by
Tom Harrison
(1/29/02 Version)
Preface: The Basics
While we have attempted to make the 16" telescope as easy to use as possible, no matter what we do, events will happen that require you to understand how the telescope, dome, and software operate. This is especially true if you plan to use some, or all of these components, in the computer-controlled mode. But no matter how you use the telescope, you must know the sky well enough to find and identify a 1st magnitude star!!! Due to the wide range in experience level encountered within our department, this manual is written at a level that will allow those with extremely limited observing experience to properly use the 16" telescope. We apologize in advance to experienced observers. We start with a simple message:
***It is impossible to make a telescope completely foolproof***
The Telescope Mount:
The 16" Meade LX 200 is a fork-mounted equatorial telescope. The polar axis of the telescope is parallel to the long forks holding the optical tube assembly ("OTA"), runs through the center of the Hour Angle bearing, and, ideally, points to true north (the point defined by the rotation axis of the Earth). That is, the angle between the polar axis and our horizon is exactly our latitude: 32.277o. If the telescope was perfectly aligned (ignoring the effects of atmospheric refraction), a motor/gear system that completed one revolution of the Hour Angle axis per day would allow us to track astronomical objects. This, of course, is never the case. First, the polar alignment of the telescope will never be perfect (given how difficult it is to adjust the 16", it will remain imperfect!). Secondly, no motor or gear system is so good that perfect tracking is achieved. This is especially true of our 16", and of Meade telescopes in general. At the current time, there remains an rms tracking error of 3-5" in a four minute exposure near the equator. We have been told that this is as good as you can ever hope to expect with a Meade telescope.
Telescope Pointing:
Given a perfectly aligned equatorial telescope, it should be a simple case to point the telescope accurately enough for the desired target to be close to the center of the eyepiece field or CCD chip. But before you can blindly point the telescope, the telescope must know where it is starting from! The telescope control software must accurately know a) its geographical location, b) the local time and date, and c) the current position/pointing of the telescope. Thus, somewhere along the line, these attributes have to be set. In all cases, we will have the geographical coordinates physically entered into the relevant software [but if they are lost, the campus coordinates are: Longitude = 106o44'55" (= 106.7486o), Latitude = 32o16'38" (= 32.277o)]. The time must be set using an accurate source (e.g., the GOES suitcase clock described below). Finally, the telescope must be pointed to a known position (either a star, or a defined startup position, such as the "home", or "park" position). Currently, the telescope does not blindly point very well. For small movements of 10 degrees or so, the pointing is usually excellent. If one goes from far over in the NE, to far over in the SW, the pointing can be off by 2o! If we get the TPOINT software, this should improve dramatically (r.m.s. pointing of 12" has been obtained with Meade telescopes). We will discuss the ways to set the clock (see chapter 8) and the telescope positioning, below.
As we describe later, we have installed a limit switch on the declination axis to prevent the slewing of the telescope so far north that the CCD camera would be damaged by running into the hour angle axis. There is no such limit switch to prevent you from slewing, or tracking the telescope so that it is upside down (so that it breaks the cables and connectors). TheSKy software package will have appropriate pointing limits installed, but in manual mode, the telescope is not smart enough to know whether an object is above, or below the horizon! Also, the telescope, if left powered on, will continue to track: if you remember only one thing when closing up at the of end of a night, remember to power off the telescope when you leave!
The Dome:
To follow and keep the slit aligned with the telescope requires that both the dome and the telescope know where they are, and that the telescope control software is talking to the dome. We will discuss how to establish proper communications, below. To allow the dome to properly track the telescope requires some fine tuning, especially given the off-centered positioning of the 16". This has been done, and should not need further adjustment.
The Optical Tube Assembly:
The Schmidt-Cassegrain telescope consists of three optical components: a concave spherical primary mirror (16.375" in diameter), a convex aspheric secondary, and an aspheric (16") Schmidt corrector. For good image quality, exact alignment of these components is essential. This includes the relative, rotational (azimuthal) position of the corrector plate as seen by the primary! When assembled at the factory, a null test is used to find the best possible orientation of the corrector plate. Thus, disassembly of the optics components should not be attempted without proper guidance. The secondary mirror can be quite easily adjusted to improve the centering of the optics, but note that it can be loosened sufficiently to allow it to fall down onto the primary! So please do not tamper with the optics. Even proper cleaning requires special care, and should only be done under proper supervision. Remember that this telescope cost $16,000, and will be difficult to replace.
