heliocentric Heliocentric means "using the Sun as the center". It usually refers to the concept that the Earth and other planets orbit the Sun, as opposed to the earlier idea that everything revolves around the earth (the geocentric theory of Ptolemy and others). In this program, a "heliocentric" datum means "measured from the Sun", while a "geocentric" datum is measured from the center of the Earth. A topocentric datum is measured from the observer's position on the surface of the Earth. Heliocentric position When you ask for "more info" on a planet, you will be told its heliocentric position, the place where it would be found relative to the Sun. (Helios is the Greek word for the Sun.) HH Herbig-Haro objects are small emission nebulae, which are shock-exited by the interaction of gaseous material, expelled from protostars, with the surrounding material. Reference: Herbig, G.H.: 1975, Lick Observatory Bulletin, No. 658; Draft catalog of Herbig-Haro objects. HICK Hickson The Hickson catalog lists 100 compact groups of galaxies, such as Stephan's Quintet and similar groups. It was compiled by searching the entire set of Palomar Observatory Sky Survey plates for small groups of galaxies. Many of these groups are extremely dim, but they should be of interest to CCD observers and those with extremely powerful telescopes. A galaxy in the Hickson catalog is described by a number and a letter. HICK 34C, for example, is the third galaxy found in cluster #34. Some clusters contain up to seven galaxies. You can find an object by its Hickson number by using the Go to Hickson option in the Go to Galaxy menu in the Go To menu. High-Precision Subset HPS Of the stars in the PPM, 31,841 belong to the HPS, or High-Precision Subset. The positions and proper motions of stars in this subset are considered to be to better than normal accuracy. Positions are usually good to about .12 arcsecond; proper motions are usually accurate to about .24 arcseconds/century. Hilda The gravity of Jupiter has a strong effect on the orbits of asteroids, making some periods of revolution around the Sun more likely, others less so. In particular, if an asteroid takes 2/3 as long as Jupiter to orbit the Sun, Jupiter's gravity will tend to "hold" it in that orbit. This is an example of resonance. The first asteroid found with this property was Hilda. Subsequent examples are members of the Hilda orbital family. Hipparcos HIP The Hipparcos (HIP) data was collected as part of the mission of the Hipparcos satellite. It contains the most precise measurements of positions, parallaxes, proper motions, and magnitudes ever made, far better than in any other catalog. Unfortunately, it only contains data for 118 218 stars; so for most dimmer stars, other data sources must be used. It contains most stars down to magnitude 8, with a sampling of dimmer stars. The dimmer stars were mostly chosen for unusual or interesting properties: variables, multiple stars, nearby stars, and so forth. Hipparcos satellite The Hipparcos satellite was a European Space Agency experiment to collect vastly improved information about the fundamental properties of stars. Because it was above the atmosphere, it was able to collect extremely precise parallax, proper motion, and magnitude data for a total of over 1 million stars. The Hipparcos and Tycho datasets resulting from this effort are used by Guide as the basic data for all stars brighter than about magnitude 10.5, and many stars fainter than this. hotkey ? ?1 Click for first page of hotkeys !Cursor keys pan (or move mouse; use CTRL-F4 to toggle in DOS) Space bar to stop drawing ! Switch to French Enter to force a redraw ~ Switch to German Del "right mouse button" " Switch to Italian Ins "left mouse button" ' Switch to Spanish 5 (on numeric keypad) centers cursor (DOS) % toggle colored stars ALT-F1 toggle ecliptic (DOS) $ toggle star outlining ALT-F2 toggle horizon (DOS) # star display dialog ALT-F3 toggle gal. equator (DOS) & enter alt/az ALT-F4 quit ( set cross-marks on trails Alt-F5 Language menu (DOS) ) go to new level Alt-F6 Create RealSky image * zoom in Alt-F8 "Full" cursor (DOS) + brighten stars Alt-F9 Toggle user datasets , Glossary Alt-F11 Clear all RealSky images - dim stars CTRL-F1 or F11 aim LX-200 / zoom out CTRL-F2 