UNIVERSITY COLLEGE LONDON. Use of The Meade LX200 Telescopes

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1 UNIVERSITY COLLEGE LONDON University of London Observatory 1B30 Practical Astronomy Use of The Meade LX200 Telescopes 1 Introduction: The Meade LX200 The Meade telescopes at ULO (two 10-inch Schmidt-Cassegrain telescopes and one 7- inch Maksutov) are part of the Meade LX200 series of microprocessor-controlled instruments. The LX200 telescope is operated from a handset, which performs various keypad functions and has a display window providing access to a number of advanced menu functions. It has a built-in library of celestial objects, comprising 110 Messier objects, several thousand NGC objects, 351 stars, and the major planets; objects in this library can be accessed quickly and easily using the automatic slew functions of the telescope. The telescope also has an interface which permits autoguiding with a CCD camera. The LX200 can be operated on an altazimuth or an equatorial mount, although at ULO the telescope will usually be mounted equatorially. This document is intended to summarize the essential details of the telescope operation for demonstrators and students; it is not intended to be complete. For further information, refer to the Instruction Manual for the Meade LX Handling the LX200 The telescope and its optics are to be treated with the utmost respect: NEVER touch the corrector (objective) lens of the telescope; DO NOT stand in such a way that one may inadvertently breathe on the corrector lens; please treat the eyepieces with the same respect as the telescope: only one eyepiece should be out of its case at any one time; take special care not to touch or breathe on the eyepiece lenses. Two LX200 telescopes are mounted equatorially on pillars in the Fry dome building. On clear nights, a third telescope will either be mounted equatorially on one of the pillars behind the South Wing of the Radcliffe dome, or mounted altazimuth on a field tripod on the roof of the Allen telescope building. For demonstration purposes, this telescope may sometimes be mounted indoors on the tripod. The telescopes are heavy, and for reasons of safety, the mounting of the telescope should always be done by two members of staff, at least one of whom should be a technician. 3 Dome Control The dome control system incorporates two sets of controls one for opening the shutter and one for dome rotation. It is important that one has regard for the safety of individuals and equipment when operating the domes. Always take special care when using ladders or steps. U O L

2 1. Whenever the dome shutter is opened or closed, the telescope must be covered or moved to a position where dislodged grit and dirt cannot fall onto the telescope objective lens. At the beginning of the night, leave the telescope covers on until the dome is fully open. At the end of the night, cover the telescope first before the dome is closed. 2. The park position for the dome is with the shutter to the NE, so that the shutter motor control is SW of the telescope pier and safely accessible from the observing platform. 3. On first entering the dome, and with the dome in the park position, the shutter power-lead should be uncoiled from the stow-hooks (a ladder or step is required) and plugged into the power supply on the South wall. The shutter can then be opened using the controls ( FOR ward). The person operating the controls should stand next to the controls while the shutter is in motion, ready to turn it off if a problem occurs. When the shutter is fully open, the power automatically cuts out, and the controls should be switched to the OFF (central) position. N.B. The power lead must then be disconnected and safely stowed on the hooks before anything else is done. 4. The dome can be rotated using the handset attached to the pillar or on the South wall, or in the control room. 5. At the end of the night, the dome should be moved to the park position and the shutter power-lead uncoiled and plugged in. The shutter is closed by selecting REV (erse), and again, the operator should stand ready by the controls until the dome is closed. The controls should then be moved to the OFF (central) position, and the power lead disconnected and safely stowed on the hooks. 6. Note that when opening the shutter, the lower section gets picked up by default, but obscures the zenith when fully open. If you wish to observe near the zenith, the pick-up section can be left down (obscuring objects at lower altitudes) if one person releases the catches by pulling on the chain while another operates the shutter. The catches engage automatically when the shutter is next closed. The whole process of closing, dropping or picking up the lower section, and reopening takes about 3 4 minutes, so it is not horribly inconvenient to change over; but note that (a) the dome must always be rotated to the park position first, to enable power to the shutter to be supplied; (b) as noted above, the telescope must be moved to protect it from dislodged particles of dirt; (c) efficient observing requires students to think ahead (!) about where their targets are placed to avoid having repeatedly to lower or raise the pick-up section. 4 Telescope Control The telescope is controlled with the handset, using either the keypad control buttons or one of several automatic slew functions. The automatic slew functions are described in 7.