Currently, focusing the telescope can be somewhat painful. In this telescope design, focusing is accomplished by moving the primary mirror. The mirror slides up and down on the central baffle tube, and rocks back and forth, and has considerable backlash. There is a quick and easy fix for this, and we hope to implement it soon.
The CCD Camera:
The CCD camera is also straightforward to use. The only moving parts are the filter wheel, and the camera shutter. However, to achieve low-noise performance, the CCD chip must be cooled. Thus, before one can begin imaging, the chip has to be cooled to its operating temperature. There is a stand-alone CCD imaging software package that can be used to set this temperature. Like the telescope and dome, the CCD must talk to the computer, and thus a link needs to be established. The ST-7 CCD camera has an auxiliary, smaller CCD chip for autoguiding. We will describe the operation of the CCD camera in a separate chapter. Note that there is a special box attached at the telescope focus with an internal flip mirror that allows light to be sent to the eyepiece, or to the CCD.
Organization of this Manual
We have organized this manual with chapters in order of increasing sophistication. The first three chapters allow you to quickly get on the sky, and start observing in a manual mode, and closing down at the end of the night. The fourth chapter describes computer-controlled observing-this should be the normal mode of operation. The remaining chapters describe the more technical aspects of the observatory. At the end, we have compiled technical reference documentation to either help debug various problems, or full descriptions of how the various aspects of the telescope, dome, CCD, and other software packages work (including manufacturers manuals).
While we first describe how to observe without using the computer, it is very easy to observe using "TheSky" software package, and we recommend that you only resort to the basic, manual observing modes, in cases of emergency (such as a dead computer or cabling problem). Without some care and experience, manual observing will probably cause the telescope and dome to lose their auto-pointing capabilities. Note that the manual observing procedures do outline how to power-on the telescope and dome. Please read these sections to familiarize yourself with those aspects of the observatory.
After the sections on observing with the 16", we have assembled some basic trouble-shooting guides for aligning the finder scope, power problems, image quality issues, and homing the dome. As experience is gained we will certainly encounter other problems. Please make notes of these problems, including what you were doing right before the problem occurred (if anything). Then pass them on to the appropriate person.
Table of Contents
1. Basic, Fully Manual Observing, Opening Procedure ..................... 6
2. Basic, Fully Manual Observing, Closure Procedure ..................... 7
3. Observing using the LX200 hand paddle-"deep sky" objects & more .................... 8
4. Computer-Controlled Observing: Start-up ..................... 10
5. Computer-Controlled Observing: Shut-down ..................... 13
6. Troubleshooting Dome problems & Understanding how it works ..................... 14
7. Improving Telescope Pointing Accuracy ...................... 15
8. Setting the telescope time and date ...................... 16
Everything else is yet to come!
1) Manual Observing: Opening Procedure
If you want to get on the sky quickly, and just look at objects such as the moon, this is the start-up procedure. *****Note that computer-aided observing is now the norm, and manual observing will cause problems with the "home" locations of the telescope and of the dome, and should probably not be used!*****
Step 1. Power on the telescope using the small (slide) switch on the telescope "Power Panel" (if you can't find this switch, see the Meade LX200 manual, Figure 7, their page 28, for the switch location).
Note that the telescope should execute some small motions (you can hear the motors whirring), and that several of the red LED segments should light. If not, see troubleshooting power problems, below. The hand paddle LCD display should briefly read "Meade", flash '16" Version 8.37L', and then finally say "Telescope/Object Library" (on separate lines).
Step 2. Power on the dome rotation box, and the shutter control box.
The dome rotation box is by the eastern doorway. It has the "dome right", "dome left" buttons on it. The power is the rocker switch on the south side of the box. The central, red LED should light. The slit control box is located near the base of the dome opposite the slit. The power switch is located just as the rotation box (that "power on-off" button on the front face of the box with "stop" written above it is the emergency stop, and has nothing to do with the power!). It also has an LED to signal the presence of power. The "home" position of the dome under computer control (see chapter 4) has the slit oriented to the south. You might have to rotate the dome using the "dome right"/"dome left" buttons to move the box to a convenient location.
