B's progenitor was a super-massive star located in a dense molecular cloud; the stellar wind of this star drove a wind cavity into the cloud and the explosion occured in this cavity (Keohane et al. 2007). The unusual barrel-shape of the W49B remnant has led Ioka et al. (2004) to suggest that it represents a remmant of a gamma-ray-burst explosion, resulting in two highly-relativistic jets, with the X-ray emission (top image) tracing the jets up to the point where they hit the cloud at the edge of the cavity and cause X-ray emission to flare out. Even without this speculative scenario, which predicts a degree-wide source of hard gamma rays, the relatively young age of the remnant combined with its embedding in a cloud serving as target for gamma-ray production by cosmic rays accelerated in the supernova shock make this a promising target for gamma ray observations, and indeed W49B was observed by H.E.S.S. as early as 2005. The first detection in gamma rays was, however, reported at GeV energies by Fermi (Abdo et al. 2010). About 60 hours of observations accumulated by H.E.S.S. combined with advanced analysis techniques have now resulted in the detection of W49B as - at the scale of the H.E.S.S. resolution of about 5 minutes of arc - point-like source of TeV gamma rays, with a statistical significance of 8.8 sigma and a flux equivalent to 0.5% of the Crab Nebula flux (Fig. 2). The energy spectrum of gamma rays is rather steep, with a spectral index of about 3 between 0.3 TeV and 10 TeV, and matches smoothly with the lower-energy spectrum by Fermi (Fig. 3). Gamma-ray emission from the direction of W49A is also indicated for the first time, at a significance in excess of 4.4 sigma (Fig. 2). The gamma-ray signal is coincident with the densest part of the molecular cloud. Since the supernova shock of W49B is observed to be interacting with the molecular cloud in which the supernova exploded, the detection of W49B at GeV and TeV emission is a strong indication for a hadronic nature of the accelerated particles. In case of W49A, shocks created by the strong winds of numerous massive stars provide a plausible mechanism for particle acceleration. Recently, evidence for the presence of two expanding shells in W49A with an energy in the 10^49 erg range was found by Peng et al. (2010), providing an appropriate source of energy. Distance from Earth: 36 K ly Right
Altair
The 12th brightest star in the sky with an apparent magnitude of 0.77, Altair is one of the vertices of the Summer Triangle (along with Vega and Deneb). It is flattened at the poles due to its high rotation speed. The name Altair comes from a shortened version of the Arabic phrase "the flying eagle". Altair is a A7V star and it's 16.8 LY away
Hyades star cluster
The Hyades are the closest open cluster to us at 151 LY away, located in the constellation Taurus. The 4 brightest stars in the Hyades (formerly A-class stars, now off the main sequence) form a V shape along with Aldebaran. It could share a common origin with the Beehive Cluster (M44). The name is from ancient Greek mythology- Hyades was the collective name of several weeping sisters who were turned into stars and therefore associated with rain.
Mizar and alcor
The sextuple system Mizar and Alcor is located on the handle of the Big Dipper Asterism in Ursa Major. Mizar is actually made up of two binary systems, while Alcor is a binary system itself. The stars have an apparent magnitude of 2.23. It looks like a single star at a glance, but a person with keen eyesight can see both Mizar and Alcor. For this reason, it has been important to navigators and explorers throughout history. However, Mizar is not actually in a system with Alcor; they are separate star systems that appear very close from Earth.
HL tau
This very young star is dim and located 520 light years away in the constellation of Taurus. The star has a very large and bright "accretion disk", which is a disk of gas and dust surrounding the star. Because of this, it was a good candidate to witness a planet in forming, called a "protoplanet". After a few studies, it was revealed that there was a ball of Gas and Dust 14-times the mass of Jupiter -- A planet forming. It is the youngest planet ever discovered
Vega
Vega is the 5th brightest star in the night sky and the 2nd brightest in the northern celestial hemisphere. It is an A0V star approximately 25 LY away that is flattened at the poles due to its high rotation speed. Vega is 1/10 the age of the Sun, but it's already halfway through its life as a main sequence star. There is the possibility that Vega has its own little solar system of sorts- it may have orbiting planets. Vega is a vertex of the Summer Triangle (the other vertices are Altair and Deneb). The name is derived from the Arabic phrases for either "falling eagle" or "swooping vulture".
W3 main
W3 is a region where many massive stars are forming in a string of stellar clusters, located about 6,000 light years from Earth in the Perseus arm of the Milky Way galaxy W3 is a giant gas cloud containing an enormous stellar nursery, some 6,200 light-years away in the Perseus Arm, one of our Milky Way galaxy's main spiral arms. By studying regions of massive star formation in W3, scientists have made progress in solving one of the major conundrums in the birth of massive stars.The W3 star-formation complex is one of the largest in the outer Milky Way, hosting the formation of both low- and high-mass stars. The distinction between low- and high-mass stars is drawn at eight times the mass of our own sun: above this limit, stars end their lives as supernovae. W3 is a region where many massive stars are forming in a string of stellar clusters, located about 6,000 light years from Earth in the Perseus arm of the Milky Way galaxy. W3 is part of a vast molecular cloud complex that also contains the W4 superbubble (not seen in this image). Scientists believe that the extraordinary amount of star formation in W3 has possibly been influenced by neighboring W4, an inflating bubble of gas over 100 light years across. W4 may directly trigger the birth of W3's massive stellar clusters as it expands and sweeps up molecular gas into a high-density layer at its edge, within which stars can form. Another possible scenario is that W4's expansion has caused a domino effect of star formation, forming the cluster IC 1795 (seen as a clump of X-ray sources in the bottom left corner of this image) which in turn triggered formation of the young, massive clusters in W3. In this composite image of one of the many star-forming complexes of W3, called W3 Main, green and blue represent lower and higher-energy X-rays, respectively, while red shows optical emission. Hundreds of X-ray sources are revealed in this central region of W3 Main. These bright point-like objects are an extensive population of several hundred young stars, many of which were not found in earlier infrared studies. These Chandra data show that W3 Main is the dominant star formation region of W3. Because its X-ray sources are all at the same distance, yet span a range of masses, ages, and other properties, W3 is an ideal laboratory for understanding recent and ongoing star formation in one of the Milky Way's spiral arms. Distance from Earth: 6 K ly Right ascension: 2h 25m 40.6s Declination: 62° 05' 52.40"
Arcturus
With an apparent magnitude of -0.05 (can vary by 0.04), Arcturus is the fourth brightest star in the nighttime sky. However, it is less bright than Alpha Centauri A and B combined, which means that it is the third brightest individual star in the night sky. Arcturus might actually be a binary star with a companion around 20 times or so dimmer, at the very edge of our ability to detect it. Arcturus is about 36.7 LY away and is a K1.5III star. The name is derived from Arabic for "bear guard", because it is close to both Ursa Major and Ursa Minor.