Beta Mon BETA MON (Beta Monocerotis). Dim constellations commonly hold remarkable sights. The luminary of Monoceros , the Unicorn, a modern constellation, is among them. None of the stars within the constellation carry proper names; the brighter ones are called out only by their Greek letters. While "Alpha" usually denotes the brightest star of a constellation, in the Unicorn -- as in neighboring Orion -- the brightest is fourth magnitude (3.92) Beta, which just barely nudges out Alpha Monocerotis (magnitude 3.93). Beta offers a bit of a subterfuge, however, as the telescope shows it to be a glorious triple star. If we take Beta's stars singly, then Alpha quite wins the brightness prize. At a distance of 690 light years, the three are lettered from west to east A, B, and C. B and C make a double 2.8 seconds of arc apart, while A stands off from them by 7.4 seconds of arc. B and C mostly likely orbit each other, while A orbits the pair. And most likely the distances are foreshortened, so A is really farther away in the background or foreground.

The wonder of the trio is that they are close to identical. B and C span the border of sixth magnitude (5.4 and 5.6), while A tops them a bit at bright fifth (4.6). All are hot, blue-white B (class B3) stars with temperatures near 18,500 Kelvin. Star A, the most luminous, shines with 3200 solar luminosities, while B and C come in at 1600 and 1300 Sun s. The masses of the three (in order A, B, C) are 7, 6.2, and 6 solar. All are hydrogen-fusing dwarfs. Born only 34 million years ago, A (the most massive) is a bit farther along in its evolution, and has another 9 million years left before it gives up core-hydrogen- fusion and starts to become a giant.

Given the minimum distances of 590 Astronomical Units that separate B and C, and 1570 that separate A from B-C, the B-C pair takes at least 4200 years to orbit each other, while A takes at least 14,000 to circuit the closer pair. Viewed from A, the B-C pair could be up to 20 degrees apart. The identity of the three continues with their rotations. A, B, and C rotate with respective minimum equatorial speeds of 346, 123, and 331 kilometers per second (compared with the Sun's 2 km/s). As a result, all three are "B-emission" stars that are outfitted with circulating circumstellar disks. A 12th magnitude star lurks within the system, though it is most likely a line-of- sight interloper. Star Facts: The Basics of Star Names and Stellar Evolution Star Facts: The Basics of Star Names and Stellar Evolution By Charles Q.

Choi, Space.com Contributor | December 16, 2014 09:41pm ET MORE Credit: University of Leicester Stars are giant, luminous spheres of plasma. There are billions of them — including our own sun — in the Milky Way Galaxy. And there are billions of galaxies in the universe. So far, we have learned that hundreds also have planets orbiting them. History of observations Since the dawn of recorded civilization, stars played a key role in religion and proved vital to navigation. Astronomy , the study of the heavens, may be the most ancient of the sciences. The invention of the telescope and the discovery of the laws of motion and gravity in the 17th century prompted the realization that stars were just like the sun, all obeying the same laws of physics. In the 19th century, photography and spectroscopy — the study of the wavelengths of light that objects emit — made it possible to investigate the compositions and motions of stars from afar, leading to the development of astrophysics. In 1937, the first radio telescope was built, enabling astronomers to detect otherwise invisible radiation from stars.

In 1990, the first space-based optical telescope, the Hubble Space Telescope , was launched, providing the deepest, most detailed visible-light view of the universe. Star naming Ancient cultures saw patterns in the heavens that resembled people, animals or common objects — constellations that came to represent figures from myth, such as Orion the Hunter, a hero in Greek mythology. Astronomers now often use constellations in the naming of stars. The International Astronomical Union, the world authority for assigning names to celestial objects, officially recognizes 88 constellations . Usually, the brightest star in a constellation has "alpha," the first letter of the Greek alphabet, as part of its scientific name. The second brightest star in a constellation is typically designated "beta," the third brightest "gamma," and so on until all the Greek letters are used, after which numerical designations follow. A number of stars have possessed names since antiquity — Betelgeuse , for instance, means "the hand (or the armpit) of the giant" in Arabic. It is the brightest star in Orion, and its scientific name is Alpha Orionis. Also, different astronomers over the years have compiled star catalogs that use unique numbering systems.

The Henry Draper Catalog, named after a pioneer in astrophotography, provides spectral classification and rough positions for 272,150 stars and has been widely used of by the astronomical community for over half a century. The catalog designates Betelgeuse as HD 39801. Since there are so many stars in the universe, the IAU uses a different system for newfound stars. Most consist of an abbreviation that stands for either the type of star or a catalog that lists information about the star, followed by a group of symbols. For instance, PSR J1302-6350 is a pulsar, thus the PSR. The J reveals that a coordinate system known as J2000 is being used, while the 1302 and 6350 are coordinates similar to the latitude and longitude codes used on Earth. A young, glittering collection of stars looks like an aerial burst. The cluster is surrounded by clouds of interstellar gas and dust—the raw material for new star formation.

The nebula, located 20,000 light-years away in the constellation Carina, contains a central cluster of huge, hot stars, called NGC 3603. Credit: NASA, ESA, R., F. Paresce, E. Young, the WFC3 Science Oversight Committee, and the Hubble Heritage Team Star formation A star develops from a giant, slowly rotating cloud that is made up entirely or almost entirely of hydrogen and helium. Due to its own gravitational pull, the cloud behind to collapse inward, and as it shrinks, it spins more and more quickly, with the outer parts becoming a disk while the innermost parts become a roughly spherical clump. According to NASA, this collapsing material grows hotter and denser, forming a ball-shaped protostar . When the heat and pressure in the protostar reaches about 1.8 million degrees Fahrenheit (1 million degrees Celsius), atomic nuclei that normally repel each other start fusing together, and the star ignites.

Nuclear fusion converts a small amount of the mass of these atoms into extraordinary amounts of energy — for instance, 1 gram of mass converted entirely to energy would be equal to an explosion of roughly 22,000 tons of TNT. Evolution of stars The life cycles of stars follow patterns based mostly on their initial mass. These include intermediate-mass stars such as the sun, with half to eight times the mass of the sun, high-mass stars that are more than eight solar masses, and low-mass stars a tenth to half a solar mass in size. The greater a star's mass, the shorter its lifespan generally is. Objects smaller than a tenth of a solar mass do not have enough gravitational pull to ignite nuclear fusion — some might become failed stars known as brown dwarfs . An intermediate-mass star begins with a cloud that takes about 100,000 years to collapse into a protostar with a surface temperature of about 6,750 F (3,725 C). After hydrogen fusion starts, the result is a T-Tauri star , a variable star that fluctuates in brightness.

This star continues to collapse for roughly 10 million years until its expansion due to energy generated by nuclear fusion is balanced by its contraction from gravity, after which point it becomes a main-sequence star that gets all its energy from hydrogen fusion in its core. The greater the mass of such a star, the more quickly it will use its hydrogen fuel and the shorter it stays on the main sequence. After all the hydrogen in the core is fused into helium, the star changes rapidly — without nuclear radiation to resist it, gravity immediately crushes matter down into the star's core, quickly heating the star. This causes the star's outer layers to expand enormously and to cool and glow red as they do so, rendering the star a red giant . Helium starts fusing together in the core, and once the helium is gone, the core contracts and becomes hotter, once more expanding the star but making it bluer and brighter than before, blowing away its outermost layers. After the expanding shells of gas fade, the remaining core is left, a white dwarf that consists mostly of carbon and oxygen with an initial temperature of roughly 180,000 degrees F (100,000 degrees C).