Step 3. Open the Shutter
Press the open windscreen button. This will first open the shutter, and then lower the windscreen flap. If for some reason you hit the emergency stop button (resist this urge), you must cycle the power on the shutter control box to reset this box, and allow further motions (see chapter 6). Alternatively, one could open just the shutter ("open sh" button), and windscreen separately.
Step 4. Remove the telescope objective cover.
Using the hand paddle, slew the telescope eastward until you can reach the metal cover that covers the corrector plate at the top end of the telescope. Remove this cover slowly (it sticks partially due to vacuum pressure), and place it out of the way of foot traffic.
Step 5. Slew telescope using hand paddle, align dome slit with right/left buttons, locate objects using the finder scope, and observe!
2) Manual Observing: Closure Procedure
Step 1. Replace the telescope objective cover, power-off telescope.
Manually slew the telescope to an eastern position, and replace metal objective cover. Then slew the telescope back to a vertical position. Turn the telescope power switch to "off". This is critical, or else the telescope will wind-up the various cables, and possibly destroy vital components! If you remember to do one thing, and one thing only, make sure it is turning off the telescope power.
Step 2. Close shutter and windscreen. Turn off shutter power.
Rotate the shutter control box to a convenient azimuth, and hit the "close all" button. The windscreen will first close, and then the shutter will follow. After this is done, simply turn the power off.
Step 3. Turn off power to dome rotation box.
Step 4. Close the observatory doors and lock them.
3) Manual Observing using the LX200 Hand Paddle
The LX200 series of telescopes have an internal computer that allows the telescope to point and track, as well as store catalogs of various types. To access these, you must become familiar with the hand paddle. If you are not already familiar with the hand paddle, please read the 16" Instruction Manual's "The LX200 Keypad Hand Controller" section on page 25 of the manual for a description of the various buttons. You will need to understand this if you wish to use the hand controller to access the various hard-wired features of the LX200. Other than setting the telescope's internal clock, calibrating the pointing, and selecting catalogued targets, you should not mess around with the hand paddle, as you could reset many VITAL telescope parameters!
Note: If you ever press the wrong paddle key and get stuck somewhere you do not want to be, simply press the "MODE" key, and it will take you back to the startup menu/window.
The opening and closure procedures are identical to those for "Manual Observing" described on the preceding two pages.
Step 1. Finding a Bright Star
Once you have got everything powered up, and the dome opened, we need to find a star that is known to both you and the telescope. In the summer and fall, Vega is a good choice. In the winter and spring, Betelguese or Capella are excellent choices. Beginning on page 51 of the 16" Instruction Manual are some rudimentary sky maps to get yourself oriented. The centerfold of Sky & Telescope is also useful for this purpose. An abbreviated list of useful bright stars for use with the 16" (including catalogue numbers) can be found on page 50 of the Instruction Manual.
Find one of these bright stars, manually slew the telescope and dome to this star, and center it in the telescope's main eyepiece.
Step 2. Calibrating the Telescope Pointing
Once the star is centered, hit button "6" on the hand controller (this button also says "STAR"), enter in the catalog number (for example Vega is star 214), and press the "ENTER" button. The LCD display will show an abbreviated description of this star (including its V magnitude). Now hold the ENTER button down until the hand paddle beeps. This calibrates the telescope's position (setting the internal sidereal clock).
Step 3. Slewing to a Catalogued Object
The LX200 has an internal catalogue containing 64,359 objects. The Messier catalogue is in here, the "Computerized" NGC is in here, as is the General Catalogue of Variable Stars (GCVS). The positions of all eight planets are known to the 16", as are some 351 stars of interest (calibration stars, double stars, etc.). There are a number of ways to access this data, and I refer you to the Instruction Manual, pages 37 to 40 to see how to use them, and to Appendix C (page 53) for the complete list of what is stored in the LX200's memory.
It is likely that you will only use a few of the these routines, the bright star and/or planet locator, the Messier catalogue, and possibly the CNGC catalogue (I have found the GCVS access to be nearly useless).