3 4.1 Basic motion control N.B. When the telescope is powered up, the telescope drive is always ON. The keypad buttons N, S, E and W slew the telescope in the chosen direction. The rate of motion is set by the SLEW, FIND, CNTR and GUIDE keys: SLEW is the fastest rate, then FIND (for homing in, perhaps using the finder), CNTR (centring in the main field) and GUIDE (really small adjustments). The rate selection is indicated by the LED next to each key. Students should NEVER try to move the telescope by hand: they should NEVER unclamp the telescope axes NOR should they try to adjust the telescope position using the knurled controls. To do so will damage the telescope control motors. 4.2 Focussing The focus knob is located on the rear cell of the telescope, to the lower right of the eyepiece holder. (For CCD imaging or where very fine control is required, an electric focusser may also be available.) 5 General Precautions when Observing Please take care when observing with the telescope; always make sure that you understand what you are trying to do if you take a decision to move the telescope. In particular, take note of the following precautions: 1. Always think about where the telescope is going to move to before you move it. You should always be able to anticipate (by knowing an object s RA and Dec and the sidereal time) approximately where in the sky the telescope will move to when selecting an automatic slew function. If it then appears to be doing something unexpected, there may be time to take emergency action. 2. Do not use any of the automatic functions of the telescope (GOTO coordinate routine, object library functions, etc.) unless you are certain that the telescope has been correctly set up in ALTAZ or POLAR mode (if you re not sure, check with a demonstrator). If incorrectly set up, an automatic slew to a given position may drive the telescope through the forks; damage shall then certainly be done, either to the dewcap or to a CCD camera mounted at the breech end. 3. Do not unclamp the telescope axes once the telescope position has been initialized in the set-up procedure ( 8), since the telescope will lose its position. In this event, none of the automatic slew functions of the telescope should be operated before the telescope position is initialized again. 4. Watch out that the declination-motor cable or CCD power/data cables do not get snagged when the telescope is moving towards a large (positive or negative) hour angle. 5. In an emergency (e.g., if the telescope appears to be slewing in a direction where something might get damaged) power off using the switch on the front panel. Then go and fetch a demonstrator or technician to switch it back on again and check the system. Note that if observing is to continue, the telescope coordinates will have to be initialized again using a known object.

4 6 Keypad Functions The basic functions of the hand-set keys are summarized below. Telescope motion keys: SLEW, FIND, CNTR, GUIDE: select the slew rate (selection indicated by LED) N, S, E, W: slew the telescope in the chosen direction GOTO: initiates GOTO coordinate routine/slews to library object displayed Display menu keys: ENTER: selects a menu option MODE: exits menus/cycles through the telescope modes PREV/NEXT: scrolls the menu options Library objects can most straightforwardly be selected using the keys: M: Messier objects STAR: stars, variable stars, double stars and major planets; planets are selected by the STAR number 90x, where x = 1 9 (e.g., Jupiter = 905). CNGC: NGC objects Press the appropriate key and type in the numeric identifier for the object you wish to find. ENTER cycles through summary information on the object; press GOTO to slew the telescope to the object. Copies of the Meade star and Messier catalogues, and a subset of the NGC, are available in the control room. Editing functions (for use with numeric keys): ENTER: press and hold to set or change a value E, W: move cursor left and right PREV/NEXT: cycles through alphabet or changes sign (+/ ) Other keypad functions: RET: sets the brightness and pulse rate of an eyepiece reticle; hold the key down and use PREV/NEXT to adjust brightness, and GUIDE/CNTR/MAP or CNGC to adjust the pulse rate. FOCUS: sets the telescope focus; hold the key down and use PREV/NEXT to adjust. Select SLEW or FIND for fast focussing, CNTR or GUIDE for fine focussing. MAP: toggles the map-reading light

