Yale Bright Star Catalog Application by R. Quance -------------------------------------------------------------- A demonstration of the capabilities of HyperLINK through a simple application. This is the beginning of a star catalog that has over 9000 stars. The Yale Bright Star Catalog (YBS) contains information on stars down to about magnitude 6 (or about the limits of the naked eye). The information describes the properties of individual stars, including size, distance, color, type, motion and others. Only the first 20 entries have been entered, if you're not lazy like me you can find the data for the remaining stars in the Spaceport R/T on GEnie. The files are: YBS1CAT.ARC through YBS8CAT.ARC. There are a few catalog readers also in the Spaceport libraries such as YBS_ST2.ARC to help you read the information in these files. How to use ------------ Load the HAP and its files into the HyperLINK directory. Run HyperLINK and load in the YBS.HAP application, looks nice don't it. Using the arrow buttons you can scroll through the data. When you hit YBS No. 7 move the mouse down to the "?" in the bottom left corner and click on it. This shows you a picture of the constellation where the star will be found ( it looks better in monochrome ). There are a few indexes that can be used in sorting the data as well as online help. By double-clicking on the label for each field you will get a description of what the field is telling you and how the data is used, there is room for expansion here. Field Descriptions -------------------- YBS No. : This is the YBS Catalog number for the selected star. There are over 9000 stars in the actual catalog. Only the first 20 are shown here, others can be added if you wish to add them yourself. R.A. : To understand R.A. (Right Ascension) we have to get a picture in our minds of what we are looking at when we look at the night sky. Imagine the Earth is surrounded by a huge black hollow sphere with pinholes through it. The light shining through the pinholes marks the locations of the stars. Now to get the coordinates of the stars we'll have to lay a grid over the inside of the "Celestial Sphere". We're going to need lines similar to lines of longitude (vertical) on a globe, but what do we use for a scale, Hmmm... Let's see, the Earth rotates once every 24 hours, that's it, we'll use 24 segments. We can further divide each down into minutes (60 minutes) and seconds (60 seconds). So, every 1 hour of R.A. is divided down into 3600 smaller segments (seconds). Hmmm, so where do we start counting from and which direction do we go? We'll just have to use some event that occurs every year to mark the staring point, the "Vernal Equinox" is what we'll use, or the point where the sun crosses the Equator in the springtime. Since it varies from year to year we'll have to specify a date to use as a reference, or Epoch. Most stars catalogs are based on a particular Epoch, e.g. 2000.0 or 1950.0. This means that the locations of the stars are measured from the point where the sun crosses the Equator on that Epoch date. So, which way do we go? Well, if we point our telescope at a particular star and don't move it for 1 hour, we will be looking at a point 1 hour of R.A. east of the star we had it pointed at, that's the direction we'll use. We can use the Earths rotation as a clock to find our way around the sky. If we're looking at a star that is 1 hour of R.A. above the eastern horizon and we want to look at a star that has an R.A. of 2 hours more than the star we are looking at. We'll have to wait 2 more hours for it to appear in the same position as the first star. Confusing, I know, but that's about as simple an explanation as I can give... Dec. : To understand Declination (Dec.), we have to go back to the "Celestial Sphere" we created in the R.A. section above. We have the vertical lines (R.A.), but we still need the horizontal lines that represent lines of latitude. These lines start at the "Celestial Equator", which closely matches the position of our own equator. The scaleing is the same as we use on our globe, with +90 degrees and -90 degrees, starting with 0 degrees at the celestial equator and ending at the celestial North and South poles. Each degree of declination is further broken down into minutes (60 minutes) and seconds (60 seconds). Now we can find the coordinates for a particular star by using the R.A. and Declination of the star, it's just like looking from the inside of a globe of the Earth. We can see the vertical and horizontal lines marking longitude and latitude, only it's dark and we only see points of light not the back of the continents on this sphere... Distance : This is the distance from the Earth in "Light Years". The light year is the distance light will travel in one year. It's actually quite a long distance, since light travels 