Since white dwarves have no fuel left for fusion, they grow cooler and cooler over billions of years to become black dwarves too faint to detect. (Our sun should leave the main sequence in about 5 billion years.) A high-mass star forms and dies quickly. These stars form from protostars in just 10,000 to 100,000 years. While on the main sequence, they are hot and blue, some 1,000 to 1 million times as luminous as the sun and are roughly 10 times wider. When they leave the main sequence, they become a bright red supergiant, and eventually become hot enough to fuse carbon into heavier elements. After some 10,000 years of such fusion, the result is an iron core roughly 3,800 miles wide (6,000 km), and since any more fusion would consume energy instead of liberating it, the star is doomed, as its nuclear radiation can no longer resist the force of gravity. When a star reaches a mass of more than 1.4 solar masses, electron pressure cannot support the core against further collapse, according to NASA. The result is a supernova.

Gravity causes the core to collapse, making the core temperature rise to nearly 18 billion degrees F (10 billion degrees C), breaking the iron down into neutrons and neutrinos. In about one second, the core shrinks to about six miles (10 km) wide and rebounds just like a rubber ball that has been squeezed, sending a shock wave through the star that causes fusion to occur in the outlying layers. The star then explodes in a so-called Type II supernova. If the remaining stellar core was less than roughly three solar masses large, it becomes a neutron star made up nearly entirely of neutrons, and rotating neutron stars that beam out detectable radio pulses are known as pulsars. If the stellar core was larger than about three solar masses, no known force can support it against its own gravitational pull, and it collapses to form a black hole . A low-mass star uses hydrogen fuel so sluggishly that they can shine as main-sequence stars for 100 billion to 1 trillion years — since the universe is only about 13.7 billion years old , according to NASA, this means no low-mass star has ever died.

Still, astronomers calculate these stars, known as red dwarfs , will never fuse anything but hydrogen, which means they will never become red giants. Instead, they should eventually just cool to become white dwarfs and then black dwarves. Constellations ancient and modern grace the skies year round. Let's see what you know about the star patterns that appear overhead every night. SkyEye - The Greek Alphabet and Other Symbols SkyEye The Greek Alphabet and Other Symbols The Greek Alphabet Johann Bayer was a celestial cartographer compiled a star catalogue using what are now known as Bayer designations. A star's Bayer designation is a lower case Greek letter, followed by the genetive form of its parent constellation's Latin name. Under this system, the brightest star in a constellations is usually assigned the Greek letter alpha α, the next brightest star beta β and so on, but there are a number of exceptions to this rule. If there are more than 24 stars in the constellation needing a designation, lower case Latin letters (a, b, c, …, z) are used in place of lower case Greek letters. In constellations with very large number of stars, upper case Latin letters (A, B, C, …, Q) are also used.

(Bayer did not use upper case letters beyond the letter Q.) Since Greek letters are not always familiar to non-scientists, a list of the alphabet is given below. Lower Case Star Names STAR NAMES Proper Names The naked-eye stars carry a huge number of names that range from the intimately familiar to the hopelessly obscure, each one having a different reason for being. Vega , the fourth brightest star in the sky, has over 40 different names! Star names are either of ancient origin, of more recent historical origin, or are assigned by astronomical organizations under the umbrella of the International Astronomical Union (the organization of professional research astronomers). No private organizations have the rights to name stars. The best-known and most-familiar names are "popular names," real names like those used for people. The oldest of all names, proper names are a mixed lot that descend from a variety of ancient (and even modern) languages that relate to the positions or the characters of the stars. Among the oldest are those from ancient Greek. Sirius , for example, means "searing" or "scorching," appropriate for the brightest star in the sky.

Procyon comes from the Greek "pro kion," before the dog," as from the northern hemisphere it rises before the "Dog Star," Sirius; Castor honors one of the ancient Greek warrior twins; Arcturus means "bear driver," as this brilliant star follows the Greater Bear around the pole. A smaller number ( Regulus , the "little king" in Leo), Polaris , the "pole star" in Ursa Minor ) come from Latin. By far the greatest number, however, hundreds of proper names, descend to us from the Arabic of the middle ages, when the astronomers of the Arabia adopted the Greek constellations from Ptolemy and applied their own names to the stars, most in some way appropriate to the locations of the stars within their parent constellations. "Deneb," for example, means "tail." The name appears in many forms, such as Deneb in Cygnus (the tail of the Swan), Denebola in Leo (the Lion's tail), and Deneb Kaitos in Cetus (the sea-monster's tail). Others were derived from the constellations that the Arabs had made for themselves.

When the Arabic texts were translated back into Latin, these star names were passed down to us, but often in a highly corrupted form that either changed the meaning, or in extreme cases left us with no meaning at all. Other names were mistakenly transferred from one star to another, so that a name might even refer to a different constellation (Greek or Arabic) rather than to the one of the star's actual residence. Greek Letter Names To bring order out the chaos of proper names, around the year 1600 Johannes Bayer, in what is now Germany, applied lower case Greek letter names to the stars more or less in order of brightness, which if followed strictly would render the brightest star in a constellation "Alpha," the second Beta," and so on. To the Greek letter name is appended the Latin possessive form of the constellation name. Thus the brightest star in Lyra, Vega (an Arabic proper name), becomes Alpha of Lyra or Alpha Lyrae (where "Lyrae" means "of Lyra.") The brightness rule is commonly violated, however, as Bayer also clearly factored in the position of the star within the constellation, as in Ursa Major , where the stars of the Big Dipper are lettered west to east.

As another good example, though Adhara in Canis Major (the Greater Dog) is first magnitude and the second brightest star in the constellation, it received "Epsilon," probably because of its lower (more southerly) position within the starry figure. With only 24 letters in the Greek alphabet, few stars could receive Greek letter names. Bayer therefore followed the lower-case Greek alphabet with upper case A and then lower-case Roman letters. These are rarely used nowadays, however, and only a few vestiges like " h Persei " (a star cluster in Perseus ) survive. Though the number of names is increased by applying numerical superscripts to stars that fall near one another (a string of stars in Orion becoming Pi-1, Pi-2, Pi-3 Orionis , and so on, expressed as superscripts), the system was still limited to the brighter stars, faint naked-eye stars rarely qualifying. Others applied Greek and Roman letters to the later modern constellations. The eighteenth century's Nicholas-Louis de Lacaille was particularly notable for his work in the part of the southern hemisphere that Bayer could not see.

Flamsteed Numbers To organize more of the naked eye stars, in the eighteenth century John Flamsteed (who created one of the great star catalogues of the time) listed the stars by position ( right ascension , the sky's analogue to terrestrial longitude) within the constellation boundaries. Serial numbers applied by Edmund Halley then gave the star's relative location from west to east within the constellation. For example, 1 Lyrae would be the western-most numbered star in Lyra, 2 Lyrae the next, and so on (Vega is 3 Lyrae). In general, first magnitude (and a few special) stars are commonly known by their proper names. Greek-letter names are then used until they run out, and then the Flamsteed numbers. From England, Flamsteed could see only so far into the southern hemisphere, so deep southern constellations have no numbers. The handful of exceptions (30 Doradus in the Large Magellanic Cloud , the globular cluster 47 Tucanae ) are vestiges of other systems that did not survive.

