Quasar Quasars, or QSOs, or "quasi-stellar objects", look, as the name implies, a lot like stars. A closer look shows that they are extremely far away (the most distant observable objects in the sky). In order to be so bright, but so far away, they have to produce enormous amounts of energy. They can also be observed to be very small, and the leading theory as to what can make an object so small produce so much energy assumes a black hole in the center of a galaxy. The black hole sucks in surrounding gas and stars, which form a tremendous accretion disk, which produces immense amounts of energy in the form of heat (infrared radiation), light, X-rays, and gamma rays, as the matter falls in. Some of these objects vary in brightness and were labelled as variable stars by mistake, such as BL Lac. Quick Info Alt-Q The Quick Info option in the Help menu provides a list of such data as current planet positions, bright comets and asteroids, sidereal times, the visual magnitude limit and field rotation rate at the chart center, calendar data, and so forth. It can be reached with the Alt-Q hotkey. R CrB R CrB stars are named, logically enough, after the variable star R CrB. This star is usually visible at about magnitude 6, just barely invisible to the unaided eye. Every now and then, it will suddenly drop to about magnitude 14, then recover to mag 6 again. RA second The usual unit for measuring very small angles is the arcsecond. Angles measured in arcseconds are denoted with the " (double quote) symbol, as in, "The object was 34" across." Unfortunately, from time to time, another unit, the RA second, is used. One RA second is the angle through which the earth turns in one second, just as an RA minute is the angle through which the earth turns in one minute and an RA hour is the angle through which the earth turns in one hour. Guide mostly avoids the use of RA seconds, and will usually multiply such values by 15 and display them as arcseconds. In a few cases, however, a source catalog will provide data in RA seconds and Guide will follow suit. RA/dec format The RA/dec format dialog option in the Settings menu provides a way to choose how RA and declination values are shown in Guide. By default, they are always shown in the J2000 equinox and with decimal seconds. But coordinates are often given by some sources in decimal minutes or degrees, or in the B1950 epoch. The format you choose in this dialog will be used in displaying coordinates throughout Guide. But you can always enter coordinates in any format you choose; Guide will figure out the format and will still understand your entry, even if its format does not match that chosen in this dialog. Also, this dialog box provides options to set the formats used in showing latitude/longitude values, and to toggle between metric and English units. Radial and/or Rotational Velocity radial velocity rotational velocity If you examine an object's spectrum, you will often see that the star is redder or bluer than you would expect. This is caused by the Doppler shift: the object is moving toward or away from the Earth. By measuring the amount of shift, you can find the object's velocity. Notice that this only tells you the speed of approach or receding; the object could be moving sideways at any speed and the spectrum wouldn't show it (though proper motion studies might). This speed is therefore called a radial velocity. Also, you may see that a given spectral line is "blurry". If an object spins quickly, the spectrum of the side approaching you will be bluer than usual; that going away will be redder than usual, once again because of Doppler shift, and once again, measuring the blurring tells you how fast the object spins. Unfortunately it only tells you the spin speed relative to Earth: an object could have a lot of spin most of which is sideways to us (i.e., its axis is pointed at us, or nearly so), and we would never know. Radial galaxy velocity According to present thinking, there is a direct linear relationship between how fast a galaxy moves away from us and how far away it is; i.e., the faster it moves away, the farther away it is. The problem is that the exact relationship is not all that well known. We can measure the speed at which a galaxy recedes with some precision, using the Doppler shift. Measuring how far away galaxies are requires the use of much less precise techniques. This program will only give the radial velocity (if it's been measured for the galaxy in question). The corresponding distance depends on the "Hubble constant", the value of which has been a matter of intense debate for many decades.. radiant The meteors from a meteor shower generally appear to "radiate" from one point in the sky. That point is called the radiant, and usually provides the name of the shower; for example, the radiant of the Perseids is in Perseus. Radius or Diameter Most stars appear as pinpoints in any instrument we have available today. A few of the larger and closer stars have apparent angular diameters that can be measured. Knowing