An Observer's Guide for the 2.4m Hiltner Telescope

John Thorstensen, Dartmouth College

with contributions from Jules Halpern (Columbia), Rick Pogge (OSU) & Eric Galayda (MDM)

Updated: 2019Jan15


PDF Version (88KB)


MDM Observatory's 2.4m Hiltner telescope is among the largest telescopes in the world that always operates without a night assistant.

It is therefore essential that all observers be familiar with how it works, and attuned to their responsibiities. Each observer is responsible to the MDM observer community for the safety of the equipment, and each observer is responsible to the astronomical community for the integrity of their data. If you're attentive, thoughtful about technical matters, and patient with detail, it's not difficult to get good data at MDM and have a great time getting it, but if you gloss over the difficulties, you will pay.

This document is a guide to observing with the 2.4m. It contains checklists for operating the equipment, designed to prompt experienced users who haven't observed recently, and more detailed sections intended to elucidate common procedures for novices. This document is not intended to replace the more detailed manual in the control room (also available in a web-based version). When in doubt, "Read The Fine Manual".

If you read this document carefully, understand the information discussed here and follow the procedures conscientiously, it will help you avoid many common problems and result in a happier and more productive run. I've spent many hundreds of nights observing on the 2.4m over the years since it was built in 1985, and I've tried in this manual to give you the benefit of that experience. Don't just skim it.

I should be careful here to note that novice observers must be trained at MDM in person by a qualified observer before they can observe alone. MDM has a very small staff, and there simply are not enough people on site to train novices. Since it is hoped that novices will read this guide before their first run, I include some material aimed at them, but novices must not arrive expecting to teach themselves how to observe. Seasoned observers with experience elsewhere may be able to get by on their own. However, if you are such an observer, you shouldn't be overconfident -- MDM has idiosyncracies that you ignore at your peril. Don't forget, there's no night assistant to get you out of a jam.

Organization of this Guide

The first part of this guide is a set of terse checklists to prompt the experienced but slightly rusty observer. The second gives detailed checklsts, a version of the terse lists in which background information and reasoning is given at every step. The third is a set of remarks for the first-time observer, essentially an attempt on my part to resurrect some of the good aspects of the observing culture I grew up with. Subsequent chapters offer overviews of the important telescope systems: computers, telescope, MIS, guide/acquire cameras, and so on.

Note that there are quite a few instrument combinations available, some of which I've never used personally. I'll try to make clear when an item or a statement refers only to a particular setup.


Terse Checklists

Some rules ... [Detailed version.]

Before the Run [Detailed version.]

First day [Detailed version.]

Opening [Detailed version.]

During the Night [Detailed version.]

Gotchas! And known bugs. [Detailed version.]

Closing [Detailed version.]

At the end of your run [Detailed version.]


Annotated Checklists

Some rules ... [Terse version.]

Never, never attempt to clean any optical surface.
The telescope mirror reflects light because it has an incredibly thin and delicate coating of aluminum, which can easily be damaged by ill-advised attempts to clean it. Re-aluminizing the mirror is very expensive (around $10,000, or six months of support for a grad student), time-consuming, and not without risk -- the entire back end of the telescope must be taken off and the mirror taken up the mountain. The staff cleans the mirror periodically using specialized techniques. No matter how filthy it looks, it is strictly off-limits to observers. Lenses and filters are also not to be messed with -- their antireflection coatings can be delicate as well. Finally, diffraction gratings are incredibly delicate and cannot be cleaned -- don't even think about it.

Observers are not allowed to repair or modify Observatory equipment, nor to change instruments.
When trouble arises, you are allowed to turn things on and off and troubleshoot -- mindfully! -- in order to get yourself out of a jam, but you're not allowed to undertake major repairs or adjustments (e.g., don't try to swap out an electronics board unless directly told to do so by the staff, don't try to balance the telescope yourself, don't dismount the dewar and try to pump it down yourself). Instrument changes can only be done by the staff -- it's a skilled job requiring specialized tools and procedures. Use common sense!

Respect the telescope operating limits.
These are elaborated on later in this document. The purpose of the limits is to avoid damaging the telescope. Damaging the telescope is not something you want to do. The Director reserves the right to ban careless or incompetent observers from MDM. Don't be one of them.

Observatory vehicles are for official use only.
They're not for sightseeing in Tucson. Strictly business!  

Close curtains and dark shades at night.
The 12-meter radio telescope just down the road uses dim red light at night to avoid disrupting our operations. Let's not give them the idea that bright white light is fine. Also, it looks terrible to see blazing white light pouring out from an observatory at night -- even if the actual impact up at the top of the mountain is minimal, it makes us look like irresponsible tenants. If it's pouring, of course, no one cares that much, but if there's a possibility that anyone is working, button up.