Catalogue Names To include yet more stars, constellations are dropped and the stars are named according to position, generally right ascension, or angle to the east of the Vernal Equinox . (The Vernal Equinox is the point in Pisces where the ecliptic, the path of the Sun, crosses the celestial equator going north and where we find the Sun on the first day of northern spring.) Catalogues fall into two broad categories: general and special interest. The most basic of the general variety is the "Bright Star Catalogue," which serially numbers 9000 naked-eye stars through sixth magnitude from west to east beginning at right ascension zero hours (zero degrees) for the year 1900. ( Precession , the 26,000-year wobble in the Earth's axis, changes the right ascensions with time, usually increasing them.) Though now published at Yale, it derives from a catalogue produced at Harvard, so the star names take on the name "HR" for "Harvard Revised." Vega = Alpha Lyrae = 3 Lyrae = HR 7001. Stars below naked-eye visibility need catalogue names too.

The most famed general catalogue for fainter stars, the "Bonner Durchmusterung" (the Bonn Survey), was compiled in Germany in the nineteenth century and lists stars through around tenth magnitude (some 50 times fainter than the eye can see alone). It divides the sky into declination strips one degree wide and then serially numbers the stars from west to east according to the stars' right ascensions (for the year 1855). (Declination is the sky's analogue to terrestrial latitude; it gives the angular separation of a star from the celestial equator.) The catalogue name incorporates the declination. Vega, for example, is also "BD+38° 3238," which means the 3238th star in the declination strip between 38 and 39 degrees north. The BD covers stars to -2 degrees declination (2 degrees south of the celestial equator). The rest of the southern hemisphere is covered by the "Cordoba Durchmusterung" (the Cordoba, Argentina, Survey), or CD.

Canopus (HR 2326) is CD- 52°914, or the 914th listed star between declination 52 and 53 degrees south. BD and CD are sometimes combined as "DM" for "Durchmusterung." Precession has now moved many stars out of their original declination strips. The most commonly used catalogue for fainter (as well as brighter) stars is the Henry Draper (HD) Memorial Catalogue, which serially numbers stars through roughly tenth magnitude to the east of the vernal equinox (according to right ascension in the year 1900) independently of declination. The HD catalogue, while a general tool for star names, is also a specialty catalogue, and was created to list the spectral classes of over 300,000 stars. Vega is HD 172167, Canopus HD 45348. In the 1960s over ten positional catalogues were combined into the Smithsonian Astrophysical Observatory (SAO) star catalogue.

It serially numbers over 250,000 stars (according to right ascensions for the year 1900) to ninth magnitude in 10 degree declination strips from north to south, each strip picking up where the last one left off. Vega is SAO 067174, Canopus SAO 234480. Though it enjoyed some popularity, it is no longer commonly in much use. The specialty Hipparcos Catalogue is also of general use. The Hipparcos satellite was flown in the 1990s to measure precise distances (through accurate parallaxes) to nearby stars. Over 100,000 stars are listed. Vega is HIC 91262, Canopus HIC 30438. Beyond these and many other catalogues, fainter stars are named only by coordinates (right ascension and declination) for a specific year. The Hubble Space Telescope Guide Star Catalogue, for example, lists 19 million stars between 6th and 16th magnitude.

Double and Multiple Stars A huge number of stars are double or multiple, the individuals locked in orbit around each other. The components of very wide doubles that have Greek letter names are often distinguished by applying superscripts to the Greek letters from east to west (as noted in the earlier section on Greek letter names). Zubenelgenubi , Alpha Librae, is a wide double; the western of the two is Alpha-1, the eastern Alpha-2, even though Alpha-2 is much the brighter. Most of these are not physical doubles but line of sight coincidences. When the stars are close to each other, a system of Roman letters generally applied in order of discovery or of descending brightness (often the same thing) is used. The principal component is "A," the next brightest "B," and so on. Brilliant Sirius is accompanied by a faint white dwarf . The naked-eye star is Sirius A, the dim companion Sirius B. Close companions, particularly planets, are often given lower case letters. If a planet were to be discovered orbiting Sirius A (there is none so far as we know), it would be Sirius Ab, rendering Sirius itself Sirius Aa. Variable Stars A great many stars are variable in brightness.

The first found, among them Mira and Algol , were bright and had proper or Greek letter names. But as more were discovered, astronomers needed a systematic naming system. Since the last Roman letter in any constellation was "Q," they adopted "R" for the first variable found that did not already have a name, to which was appended the Latin possessive of the constellation name. The first such variable known in Cygnus is thus R Cygni, the first in Aquila R Aquilae. The sequence continued with new discoveries to Z. Finding more, astronomers went back up the alphabet to use double letters, beginning with RR, then going to RS, RT...RZ, then to SS, ST...SZ, TT, TU...and finally down to ZZ. To accommodate increasing numbers, the system then went to the top of the alphabet, to AA, AB...AZ, BB, BC...BZ, CC...and so on to QQ...QZ, with J left out to avoid confusion. After 334 letter combinations, astronomers just gave up and used "V" followed by a number, V335 Sagittarii following QZ Sagittarii.

Through the names, the astronomers of the past 3000 years have brought order to the seeming chaos of the sky. All the stars you can see even through a relatively large telescope have names. We know them and know where they are. Copyright © James B. Kaler. All rights reserved. These contents are the property of the author and may not be reproduced in whole or in part without the author's express consent except in fair use for educational purposes. This page was last modified on 14 February, 2014. Thanks to reader number . Sky Publishing - Names of the Stars NAMES OF THE STARS Adapted from Sky & Telescope IF A ROSE by any other name would smell as sweet, would BD +38°3238 by any other name sing more sweetly to lovers down from the summer sky? Everyone who starts out in astronomy faces a bewildering variety of numbers and letters denoting the great works of creation. Sometimes the nomenclature almost seems designed to confuse.

Anyone can look up and recognize a star as Vega -- so why does it also need the names BD +38°3238, Alpha Lyrae, 3 Lyrae, HR 7001, GC 25466, HD 172167, SAO 67174, ADS 11510, and dozens of others? At least beginners aren't alone in their confusion. The First Dictionary of the Nomenclature of Celestial Objects, 1983, describes well over 1,000 different naming systems currently in use, mostly for faint objects studied by professionals. Its editors despair of the list ever being made orderly, reasonable, or complete. Celestial nomenclature is too freakish for that, too full of schemes from times long past that just grew. A well-rounded amateur needs to know only a tiny fraction of these naming systems. In this article we'll cover those most often encountered for stars, with their meanings and histories. Another article covers nomenclature of deep-sky objects. Where the Heck Is Zujj Al Nushshabah?

Since ancient times stars, like people, have had their own proper names, such as Vega or Deneb. But today proper names are widely used only for the brightest few dozen stars -- and it's a good thing. Star names are poetic and embody old constellation lore (usually in garbled Arabic), but confusion runs wild. "Deneb" to most people interested in astronomy means the brightest star in Cygnus. But the same name has also been bestowed, at some time, on at least five other stars. It simply means "tail," a body part that a lot of constellations possess. Which one do you really mean? Moreover, the list quickly becomes too big. The Yale Bright Star Catalogue, 4th edition, 1982, gives some 845 star names, more than most people would ever want to memorize. Every astronomer knows what you mean by Sirius or Polaris, but not one in a hundred could identify Pishpai (Mu Geminorum), Alsciaukat (31 Lyncis), Dhur (Delta Leonis), or Zujj al Nushshabah (Gamma Sagittarii).