this and a star's distance can tell you how big it really is. Rapid irregular The rapid irregular type of variable star will change in brightness by about .5 to one magnitude for a few hours or days. They are a lot like Orion type variables, and in fact, the boundary between the two is blurry. The main feature of the rapid irregular variables is that they are not in a nebula (and therefore must have a different reason for varying than Orion type variables do). It takes some care to make sure these objects are really irregular, and not some periodic or BL Lac object. Rapid-change Orion type A rapid-change Orion type is simply an Orion type variable that has been observed to change brightness very rapidly, by about one magnitude in one to ten days. Rapidly oscillating Alpha CVn Rapidly oscillating Alpha CVn stars are variable stars with strong magnetic fields, with strong, nonradial oscillations (basically, they quiver like Jello). The variations take place on a time scale of a few minutes, and are small (about .01 magnitude). In addition, they show the sort of variations found in normal Alpha CVn stars. RASNZ The Variable Star Section, Royal Astronomical Society of New Zealand (VSS RASNZ) gathers and distributes data regarding variable stars; especially those in the southern skies. The VSS RASNZ has members throughout the southern hemisphere and low northern latitudes. Most southern variables are poorly observed - if at all - and the VSS RASNZ welcomes observations from amateur (and professional) astronomers. For further information, contact: VSS RASNZ PO Box 3093 Greerton, Tauranga NEW ZEALAND Tel. / Fax +64 7 541 0216 Internet: varstar@voyager.co.nz RC3 Third Reference Catalog The RC3 (Third Reference Catalog) contains information on over 23,000 galaxies. Should you click on a galaxy in this catalog, information from the RC3 as to the object position, size, etc. will be provided when you "click for more info". The RC3 was compiled by G. and A. de Vaucouleurs, H. G. Corwin, R. J. Buta, G. Paturel, and P. Fouque. RCW Reference: Rodgers, A.W., Campbell, C.T. and Whiteoak, J.B.: 1960, Monthly Notices Roy.Astron.Soc. 1221,103. A catalogue of H-alpha emission regions in the Southern Milky Way. Real-time This menu item causes animation to run in "real time.", i.e., planets and asteroids are shown in their current location, based on the time provided by the computer's built-in clock. Also, the altitude and azimuth shown for clicked-on objects is updated to match the actual alt/az for that object. RealSky image Alt-F6 If you have the eight-CD set of RealSky images from the Astronomical Society of the Pacific, you can extract images from those CDs and have them displayed in the background of Guide's charts. To do this, center the chart on the object of interest, and click on the RealSky image in the Extras menu. Guide will ask for the size of the image to extract, in arcminutes. You can just enter, for example, "20" for a 20x20 arcminute region; or "20x30" for a region 20' wide and 30' high. Guide will then start up a separate process to extract the image. You'll be asked to insert a RealSky CD and hit Enter. (You may need to do this twice on some systems before the CD is properly recognized.) The process will give you a "percent completed" progress report, and will then ask you to re-insert the Guide CD-ROM. Do so, and hit Enter (again, a repetition may be necessary). Control will be returned to Guide, and the image will be shown, correctly oriented on the chart. You can zoom in and out on it, and print it if desired. You can also access this option with the Alt-F6 hotkey. There is also an option available to clear RealSky images when desired. redshift If an object is moving away from us, we see a shifting of its light toward longer wavelengths. This is an example of Doppler shift. It can be measured to give a velocity, expressed either in kilometers/second or in terms of the speed of light. The figure is the object's redshift. Reflecting binary A reflecting binary variable is a type of variable star where light from the hotter star is reflected from the cooler star. So when the hotter star is closer to us, the amount of light from the pair is raised. Since the stars have to be close together for this effect to be really noticeable, they may eclipse one another as well. Usually, the range of brightness variation is .5 to 1 magnitude. An example of this class is KV Vel. reflection nebula A reflection nebula happens when a nebula is lit up by a star on the inside. Light from the star is reflected by gas in the nebula. This is different from an emission nebula, which gets heated up by a star on the inside to the point where it glows on its own. refraction Refraction refers to the bending of light as it passes through different media. The bending as it passes from, for example, air through water is quite obvious; the bending as it passes from vacuum to air, or between different densities of air, is not as obvious. The effect of refraction is to make objects appear higher in the sky