The parsec is a unit of length used to measure large distances to astronomical objects outside the Solar System. A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond, which corresponds to 648000/π astronomical units. One parsec is equal to 31 trillion kilometres or 19 trillion miles; the nearest star, Proxima Centauri, is about 1.3 parsecs from the Sun. Most of the stars visible to the unaided eye in the night sky are within 500 parsecs of the Sun; the parsec unit was first suggested in 1913 by the British astronomer Herbert Hall Turner. Named as a portmanteau of the parallax of one arcsecond, it was defined to make calculations of astronomical distances from only their raw observational data quick and easy for astronomers. For this reason, it is the unit preferred in astronomy and astrophysics, though the light-year remains prominent in popular science texts and common usage. Although parsecs are used for the shorter distances within the Milky Way, multiples of parsecs are required for the larger scales in the universe, including kiloparsecs for the more distant objects within and around the Milky Way, megaparsecs for mid-distance galaxies, gigaparsecs for many quasars and the most distant galaxies.
In August 2015, the IAU passed Resolution B2, which, as part of the definition of a standardized absolute and apparent bolometric magnitude scale, mentioned an existing explicit definition of the parsec as 648000/π astronomical units, or 3.08567758149137×1016 metres. This corresponds to the small-angle definition of the parsec found in many contemporary astronomical references; the parsec is defined as being equal to the length of the longer leg of an elongated imaginary right triangle in space. The two dimensions on which this triangle is based are its shorter leg, of length one astronomical unit, the subtended angle of the vertex opposite that leg, measuring one arc second. Applying the rules of trigonometry to these two values, the unit length of the other leg of the triangle can be derived. One of the oldest methods used by astronomers to calculate the distance to a star is to record the difference in angle between two measurements of the position of the star in the sky; the first measurement is taken from the Earth on one side of the Sun, the second is taken half a year when the Earth is on the opposite side of the Sun.
The distance between the two positions of the Earth when the two measurements were taken is twice the distance between the Earth and the Sun. The difference in angle between the two measurements is twice the parallax angle, formed by lines from the Sun and Earth to the star at the distant vertex; the distance to the star could be calculated using trigonometry. The first successful published direct measurements of an object at interstellar distances were undertaken by German astronomer Friedrich Wilhelm Bessel in 1838, who used this approach to calculate the 3.5-parsec distance of 61 Cygni. The parallax of a star is defined as half of the angular distance that a star appears to move relative to the celestial sphere as Earth orbits the Sun. Equivalently, it is the subtended angle, from that star's perspective, of the semimajor axis of the Earth's orbit; the star, the Sun and the Earth form the corners of an imaginary right triangle in space: the right angle is the corner at the Sun, the corner at the star is the parallax angle.
The length of the opposite side to the parallax angle is the distance from the Earth to the Sun (defined as one astronomical unit, the length of the adjacent side gives the distance from the sun to the star. Therefore, given a measurement of the parallax angle, along with the rules of trigonometry, the distance from the Sun to the star can be found. A parsec is defined as the length of the side adjacent to the vertex occupied by a star whose parallax angle is one arcsecond; the use of the parsec as a unit of distance follows from Bessel's method, because the distance in parsecs can be computed as the reciprocal of the parallax angle in arcseconds. No trigonometric functions are required in this relationship because the small angles involved mean that the approximate solution of the skinny triangle can be applied. Though it may have been used before, the term parsec was first mentioned in an astronomical publication in 1913. Astronomer Royal Frank Watson Dyson expressed his concern for the need of a name for that unit of distance.