This list is not exhaustive (see checklists).
As an observer you have numerous other responsibilities and stipulations, most of which are pointed out in these checklists as they come up in sequence. Also, any list of rules can't cover all eventualities -- use your judgment!

Before the Run [Terse version.]

Fill out Web-based observing run form.
It is essential that the staff know your plans with two weeks' advance notice. Observers who do not fill out their observing forms run the risk of forfeiting their time!! Go to and bring up the Observing Preparation Form. Note that there's also a great deal of useful information accessible via this page.

Clear early arrival with previous observer.
It's a good idea to arrive the night before your observing run in order to settle in and acclimate. However, you can only do this with the knowledge and permission of the previous observer. Be sure to contact them well in advance to ensure it's OK. The MDM schedule is on the web. If you don't get permission you'll just have to stay downtown. There's a row of inexpensive hotels right by the airport -- La Quinta isn't bad.

Generate coordinate list files if needed.
If you have a lot of targets, you can save considerable time at the telescope by preparing coordinate lists ahead of time. The TCS (telescope control system) expects one object per line of the form
my_object 18 23 23.28 -0 14 14 2000
where the fields are a name without blanks, the RA and dec in the usual sexagesimal form (hours minutes seconds and degrees minutes seconds), and the coordinate equinox (i.e., "epoch"). Note that you can't use colons to delimit the fields - they have to be blanks. Otherwise, the format is free (you don't have to get the information into specific columns). You'll be selecting objects from the list by typing their names, so you'll want to make the names simple and mnemonic (e.g., tausource rather than 4E_0235.27389+123457-a).

If you have lots and lots of targets in different categories, it's also a good idea to split these out into separate lists, which work nicely in the JSkyCalc program.

Review time-and-the-sky if needed, and become familiar with JSkyCalc
If you're a grizzled veteran, you'll know time-and-the-sky pretty well. But if you're a relatively inexperienced observer, or if someone else was calling the shots on that one trip you made, then you'd better get familiar with time-and-the-sky calculations. Even though you've undoubtedly studied this stuff in more than one astronomy class, it's amazing how little of it sticks until you use it extensively. You'll need to understand in your gut (not just your head!) the concepts of right ascension (Quick! Which way does it increase?), declination, sidereal time, hour angle (Quick! How are RA, HA, and ST related?) and airmass. If you're doing stellar spectroscopy you may even need to understand the parallactic angle. You might find my own somewhat elementary monograph on time-and-the-sky to be helpful.

It should be especially useful to spend some time playing with JSkyCalc, which, being in Java, "just works" on almost any computer. I mention this here not just because of pride of authorship, but because at MDM there is a special version for the 2.4m telescope, which lets you select guide stars for your target and move the guide probe with a mouse click. This is extremely useful in guiding and acquisition.

While you're at it, be sure your targets will be observable, and that the moon isn't going to be a problem. JSkyCalc has features designed especially for this, such as the airmass graphs and sky view. You can anticipate and avoid many difficulties through the simple exercise of sketching a dusk-to-dawn timeline for your first night.

Blank data media
There are usually some DVDs at MDM, but it's a good idea to bring along a few blanks, or better yet, an external HD to record your data. If you bring a laptop with a fair amount of free hard-drive space, you may also be able to copy the data onto its drive using scp or rsync (though I'd worry if a laptop contained the only copy). If your data volume isn't too big, you might even be back it up onto a USB memory stick -- but again, I wouldn't make that your only copy!  Data are trypically removed from MDM machines, without notice, after 2 weeks.

The internet from the mountain has somewhat limited bandwidth. If your images are fairly modest, you may be able to just send them home via sftp or scp. If you're taking short exposures with the 4k all night, this may be a bit much. In any case, it is a very good idea to put your precious images on some kind of medium.

Observatory computers run Unix and Linux, with Xwindows - familiarity advisable.
If your home computing environment is Unix, you'll quickly figure out the MDM environment. If you're not familiar with Unix, you should learn the rudiments - how to list directories, change directories, copy and remove files, send mail, and so on. The observatory computers interact through Xwindows, using the K window manager. Most observers won't have any particular issues with it, but if you've been in a cave for the last few decades you might want to look into it.

Ensure that ssh is available on your home machine.
If you anticipate communicating with a machine at home, you should anticipate using the ssh ("secure shell") protocol. Otherwise you'll be sending passwords in clear over the net. That means installing ssh and sshd on your home machine and ensuring that its daemon is properly started at boot time. Your home system administrator can help with this. Either ssh1 or ssh2 is acceptable.

Bring means of payment to settle up vehicle and/or OSMOS slit mask charges (as applicable), and to pay for any meals you take at the Kitt Peak cafeteria.
MDM charges for MDM vehicle use as well as OSMOS multi-object slit mask fabrication. The most convenient way to settle this is through a PayPal account. Charges for meals taken at the Kitt Peak cafeteria can be settled with a check or credit card in the admin. building located at the summit.