186,282 miles per second. Let's use a little math to figure out the distance. How many seconds in a year? There are 60 seconds in a minute, 86,400 seconds in one day and 31,536,000 seconds in one year. Multiply that by 186,282 and you get the idea. That's quite some distance isn't it? Parallax : Since the Earth revolves around the Sun each year with an orbit that is 186 million miles in diameter, the stars that are closer the our solar system appear to move in little circles against the more distant background stars. This apparent motion is known as parallax. The parallax angle is the angular difference in the postion of a star when viewed from opposite sides of the sun. When the star is closer to the ecliptic (or the path of the Sun across the sky) it becomes more elliptical (oval). As a result we'll have to use the longest distance from the center of the ellipse ( semi-major axis ) to make all our measurements. This information can be useful in determining the distance of nearby stars... Type : This tells you whether the star is all by itself or is made up of multiple stars. Double stars are actually two stars that appear close together but are actually some distance apart, they just happened to appear along the same path. Binary stars are multiple stars that are in close proximity to each other and actually orbit around each other. Annual Proper Motion (R.A.) : Since all things are never permanent so it is with stars too. Although you can't notice it, except over long periods of time, the stars are actually moving. The Annual Proper Motion (R.A.) is a measure of how far the star will have moved over a period of one year. A positive number means that the star is moving eastward, a negative number means it's moving the opposite way. We can use this information to help determine the distance the star is away or speed the it's traveling or where it will be sometime in the future. Annual Proper Motion (Dec.) : Represents how far the star has moved in Declination over a period of one year. If the number is postive then it's moving in a northward direction, if it's negative then it's moving south. This information is of the same importance as that mentioned in the Annual Proper Motion (R.A.) above.... Spectral Class : We can classify stars according to characteristics in their spectra. You have probably noticed, on a clear night, that stars have different colors. There are seven basic types of spectral class, based on the colors emitted at varying surface temperatures of these stars. Depending on the elements present within the star, certain bands of light will be absorbed by these elements. They appear as black lines in the spectral color of the star and are called, of all things, "Absorbtion Lines". The basic spectral types are described here with their absorbtion lines (elements): Type Absorbtion Lines ------------------------------------------------------------- O Ionized Helium (He II) B Neutral Helium, first appearance of Hydrogen A Hydrogen dominant, plus singly ionized metals F Hydrogen weaker, ionized calcium (Ca II) G Ca II prominent, weak Hydrogen and neutral metals K Neutral Metals prominent M Molecular Bands, mostly Titanium Oxide (TiO) Each of these seven types is further divided into 10 classes, with a class of "5" occuring half way between two types. (e.g. A5 is half way between A0 and F0). The age of a star can be determined by the elements present within it. The types O, B, and A are of the "early type", with K and M being of the "late type". Since within each type, a brighter star can be more luminous (emit more light), the absorbtion lines tend to get narrower. So to take this into account, we add a "Luminousity Class" to each star. We use Roman numerals to add the luminousity class to our star, they are shown in the list here: Luminousity Class Description ------------------------------------------------- I Supergiants II Bright Giants III Giants IV Subgiants V Main-Sequence Dwarfs VI Subdwarfs VII White Dwarfs Some of these classes, especially the Supergiants, can be divided further with suffixes (e.g. a, ab and b). You might see a spectral class like " K0III " or " M2Iab", can you figure these out? If there are any non-standard features found within a stars spectra, they will be noted by small letters following the luminousity class. Here is a list of these features: Feature Description -------------------------------------------------------- e Emmision Lines (f in some O-type stars) m Metallic Lines n Nebulous Lines p Peculiar Spectrum q Blue Shift absorbtion and Red Shift emmision (presence of an expanding shell) v Variable Spectrum I'll bet you're really confused now!!! Hang in there... Absolute Magnitude : Magnitude is a measure of the brightness of a star. Since stars at a greater distances may be just as bright as stars nearby, but at greater distances