5 7 The Display Menu The principal display menus are selected with the MODE key, which cycles through the following 5 modes (the most useful displays for most observers are marked *): Mode 1: TELESCOPE functions/object LIBRARY This mode is the root menu for the TELESCOPE and OBJECT LIBRARY menus. Use PREV/NEXT and ENTER to select the desired menu; these are the most detailed menus and are described further in 6.1. * Mode 2: RA and DEC/GOTO coordinate routine This mode displays the RA and DEC of the current telescope position; ENTER toggles between a display of the altitude and azimuth and the RA and DEC of the current position. [N.B. The telescope measures azimuth through W (clockwise) from due SOUTH; the usual convention is to measure through E from NORTH]. GOTO enables a slew to a given position. The new RA and DEC are inserted using the numeric keypad (use PREV or NEXT to change the sign of DEC). ENTER starts the slew. * Mode 3: LOCAL and SIDEREAL TIME/DATE This mode displays the current local time and local sidereal time. The local time has been set to UT for ULO. ENTER gives a display of the current date (US style: MM/DD/YY). Mode 4: TIMER/FREQ This mode provides a timer, and allows the tracking speed of the telescope to be adjusted, e.g., for lunar or planetary observations. Select the appropriate option with PREV/NEXT and ENTER. The timer is set initially to a 12-hour countdown; use the editing function-keys to change the initial countdown time if necessary. ENTER starts and stops (or pauses) the countdown. The FREQ option allows the drive rate of the telescope to be adjusted in tenths of a hertz between Hz, in order to track an object such as the Moon, a planet or a comet (the lunar rate is 57.9 Hz; the mean planetary rate is 60.0 Hz). The ENTER key cycles through the following options: 60.1 Q sidereal rate (quartz) this is the default 60.1 M manual reset using the editing function-keys 60.1 M manual adjust in steps of ±0.1 Hz using PREV/NEXT. Mode 5: All displays OFF/Brightness adjust This mode clears the display and backlighting. To adjust the level of backlighting for the handset display, hit ENTER and use the PREV/NEXT keys.

6 7.1 TELESCOPE function/object LIBRARY menus The options in the TELESCOPE function menu are: (N.B. The range of available options here is different for each of the telescopes. Only a few functions are described below.) Students should not need to access this menu at all! If it necessary to adjust the telescope set-up or operating mode, this should only be done by a technician or demonstrator. 1. SITE: Option to insert the latitude and west longitude of the observing site (ULO has been preset). 2. ALIGN: Option for setting up in ALTAZ, POLAR or LAND mode of observing; see SMART: (POLAR mode only) Smart Drive functions to correct for a periodic error in the worm gear; see 9. The options in the OBJECT LIBRARY menu are: 1. OBJECT INFO: ENTER cycles through a summary description of the object selected, the RA and DEC, and a block-diagram display of the slew distance to the object. 2. START FIND: Begins a search for library objects close to the current telescope position. PREV/NEXT browse through the object library; GOTO slews to the selected object; ENTER cycles through summary information as in option (1). 3. FIELD: Indicates how many library objects are in the field of view centred on the current telescope position. 4. PARAMETERS: Allows the parameters for an object search or DEMO programme to be defined. The parameters are: 1. TYPE: set the type of object to be included in the search. The GPDCO codes refer to Galaxies, Planetary nebulae, Diffuse Nebulae, Globular clusters or Open clusters. The codes can be switched to enable/disable a search for that type of object. 2. BETTER: set minimum visual quality rating for objects in the search. 3. HIGHER: set minimum altitude for objects to be observed. 4. LARGER: set minimum size for objects. 5. SMALLER: set maximum size for objects. 6. BRIGHTER: set minimum brightness (i.e., maximum magnitude) for objects. 7. FAINTER: set maximum brightness (i.e., minimum magnitude) for objects. 8. RADIUS: set the radius of the FIELD for option (3) above. Use the editing function keys to change the value of a parameter.