or F12 recenter on LX-200 loc 1-9 go to level 1-9 CTRL-F3 Toggle Chart Mode ; find an asteroid CTRL-F4 use mouse to pan (DOS) = find a planet CTRL-F6 toggle Telrad (DOS) > select constellation CTRL-F8 Recenter CCD frame ? this list CTRL-F9 Enter current time as text @ toggle overlays menu Ctrl-F11 Reset line of variation Ctrl-F12 Add objects from an MPC file ALT-, Enter an ecliptic coordinate (DOS) ALT-. Enter a galactic coordinate (DOS) Alt-/ Set GRS position (DOS) CTRL-A toggle animation Alt-[ Coordinates menu CTRL-B enter Bayer/Flam desig ALT-0 set time to 0:00 UT CTRL-D data shown menu ALT-1...9 go to level 10-19 CTRL-E enter new epoch (DOS) ALT-A animation menu CTRL-F CCD frame on/off ALT-B back up one chart CTRL-H set home planet ALT-C printer setup menu (DOS) CTRL-K add a new comet ALT-D display menu (DOS) CTRL-L toggle legend ALT-E enter RA/dec CTRL-N find NSV star ALT-F File menu CTRL-T measurements menu ALT-G "go to" menu CTRL-U set mag text limit (DOS) ALT-H Help menu CTRL-V or \ find variable ALT-I inversion dialog CTRL-X enter longitude ALT-K go to comet CTRL-Y enter latitude ALT-L "flashlight" mode (DOS) CTRL-Z enter altitude ALT-M select video mode (DOS) F1 get help ALT-N show full sky view overhead F2 print (DOS) ALT-O overlay menu F3 set current time ALT-P Create a PostScript chart F4 scope control ALT-Q "quick info" F5 user object dialog ALT-R red mode toggle F6 reset level size ALT-S settings menu F7 toggle to prev chart (DOS) ALT-T time dialog F8 create list of stars (DOS) ALT-U find 'opposition' point F9 color settings menu ALT-V "freeze" view (DOS) F10 "stretch" printouts (DOS) ALT-W horizon dialog [ double anim rate Alt-X Extras menu ] halve anim rate ALT-Z north/zenith up { go to mark menu I find IC object | delete a mark M find Messier object } save a mark N find NGC object SHIFT-F1 rotate chart (DOS) SHIFT-F2 change scope delay time (DOS) SHIFT-F3 add to print queue (DOS) SHIFT-F4 flush print queue (DOS) Shift-F9 Tables menu (DOS) Shift-F11 Extract A1.0 (DOS) Tab full-screen mode (DOS) Click on a point with right mouse button to get info on an object Click on a point with left mouse button to recenter on that point Click on a point with middle mouse button to recenter on that point and simultaneously zoom out one level Click and drag right button to find distance and position angle Click and drag left button to zoom and recenter Hpmag Magnitudes given by the Hipparcos dataset were measured using a device sensitive to a wide range of wavelengths (mostly visual). These magnitudes are unique to the detector on the satellite; they correspond roughly, but not exactly, to visual magnitudes, and are called "Hipparcos magnitudes", symbolized as Hpmag. HR Bright Star The Yale Catalog of Bright Stars, or HR catalog, is a list of 9,096 of the brightest stars in the sky. This isn't a lot of stars -- in fact, it's much smaller than the 258,857 stars in the SAO catalog or the 18 million objects in the GSC catalog -- but it does contain a lot of interesting information on each star, such as its Bayer and Flamsteed designations, proper motion, parallax, magnitude, and miscellaneous comments. You can find a star's HR number by clicking on it with the right mouse button. (Of course, it may not have one.) You can go to any HR star by using the Go to Yale (BSC) option in the Go to Star menu, in the Go To menu. Hubble class Some galaxies shown by this program have been classified as elliptical (E), spiral (S), barred spiral (Sb), or irregular (I), or other categories, known as the galaxy's Hubble class. IC Index Catalog The IC, or Index Catalog, is an extension of the NGC list of galaxies, nebulae and clusters. It contains positions and descriptions for over 5,000 objects. illuminated As planets and moons move in their paths, the amount of area that appears illuminated varies as well. For example, at Full Moon, almost 100% of the Moon is illuminated; at New Moon, almost 0%. A solar system object's apparent brightness varies according to how fully illuminated it is, how close it is to you, and how close it is to the Sun. Among planets, Mercury and Venus range from 0% (no illumination) to 100% (full illumination). They can do this because they orbit more closely to the Sun than we do, and can pass between us