More tractable is the Greek-letter system introduced by the German astronomer Johann Bayer in 1603. In his beautiful star atlas Uranometria published that year, Bayer identified many stars in each constellation with lower-case Greek letters. He often named a constellation's brightest star Alpha, then sorted the rest into brightness classes and assigned letters within each class in order from the head to the feet of the traditional constellation figure. Bayer's letters caught on immediately. They are used with the Latin genitive of the constellation name, so the leading star in Centaurus is Alpha Centauri. This simply means "Alpha of Centaurus." Back when most educated people knew Latin and Greek this phrasing flowed off the tongue naturally, but today it's many skywatchers' first exposure to the Greek alphabet and Latin declensions. Sooner or later everyone who deals with stars has to sit down and learn the Greek letters and the genitives of the 88 constellation names (listed in the back of most astronomy handbooks). There are swarms of stars per constellation but only 24 Greek letters.

Sometimes one letter is used repeatedly with superscripts to cover several adjacent stars, such as Pi¹ through Pi 6 Orionis, the ragged row forming Orion's Shield. But as more and more stars needed names because of better sky surveys, astronomers adopted numbers. Around 1712 England's Astronomer Royal, John Flamsteed, began numbering stars in each constellation from west to east in order of right ascension -- a big help when looking for a star on a map. For instance, 80 Virginis is east of 79 Virginis and west of 81 Virginis (at least in the coordinate system Flamsteed used, equinox 1725, which still matches today's celestial east and west pretty well). All bright stars were numbered whether they had a Greek letter or not, which is why Alpha Lyrae is also 3 Lyrae. In all, 2,682 stars received Flamsteed numbers. The highest number within any constellation is 140 Tauri. All nice and logical -- but when it comes to celestial nomenclature, there's a fly in every ointment.

When the constellation borders were formalized in 1930, many Flamsteed stars found themselves stranded in exile. Thus 30 Monocerotis is today considered to be in Hydra, and 49 Serpentis is in Hercules. Such names are best discreetly swept under the rug, never to be used. Nobody got around to numbering stars farther south than could be seen from England. So in far-southern constellations one often encounters upper- and lower-case Roman letters, such as g Carinae and L² Puppis. These were applied all over the sky by various star mappers from Bayer on, but in the northern sky they have largely passed out of use. Herculean Lists By the 19th century all these naming efforts were falling far short of the mushrooming need. Telescopes were revealing stars by the hundreds of thousands, every one of them an individual crying out for its own identity. In 1859 the German astronomer F. W. A. Argelander at Bonn Observatory began measuring star positions with a 3-inch refractor to compile a gigantic list, the Bonner Durchmusterung (Bonn Survey).

The BD eventually included 324,188 stars to about magnitude 9.5. Argelander and his successors divided the sky into thin bands 1° of declination wide wrapping around 24 hours of right ascension. Stars within each band were numbered in order of right ascension; constellations were ignored. Thus Vega's designation BD +38°3238 means it was the 3,238th star counting from 0 h right ascension in the zone between declination +38° and +39°. The original BD covered just over half the sky, from the north pole to declination -2°. A later southward extension, the SBD, continued the system down to declination -23° to garner another 133,659 stars. The Cordoba Durchmusterung (CD or CoD) completed the job to the south celestial pole with 613,953 more, so that visual durchmusterung, or "DM," names were bestowed on a grand total of 1,071,800 stars.

The BD, with its detailed star charts to 9th or 10th magnitude and its reliable, well-checked list of positions, remained an essential everyday tool of working astronomers for nearly a century. Durchmusterung designations are still often encountered. The star magnitudes in these catalogs, however, are notoriously unreliable by modern standards. Most were merely quick eyeball estimates. Variable stars have a naming system all their own. This too was instigated by the energetic Argelander. He denoted the first variable star found in a constellation by the capital letter R with the genitive of the constellation name, since the previous letter, Q, was the highest Bayer had gone in Roman star lettering. The next variable would be named S, and so on to Z. After Z came RR, RS, and so on to RZ, then SS to SZ, on up to ZZ. If a variable already had a Greek letter, Argelander left it alone. But new variable stars kept getting discovered! After ZZ, astronomers decided to go to AA, AB, and on to AZ (omitting J since in some languages it could be confused with I), then BB to BZ, on up to QZ.

Even these 334 designations proved insufficient for the variables in some crowded constellations. Rather than start an even more awkward three-letter system, astronomers ruled that further variables in a constellation would simply be designated V335, V336, and so on forever. It was a wise move. By 1990 the highest numbered variable was V4153 Sagittarii. Multiplying Catalogs The next great, widely used star list to appear after the BD was the Henry Draper Catalogue of stellar spectra, compiled by Annie J. Cannon at Harvard from 1911 to 1915 and published from 1918 to 1924. It includes 225,300 stars numbered in simple order of right ascension. More were added later in the Henry Draper Extension; these bear HDE numbers. Any star with an HD or HDE designation is guaranteed to have had its spectrum measured. Meanwhile another catalog had been issued at Harvard: the Revised Harvard Photometry of 1908, which sought to provide accurate magnitudes for the brightest 9,110 stars to about magnitude 6.5.

Stars in this catalog bear HR numbers. Even now the HR list remains the basis of the modern Yale Bright Star Catalogue, widely used for its detailed information about naked-eye stars. Perhaps the most common star-numbering system today is the SAO designation. It refers to the Smithsonian Astrophysical Observatory Star Catalog (1966), which also was produced (with companion star charts) on Harvard's campus. This catalog gives very accurate positions for 258,997 stars to about 9th magnitude, though coverage is spotty for the fainter ones. The SAO stars are numbered by right ascension within 10° bands of declination from the north to the south pole. SAO numbers have almost completely supplanted the once widely used GC designations, taken from the General Catalogue of 33,342 Stars by Benjamin Boss (1937). The latest and greatest star list is the Hubble Space Telescope Guide Star Catalog. It is too big ever to print; instead it's distributed on two CD-ROMs.

The GSC lists positions generally good to nearly 1 arcsecond and magnitudes accurate to a few tenths for 18,819,291 objects from 9th to usually about 13th or 14th magnitude, sometimes as faint as 15th. Of this total, 15,169,873 are listed as being stars; most of the remaining 3.6 million objects are small, faint galaxies. Most have never been examined by human eyes; they were measured automatically from photographic plates. A typical individual in this list is GSC 1234 1132, a 13.3-magnitude luminary in Taurus. The first four digits specify one of 9,537 small regions of the sky; the last four give the object's serial number within this region. Many more lists have been compiled for special purposes. A star with an ADS number is in the Aitken double star catalog (1932); IDS refers to the Index Catalogue of Visual Double Stars (Lick Observatory, 1963).