A hint on getting good pointing results:
As described in the Preface, the pointing of the 16" is not very good. Slewing more than 10 or 15 degrees at a time generally (not always!) produces poor results. Thus, to slew to a faint target (e.g. M57) it is best to slew to a nearby bright star (e.g. Vega), and calibrate the pointing (Step #2, above).
Bright stars and Planets: For any "star" in the catalogue simply hit the STAR button (#6) on the paddle, input the star's number, hit ENTER, and then the "GO TO" button. If this is an intermediate slew to get close to a fainter target (e.g., a Messier object), center the star in the eyepiece and execute Step #2, above. The LX200 can find all of the planets. They are simply coded as star 901 for Mercury, star 902 for Venus.... to star 909 for Pluto. So, to go to Mars, simply hit STAR, input the number 904, hit ENTER, and GO TO (of course, you should be sure that Mars is above the horizon!).
Messier and NGC objects: These are found in the same fashion as the planets and bright stars. Simply find a nearby bright star, calibrate the telescope pointing. For Messier objects hit the "M" button (number 8 on the keypad), input the catalogue number of the desired object, hit ENTER, and GO TO. For the CNGC simply do the same, but hit the CNGC button (number 3) before imputing the catalogue number.
Other, non-catalogued source positions: If you wish to slew to some source with known coordinates (precessed to 2000.0), the procedure is similar to that used in the case of Messier/CNGC objects-first slew to and calibrate the pointing on a bright star near the source of interest. After this procedure, the coordinates (RA and Dec) of the current position will be displayed on the Keypad. Hit the GO TO button. The keypad will beep, and a blinking cursor will appear on the first digit of the RA. Simply input in the hours, minutes and seconds (in sequence), and then hit ENTER (if you need to back up to correct an error, use the West key). After entering the RA, the blinking cursor now appears on the Declination. Simply enter in the degrees, minutes and seconds of the declination (in sequence). If you need to change the sign of the declination, simply use the West button to back up over the sign, hit the NEXT button, then the East button, and continue entering the coordinates. Hit the ENTER key, and the telescope will slew to the chosen position.
4) Computer-Controlled Observing: Start-up
Step 1. Follow steps 1 and 2 from the Manual Observing "Opening Procedure" on page 6 (i.e., power-on the dome rotation box, the dome shutter control box, and the telescope). Do not remove objective cover.
Step 2. Power-on the computer. First turn on the power at the power-strip, and then the actual computer power (big button on front of the PC).
Step 3. Login. There are several accounts. The default is set to "ta", the password is "lx200emc".
Step 3. Double click on the "Automadome" icon to start-up the dome control software.
Step 4. Then click on dome | link | establish to allow the computer to talk to the dome.
Step 5. Then click on dome | find home to allow the dome to initialize* (that is, to find its "home" azimuth). It will notify you of this when complete.
*At this point the dome slowly rotates clockwise (to the right) to find the optical sensor that defines zero. This should take a few seconds. If the dome continues to rotate, click the "emergency stop" button, then manually rotate the dome back (CCW, using the dome "left" button on the rotation power box) so that the optical Home sensor is just to the north (left) of the actual dome rotation motor. Then re-do step 5. Unfortunately, this will have to be done quite frequently.
Step 6. Now click dome | open shutter, this will (after a brief pause) first open the shutter, and then lower the windscreen. This entire process takes several minutes, and will stop when done. Minimize (do not destroy) this window with a mouse click.
Step 7. Double click on the "TheSky" icon to start-up the TheSky software package--note that this takes about 45 seconds! A star map of the current sky overhead will be displayed.
Step 8. Do a ctrl-shift-D from within this window (the star map window!) to bring up a dome control window. Do a dome | link | establish to allow TheSky to talk to the dome (yes this is done twice during the start-up!). You can now also minimize this window.
Step 9. Having the telescope find its "home" position. If the telescope was properly parked (pointing due south, at declination = 0o) from the last outing (see closure procedure, below, to insure this always happens!)1, we can quickly command the telescope to find its home position from either the TheSky, or using the hand paddle by performing the following steps (if the following is confusing to you, see page 25 of the Instruction Manual for the LX200 paddle).
