This program is now obsolete, and is replaced by RTGUI, a 32-bit Windows application. See
www.debunker.com/astro/rtguipage.html .
The old MS-DOS RT program remains available at www.debunker.com/astro/rt_702.zip There will be no further enhancements or bug fixes.
(This document was last updated Aug. 21, 2003, for the final Version 7.02 )
This software may be freely distributed and copied for non-commercial uses, provided that the program and this documentation file are not modified in any way. This program may not be sold, and is provided without any guarantee or warrantee whatsoever. Use this program at your own risk. You should watch your telescope carefully whenever it is in motion, and stop it immediately if any problem is detected. The author is not responsible for any possible equipment malfunctions or injuries caused by this software, or by careless use of mechanized telescopes. Do not utilize "Goto" functions in the daytime to avoid the danger of permanent eye damage from slewing in the vicinity of the sun. Do not attempt to observe the sun unless you are using a proper commercially-manufactured solar filter.
Features of "RT": Rapidly locate stars or deep-sky objects from catalogs Locate Sun, Moon, and Planets Controls some "Goto" telescopes to slew directly to the selected object! Displays Altitude and Azimuth of Astronomical Objects In Real-Time Creates observing log, automatically records significant data
System Requirements and Installation: Runs fine on practically any PC, requires only minimal system resources. Runs in a DOS box under Windows, or using "Windows explorer". Unzip RTASTRO.ZIP to any directory (recommended: c:\rtastro). Open an MSDOS prompt (Start->Programs->MS-DOS Prompt) and from inside it "cd" to the directory where RT was installed. Type "rt". A shortcut to the desktop is recommended.
"Goto" Telescopes Supported: Version 6.0 supports the following Celestron telescopes: Original "Baby Nexstar" family: Nexstar 60, Nexstar 80, Nexstar 114 family;The original Nexstar 4. Nexstar 5 and Nexstar 8 Nexstar 11GPS, 8GPS; the new Nexstar 4; and the new "Baby Nexstar" family (60, 80, 114).
Description: This software allows one to determine an object's position and visibility very quickly. It also allows one to select a sequence of objects according to magnitude, constellation, object type, or elevation, and locate each one. You can make observing notes on each object, with real-time data automatically saved in the observing log. RT corrects the positions of objects in catalogs for precession, and also corrects their apparent position for atmospheric refraction. It contains a very accurate determination of local sidereal time. This information is updated continuously, yielding accurate real-time values for an object's altitude, azimuth, and for sidereal time, for as long as you wish.
Supported "Goto" telescopes can be made to slew directly to the selected object using the option "G". Your telescope's data connector must be attached to one of your computer's serial ports (COM1 - COM4) using a special cable, in accordance with the instructions provided in your telescope's manual. No attempt will be made to slew to an object that is not above the horizon. However, if the time on either your telescope or on your computer is set incorrectly, this may cause an attempt to slew to an object below the horizon. You must always watch your telescope when it is in motion, and be ready to stop its motion if something goes wrong.
RT allows you to select an object, for which the altitude and azimuth are displayed in real time. You will see these values constantly changing, as the object marches across the sky. The program also provides a real-time display of local clock time, GMT, and local Sidereal Time. Upon entry, it reads the system clock, from which all the other times are derived. The default background color of the screen is red, which will not interfere with your dark-adapted vision. You also have the option to operate in black-and-white.
This software was initially written to make life easier for owners of Dobsonian reflecting telescopes, which use simple alt-azimuth mountings, instead of the heavier and more expensive equatorial mountings found on many telescopes. However, it has turned out to be quite valuable for observers using other telescopes, or binoculars.
RT is a real-time program, intended to be used on a computer just a few steps away from your telescope. Even if you cannot take your computer to your observing site, RT can be used in advance, to help plan the evening's observing.
There is a default location file named RT.HOM, in which is stored information about the observer's location and configuration. You do not have to repeatedly enter your latitude, longitude, and time zone each time you start the program. If you observe from more than one location, you can create different location (or ".hom") files and load each one appropriately. You can also change the observer's location temporarily, in memory, and you can save your changes to disk. This file also stores the model of GOTO telescope you are using (if any), and the Com port you are using to communicate with the telescope (COM1-4).