they appear to be fainter, we'll have to find way to describe their actual brightness. We do this by calculating the brightness of a star if it were at a standard distance away. We use 10 parsecs (33 light years) as the standard distance. The result is the "Absolute Magnitude" or the magnitude the star would be if it were 10 parsecs away. Visual Magnitude : This is a measure of the brightness of a star as it appears to the human eye. There are no corrections applied to this measurement, what you see is what you get. The magnitude scale is based on an early scale used by Hipparchus in the 2nd century B.C. It classed stars into 6 catagories, the brightest stars were magnitude 1, the next less bright were magnitude 2, and so on to magnitude 6 which were the faintest stars visible to the naked eye. This scale was later expanded, to help with telescopic measurements, to include postive (+) and negative (-) magnitudes. As well it was found that a 1 magnitude difference worked out to a difference in brightness by a ratio of 2.5, and a 5 mag. difference in brightness between two stars resulted in a brightness ratio of 2.5^5, or nearly 100. The brightest star in the sky would now be -1.46 mag. (Sirius), according to the new scale and the faintest stars seen in a 3" telescope are at the 11th magnitude... Color : The electronic measurement of a stars brightness is usually done through four different color filters. These colors are (U)ltraviolet (350 nm), (V)iolet (410 nm), (B)lue (470 nm) and (Y)ellow (550nm). The "Color Index" is the difference in magnitude of a star measured through two of the filters, usually B-V or U-B. In this case we are using the B-V difference. Common Name : This is the name of the selected star. It can be the proper name (e.g. Rigel), the Bayer letter ( e.g. mu Cygni), Flamsteed numbers (e.g. 31 Orionis). The Bayer letter is usually a Greek letter followed by the constellation name and the Flamsteed number is a number followed by the constellation name. The Greek alphabet is difficult to represent here, we will have to use the following representation of the characters (e.g. Gamma Orionis - Bellatrix): Alpha Beta Gamma Delta Epsilon Zeta Eta Theta Iota Kappa Lambda Mu Nu Xi Omicron Pi Rho Sigma Tau Upsilon Phi Chi Psi Omega Constellation : There are 88 constellations that represent fixed areas of the sky. They were originally determined by the early Greeks to represent characters from their mythology and are still used today. The following is a list of the constellations and their abbveviations: Name Genitive Abbreviation -------------------------------------------------------------------- Andromeda Andromedae And Antlia Antliae Ant Apus Apodis Aps Aquarius Aquarii Aqr Aquila Aquilae Aql Ara Arae Ara Aries Arietis Ari Auriga Aurigae Aur Bootes Bootis Boo Caelum Caeli Cae Camelopardalis Camelopardalis Cam Cancer Cancri Cnc Canes Venatici Canum Venaticorum CVn Canis Major Canis Majoris CMa Canis Minor Canis Minoris CMi Capricornus Capricorni Cap Carina Carinae Car Cassiopeia Cassiopeiae Cas Centaurus Centauri Cen Cepheus Cephei Cep Cetus Ceti Cet Chamaeleon Chamaeleontis Cha Circinus Circini Cir Columba Columbae Col Coma Berenices Comae Berenices Com Corona Australis Coronae Australis CrA Corona Borealis Coronae Borealis CrB Corvus Corvi Crv Crater Crateris Crt Crux Crucis Cru Cygnus Cygni Cyg Delphinus Delphini Del Dorado Doradus Dor Draco Draconis Dra Equuleus Equulei Equ Eridanus Eridani Eri Fornax Fornacis For Gemini Geminorum Gem Grus Gruis Gru Hercules Herculis Her Horologium Horologii Hor Hydra Hydrae Hya Hydrus Hydri Hyi Indus Indi Ind Lacerta Lacertae Lac Leo Leonis Leo Leo Minor Leonis Minoris LMi Lepus Leporis Lep Libra Librae Lib Lupus Lupi Lup Lynx Lyncis Lyn Lyra Lyrae Lyr Mensa Mensae Men Microscopium Microscopii Mic Monoceros Monocerotis Mon Musca Muscae Mus Norma Normae Nor Octans Octantis Oct Ophiuchus Ophiuchi Oph Orion Orionis Ori Pavo Pavonis Pav Pegasus Pegasi Peg Perseus Persei Per Phoenix Phoenicis Phe Pictor Pictoris Pic Pisces Piscium Psc Piscis Austrinus Piscis Austrini PsA Puppis Puppis Pup Pyxis Pyxidis Pyx Reticulum Reticuli Ret Sagitta Sagittae Sge Sagittarius Sagittarii Sgr Scorpius Scorpii Sco Sculptor Sculptoris Scl Scutum Scuti Sct Serpens Serpentis Ser Sextans Sextantis Sex Taurus Tauri Tau Telescopium Telescopii Tel Triangulum Trianguli Tri Triangulum Australe Trianguli Australis TrA Tucana Tucanae Tuc Ursa Major Ursae Majoris UMa Ursa Minor Ursae Minoris UMi Vela Velorum Vel Virgo Virginis Vir Volans Volantis Vol Vulpecula Vulpeculae Vul If there are any questions or comments, please send them to me at my GEnie address: R.QUANCE I hope you enjoy using this HyperLINK application and find it of some use. I will eventually find a way to load the data for all 9000 stars into this HAP, so stay tuned..... Robert W. Quance