and the Sun (just as the Moon can). The other planets are always close to 100% illuminated. inclination of orbit Most objects that circle the Sun have orbits in roughly the same plane as the Earth's orbit, called the ecliptic. That's why the planets, and most asteroids, are always found in a fairly narrow band around the sky, passing (mostly) through the zodiac constellations. The angle of an object's orbit with the Earth's orbit is the inclination of orbit, measured in degrees. For most asteroids, this is under ten degrees. index marks ( The index marks menu option toggles between the addition of index marks to planetary trails, and their omission. When you click this item on, you'll be asked for the frequency at which index marks should be added to trails. If you are creating (or have created) a trail with the animation step size set to two days, for example, and you would like an index mark every ten days, you would enter 5 here. You can reach this option at any point in Guide with the ( hotkey. infrared The human eye can see a range of visible light from red to blue. Light just outside the red limit is called infrared, or "heat", radiation. Its wavelength ranges roughly from 1 millimeter down to 700 nanometers. As you might expect from "heat" radiation, infrared radiation is associated with warm objects. For example, some night-vision equipment detects warm-blooded animals by the infrared radiation they emit. The IRAS satellite examined a wide range of objects, such as galaxies, comets, and asteroids, in the infrared. interference interferometry speckle interferometry interferometer interferometric When you have two (or more) sources of light at the same wavelength, the waves can either add together or cancel out. This process is called interference, and the gadgetry that makes use of this fact is called an interferometer. The first astronomical use of this was in the 1920s, when it was used to find the angular diameter of the star Betelgeuse in Orion. Betelgeuse is large enough so that, with the right equipment and the correct setting, the hills in interference patterns caused by light from one side of the star would just fill up the valleys in those caused by from light from the other side. By measuring where that happens, you can determine the angular diameter of the star. Unfortunately, current interferometers can only measure the sizes of a few stars with very large apparent diameters. Inversion dialog ALT-I The Inversion dialog lets you invert or flip the screen to match what you see in your telescope. Because your average scope does involve mirrors and lenses, it's likely that by the time an image passes through and is reflected by all of them, it will be oriented in one of the following ways: upright inverted flipped N/S flipped E/W All four options are available in this menu, with the current choice marked with a check mark. The menu also has an option for adding any desired rotation, and four radio buttons to select between celestial north, the zenith, or ecliptic or galactic north at the top of the chart. Which way your scope actually flips the image depends on what kind of scope you have and what eyepieces you are using. You can reach this menu at any time with the ALT-I hotkey. Also, if the legend is shown and the compass box is turned on, you can click on the compass box to reach this menu. @c 50,135,15 head @m 50,150 start at neck @l 50,180 go to crotch @l 35,210 right foot @m 50,180 crotch @l 65,210 left foot @m 20,125 right hand @l 35,155 rt should @l 65,155 lft should @l 70,185 left hand @c 150,195,15 head: inverted guy @m 150,180 start at neck @l 150,150 go to crotch @l 165,120 right foot @m 150,150 crotch @l 135,120 left foot @m 180,205 right hand @l 165,175 rt should @l 135,175 lft should @l 130,145 left hand @c 250,195,15 head: flipped N/S guy @m 250,180 start at neck @l 250,150 go to crotch @l 235,120 right foot @m 250,150 crotch @l 265,120 left foot @m 220,205 right hand @l 235,175 rt should @l 265,175 lft should @l 270,145 left hand @c 350,135,15 head: flipped E-W guy @m 350,150 start at neck @l 350,180 go to crotch @l 365,210 right foot @m 350,180 crotch @l 335,210 left foot @m 380,125 right hand @l 365,155 rt should @l 335,155 lft should @l 330,185 left hand Io Io is the innermost