Your telescope must already be properly aligned before any Goto functions can be performed. Alignment is performed in the usual way, using the hand controller. Connect the computer to your telescope prior to alignment, but do not attempt to use the RT program until after the scope is successfully aligned.
Telescope Choices:
0. No telescope.
1. Original Celestron "Baby Nexstar" family: Nexstar
60, Nexstar 80, Nexstar 114. Original Nexstar 4.
2. Celestron Nexstar 5, Nexstar 8.
3. Celestron Nexstar GPS family: GPS11, GPS8; new Nexstar 4; new
"Baby Nexstar" family; also Ultima 2K.
The "original" Nexstar 60, Nexstar 80, or Nexstar 114 was manufactured until the latter part of 2001. If you are not sure which version you have, the old controller offers only the "Auto-Align" mode for alignment, the new controller offers several choices. With the original Baby Nexstars (60, 80, 114) and the original Nexstar 4, you must press a key on the telescope keypad between successive slews, or your telescope may lock up and require re-alignment. A reminder is provided for this purpose in the program, but it does nothing for the scope except to remind you to use the keypad. With the new Baby Nexstars, you must put the scope in "RS-232 Mode" before it will accept commands from the PC. Use the "Utilites" menu to set this. While in RS-232 mode, the PC has full control over the scope's GOTO functions.
Catalog Searches: Once inside the program, you can can look up objects, by name, in one of the catalogs. You can also enter the Right Ascension and Declination of any object directly. The default catalog "FULL.CAT" is made up from the following:
MESSIER Catalog, the Floppy Almanac's catalog of all 109 Messier objects (M110 is added later)
NGC Catalog - the full Revised NGC catalog, with a few other interesting objects added at the end. Most of the well-known deep-sky objects can be found by their common names ("HELIX", "VEIL", etc.), using 8 letters or less.
The Yale Bright Star Catalog, Version 5. It contains 9096 stars brighter than magnitude 6.5. Stars can be found in this catalog by their Greek letter designation (ALP ORI) or numeric designation (12 AND). If a star has both designations, the Greek letter predominates, and the numeric designation is not included. A star can also be found by its number in the Yale Bright Star Catalog by placing a Y in front of the number (Y500), or by its SAO designation when preceeded by an S (S 308), but only for those objects that are contained in the Yale catalog.
105 named stars from the Floppy Almanac's Fundamental Catalog of Stars (the Yale catalog is much more complete, but does not contain the stars' common names such as "SIRIUS" or "POLARIS".)
Also included in this package is "RADIO.USN", a list of celestial radio sources. (Since nearly all radio telescopes have alt-azimuth mountings, amateur radio astronomers will find RT to be very useful!)
The default catalog for RT is FULL.CAT. All attempts to find an object ("F") or objects ("M") will initially be made in this catalog. You may change catalogs at any time by typing "C". Each object in a catalog has at least one name, of not more than eight characters, and may have as many as three names. Messier objects can be found by typing their M number (example: M 35). Spaces are ignored during catalog searches, so M35 and M 35 will both find this object. Messier objects appear in the FULL catalog twice; once in the Messier portion of the catalog, and once in the Revised NGC portion under their NGC numbers. The latter entry also contains the more common Messier number, for identification. Some of the NGC objects contain constellation names, others do not. NGC objects are found by entering just their numbers, up to 4 digits (from 1 to 7839). Do not enter the characters "NGC".
Stars can be found by their common names (i.e. RIGEL), or their Greek designation (BET ORI). In the case of multiple stars, there is a number following the Greek letter (GAM1 ARI) that must be allowed for in searches. The Yale bright star catalog number (Y 100) can be used, or the SAO number (S 308) only if the star is in the Yale Bright Star Catalog. These catalogs are in ASCII text form. If you are unsure of what they contain, you can examine them. It is not recommended that you use an editor to change or add items to the catalog, because if the location of the fields on the line changes, major errors may result. RT will add catalog items for you, after you type in their parameters. You may use an editor to remove old items from a catalog, so long as you can delete the line CLEANLY, leaving no spurious characters behind.