7 8 Telescope Alignment In order to observe astronomical objects the telescope must be set up in ALTAZ or POLAR mode, depending on whether the telescope is mounted on an altazimuth or an equatorial mount. This should only be done by a demonstrator or a technician. To specify how the telescope has been mounted, select the ALIGN option from the TELESCOPE function menu; use PREV/NEXT and ENTER to choose ALTAZ or POLAR mode, depending on how the telescope is mounted. 8.1 Setting up in POLAR mode reinitializing coordinates N.B. Only a qualified technician or demonstrator should attempt to go through the full polar-alignment sequence. The alignment of the domed Meade telescopes only occasionally needs refining. For a typical night s observing, the telescope position can be initialized at the beginning of the night, if necessary, by carrying out the following procedure. For a permanently mounted, polar-aligned telescope, the telescope position can be re-initialized, or refined, as follows: 1. find a bright star from the LX200 catalogue of alignment stars (e.g., from Table 1); 2. slew the telescope to the star (using the object library if the telescope is already reasonably well aligned); 3. centre the star in the field of the telescope; 4. call up that star from the object library by pressing STAR followed by the LX200 star number; 5. press and hold the ENTER key until COORDINATES MATCHED is displayed. N.B. In the normal course of observing, if one is too heavy-handed on the ENTER key, one may inadvertently hold it down too long and unintentionally reset the telescope coordinates (while not pointing at the selected object). Of course, this will wreck the pointing. It is worth being aware of this possibility, in case one sees COORDINATES MATCHED when it is not expected! If this occurs, the pointing needs to be correctly re-initialized, of course, before observing can continue. 8.2 Setting up in ALTAZ mode When set up outside on a field tripod, the Maksutov LX200 7-inch telescope is often used in ALTAZ mode. Although the telescope can be initialized by the above onestar routine, the best alignment and pointing is achieved by using a two-star alignment routine. 1. Make sure the tripod is as level as possible (using the bulls-eye spirit level). 2. The alignment routine begins with a prompt to select one of the stars from its catalogue of alignment stars (Table 1). Make sure that the selected star is clearly visible from your observing site. The observer is prompted to align the telescope with the chosen star; when it is centred in the field of view, hit ENTER. Then a second star must be selected and again centred as before. Press ENTER. 3. Check the alignment by slewing to the coordinates of a known object (using GOTO) and see how accurately the telescope is pointing.

8 Demonstrators note: To set up in ALTAZ mode indoors (e.g., for training), power off and unclamp the telescope; then move the telescope to read 000 azimuth (0 h hour angle) and 0 altitude. On power up, the telescope will be initialized roughly to these values. Check that the telescope is in ALTAZ mode before proceeding. 9 Smart Drive Functions The telescope incorporates a facility to correct for the periodic error of the worm gear: imperfections in the gear will tend to speed up or slow down the drive rate in a repeatable pattern with a period of eight minutes (one rotation of the worm). In general, students should NOT attempt to use this facility; if the Smart Drive has already been trained to make corrections for the periodic error, fiddling with it will ruin the existing rate adjustments. There are five options in the SMART menu: 1. LEARN: Guide on star using NSEW keys; after eight minutes, the training sequence is complete. The rate corrections are retained in memory, even when the telescope is powered off. 2. UPDATE: Repeat the LEARN routine as often as necessary; the Smart Drive will average the training sequences. 3. ERASE: Erase the memory of all previous training (use with caution!). 4. DEC LEARN: Training routine to correct for declination drift, e.g., to compensate for poor polar axis alignment, or to guide more accurately on comets or asteroids. 5. DEC CORRECT: Activate the declination drift correction.

9 10 Training Check List On completion of training, the student should be able to do the following: describe or demonstrate the safe and correct procedures for operating the telescope dome; demonstrate the proper use and handling of eyepieces and other basic equipment; move the telescope in any direction, and select the rate of motion; focus the telescope; display and read the current position of the telescope in equatorial coordinates; display and read the sidereal time, and give a brief definition of sidereal time; estimate roughly where an object of given RA and DEC should be at a known sidereal time; move the telescope to a given RA and DEC using the GOTO coordinate routine; move the telescope to a given library object; define the parameters which govern a search through the object library; search through the object library and slew to chosen library objects. All students will be examined individually and are expected to demonstrate basic competence in operating the telescopes. Author: Steve Fossey Last revision: October 2004

10 Table 1: LX200 Alignment Star Library Name* Bayer α δ HR LX200 h m (LX200 list) Designation Number Number DIPHDA β Cet HAMAL α Ari MIRA o Cet POLARIS α UMi ALDEBARAN α Tau RIGEL β Ori CAPELLA α Aur ALNILAM ɛ Ori BETELGEUSE α Ori BOGARDUS θ Aur SIRIUS α CMa CASTOR A α Gem PROCYON α CMi POLLUX β Gem ALPHARD α Hya REGULUS α Leo DENEBOLA β Leo SPICA α Vir ALKAID η UMa ARCTURUS α Boo ALPEKKA α CrB ANTARES α Sco VEGA α Lyr ALBIREO β Cyg ALTAIR α Aql DENEB α Cyg ENIF ɛ Peg FOMALHAUT α PsA MARKAB α Peg * Italic font indicates star is not easily observed from Mill Hill. Bright Star Catalogue number (HR = Harvard Revised). LX200 catalogue number.