He proposed the name astron, but mentioned that Carl Charlier had suggested siriometer and Herbert Hall Turner had proposed parsec. It was Turner's proposal. In the diagram above, S represents the Sun, E the Earth at one point in its orbit, thus the distance ES is one astronomical unit. The angle SDE is one arcsecond so by definition D is a point in space at a distance of one parsec from the Sun. Through trigonometry, the distance SD is calculated as follows: S D = E S tan 1 ″ S D ≈ E S 1 ″ = 1 au 1 60 × 60 × π
The Local Group is the galaxy group that includes the Milky Way. Its has a total diameter of 3 Mpc, a total mass of the order of 2×1012 solar masses, it consists of two clusters of galaxies in a "dumbbell" shape, the Milky Way and its satellites on one hand, the Andromeda Galaxy and its satellites on the other. The two clusters are separated by about 0.8 Mpc and move towards one another with a velocity of 123 km/h. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster; the total number of galaxies in the Local Group is unknown but known to exceed 54, most of them being dwarf galaxies. The two largest members, the Andromeda Galaxy and the Milky Way, are both spiral galaxies with masses of about 1012 solar masses each, each have their own system of satellite galaxies: The Andromeda Galaxy's satellite system consists of Messier 32, Messier 110, NGC 147, NGC 185, Andromeda I, And II, And III, And V, And VI, And VII, And VIII, And IX, And X, And XI, And XIX, And XXI and And XXII, plus several additional ultra-faint dwarf spheroidal galaxies.
The Milky Way's satellite galaxies system comprises Sagittarius Dwarf Galaxy, Large Magellanic Cloud, Small Magellanic Cloud, Canis Major Dwarf Galaxy, Ursa Minor Dwarf Galaxy, Draco Dwarf Galaxy, Carina Dwarf Galaxy, Sextans Dwarf Galaxy, Sculptor Dwarf Galaxy, Fornax Dwarf Galaxy, Leo I, Leo II, Ursa Major I Dwarf Galaxy and Ursa Major II Dwarf Galaxy, plus several additional ultra-faint dwarf spheroidal galaxies. The Triangulum Galaxy is the third largest member of the Local Group, at about 5×1010 M☉, the third spiral galaxy, it may not be a companion to the Andromeda Galaxy. Pisces Dwarf Galaxy is equidistant from the Andromeda Galaxy and the Triangulum Galaxy, so it may be a satellite of either; the membership of NGC 3109, with its companions Sextans A and the Antlia Dwarf Galaxy, is uncertain due to extreme distances from the center of the Local Group. The other members of the group are gravitationally secluded from these large subgroups: IC 10, IC 1613, Phoenix Dwarf Galaxy, Leo A, Tucana Dwarf Galaxy, Cetus Dwarf Galaxy, Pegasus Dwarf Irregular Galaxy, Wolf–Lundmark–Melotte, Aquarius Dwarf Galaxy, Sagittarius Dwarf Irregular Galaxy.
The term "The Local Group" was introduced by Edwin Hubble in Chapter VI of his 1936 book The Realm of the Nebulae. There, he described it as "a typical small group of nebulae, isolated in the general field" and delineated, by decreasing luminosity, its members to be M31, Milky Way, M33, Large Magellanic Cloud, Small Magellanic Cloud, M32, NGC 205, NGC 6822, NGC 185, IC 1613 and NGC 147, he identified IC 10 as a possible part of Local Group. By 2003, the number of known Local Group members had increased from his initial 12 to 36. Smith's Cloud, a high-velocity cloud, between 32,000 and 49,000 light years from Earth and 8,000 light years from the disk of the Milky Way galaxy HVC 127-41-330, a high-velocity cloud, 2.3 million light-years from Earth Monoceros Ring, a ring of stars around the Milky Way, proposed to consist of a stellar stream torn from the Canis Major Dwarf Galaxy Galaxy cluster List of nearest galaxies List of galaxy clusters IC 342/Maffei Group, the group of galaxies nearest to the Local Group Local Supercluster List of Andromeda's satellite galaxies List of Milky Way's satellite galaxies The Local Group of Galaxies, SEDS Messier pages A Survey of the Resolved Stellar Content of Nearby Galaxies Currently Forming Stars, Lowell Observatory van den Bergh, Sidney.
"Updated Information on the Local Group". The Publications of the Astronomical Society of the Pacific. 112: 529–536. ArXiv:astro-ph/0001040. Bibcode:2000PASP..112..529V. Doi:10.1086/316548
The Carina–Sagittarius Arm is thought to be a minor spiral arm of the Milky Way galaxy. Each spiral arm is a diffuse curving streamer of stars that radiates from the galactic center; these gigantic structures are composed of billions of stars and thousands of gas clouds. The Carina–Sagittarius Arm is one of the most pronounced arms in our galaxy as a large number of HII regions, young stars and giant molecular clouds are concentrated in it; the Milky Way is a barred spiral galaxy, consisting of a central crossbar and bulge from which two major and several minor spiral arms radiate outwards. The Carina–Sagittarius Arm lies between two major spiral arms—the Scutum–Centaurus Arm the near part of, visible looking inward i.e. toward the galactic centre with the rest beyond the galactic centre and the Perseus Arm, similar in size and shape but locally positioned outward. It is named for its proximity to the Sagittarius and Carina constellations as seen in the night sky from Earth, in the direction of the galactic center.