I have modified the original MESSIER.USN file to include an object type, and a constellation name. Each object is given an object type of up to eight letters, either GLOBULAR, GALALXY, DIFFUSE, PLANETARY, OPEN CLU, or STARS (for Messier's little errors!). Each item also contains its constellation name, which is truncated at eight letters where necessary. Any unique truncation of a name is permissible; for example, GLOB will do for finding a GLOBULAR. To find a unique object, type "F" and enter its designation, such as M31. To find a sequence or category of objects, type "M" which tells RT to begin a search for multiple objects. You may then enter GALAXY as a name, for example, if you wish to observe galaxies. In this mode, RT allows you to specify a minimum altitude, and all items below this altitude will be ignored. You can also specify a minimum magnitude. Hence, you may choose to locate all galaxies having an elevation of at least 35 degrees, brighter than magnitude 11. RT pauses after finding each object for as long as you like, tracking it all the while, until you tell it to either find the next object, or return to the main menu.
You can also search for deep-sky objects in a given constellation. For example, when Virgo is well-placed for viewing, you can ask it to find all objects containing the name VIRGO. If, while you are searching for an object, you change your mind or discover you have made a mistake, pressing any key will terminate the search, and return you to the main menu. If the catalog contains objects fainter than you are likely to be able to see, you may wish to specify a limiting magnitude when finding multiple objects. If, for example, your telescope (or sky conditions) do not permit you to see objects fainter than magnitude 10, you can ask to see all objects in Virgo of magnitude 10 or brighter. (Not all of the fainter objects in this catalog have their constellation names listed, and a search by constallation name will miss these.) Many entries in the RNGC catalog do not contain magnitudes. In that case, the magnitude will be given as 20. The faintest actual magnitude given is approximately 17. "Magnitude 20" actually means "unknown magnitude," that number being chosen (rather than zero) to enable you to exclude it when searching for brighter objects.
RT recognizes the "star" (*) as a wild-card character. For example, a repeated search on "M*" (or "M *") will find ALL M-objects, one after another. You can use this, for example, to find all M-objects above a given elevation. The first 3 letters of the common name of the object (for example, RIN for "ring"; 2 letters for M numbers of 100 or more) are added at the back of the M-number field. You may find, for example, the DUMBBELL nebula as "* DUM". Only ONE wild-card character may be included in each name string. Spaces are NOT ignored while matching characters occurring after wild cards.
Thus, M27, 6853, and DUMBBELL all refer to the same object. You may find that object in the FULL catalog using any one of these names. You may also truncate the name, so long as the portion entered is unique. For example, you can abbreviate DUMBBELL as DUMB, and still find that object.
Recording Observations: When you have found an interesting object, you may wish to record your observations of it. Typing "O" will open the Observing Log, which is a text file named "RTLOG.TXT". The first time it is opened, it will automatically record the date, local time, GMT, and location, as well as the GOTO telescope type. Each time you open the log for a new object, it automatically records the object's names from the catalog, its current elevation, as well as the local time. This saves you the trouble of entering this information yourself. An input line is opened for you to record your observations. Press "enter" when you reach the end of the line. You may enter as many lines as you like, until you enter a blank line, which returns you to the main menu. RT is not a full editor for the observing log, and it is not able to display or change a line after you have entered it. If you wish to add more notes before moving on to the next object, you may type "O" again; this time the object name and the time will not be repeated.
Finding Solar System Objects: These are not, of course, loaded from catalogs (nor may their position be saved in one). RT contains the orbital elements for each of the major planets, as well as for the moon. By selecting the option "P", you may obtain the current RA, DEC, Altitude, and Azimuth for any of the eight major planets, the sun, or the moon, at whatever time and location is currently specified. Additionally, for each solar system object other than the sun the difference in ecliptic longitude is given between that object and the sun. For example, if the elongation of Venus is given as "40 Degrees Morning", then that object can be seen in the morning sky, 40 degrees west of the sun, as measured along the ecliptic. For the moon, the phase is given: for example, "LAST QTR." If the time or location is changed, information about the object being tracked will be updated accordingly. Solar system objects are "tracked" in real time, exactly like objects from catalogs, although their position in their orbit is only computed once, and is not continuously updated. Because many second-order factors are ignored, the positions of solar system objects are not highly precise, although they should be accurate enough for "goto" purposes.