These comprehensive lists are more rational than the 150-odd types of older double-star designations you are likely to encounter, generally named for astronomers who published lists, however short, of their own discoveries. Nevertheless the older names are so much a part of double-star usage that there will be no getting rid of them. Lunar occultation observers often refer to stars by ZC number, referring to the Zodiacal Catalogue of stars that the Moon can cover. And so on, and so on. P.S.: Name-It-Yourself Stars Are a Hoax! Often Sky & Telescope gets inquiries about companies that advertise on the radio or on the Web that they will name a star for you or a loved one for about $50. You get a pretty certificate and some papers. Is this for real, we are asked? No. The certificate is a "novelty item" only. With just as much validity, you can step outside on a clear night, choose any star you like, and name it for anyone you want. For free. We know a number of amateur astronomers who have done this for their spouses or children.

To one of the Sky & Telescope editors, Iota Ursae Majoris is "Lucy's Star" and Zeta Hydrae is "Andrew's Star." Why not? Why pay some commercial outfit to mediate your personal life? Even a fancy certificate, if it appeals to you, can be made with shareware for a lot less than $50. One star-naming company advertises that it keeps the names in a Swiss bank vault, as if that means something. If that appeals to you, you can put a piece of paper with a star name in your own bank's safe-deposit box. But why bother? Sometimes planetariums "sell" stars on their domes to help raise needed funds. They are careful to tell donors that the certificate they get denotes a contribution to a worthy institution, not the purchase of a real star name. If you insist on paying someone else to pretend to name a star, this is a more worthwhile way to do it. Alan MacRobert is an associate editor of Sky & Telescope magazine and an avid backyard astronomer. Stars and Constellations Stars and Constellations There are some 6,000 stars visible to the naked eye.

Most of these stars can only be seen from locations far from the bright lights of a city or town. If you really want to see the stars, you either have to go to Hollywood or get out of Dodge. Star Names Some of the brighter stars have proper names, but most don’t – there are just too many to give each one a name. Instead, astronomers have devised a system that assigns names to naked-eye stars based on their brightness and the name of the constellation they belong to. Following a centuries-long tradition, the brightest star in a constellation is designated by the first letter of the Greek alphabet, Alpha, followed by the genitive form of the Latin name of its constellation. For example, the brightest star in the constellation Orion is called Alpha Orionis. It also has a proper name: Rigel. (We’ll talk more about constellations later. Right now we’re going to focus on individual stars.) When the letters run out, stars are identified by various alphanumeric designations. A funny thing about Rigel: even though it’s the brightest star in Orion, its designation is Beta Orionis.

Astronomers originally thought that Betelgeuse, another star in Orion, was a little bit brighter, but improvements in photometers in the 20th century revealed that Rigel is actually the brighter star (it’s possible that Betelgeuse might have been brighter in the past, when astronomers first began to designate stars with Greek letters). Bright Stars and Dim Stars Long before the invention of the telescope, astronomers also came up with a numerical system for classifying stars by their brightness. They decided that the brightest stars would be called First Magnitude. Those half as bright as First would be called Second Magnitude, then Third Magnitude, and so on down to Sixth Magnitude, which denotes the dimmest stars visible to the naked eye. We use a modified form of this system today. The brightest star in the nighttime sky is called Sirius. It’s in the constellation Canis Major, the Big Dog, and it’s sometimes called the Dog Star. Its magnitude is minus 1.4, which we write as –1.4. This may seem a little confusing, but it isn’t that hard to understand. A couple of centuries ago, astronomers decided to make the magnitude scale more precise.

They knew the Sun and Moon and some of the planets are brighter than the brightest stars, so these were given negative magnitudes. They also realized that a First Magnitude star is actually a bit more than twice as bright as a Second. In order to keep Sixth Magnitude as the faintest star visible to the naked eye, astronomers recalibrated the magnitude system to follow a logarithmic scale . Each stellar magnitude is about 2.5 times brighter than the next lower magnitude so that the difference of five magnitudes is a brightness factor of (exactly) 100. With a telescope, you can see stars much dimmer than Sixth Magnitude. TheSkyX database includes stars down to about 14th Magnitude. On a clear, moonless night, people who live in cities or suburbs can rarely see stars dimmer than Third Magnitude. If you’re just starting to learn the names of the brighter stars and constellations, you should set the magnitude filter in TheSkyX to Second or Third magnitude.

That way, when you go out at night to compare what you see on your computer to what you can see in the real sky, you won’t be confused by a screen display that shows more stars than you can actually see from your location. Setting the Magnitude Limit This command tells TheSkyX to only display stars, galaxies, clusters, or any other object type, or combination of object types, that has magnitude information, that are brighter or fainter than a selected magnitude. Controls for editing the magnitude limits are found on the Chart Elements window on the Display menu. The following example demonstrates how to change the magnitude limits for all celestial objects. 1. Make sure the Chart Elements window is visible. If it’s not, select the Chart Elements command from the Display menu to show it. 2. Highlight the Celestial Objects text by clicking on it. This selects the 40 chart elements in the Chart Elements node. 3. Click the Edit Attributes button. 4. Near the bottom of the Chart Elements window you’ll see a tab labeled Magnitude Limits. You can enter a value between 30.0 and –6.0, or change the magnitude using the sliders. Figure 71: Magnitude Limits tab on the Chart Elements window.

The attributes of chart elements (including lower and upper magnitude, angular size, font properties and colors) can be changed individually or as a group based on the items that are selected in the Chart Elements list. Number of Selected Chart Elements (Selected) This text shows the name of the selected chart element or the number of selected chart elements in the Chart Element list. Show Only Brighter Stars (Hide fainter than) Specify the magnitude of the faintest objects to be displayed on the Sky Chart. For example, if you live in a light polluted city and want to approximate the stars you can see on typical night’s sky, enter magnitude 1 or 2. Show Only Fainter Stars (Hide brighter than) The Hide Brighter Than controls provide additional filtering, displaying objects only within a specified brightness range. Larger magnitude values represent dimmer objects. The brightest objects have negative magnitudes. As you move the slider the number of stars on the Sky Chart changes to reflect the changing magnitude limits. Like land maps, star charts can be overlaid with a variety of lines and markings intended to highlight specific celestial features and help you find objects at specific coordinates.

The Chart Elements menu lets you display or hide various reference lines and symbols, but you should be aware that even though the cosmos mostly consists of empty space, a star chart can get very crowded very quickly. The celestial equator and lines of right ascension and declination can be added to the Sky Chart, for example. Experiment with this feature by clicking on the box next to a listed chart element to see how it affects the display. A Star to Guide You For people living in the northern hemisphere, probably the most noteworthy star is Polaris, the North Star. It always stays in the same part of the sky, every night, 365 days a year. The reason for this is fairly simple: Polaris happens to be located almost directly above our North Pole. As the Earth rotates on its axis, other stars rise and set, but because Polaris is right above the pole, it always seems to stay in the same place. How high Polaris is above your horizon is a direct way to find your latitude. If Polaris is 40 degrees above the local horizon, for example, you must be somewhere on the 40th latitude line.

Philadelphia and Denver are both very close this latitude, as are Naples, Italy and Beijing, China. The stars you can see on any given date and (local) time are essentially the same for all of these cities, and any other place along this line of latitude. More than anything else, latitude determines what you can see in the sky. The North Star is not visible from the Southern Hemisphere, as are most of the stars and constellations near it. And there are all sorts of stars and constellations visible from the Southern Hemisphere that we never get to see in the North (the Moon and planets are visible from both hemispheres). TheSkyX can show you what the sky would look like from any place in either hemisphere. Double Stars A little more than half of all stars actually travel in pairs, orbiting each other in space. The American astronomer Henrietta Leavitt once quipped that three stars out of every two are double. Most of them appear as single stars to the naked eye. You need good binoculars or a small telescope to resolve them as double stars (there are also triple stars and groups consisting of four or even more stars).