The arm dissipates near its middle, shortly after reaching its maximal angle, viewed from our solar system, from the galactic centre of about 80°. Extending from the galaxy's central bar is the Sagittarius Arm. Beyond the dissipated zone it is the Carina Arm. In 2008, infrared observations with the Spitzer Space Telescope showed that the Carina–Sagittarius Arm has a relative paucity of young stars, in contrast with the Scutum-Centaurus Arm and Perseus Arm; this suggests. These two appear to be concentrations of gas, sparsely sprinkled with pockets of newly formed stars. A number of Messier objects and other objects visible through an amateur's telescope or binoculars are found in the Sagittarius Arm: M11, the Wild Duck Cluster in Scutum Open Cluster M26 in Scutum M16, the Eagle Nebula in Serpens M17, the Omega Nebula in Sagittarius Open Cluster M18 in Sagittarius Globular Cluster M55 in Sagittarius M24, the Sagittarius Star Cloud Open Cluster M21 in Sagittarius M8, the Lagoon Nebula in Sagittarius NGC 3372, the Carina Nebula in Carina http://members.fcac.org/~sol/chview/chv5.htm Messier Objects in the Milky Way
Large Magellanic Cloud
The Large Magellanic Cloud is a satellite galaxy of the Milky Way. At a distance of about 50 kiloparsecs, the LMC is the second- or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal and the possible dwarf irregular galaxy known as the Canis Major Overdensity. Based on visible stars and a mass of 10 billion solar masses, the diameter of the LMC is about 14,000 light-years, making it one one-hundredth as massive as the Milky Way; this makes the LMC the fourth-largest galaxy in the Local Group, after the Andromeda Galaxy, the Milky Way, the Triangulum Galaxy. The LMC is classified as a Magellanic spiral, it contains a stellar bar, geometrically off-center, suggesting that it was a barred dwarf spiral galaxy before its spiral arms were disrupted by tidal interactions from the Small Magellanic Cloud, the Milky Way's gravity. With a declination of about -70°, the LMC is visible as a faint "cloud" only in the southern celestial hemisphere and from latitudes south of 20° N, straddling the border between the constellations of Dorado and Mensa, appears longer than 20 times the Moon's diameter from dark sites away from light pollution.
The Milky Way and the LMC are expected to collide in 2.4 billion years. Although both clouds have been visible for southern nighttime observers well back into prehistory, the first known written mention of the Large Magellanic Cloud was by the Persian astronomer'Abd al-Rahman al-Sufi Shirazi, in his Book of Fixed Stars around 964 AD; the next recorded observation was in 1503–4 by Amerigo Vespucci in a letter about his third voyage. In this letter he mentions "three Canopes, two bright and one obscure". Ferdinand Magellan sighted the LMC on his voyage in 1519, his writings brought the LMC into common Western knowledge; the galaxy now bears his name. Measurements with the Hubble Space Telescope, announced in 2006, suggest the Large and Small Magellanic Clouds may be moving too fast to be orbiting the Milky Way; the Large Magellanic Cloud has a spiral arm. The central bar seems to be warped so that the east and west ends are nearer the Milky Way than the middle. In 2014, measurements from the Hubble Space Telescope made it possible to determine that the LMC has a rotation period of 250 million years.
The LMC was long considered to be a planar galaxy that could be assumed to lie at a single distance from the Solar System. However, in 1986, Caldwell and Coulson found that field Cepheid variables in the northeast portion of the LMC lie closer to the Milky Way than Cepheids in the southwest portion. More this inclined geometry for field stars in the LMC has been confirmed via observations of Cepheids, core helium-burning red clump stars and the tip of the red giant branch. All three of these papers find an inclination of ~35°, where a face-on galaxy has an inclination of 0°. Further work on the structure of the LMC using the kinematics of carbon stars showed that the LMC's disk is both thick and flared. Regarding the distribution of star clusters in the LMC, Schommer et al. measured velocities for ~80 clusters and found that the LMC's cluster system has kinematics consistent with the clusters moving in a disk-like distribution. These results were confirmed by Grocholski et al. who calculated distances to a number of clusters and showed that the LMC's cluster system is in fact distributed in the same plane as the field stars.