Converting Alt, Az to RA, Dec: RT also allows you to do the opposite of finding objects in the catalog. When you run across interesting objects in the sky, you can obtain their R.A. and Dec. if you know the altitude and azimuth. This enables you to identify what you have found (and to easily come back to it later). This function is performed using the "W" command, for "where am I in the sky?". Just enter the observed altitude and azimuth from a Dobsonian telescope's "circles", and the program, knowing the current sidereal time, will perform the inverse of the alt-azimuth function, and give you the R.A. and Declination of the object. This enables you to consult your star charts to determine what you are seeing. If there is no Messier object or NGC object near the coordinates of that fuzzy patch you see, you may have discovered a comet! You now have its coordinates, which you can telegraph to the Smithsonian Astrophysical Observatory, Cambridge, Massachusetts, posthaste!
Adding Objects to Catalogs: You can add items to any catalog by typing "A". Whatever object is currently being tracked will be added to the current catalog, unless it is a solar-system object. You may read objects from one catalog, and write them to another. You may also create your own catalog, entering object names and positions via the keyboard. When entering the name of a catalog to RT, you may specify any catalog epoch from 1900 to 2200. If you enter "return" instead of a catalog epoch, it will default to epoch 2000.
Precessing Object Positions: So long as you are operating in real-time mode, the program will "lock on" to the object you have entered, and track its progress in altitude and azimuth in real-time. The coordinates are given for the epoch of the current year. If you wish to adjust these to some other epoch, you can use the "D" command to set the date to any epoch from 1980 to 2199. The object's coordinates will automatically be precessed forward or backward to that epoch. You can then instantly return to real-time mode by typing "R".
All items tracked, whether loaded from a catalog or entered from the keyboard, are adjusted for precession to the current year (except solar system objects, which are not precessed). During the first half of the year, objects are adjusted to January 1 of the current year; after June 30, objects are adjusted to January 1 of the following year. Thus, the positions of objects will be more accurate than in any static catalog. If you load an object from a catalog of one epoch, then add it to a catalog of a different epoch, precession to the appropriate epoch will automatically be performed. All objects being tracked in real-time will automatically be precessed forward or backward to the current epoch. The precession algorithm utilized is an approximation, but is quite good enough for our purposes. It results in far better accuracy than if precession were ignored.
Adjustments for Refraction: In addition to making adjustments for precession, the program automatically adjusts for atmospheric refraction, which causes objects low in the sky to appear slightly higher than their actual positions. An object on the horizon appears to be lifted a full half-degree above its actual position; this falls off rapidly as the object rises. Thus, an object becomes visible when it is actually about a half-degree below the horizon, because of atmospheric refraction. When the Right Ascension and Declination of an object are entered either from a catalog, or from the keyboard, the resulting altitude is automatically increased by the appropriate amount for refraction. Thus, an object less than a helf-degree below the horizon will be given an altitude greater than zero.
When an observed altitude and azimuth are entered using the "W" command, the same adjustment is made in the opposite direction, decreasing the object's apparent altitude to its true altitude, from which its R.A. and Dec are computed. When an object is invisible, atmospheric refraction is ignored. Thus, when you are tracking a rising object in real-time, it jumps immediately from -0 degrees, 34.9 minutes, to 0 degrees, 0 minutes, indicating that it has just become visible to an observer at sea level with an unobstructed horizon view. As an object sets, it also instantly transitions from 0 degrees observed altitude to -34.9 minutes true altitude.
Some minor daily fluctuations occur in refraction, owing to changes in meteorological conditions. Also, as you go higher in altitude, the horizon appears to recede slightly. Thus, an observer at high elevations may be able to see objects which are a little below the horizon at sea level. Neither of these factors is allowed for in the program. Ignoring the slight effects of elevation above sea level and temperature and pressure changes,all objects having zero or positive altitude are potentially observable, and all objects having negative altitude are invisible.
Daylight Savings Time: No attempt was made to automatically adjust for DST in the program. You have two options on how to deal with this.
A: Leave your system clock set to Standard Time all year. This is workable, but may at times be inconvenient.
B: Twice a year, you will use the "L" option to change your "RT.HOM" file as well as any other location file you may be using to reflect the changing offset from Greenwich Mean Time. For example: in the Pacific Time Zone, while on Standard Time, you are 8 hours earlier than GMT. While on Daylight Time, you are 7 hours earlier than GMT. You must change this whenever you go on or off Daylight Time.