than they otherwise would. Objects more than halfway from the horizon to the zenith (i.e., with an altitude greater than 45 degrees) are almost totally unaffected. Objects near the horizon can be shifted by a degree or so. The shift is not always the same from one part of the sky to another; this is why the rising and setting sun often looks distorted, and why mirages can occur at some times but not others. A further complication is that air masses move continuously, creating complex and unpredictable refractive effects. That causes the continous moving and deformation of telescopic images known as seeing. Guide computes refraction using the temperature and pressure data you supply in the Location dialog. Despite this, the actual observed refraction can vary by several arcseconds from the computed refraction. repeating nova A repeating nova is much like a garden-variety nova, except that the explosions will repeat after a few decades. A good example is T Pyx. Normally, this star stays at about magnitude 14. In 1890, 1902, 1920, 1944, 1967, and 1997, it suddenly leapt up to about magnitude 6 or 7. It then stays bright for a while, dropping back over months. Republican calendar The French Republican Calendar was established in 1793 and abolished in 1806; it's only of historical interest now, and was apparently never used outside of France. But it does shed light on the idealistic psychology of the Republic; it reflects a true optimistic belief that a new age of reason was dawning. Under the Republic, almost everything "old" and "irrational" was to be replaced by new, rational thinking. Feet, inches, and pounds were thrown out to make way for the metric system; the clumsy units of hours, minutes, and seconds were replaced with decimal versions; and a new calendar, with twelve months of 30 days each, was introduced. The months were: Vend‚miaire (Vintage) = 22 Sep to 21 Oct (roughly) Brumaire (Mist) = 22 Oct to 20 Nov Frimaire (Frost) = 21 Nov to 20 Dec Niv“se (Snow) = 21 Dec to 19 Jan Pluvi“se (Rain) = 20 Jan to 18 Feb Vent“se (Wind) = 19 Feb to 20 Mar Germinal (Seed-time) = 21 Mar to 19 Apr Flor‚al (Blossom) = 20 Apr to 19 May Prairial (Meadow) = 20 May to 18 Jun Messidor (Harvest) = 19 Jun to 18 Jul Thermidor (Heat) = 19 Jul to 17 Aug Fructidor (Fruit) = 18 Aug to 16 Sep The archaic, illogical, meaningless month names of the old calendar were replaced with logical, meaningful names. Months such as "July" and "August", named after utterly undemocratic Roman emperors, were discarded. The month names within each season rhyme, probably as an aid in remembering them. This does leave five "extra" days at the end of each year (six days, in leap years). These were given the following names: Jour de la vertu (Virtue Day) Jour du genie (Genius Day) Jour du travail (Labour Day) Jour de l'opinion (Reason Day) Jour des recompenses (Rewards Day) Jour de la revolution (Revolution Day) (leap years only) The first day of the calendar, 1 Vend‚miaire 1, corresponds to Gregorian 22 September 1793 (keeping in mind the Republican Calendar wasn't actually established legally until 5 October 1793). The thirty days of each month were organized into three weeks of ten days each. The Republican leaders were in part trying to evade the religious aspects of a seven-day week, and presumably also liked having a "decimal" week. Unfortunately, providing one day of rest every tenth day, instead of one every seven days, was not a popular move. Leap years are those divisible by four, except for those divisible by 128. This slight deviation from the Gregorian scheme, in which leap years are those divisible by four, unless divisible by 100, unless divisible by 400, is slightly simpler and gives a calendar that is _much_ closer to the true tropical year. Unfortunately, when first devised, the French attempted to have New Years Day line up with the autumn equinox, which is not particularly regular and was probably a real pain in a world without pocket calculators. Thus, between 1 AR and 20 AR, leap years occurred a year early; i.e, years 3, 7, 11, and 15 AR were leap years; after that, they were supposed to revert to the rule described above. There are also claims that leap years were to follow the Gregorian "4, 100, 400" rule. I have no real evidence to support one scheme over the other. But I suspect that a revolution so devoted to revising every aspect of human existence that it changed names of all months, "regularized" each to be 30 days, and made a week ten days long, probably went out of its way not to produce a calendar resembling that proposed by a medieval, pre-scientific Pope. Also, the fact that it would be an almost perfect match to the tropical year would lend support to the scheme. In any case, the irony of the Republic creating a calendar that would be good for a hundred thousand years is interesting, considering that the Republican calendar was abolished in Year 14. retrograde prograde If you viewed the solar system from well above the north pole of the Sun, you would see that almost all objects