Some double stars are true binaries , meaning they are gravitationally bound to each other and orbit a common point in space. Others only appear to be double because they happen to lie along the same line of sight from Earth, but are in fact many light years apart and not tied to each other by gravity. One of the best-known double stars in the sky is called Mizar. It’s located in the handle of the Big Dipper. Mizar is visible only from the Northern Hemisphere, and is easiest to find in the evening sky in Spring. Select the Find tab from the vertical tabs on the left side of TheSkyX’s window. Type Mizar into the Search For text input, then click the Find button. A double red “bull’s eye” will encircle the star in the Sky Chart. The Big Dipper is one of the northern sky’s most recognizable asterisms (this term is described below). Being able to find it will help you find other nearby constellations, such as Cassiopeia. Once you’ve mastered these constellations, others will be easier to learn. Another good thing about being able to find the Big Dipper: it will make it easy for you to find Polaris, and therefore true north.

The two stars at the end of the cup of the dipper point to Polaris. Imagine a line connecting these two stars. Extend it in the direction the cup is pouring, about five times the distance between the two stars. The star you see at the end of that line is Polaris. Variable Stars Fortunately for us, and everything else that lives on Earth, the Sun radiates energy at a very nearly constant rate. But there are some stars that change in brightness dramatically over the course of a few months, and in some cases, just a few days or even hours. These are called variable stars , and TheSkyX distinguishes them with a small red “v” to the lower left of the star. The most notorious variable star is called Algol, a name derived from an Arabic word that means demon. Located in the constellation Perseus, its rhythmic dips in magnitude can easily be observed with the naked eye. Every 2.867 days, over the course of just a few hours, Algol falls from second magnitude (2.1) to third (3.4) and back. During these periodic dimmings, you can gauge its changing brightness by comparing it to other nearby stars.

The evening sky in Autumn is the easiest time to find this fascinating object (it is only visible from the Northern Hemisphere). It may have been considered demonic in ancient times, but today we know this innocent star has a companion that orbits it every 2.867 days. Algol dims when that companion passes in front of it from our perspective. Such stars make up a special class called eclipsing binaries . Finding Your Way Around The Sky Finding Your Way Around The Sky Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay First-time Visitors: Please visit Site Map and Disclaimer . Use "Back" to return here. Brightness of Stars Astronomers describe the brightness of objects in the sky in terms of magnitude. This scale was originally devised by the Greek astronomer Hipparchus over 2,000 years ago, and the modern version is largely an extended and more accurate version of the ancient scale. Hipparchus called the 20 or so brightest stars in the sky magnitude 1, and stars just visible to the unaided eye are magnitude 6. Faint objects have large magnitude numbers, bright objects have small numbers.

Each step of one magnitude corresponds to an increase or decrease of about 2.5 times in brightness; a five-magnitude step means a 100-fold increase or decrease. Unfortunately, because Hipparchus followed the natural tendency to rank the most prominent objects as first magnitude, very bright objects can have zero or even negative magnitudes, and scales with zero and negative numbers are often very confusing to beginners. A zero magnitude star doesn't mean no brightness, it means a very bright star. We can also define fractional magnitudes. The nearest star beyond the Sun, Alpha Centauri, has a magnitude of zero. Sirius, the brightest star besides the sun, has a magnitude of -1.4. Venus at its brightest has a magnitude of -4 A crescent Moon is about magnitude -8, the full Moon about -12 The Sun is about magnitude -27 The table below shows the number of stars of each magnitude and the total number of stars of equal or greater brightness. At each step the number of stars visible roughly triples. Magnitude 8,768 The Constellations Every culture has told stories about the stars, and grouped the stars into constellations.

These differ radically from one society to the next; traditional Chinese constellations bear almost no resemblance to Western constellations. Most of the constellations now accepted in astronomy are based on traditional Western and Near Eastern star lore, with a few 17th and 18th-century additions to fill in unmapped areas (and make a name for the inventor), and map the southern skies. At one time, a few stars were parts of two constellations, and about a quarter of the stars in the sky were "unformed"; they belonged to no constellation. Now the constellations have fixed boundaries that preserve, as much as possible, the traditional constellation figures. There are 89 constellations that cover the entire sky. Every star belongs to one, and only one, constellation. The constellation names are Latin. The constellations we see from Earth are patterns of stars more or less in the same direction as we see them from Earth. Most of the objects in a constellation are at widely different distances, and not physically connected with each other.

For example, "in" the constellation Virgo, we might find the Moon (240,000 miles away), Jupiter (480 million miles), the bright star Spica (220 light years) and the Virgo Cluster of galaxies (40 million light years). If we were to travel to a distant star, none of the constellations would be recognizable any more. Names of the Stars Only a few of the brightest stars have proper names. Each culture has its own star traditions, and most of our star names were invented by the Arabs. They came into English when Arabic learning came to Europe in the Middle Ages, often with interesting misspellings. For example, the Arabs called a bright red star in Orion Yad-al-Jawza, the Shoulder of Orion, but the Arabic characters for Y and B look much alike. A medieval scholar mistook the Y for a B when transcribing the name into Roman letters, and Betelgeuse it has been to this day. A few star names originated in other ways. Regulus means "little king" in Latin. Cor Caroli, Latin for "heart of Charles" was named in honor of the deposed and executed Charles I of England.

Star Catalogs Most stars are designated in accordance with some star catalog. A common system is that of Johannes Bayer, who in 1603 used Greek letters for the stars in each constellation, usually, but not always, starting with alpha for the brightest star and proceeding roughly in order of decreasing brightness. Since Bayer estimated brightness by eye, his system is only approximate. In the case of the Big Dipper, he simply started with alpha at the northern pointer star. When he ran out of Greek letters, he used lower-case Roman letters and then capitals. In Bayer's system, Sirius, the brightest star besides the Sun, is Alpha Canis Majoris, the brightest star in the constellation Canis Major. Later on, in 1725, John Flamsteed employed a system that numbered stars in the order in which they crossed the meridian. In Flamsteed's system Sirius is 9 Canis Majoris, the ninth star in Canis Major.

Fainter stars are listed in great catalogues like the Bonn Durchmusterung (Sirius is BD -16 1591 in this catalog) or the Palomar Sky Survey and more recently, the Hipparcos Catalog (Sirius is HIP 32349). Usually each star designation has an abbreviation for the catalog and then the catalog number of the star. The overwhelming majority of very faint stars have no designation, unless they happen to be of unusual interest. At times various organizations have offered to name stars after people, in return for a fee. Some such enterprises have been run in jest, to raise money for charity; others are merely aimed at the gullible, but none have any official standing. Astronomers are under no obligation to use purchased star names. A Tour of the Sky Note: the following is written for Northern Hemisphere viewers. In order to find your way in the sky, there are two things to bear in mind: Constellations move across the sky As the constellations move, they change orientation. They also change position and orientation if you change your latitude (move north or south).