Check your Computer Clock: Many computers' internal clocks are not highly accurate, and may run several minutes fast or slow over the course of weeks. Also, some programs interfere with accurate timekeeping. The successful use of alt-azimuth setting circles requires that the time be accurately set. Before you begin a night's observing, set your computer's clock by some accurate time source. Many programs exist to set the time accurately over the internet, from time servers. You may also use the start of a radio network's hourly newscast, or short-wave radio time signals. Because the "Goto" slewing uses RA and DEC instead of alt-az, it is less susceptible to minor errors in timekeeping.
Searching for Deep-Sky Objects: When you type "F", to Find an object in the current catalog, RT will find only one object, the first to match the string you type. If you type "M" you can find a sequence of multiple objects. You can "goto" any of these objects that you choose. It will then give you the option after finding each object to either return to the main menu, or else find the next object in the catalog matching that ASCII string, if any. Thus, if your string is M 2*, and you choose N for Next, it will subsequently find M 20, M 21, M 22, etc. You can sequentially examine the positions of ALL of the M objects if the string you enter is M * (or even just *). If there are no further matching strings in the catalog, the current object will be kept, unless a matching object was found, but was rejected because it was below the minimum altitude.
Customizing your own "tour": You can set up your own "sky tour," much better than the one in your scope's Hand Controller. Type "M" to start a multiple search. You can then enter "*" to locate all objects having an altitude of at least 45 degrees and a magnitude of at least 9. Or you can search for every "GLOBULAR" above 40 degrees elevation brighter than magnitude 10. The possibilities are endless. (Messier objects will appear twice in this tour). When a star name appears in the tour, you have seen all of the deep-sky objects meeting your criteria.
Using the Observing Log: You can easily take notes on the objects you observe. The observing location, time, object name, object altitude, etc. are automatically recorded when you access the file RTLOG.TXT, so you need only enter a description of what you see. After your observing session is completed, RTLOG.TXT may be edited or examined using any standard text editor such as "Notepad", and the information may be copied onto the Windows clipboard and pasted into other files or other programs if desired. It is probably a good idea to start each major observing session with a fresh copy of RTLOG.TXT, i.e. all of the data previously entered having been moved to its permanent location.
Searching for Stars: You can find most well-known stars by either a common name (SIRIUS or RIGEL), by a Bayer designation (BET ORI), or Flamsteed number (61 Cyg). Spaces are ignored while searching in the catalog, as is upper/lower case. Names may be truncated where unique; if not unique, multiple matching objects may be found. Some of the fainter stars in the catalog can be found ONLY by DM number.
The rules for names in the catalog are:
A. Common name: Just type MERAK. You can also truncate the name, so long as there are enough letters to be unique. If the string is not unique, the search will return the first match that it finds.
B. Bayer Designation: Some examples from the catalog are:
BET UMA
XI GEM
OMI2 CMA
XI 2 SGR
You do not need to worry about the number of spaces between
characters in the name. By using the wildcard character, you can
find all stars in the catalog in Gemini having Bayer
designations: * GEM
C. Yale Bright Star Catalog Number:
Y 300
D. SAO Numbers (only for objects in the Yale catalog)
S 308
E. DM number (only for the 105 named stars):
1302
- 6 1241
Many of the fainter stars can be found ONLY by these designations.
Abbreviations used for the Greek letters are as follows: ALP,BET,GAM,DEL,EPS,ZET,ETA,THE,IOT,KAP,LAM,MU ,NU ,XI ,OMI, PI ,RHO,SIG,TAU,UPS,PHI,CHI,PSI,OME.
Abbreviations for the constellations are as follows: AQL,AND,ANT,APS,ARA,ARI,AUR,BOO, CAE,CAM,CAP,CAR,CAS,CEN,CEP,CET,CHA,CIR,CMA,CMI,CNC,COL,COM, CRA,CRB,CRT,CRU,CRV,CVN,CYG,DEL,DOR,DRA,EQU,ERI,FOR,GEM,GRU,HER,HOR, HYA,HYI,IND,LAC,LEO,LEP,LIB,LMI,LUP,LYN,LYR,MEN,MIC,MON,MUS, NOR,OCT,OPH,ORI,PAV,PEG,PER,PHE,PIC,PSA,PSC,PUP,PYX,RET, SCO,SCL,SCT,SER,SEX,SGE,SGR,TAU,TEL,TRA,TRI,TUC, UMA,UMI,VEL,VIR,VOL,VUL.