Finding Home with the Hand Paddle:
On the hand controller keypad press the enter button (from the teles- cope menu, see the LX200 manual page 34, section "b) Using..")
Scroll down (using the "next" button/arrow) to the "home" menu, and press enter.
Select "find" from the home menu and press "enter" (once complete, a message to the success of this effort will result). Proceed to Step 10.
Note: If you ever press the wrong paddle key and get stuck somewhere you do not want to be, simply press the "MODE" key.
Finding Home using "The Sky":
Do a Telescope | Link | Establish within TheSky to allow the computer to talk to the telescope.
Select Telescope | Options | Find Home (home will be searched-for)
If successful, proceed to step 11 (if not, see the footnote).
Step 10. Do a Telescope | Link | Establish within TheSky to allow the computer to talk to the telescope.
Step 11. TheSky will now be able to point the telescope and dome to a sky position of your choosing. But first we need to remove the telescope's objective cover. Click somewhere on the sky map at a position located to the east (about 3 or 4 hours east of the meridian, declination = +30o, works well). A cross-hair target will be drawn around this spot on the sky map, and a window with some random star's catalogue information will pop up. Click on the tiny green telescope icon on the bottom of this window, and hit "ok" on the "Confirm Slew" window that will pop up. The telescope and dome will now slew to this position. Remove the objective cover.
Step 12. Now, click on a bright star (that you can correctly identify) on the map of the sky. A cross-hair target will be drawn around this star on the sky map, and a window with the star's catalogue information (the "Object Information" window) will pop up. Click on the tiny green telescope icon on the bottom of this window, and hit "ok" on the "Confirm Slew" window that will pop up. The telescope and dome will now slew to this star (well, somewhere near this star!). Center-up this star in the eyepiece with the hand paddle. Hit the "Sync" button found in the "Telescope" menu of the Object Information window to calibrate the pointing. Remember, the pointing will not be perfect. Proceed to Chapter 7 for hints on improving telescope pointing accuracy.
Step 13. Start observing by clicking on objects in the sky map, or use one of the many catalogues within TheSky to find objects of interest (use the "Find" option, or help menus or the manual to figure this stuff out)!
Note: currently, the mode of operation just described results in consistent, but mediocre pointing (the object is consistently offset along the North-South axis). I found that pointing/slewing using the hand paddle actually achieved better results (fully described on pages 8 and 9). Until I understand why this is happening, a mixed mode of operation may be best for now. In this mode, follow everything through Step 12, above, but then switch over to the mode described on pages 8 and 9 to slew to various objects (including pointing calibration!). This will require manual rotation of the dome. Then use the shutdown procedure as outlined in the following chapter.
5) Computer-Controlled Observing: Shut-down
Step 1. Slew the telescope to some position located well to the east (as in step 11 on page 12). Replace objective cover.
Step 2. In the pop-up window for the random position used in Step 1 will be a utility for parking the telescope. To access this, click on the "telescope" tab/menu, and click on Park (and then "OK") to send the telescope to its "Home" position (the computer link to the telescope will now be terminated).
Step 3. Turn off the telescope power ASAP (to keep it from tracking too far off the home position).
Step 4. Restore the minimized dome control window. Click dome | park to properly park the dome (it should already be very close after step 2!).
Step 5. Click dome | close shutter to close the windscreen and shutter (done in that order). This takes several minutes, and will stop when done.
Step 6. Click dome | link | terminate to kill the computer link to the dome, and then kill this window (tiny "x" in upper right corner, or, file | exit).
Step 7. Exit TheSky (file | exit, or simply normal Windows kill). Kill the other automadome (the 1st/initial one) that is still running using file | exit.
Step 8. Shut down the PC (normal MS Window's procedure).
Step 9. Turn-off the power to the PC at the power strip, and turn off the power to the shutter and dome rotation boxes. Make sure the telescope power is off! You can turn of all dome power outlets using the right-most light switch by the door.
Step 10. Close and lock doors.
6) Troubleshooting Dome Problems & Understanding How it Works (in progress)
Problem: Computer will not close shutter and windscreen
Solution: If for some reason you manually opened the slit, the computer will not be able to close the shutter or windscreen. Hit the emergency stop or abort button in the dome control window on the PC, and then just manually close the dome using the "close all" button at the control box (see Step 2, on page 7).