Below are illustrations showing how the Big Dipper changes its position and orientation in the early evening hours of each season. Distances on the sky are measured in terms of angles. Lines from opposite sides of the Moon to your eye intersect at an angle of about 1/2 degree, so we say the Moon spans, or subtends, an angle of about 1/2 degree. Your fist at arm's length spans about 10 degrees. The heavens appear to rotate around two points called the celestial poles. The elevation of the pole above your horizon is equal to your latitude. Stars close to the north celestial pole circle the pole without ever hitting the horizon. Such stars are called circumpolar. Around the South Celestial Pole is a similar zone of stars that never rise. In between, is a band of stars that rise and set. Since the celestial pole is at an elevation equal to your latitude, at the North Pole the elevation of the celestial pole is 90 degrees - straight overhead. All the stars circle the pole endlessly and never rise or set. All the stars are circumpolar, and the opposite half of the sky can never be seen. At the equator, the poles are at an elevation of zero degrees.

All stars rise and set. The equator is the only latitude where all stars in the sky are visible at some time or another. On the star maps below, major constellations are joined by red lines, and less conspicuous constellations are in gray. Not all constellations are shown. Constellations are in bold type, individual stars and asterisms, or informally named groups of stars, are in italics. Above are the north circumpolar constellations. Best known is Ursa Major, the Big Dipper. The two stars at the end of the bowl are about 5 degrees apart and a line through them points to Polaris, the North Star. It is purely coincidence that we live at a time when there is a bright star close to the North Celestial Pole. There is no South Star. Apart from Polaris and one star in the bowl, Ursa Minor (the Little Dipper) is inconspicuous. The stars in the bowl include one from each magnitude, second through fifth, so it's a good guide to estimating star brightness. The star at the bend of the Big Dipper's handle, Mizar, has a faint companion called Alcor that is a good test of your eyesight.

A line from Mizar through Polaris and continued beyond takes you to Cassiopeia, easily recognized by its W shape. Two fainter constellations are Cepheus, shaped like a house, and Draco, which winds between the Dippers. In the movie Dragonheart, the dragon hero Draco sacrifices his life and takes his place among the stars, and the neat thing is that the scene actually shows the constellation accurately. The Springtime Sky In the late spring, you can use the Big Dipper as a guide to other constellations. Follow the arc of the Big Dipper's handle to the bright orange star Arcturus, then continue the arc to the bright star Spica. If you extend a line south from the Pointer stars, they take you to the constellation Leo, dominated by the bright star Regulus. A diagonal through the bowl will point to the winter constellation Gemini. South of Leo is the constellation Hydra, not very conspicuous except for one moderately bright star, but notable as the largest constellation in the sky. Later in the spring and early summer, to the east of Arcturus, you can see the pretty little circle of Corona Borealis, the Northern Crown.

To its east is Hercules, whose most obvious feature is the Keystone of four moderately bright stars. North of Hercules is a small trapezoid, the head of Draco, the only conspicuous part of the constellation. When the stars are first becoming visible, Arcturus and three other stars in Bootes and Corona Borealis form a conspicuous Y shape, shown in green. The Summer Sky The spectacular summer sky has few really bright stars but picturesque constellations galore and a glorious view of the Milky Way. The Summer Triangle consists of Deneb and Vega, almost circumpolar for the northern U.S., and Altair. Light from Altair left 16 years ago. Light from Vega left 27 years ago. Light from Deneb left before the Roman Empire fell. Deneb is the brightest star of Cygnus, the Swan, and forms its tail (Deneb means "tail" in Arabic). The Swan is flying with its outstretched neck, and the shape really reflects the constellation name. The head of the Swan, Albireo, is one of the most beautiful double stars in the sky as seen through a small telescope.

If you omit the wingtips, the rest of Cygnus forms a cross called the Northern Cross. Vega is the brightest star in Lyra, a small parallelogram capped by an equilateral triangle. Altair is the brightest star in Aquila, the Eagle, another constellation that's not a bad match for its name, though not terribly bright. Between Aquila and Cygnus is tiny Delphinus, the Dolphin, not very brilliant but very attractive and really fitting its name. Skimming the southern horizon is Sagittarius, whose stars outline a teapot, and Scorpius the Scorpion, yet another constellation that looks like its namesake. Scorpius is dominated by reddish Antares, whose name means "anti-Mars" because it looks similar to that planet. Between Scorpius and Hercules is faint, sprawling Ophiuchus and the two halves of Serpens. Because of how constellation boundaries are drawn, the Sun actually spends more time in Ophiuchus than it does in Scorpius, and every so often the astrology community gets excited at the "discovery" of a thirteenth constellation in the Zodiac. Two important points are not marked on the chart.

Between Vega and Hercules is the direction the Sun is moving relative to nearby stars. Just off the spout of the teapot of Sagittarius is the center of the Milky Way Galaxy, invisible to the eyes but detectable in radio waves. The Autumn Sky The Summer Triangle is high in the western sky in the fall but most of the constellations are associated with the myth of vain Cassiopeia, whose vanity offended the gods, who in turn sent a sea monster (Cetus) to ravage the coasts. She and her husband Cepheus consulted an oracle, who decreed that their daughter Andromeda had to be left as a sacrifice to the monster. (Notice how Cassiopeia offends the gods, but Andromeda has to be sacrificed? That's how it went in myths. The fact that Cassiopeia and Cepheus were backed by a bunch of surly guys with swords and spears had only a little to do with the oracle's judgment.) Anyway, just as Cetus and Andromeda are about to do lunch, along comes the hero Perseus, riding the winged horse Pegasus, and saves the day.

And they lived happily ever after, or at least until Perseus left his socks on the floor. The Great Square of Pegasus is the flagship of the autumn sky. Andromeda consists of two arcs of stars pointing between Cassiopeia and Perseus. Not far from the midpoint of the arcs is M31, the Andromeda Galaxy, at 2.3 million light years, the most distant object visible to the unaided eye. The zodiac constellation Aries is fairly easy to see. Pisces, Aquarius and Capricornus are rather faint. Aquarius consists of a tight little tripod of stars called the Water Jar and to other moderately bright stars. Far to the south is lonely Fomalhaut, a first magnitude star. Three variable stars of very different types are in this part of the sky. Mira in Cetus is a huge pulsating red giant star that attains second magnitude and then fades to invisibility with a period of about a year. Algol in Perseus is an eclipsing variable in which a faint star orbits a brighter one, eclipsing it every few days. Delta Cephei is the namesake of a class of variable stars that vary regularly in brightness.

The period of variation is directly related to the true brightness of the star, making it possible to use these stars as distance indicators in the Universe. The Winter Sky For Northern Hemisphere viewers, the winter sky is the richest in first magnitude stars. At twilight, the first stars to appear form a giant hexagon with reddish Betelgeuse near the center. Auriga, the charioteer, is dominated by yellow Capella, a nearly circumpolar star in the northern U.S. Taurus, the Bull, is dominated by orange Aldebaran and two star clusters, the V-shaped Hyades and the cute Pleiades. When you first see Capella in the northeast and the Pleiades rising, you know winter is on the way. Gemini is marked by the twins Castor and Pollux. Canis Major is a bright constellation crowned by dazzling Sirius, the brightest star in the sky. Canis Minor consists of yellow Procyon and one other moderately bright star. Orion dominates the winter sky, with blue white Rigel and reddish Betelgeuse at opposite corners and the three stars of his Belt. Hanging from the belt is his Sword, containing the Great Orion Nebula.