The distance to the LMC has been calculated using a variety of standard candles, with Cepheid variables being one of the most popular. Cepheids have been shown to have a relationship between their absolute luminosity and the period over which their brightness varies. However, Cepheids appear to suffer from a metallicity effect, where Cepheids of different metallicities have different period–luminosity relations; the Cepheids in the Milky Way used to calibrate the period–luminosity relation are more metal rich than those found in the LMC. Modern 8-meter-class optical telescopes have discovered eclipsing binaries throughout the Local Group. Parameters of these systems can be measured without compositional assumptions; the light echoes of supernova 1987A are geometric measurements, without any stellar models or assumptions. In 2006, the Cepheid absolute luminosity was re-calibrated using Cepheid variables in the galaxy Messier 106 that cover a range of metallicities. Using this improved calibration, they find an absolute distance modulus of 48 kpc.
This distance has been confirmed by other authors. By cross-correlating different measurement methods, one can bound the distance; the results of a study using late-type eclipsing binaries to determine the distance more was published in the scientific journal Nature in March 2013. A distance of 49.97 kpc with an accuracy of 2.2% was obtained. Like many irregular galaxies, the LMC is rich in gas and dust, it is undergoing vigorous star formation activity, it is home to the Tarantula Nebula, the most active star-forming region in the Local Group. The LMC has a wide range of galactic objects and phenomena that make it aptly known as an "astronomical treasure-house, a great celestial laboratory for the study of the growth and evolution of the stars," as described by Robert Burnham Jr. Surveys of the galaxy have found 60 globular clusters, 400 planetary nebula
Boötes is a constellation in the northern sky, located between 0° and +60° declination, 13 and 16 hours of right ascension on the celestial sphere. The name comes from the Greek Βοώτης, Boōtēs, meaning “herdsman” or “plowman”. One of the 48 constellations described by the 2nd-century astronomer Ptolemy, Boötes is now one of the 88 modern constellations, it contains the fourth-brightest star in the orange giant Arcturus. Epsilon Bootis, or Izar, is a colourful multiple star popular with amateur astronomers. Boötes is 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 visible to the naked eye. In ancient Babylon, the stars of Boötes were known as SHU. PA, they were depicted as the god Enlil, the leader of the Babylonian pantheon and special patron of farmers. Boötes may have been represented by the foreleg constellation in ancient Egypt. According to this interpretation, the constellation depicts the shape of an animal foreleg.
The name Boötes was first used by Homer in his Odyssey as a celestial reference point for navigation, described as "late-setting" or "slow to set", translated as the "Plowman". Whom Boötes is supposed to represent in Greek mythology is not clear. According to one version, he was a son of Demeter, twin brother of Plutus, a plowman who drove the oxen in the constellation Ursa Major; this is corroborated by the constellation's name, which itself means "ox-driver" or "herdsman." The ancient Greeks saw. This influenced the name's etymology, derived from the Greek for "noisy" or "ox-driver". Another myth associated with Boötes relates that he invented the plow and was memorialized for his ingenuity as a constellation. Another myth associated with Boötes by Hyginus is that of Icarius, schooled as a grape farmer and winemaker by Dionysus. Icarius made wine so strong that those who drank it appeared poisoned, which caused shepherds to avenge their poisoned friends by killing Icarius. Maera, Icarius' dog, brought his daughter Erigone to her father's body, whereupon both she and the dog committed suicide.
Zeus chose to honor all three by placing them in the sky as constellations: Icarius as Boötes, Erigone as Virgo, Maera as Canis Major or Canis Minor. Following another reading, the constellation is identified with Arcas and referred to as Arcas and Arcturus, son of Zeus and Callisto. Arcas was brought up by his maternal grandfather Lycaon, to whom one day Zeus had a meal. To verify that the guest was the king of the gods, Lycaon killed his grandson and prepared a meal made from his flesh. Zeus noticed and became angry, transforming Lycaon into a wolf and giving life back to his son. In the meantime Callisto had been transformed into a she-bear by Zeus's wife Hera, angry at Zeus's infidelity; this is corroborated by the Greek name for Boötes, which means "Bear Watcher". Callisto, in the form of a bear was killed by her son, out hunting. Zeus rescued her, taking her into the sky where she became Ursa Major, "the Great Bear". Arcturus, the name of the constellation's brightest star, comes from the Greek word meaning "guardian of the bear".