Problem: Shutter and windscreen will not manually close
Solution: If the shutter and windscreen will not close, then cycle the power on the shutter box, and then hit "close all". If this doesn't work you are in real trouble, as the shutter box supplies its own power via a recharged battery, and thus, is independent of campus power. You will have to find some way cover the telescope to prevent injuries from adverse weather. We will have to troubleshoot it the next day (Please tell someone/everyone if this occurs!!!!!!)
Problem: Dome does not accurately track telescope position.
Solution #1: The dome may have lost its position. Do a dome | park from a dome control window, and then a dome | home (see the note on page 10). Then re-slew the telescope to a bright star to check that the dome is working again.
Solution #2: In #1 doesn't work, the dome has lost its ability to find its home, or can no longer talk to the telescope. This suggests the need to have an expert help us figure out what is wrong.
Problem: Dome and Telescope are both pointing poorly.
Solution: The observatory dome gets the azimuth data of the object at which the telescope is pointing directly from the telescope, not from TheSky(!). Thus, to point the dome (and/or the telescope) accurately, the telescope has to know where it is in time and space. As described on page 2, this requires an accurate clock time, and geographical position in the telescope software. To see how to set the geographical location, refer to the LX200 manual, section D., page 20. To set the time proceed to chapter 8. Note that the dome position is not updated if you sit in one place for a long time! You have to re-slew in TheSky to update it.
7) Improving Telescope Pointing Accuracy
As we have discussed previously, the pointing of the LX200 is not that great. The
LX200 Instruction Manual discusses how to use two stars to improve absolute pointing in the manual mode of observing. Unfortunately, one of the required stars for this routine is Polaris, which is inaccessible due to our Declination limit switch (resulting from our desire to keep the CCD permanently mounted). TheSky also has a two-star alignment routine, and this should be executed at each start-up.
Step 1. Make sure the telescope's time is accurate (see Chapter 8)
Step 2. Find a bright star and "sync" the telescope as described on page 12 (step 12).
Step 3. Identify two stars in the sky with dramatically different RA's and Dec's (the goal is to have as large a separation as is feasible).
Step 4. Slew to the first star by clicking on the sky map, etc. After the telescope has finished slewing, center-up this star in the eyepiece.
Step 5. In the "Object Information" dialog box, pull down the "Telescope" menu, and choose "Align On", and click on "OK".
Step 6. Click on your second star and slew the telescope there. Repeat the procedure in step 4. After the "OK", a message describing the difference in the real separation between the stars, and the separation perceived by the 16", is produced. (If this number is greater than 0.5o, poor pointing will persist, and there is not much you can do about it!).
8) Setting the Telescope's Time and Date
As described in the preface, the telescope must have an accurate time and date to have even a remote chance of pointing correctly. Note also that the dome gets its azimuth from that generated by the telescope. The following procedure should be used to set the time and date of the computer, and then transfer that to the telescope. This procedure probably needs to be done on a weekly, or monthly basis. (Remember, if the clock is off by 1 minute, the telescope will have a blind pointing error of 15 arcminutes at the equator.)
Step 1. Power on the GOES suitcase clock (on the north wall) and wait for it to sync to the correct (GMT) time (this can take up to a minute).
Step 2. Set the computer's time: At the bottom right of the monitor will be a digital clock displaying the computer's internal, local time. Click on this time to allow you to set the internal clock. Set the local time on the computer clock using the GOES time. During the season of MST, we are 7 hours west of GMT, during daylight savings time, we are 6 hours west of GMT. Subtract this offset from the GOES GMT (yes, the GMT time will usually be on the next day for night time observing from our longitude).
Step 3. Set the telescope's time: After a link has been established to the telescope (see step 10 on page 12), we can have the computer set the telescope's clock. Pull down the "Telescope" menu, select "Options", and "Initialize" (i.e., Telescope | Options | Initialize). Click on the "Set Time" button.
This procedure can also be done manually from the Keypad/Hand Paddle by following the directions on page 19 on the LX200 Instruction Manual.