How To Construct "Dobsonian Setting Circles":
Without computer assistance, only users of telescopes having equatorial mountings could find unseen objects using setting circles, by dialing the Right Ascension and Declination of the object, after carefully aligning the polar axis of the telescope with Polaris. With this software, it becomes possible for users of telescopes on alt-azimuth mountings to find objects using a different kind of setting circle: altitude and azimuth circles, aligned only to the earth's gravitational and magnetic fields, respectively. Users of simple alt-azimuth telescopes can find objects using "setting circles", just as do their friends who have heavy and expensive equatorial mountings, or computer control. As an added advantage, you do not need to spend time carefully aligning to Polaris or anything else, as the earth's gravitational field can give you your altitude, and the earth's magnetic field can give you your azimuth. While your friends are struggling with their polar alignments, you can be pulling in various deep-sky objects!!
Install a gravity-based device for measuring elevation (a goniometer) in the center of the teflon altitude ring on your Dobsonian. This is a common carpenter's tool, and can often be found in hardware stores. Essentially this is just a weighted needle pointing downward from the center of a protractor, which enables you to directly read the angle of elevation of your tube. You do not even need to worry if your telescope is on perfectly level ground, so long as it is nearly so; the needle points correctly so long as it does not scrape the sides.
Your azimuth circle will be a magnetic compass, the best you can find, with degrees of azimuth clearly marked on the outside ring. Install it on the side of your rectangular wooden tube mount, hanging from a wooden brace like a pendulum, so that it is free to move into an exactly horizontal position. Make sure that there is NO metal anywhere nearby, not even nails or screws.
Next, run RT, and be certain that your latitude and longitude are correctly set as the default in your "home" file. Stay in real- time mode, and find "POLARIS". (It scarcely moves in the sky, thus it is good for calibrating circles). While looking at Polaris in your telescope, carefully adjust both your altitude and azimuth circles until they read what the program says they should read. This does not have to be done each time you observe, but only once, unless your circles are disturbed.
You are now ready to begin finding objects with your Dobsonian setting circles. Be careful to keep your magnetic compass away from large metal objects, or other magnets. It is not difficult to achieve accuracy good enough so that the object you want to see is nearly always in the finder field, and often is even visible in a low-powered eyepiece. (Be careful that your clock is set accurately). At worst, you may have to sweep a little.
Robert Sheaffer
Lakeside, California
Version 7.01 - August, 2003
Notes:
1. A Math Coprocessor is required by RT. Some older PCs manufactured in the 1980s may not have one. The program version RTNO87 is available for use on older PCs without a math Coprocessor. The code of the two programs is functionally identical.
2. RT exchanges object catalogs with the U.S. Naval Observatory's "Floppy Almanac" (is anybody using this program today?). Any catalog in that format may be directly utilized. The catalogs from "The Floppy Almanac" are originally from the 1987 version, with positions set to Epoch 2000. They are simply the captured output of the Floppy Almanac's catalog import/export program (CATALOG.EXE), used with option 2, "print catalog". There were several minor omissions in fields in the Messier catalog, principally magnitudes of objects, which have been filled in from other sources.
3. RT does not read status from any telescope, it only writes the current object's RA and DEC to the control port, using the data format proper for that scope's protocol. Do not attempt to "goto" an object when the telescope is already in motion, or when it is not properly aligned.
4. The format of the data in the catalogs is as follows:
Field Field Contents Units Example position format 1-8 A8 Name1, left justified --- ALP2 LIB 9-16 A8 Name2, " " --- ZUBENELG 17-24 A8 Name3, " " --- -15 3966 25-38 F14.10 J2000.0 RA hours 14.8479756946 39-52 F14.10 J2000.0 DEC degress -16.0418025010 53-62 F10.4 J2000.0 p.m. in RA s/cy -0.7350 63-72 F10.4 J2000.0 p.m. in DEC s/cy -6.8310 73-80 F8.4 Parallax arc secs 0.0490 81-88 F8.4 Radial Velocity km/s -10.0000 89-96 F8.4 Visual Magnitude or flux mag, Jy 2.9000 97-100 F4.0 Epoch of Coordinates year 1975