large satellite of Jupiter. It is about the size of the Earth's Moon, and is one of the four large Jovian satellites found by Galileo. Most of what we know about Io comes from the Voyager flybys. These show a geologically active planet, complete with volcanoes and a thin atmosphere. Io is about as far from Jupiter as the Earth is from its moon. From Io, Jupiter's diameter would appear to be that of about forty full moons. ionized ionizes ionization "Normally", an atom will have a net electrical charge of zero; it will have a nucleus with a certain number of protons and neutrons, surrounded by electrons, and the number of electrons and protons will be equal to each other. Under some circumstances, though, one or more electrons will be stripped from the atom; this is known as ionization. It takes energy to accomplish this separation; this can be provided by having the atom absorb a highly energetic photon (of ultraviolet or higher energy), or sometimes by having it collide with another atom in a very hot gas. Eventually, the atom and its lost electron are apt to recombine; when they do, they will emit a photon. IRAS Many galaxies will have listed, under their "alternate designations", an IRAS designation, from the list of objects observed by the Infrared Astronomy Satellite. In the early 1980s, this satellite performed the first detailed examination of the sky in the infrared. irregular variable Variable stars classified in this program as irregular variable stars are objects that haven't been studied well enough to determine how they vary and, in some cases, what their spectral type might be. Islamic calendar The Islamic calendar is a lunar-only calendar. It makes only a minor effort to track the solar cycle, so a given month can occur in any season. There are twelve months: Muharram (30 days) (holy month) Safar (29 days) Rabi'a I (30 days) Rabi'a II (29 days) Jumada I (30 days) Jumada II (29 days) Rajab (30 days) (holy month) Sha'ban (29 days) Ramadan (30 days) (fasting month) Shawwal Dhu (29 days) Dhu al-Q'adah (30 days) (holy month) Dhu al-Hijjah (29 days; 30 in leap years) (holy month) As you can see, months alternate between 29 and 30 days, for an average month length of 29.5 days. The actual average "lunar month" is 29.530588 days; to accommodate this, an extra day is inserted into the last month in 11 years out of every 30. The resulting calendar month is about 2.9 seconds shorter than the real lunar month. In theory, months begin with the first sighting of a crescent moon. This gives rise to several problems, such as the fact that you cannot create a calendar in advance (though some work has been done to improve predictions of crescent visibility). The above system, used in Guide, is also used in some Muslim countries. The Islamic calendar begins with 16 July 622 (Julian calendar), which corresponds to 1 Muharram 1. Be aware that there is some dissent on the subject of this starting point, with some sources stating that the date should be 15 July 622. isophotes By default, Guide draws the Milky Way and some prominent nebulae with their actual shapes. This is controlled with the isophotes option in the Display menu. Turn this option off, and the Milky Way and nebula outlines will vanish. The isophotes shown by Guide were created by Eric-Sven Vesting as part of the Nebula Databank, and were derived from RealSky images. This makes them extremely detailed and precise. Unfortunately, RealSky doesn't extend below -16 declination, and the nebulae isophotes therefore stop at that point. IUE The IUE, or International Ultraviolet Explorer, was launched in early 1978, and placed in geosynchronous orbit over the Atlantic Ocean. Its sole purpose is to examine the spectra of objects in the ultraviolet, in the 50 to 3000 Angstrom range (just below the range visible to humans). This has to be done from space, since light in that range is absorbed by the Earth's ozone layer. The spacecraft has a 45 centimeter (18 inch) telescope, with two spectrographs and television cameras to collect the data. It has collected a great deal of data about most of the brighter stars, as well as assorted novae, comets, and supernovae. It was intended to last three years, but as of this writing (January 1993), is still collecting data.