Sometimes Arcturus is depicted as leading the hunting dogs of nearby Canes Venatici and driving the bears of Ursa Major and Ursa Minor. Several former constellations were formed from stars now included in Boötes. Quadrans Muralis, the Quadrant, was a constellation created near Beta Boötis from faint stars, it was designated in 1795 by Jérôme Lalande, an astronomer who used a quadrant to perform detailed astronometric measurements. Lalande worked with others to predict the 1758 return of Halley's Comet. Quadrans Muralis was formed from the stars of eastern Boötes, western Hercules, Draco, it was called Le Mural by Jean Fortin in his 1795 Atlas Céleste. The constellation was quite faint, with its brightest stars reaching the 5th magnitude. Mons Maenalus, representing the Maenalus mountains, was created by Johannes Hevelius in 1687 at the foot of the constellation's figure; the mountain was named for the son of Maenalus. The mountain, one of Diana's hunting grounds, was holy to Pan; the stars of Boötes were incorporated into many different Chinese constellations.
Arcturus was part of the most prominent of these, variously designated as the celestial king's throne or the Blue Dragon's horn. Arcturus was given such importance in Chinese celestial mythology because of its status marking the beginning of the lunar calendar, as well as its status as the brightest star in the northern night sky. Two constellations flanked Daijiao: Yousheti to Zuosheti to the left. Zuosheti was formed from modern Zeta, Pi Boötis, while Yousheti was formed from modern Eta and Upsilon Boötis. Dixi, the Emperor's ceremonial banquet mat, was north of Arcturus, consisting of the stars 12, 11, 9 Boötis. Another northern constellation was Qigong, the Seven Dukes, which straddled the Boötes-Hercules border, it included either Delta Boötis or Beta Boötis as its terminus. The other Chinese constellations made up of the stars of Boötes existed in the modern constellation's north. Tianqiang, the spear, was formed from Iota and Theta Boötis. There were two
SIMBAD is an astronomical database of objects beyond the Solar System. It is maintained by the Centre de données astronomiques de France. SIMBAD was created by merging the Catalog of Stellar Identifications and the Bibliographic Star Index as they existed at the Meudon Computer Centre until 1979, expanded by additional source data from other catalogues and the academic literature; the first on-line interactive version, known as Version 2, was made available in 1981. Version 3, developed in the C language and running on UNIX stations at the Strasbourg Observatory, was released in 1990. Fall of 2006 saw the release of Version 4 of the database, now stored in PostgreSQL, the supporting software, now written in Java; as of 10 February 2017, SIMBAD contains information for 9,099,070 objects under 24,529,080 different names, with 327,634 bibliographical references and 15,511,733 bibliographic citations. The minor planet 4692 SIMBAD was named in its honour. Planetary Data System – NASA's database of information on SSSB, maintained by JPL and Caltech.
NASA/IPAC Extragalactic Database – a database of information on objects outside the Milky Way maintained by JPL. NASA Exoplanet Archive – an online astronomical exoplanet catalog and data service Bibcode SIMBAD, Strasbourg SIMBAD, Harvard
Small Magellanic Cloud
The Small Magellanic Cloud, or Nubecula Minor, is a dwarf galaxy near the Milky Way. Classified as a dwarf irregular galaxy, the SMC has a diameter of about 7,000 light-years, contains several hundred million stars, has a total mass of 7 billion solar masses; the SMC contains a central bar structure and is speculated to once be a barred spiral galaxy, disrupted by the Milky Way to become somewhat irregular. At a distance of about 200,000 light-years, the SMC is among the nearest intergalactic neighbors of the Milky Way and is one of the most distant objects visible to the naked eye; the SMC is visible from the entire Southern Hemisphere, but can be glimpsed low above the southern horizon from latitudes south of about 15° north. The galaxy is located across both the constellations of Tucana and part of Hydrus, appearing as a faint hazy patch resembling a detached piece of the Milky Way; the SMC has an average diameter of about 4.2° and thus covers an area of about 14 square degrees. Since its surface brightness is low, this deep-sky object is best seen on clear moonless nights and away from city lights.