Some of the stars in Orion are among the most distant stars easily visible to the eye, over 2000 light years away. According to legend, Orion was stung to death by a scorpion (Scorpius), which is why the two constellations are on opposite sides of the sky. In winter, we're looking toward the sparse outer edge of the galaxy and the Milky Way is narrow and faint. It is not shown on the chart above but runs across Auriga, Orion and Canis Major. Some Important Southern Stars South of Nashville or Santa Fe, brilliant yellow Canopus clears the horizon. It's the second brightest star in the sky and important in spacecraft navigation. It's so bright it's easy to detect, and nearly at right angles to the plane of the earth's orbit, so if a spacecraft can lock on Canopus and the Sun, it's orientation in space is fixed. First magnitude Achernar appears at Gulf Coast latitudes. Its constellation, Eridanus, represents a river, though which river varies considerably depending on the myth. Canopus belongs to a constellation called Carina, which means "keel" (of a ship) in Latin.

The stars in the lower left corner of the chart once belonged to a huge constellation called Argo, the ship sailed by Jason and the Argonauts in Greek mythology. But Ago was such a big and unwieldy constellation - bigger than the largest constellation today - that it was subdivided into three constellations: Carina, the keel, Vela, the sails, and Puppis, the stern (from which we get the expression "poop deck.") No region in the sky has four first magnitude stars so close together as the Southern Cross and nearby Centaurus. In the U.S., only Hawaii, the Florida Keys and extreme southernmost Texas can see these constellations. Follow the arc from Arcturus to Spica and keep on going. This part of the sky is just breathtaking, peppered with moderately bright stars and the Milky Way. Crux is not so much a cross as a kite with a little off-center star within it. Nearby are blue white Beta Centauri and brilliant golden Alpha Centauri, third brightest star in the sky and a near twin of our Sun. It's also a spectacular double star and the nearest star beyond the Sun.

Below and right of Spica is Corvus the Crow, a neat little trapezoid. If you can spot Corvus, just drop straight down from it to the Southern Cross. Libra has only two fairly bright stars. At one time they were considered to be the claws of Scorpius. The upright of Crux points nearly north-south and is used for direction finding in the Southern Hemisphere, since there is no South Pole star. Note that below the word "cross" in the chart there is another similar sized diamond of fairly bright stars. This grouping is called the "False Cross" because it is sometimes confused with the real Southern Cross. There's a small star within the Southern Cross that spoils the pattern. In Latin America, this star is sometimes called "Intrometida" - "the intruder." In reality, the star has every right to be where it is - it was there long before we named the constellation. It's only an "intruder" because it breaks up a pattern that we think should be there. Sky Coordinates Just like on the earth, we have latitude and longitude on the sky. The sky equivalent of longitude is called Right Ascension.

It is measured in hours, minutes and seconds of time, that is, how long it takes a given interval to move across the sky. One hour of right ascension equals 15 degrees, one minute equals 1/4 degree. The equivalent of latitude is called declination and is measured in degrees. The Celestial Equator is a line around the sky halfway between the celestial poles and is directly above the earth's equator. On the diagram above, we are seeing the celestial sphere as if we are outside it. Since we are inside it, the hours actually increase from east to west (toward the right as you face south). The numbers ascend to the right. The Ecliptic Since the earth's axis is tilted with respect to the plane of the earth's orbit, the Sun and planets appear to travel a path at an angle to our celestial coordinates. We call this path the ecliptic because eclipses occur when the Moon is exactly on it. It is tilted 23.5 degrees with respect to the celestial poles. We use the ecliptic to define zero right ascension. Where the ecliptic crosses the celestial equator going up is zero right ascension.

The sun is at this point on March 21 so this point is often called the vernal equinox. The ecliptic reaches a maximum declination of 23.5 degrees at 6 hours right ascension (summer solstice), crosses the equator headed south at 12 hours (fall equinox), and reaches a minimum of -23.5 degrees at 18 hours (winter solstice). We can define latitude and longitude based on the ecliptic, with the ecliptic as the equator of the sphere and two ecliptic poles 90 degrees away. This system is useful for describing the motions of the planets. Ecliptic latitude and longitude are described in terms of degrees, like terrestrial latitude and longitude, with zero longitude at the vernal equinox, 90 at the summer solstice, and so on. The diagram above shows how the circumpolar stars relate to celestial coordinates for 45 degrees North. A few key locations in the sky: The rightmost star in Orion's Belt is almost on the celestial equator.

The left side of the Great Square of Pegasus is just about at 0 h right ascension and the right side is close to 23 h. The spout of the teapot of Sagittarius is just a bit below the southernmost point of the ecliptic at 18 h. It's also close to the center of the Galaxy. Deneb and Capella are at 45 north, Vega at 40. Arcturus is at 20 north, Spica at 10 S. The celestial equator is one third of the way from Spica to Arcturus The left (east) sides of Auriga and Orion are close to 6 h. Denebola, the easternmost bright star in Leo is close to 12 h. The eastern wingtip of Aquila is on the celestial equator. The Water Jar of Aquarius is on the celestial equator. The Pointer Stars in the Big Dipper are very close to 11 h and the other bottom star of the bowl is at 12 h. First magnitude stars close to the ecliptic are Aldebaran, Pollux, Regulus, Spica, and Antares.

All except Pollux are close enough to be occasionally covered, or occulted by the Moon. The upright of the Southern Cross points toward the South Celestial Pole. Mu | Article about mu by The Free Dictionary Mu | Article about mu by The Free Dictionary mu (μ) 1. The 12th letter of the Greek alphabet, used in stellar nomenclature usually to designate the 12th-brightest star in a constellation or sometimes to indicate a star's position in a group. 2. Symbol for proper motion. Mu (character) (Greek letter). 1. <unit> /micro/ prefix denoting division by 10^6, e.g. mu m (micrometre, a millionth part of a metre). Sometimes written as a 'u', the ASCII character nearest in appearance. 2. <mathematics> /myoo/ In the theory of functions, mu x . E denotes the least value of x for which E = x, i.e. the least fixed point of the function \ x . E. The recursive function mu f . H f satisfies (and is defined by) the equation mu f . H f = H (mu f .

H f) An alternative notation for the same function is fix H = H (fix H) The country code for Mauritius. mu (philosophy) /moo/ The correct answer to the classic trick question "Have you stopped beating your wife yet?". Assuming that you have no wife or you have never beaten your wife, the answer "yes" is wrong because it implies that you used to beat your wife and then stopped, but "no" is worse because it suggests that you have one and are still beating her. According to various Discordians and Douglas Hofstadter the correct answer is usually "mu", a Japanese word alleged to mean "Your question cannot be answered because it depends on incorrect assumptions". Hackers tend to be sensitive to logical inadequacies in language, and many have adopted this suggestion with enthusiasm. The word "mu" is actually from Chinese, meaning "nothing"; it is used in mainstream Japanese in that sense, but native speakers do not recognise the Discordian question-denying use. It almost certainly derives from overgeneralisation of the answer in the following well-known Rinzei Zen teaching riddle: A monk asked Joshu, "Does a dog have the Buddha nature?" Joshu retorted, "Mu!"

Question: Which Greek letter usually denotes the brightest star in a constellation?
Answer: Alpha