orbit the Sun in a counterclockwise direction; almost all rotate around their axes in a counterclockwise direction; and almost all satellites orbit their planets in a counterclockwise direction. This is called prograde, or "forward", motion. However, there are exceptions to all this. Some comets orbit the sun in a clockwise direction. Venus and Uranus rotate clockwise around their axes. Triton, the largest satellite of Neptune, orbits in this reversed direction; and so do some other, small satellites of outer planets. This is called retrograde, or "backward", motion. rise/set times When you click on an object, this program calculates the times of rising and setting, as seen from the place on the earth (latitude/longitude) chosen in the Settings menu. They assume "average" refraction. For the sun and moon, "rising" occurs when the top of the object appears above the horizon, "setting" when the top vanishes below the horizon. Changing atmospheric conditions at the horizon (which is, after all, where objects rise and set) make it not possible to determine rising and setting times with more accuracy than a minute or two. Under unusual conditions, the accuracy may be still worse. Unless you are at the equator, there will be some objects that never rise and set, and are either always above or below the horizon. For example, those of us in the United States never can see the Southern Cross or the Magellanic Clouds, but we can always see the Pole Star and the Little Dipper (Ursa Minor). Objects that are always visible are called circumpolar. rotation period An object's rotation period is the time it takes it to turn once on its axis. For the Earth, the rotation period is one day. For the Sun, it is about a month; for the Moon, 27.5 days. Some asteroids have had their rotation periods measured. This is done by measuring the brightness of the asteroid over time. If the object is not very round (which happens frequently with small asteroids), or if it has bright and dull markings, the brightness will go up and down as the asteroid turns. The time it takes to go up, down, and up again will usually equal the rotation period. RR CrB The RR CrB type of variable star is not very different from the Z Andromedae type. This type is also an older, cooler star, but its variations in light are not as regular and it takes more observations to determine it. Often, there are two periods of variation superimposed on each other, sometimes reinforcing, sometimes cancelling each other out. RR Lyrae The RR Lyrae type of variable star is a radially pulsing star of spectral type A to F (hotter than the Sun), varying by .2 to 2 magnitudes in brightness. They are found, sometimes in great numbers, in globular clusters. They always have the same intrinsic luminosity, which means that if you spot some in a globular cluster, you can tell how far away that cluster is. They have short periods, of a day or less in length. RR Lyrae with two pulsation modes This type of RR Lyrae star is a variable with two cycless of pulsation, sometimes coinciding, sometimes cancelling one another out. An example is AQ Leo. The ratio of the lengths of the cycles is about .745. RS CVn The RS CVn type of variable is a close binary pair of stars with unusual amounts of activity in their atmospheres, causing pseudo-periodic variations in light. The period of light variation is close to the orbital period. The amount of variation is usually as great as .2 magnitude. They are also X-ray sources and rotating variables (as they rotate, different parts of their surfaces with different intensities become visible.) RV Tau w/long-term variation Many RV Tauri stars have, on top of the light changes normal to that class of variable star, a tendency to vary in brightness by up to 2 magnitudes over a period of 600 to 1500 days (2 to 5 years). RV Tauri RV Tauri type variable stars are supergiant stars that regularly swell and shrink. Both the brightness and spectral type vary: at their brightest, they are of type F or G (like the Sun or a little hotter); at dimmest, type K or M (cooler than the Sun). The minimum magnitude alternates between two values from one cycle to the next; the level of these values also varies over time, so that sometimes the dimmer minimum will swap places with the not-so-dim minimum value. The light curve (graph of time running horizontally versus brightness running vertically) looks like this: with a deep minimum followed by a shallow one, and so on. @m 0,200 Maximum @l 10,200 @l 20,210 @l 30,230 @l 40,260 @l 50,270 Deep minimum @l 60,260 @l 70,230 @l 80,210 @l 90,200 2nd max @l 100,200 @l 110,210 @l 120,230 @l 130,250 @l 140,260 Shallow minimum @l 150,250 @l 160,230 @l 170,210 @l 180,200 3rd max @l 190,200 @l 200,210 @l 210,230 @l 220,260 @l 230,270 Deep min @l 240,260 @l 250,230 @l 260,210 @l 270,200 4th max @l 280,200 @l 290,210 @l 300,230 @l 310,250 @l 320,260 Shallow minimum @l 330,250 @l 340,230 @l 350,210 @l 360,200 3rd max @l 370,200 @l 380,210 @l 390,230 @l 400,260 @l 410,270 Deep min @l 420,260 @l 430,230