The SMC forms a pair with the Large Magellanic Cloud, which lies 20° to the east, like the LMC, is a member of the Local Group and probably is a satellite of the Milky Way. In the southern hemisphere, the Magellanic clouds have long been included in the lore of native inhabitants, including south sea islanders and indigenous Australians. Persian astronomer Al Sufi labelled the larger of the two clouds as the White Ox. European sailors may have first noticed the clouds during the Middle Ages when they were used for navigation. Portuguese and Dutch sailors called them the Cape Clouds, a name, retained for several centuries. During the circumnavigation of the Earth by Ferdinand Magellan in 1519–22, they were described by Antonio Pigafetta as dim clusters of stars. In Johann Bayer's celestial atlas Uranometria, published in 1603, he named the smaller cloud, Nubecula Minor. In Latin, Nubecula means a little cloud. Between 1834 and 1838, John Frederick William Herschel made observations of the southern skies with his 14-inch reflector from the Royal Observatory.
While observing the Nubecula Minor, he described it as a cloudy mass of light with an oval shape and a bright center. Within the area of this cloud he catalogued a concentration of clusters. In 1891, Harvard College Observatory opened an observing station at Arequipa in Peru. Between 1893 and 1906, under the direction of Solon Bailey, the 24-inch telescope at this site was used to survey photographically both the Large and Small Magellanic Clouds. Henrietta Swan Leavitt, an astronomer at the Harvard College Observatory, used the plates from Arequipa to study the variations in relative luminosity of stars in the SMC. In 1908, the results of her study were published, which showed that a type of variable star called a "cluster variable" called a Cepheid variable after the prototype star Delta Cephei, showed a definite relationship between the variability period and the star's luminosity; this important period-luminosity relation allowed the distance to any other cepheid variable to be estimated in terms of the distance to the SMC.
Hence, once the distance to the SMC was known with greater accuracy, Cepheid variables could be used as a standard candle for measuring the distances to other galaxies. Using this period-luminosity relation, in 1913 the distance to the SMC was first estimated by Ejnar Hertzsprung. First he measured thirteen nearby cepheid variables to find the absolute magnitude of a variable with a period of one day. By comparing this to the periodicity of the variables as measured by Leavitt, he was able to estimate a distance of 10,000 parsecs between the Sun and the SMC; this proved to be a gross underestimate of the true distance, but it did demonstrate the potential usefulness of this technique. Announced in 2006, measurements with the Hubble Space Telescope suggest the Large and Small Magellanic Clouds may be moving too fast to be orbiting the Milky Way. There is a bridge of gas connecting the Small Magellanic Cloud with the Large Magellanic Cloud, evidence of tidal interaction between the galaxies; the Magellanic Clouds have a common envelope of neutral hydrogen indicating they have been gravitationally bound for a long time.
This bridge of gas is a star-forming site. In 2017, using Dark Energy Survey plus MagLiteS data, a stellar over-density associated with the Small Magellanic Cloud was discovered, the result of interactions between SMC and LMC; the Small Magellanic Cloud contains a active population of X-ray binaries. Recent star formation has led to a large population of massive stars and high-mass X-ray binaries which are the relics of the short-lived upper end of the initial mass function; the young stellar population and the majority of the known X-ray binaries are concentrated in the SMC's Bar. HMXB pulsars are rotating neutron stars in binary systems with Be-type or supergiant stellar companions. Most HMXBs are of the Be type which account for 70% in the Milky Way and 98% in the SMC; the Be-star equatorial disk provides a reservoir of matter that can be accreted onto the neutron star during periastron passage or during large-scale disk ejection episodes. This scenario leads to strings of X-ray outbursts with typical X-ray luminosities Lx = 1036–1037 erg/s, spaced at the orbital period, plus infrequent giant outbursts of greater duration and luminosity.
Monitoring surveys of the SMC performed with NASA's Rossi X-ray Timing Explorer see X-ray pulsars in outburst at more