First day [Terse version.]

Check out instrument as needed.
This is obviously instrument-dependent. Spectrographs in particular may require substantial tweaking (focusing, setting spectral ranges, etc.). If you're a first-time observer you'll want to spend some time familiarizing yourself with the equipment and the observatory.

Be sure you know the current visitor password.
The password for the visitor account changes frequently. If anything crashes you'll need it to get back up, so be certain you have the correct password.

Copy your coordinate file to hiltner.
If you have one, put your coordinate file in the home directory of visitor on hiltner. You could copy it from from your home institution using scp.

Review any local manuals.
In particular, guiding and acquisition might use a review at this point.

If you are taking any meals at the Kitt Peak cafeteria, familiarize yourself with the check-in procedures at the cafeteria.  Please send an email to MDM providing all observers' names so they can be added to the check-in list at the cafeteria.  The MDM and NOAO staff can help if needed.
Many observers don't take meals at Kitt Peak, but I believe it's a good idea to do so, because (a) it's convenient and relatively inexpensive, and (b) it's a great way to network with astronomers from around the world.

Even if the weather is clear, review the emergency (lightning) shutdown procedures.
A single lightning strike can take out the observatory for many weeks. There is a procedure for shutting the equipment off when lightning threatens, and it's important that you do all the steps in order. Find the documentation and walk through it with the staff to be sure you understand where all the items are.

If you are a first-time observer, walk through procedures and learn as much as possible.
You should have a qualified observer there to do this with.

If instrument had been changed, ask staff if focus has been preset
The different instruments are not par-focal. The staff can set the telescope focus to the anticipated focus for the new instrument, or you can do it yourself using the chart on the bulletin board, but it's important that you don't both do it! Note that focus values can vary considerably with temperature; the aim of the focus pre-set is simply to avoid being grossly out of focus. You can easily get confused on the first night if the star you're trying to find is a huge donut of light.

Become aware of water and electric power conservation.
Both of these utilities are very expensive on the mountain. Get in the habit of conserving them as much as possible. Shower quickly and efficiently (difficult since there's a very long run of pipe between the heater and the rooms).  Be especially aware of water leaks (especially things such as running toilets!).  Run lights and heaters only when necessary, and so on. If you do notice a toilet running, shut off the valve beneath the tank immediately and notify the staff. In an emergency, there is a cutoff valve under a metal plate in the sidewalk just north of the building. Room heaters are especially power-hungry and should be used sparingly -- we do have electric blankets, which draw much less power and work great.

Check sunset time etc. (when to open?); plan observations.
The link points to instructions as to how to look up the sunset time (and much, much more) with JSkyCalc. There's also a little treatise on how to use twilight time to best effect. Now that you're at MDM and have an idea as to what conditions might be like the coming night, it may be worth it to firm up your target selection and set up a timeline for your nights' observations. Of course, the planning needs of different programs are different (e.g. some are very contingent on seeing, which you won't know until you open), and weather can always change, but it's good to have a plan.

Keep an eye on the weather, maybe check it on the web.
The local National Weather Service (, is very good for local weather. It includes a forecast specifically for the Tohono O'odham region (where Kitt Peak is). Also, MDM and Kitt Peak  have links to a great deal of useful information.


Opening [Terse version.]

(For advice on when to open, look here.)

Verify safe weather conditions.

Thanks to the efforts of Jen Marshall (OSU) and Paul Hartmann (MDM), there is a large monitor that displays readings from a weather station located outside the 2.4m dome. There's also an array of humidity sensors on the mirror air conditioning system. The wind limit is pretty liberal, since a 40 mph steady wind is really howling. If the air is dusty (dust storms do occur), you must not open, even if the wind is below the limit.

I repeat here the link to the local National Weather Service site, at

If humidity is OK, be sure guide camera is on and cooling.
We use Finger Lakes CCD cameras for use as guiders, and Andor cameras for slit viewers with Modspec and Mark III. The sensors need to be cooled well below ambient to suppress thermal noise. Even though it only takes a few minutes to reach operating temperature, you'll need the camera very soon, so you should be sure it's running.
Verify that mirror support is working.
The mirror support computer is in the left-hand computer rack. There are three numbers showing forces on the three hard points which position the mirror - they should all be within a couple pounds or better of the nominal value of 29.3 pounds. The telescope must not be moved unless the mirror support air bags are working - moving the telescope without the air bags being up can damage the mirror support system! If the air bags are deflated, the images appear grossly triangular in shape (unusable for any science) and cannot be improved by focussing. If you should see this happen, it means the airbag system has failed somehow. This doesn't happen frequently, but it's important to be able to recognize it.

Open dome.
The dome shutter controls are on the northwest wall of the dome. In order for electrical power to get to the shutter, the electrical contact boxes mounted on the dome and the building need to be lined up. Unless the dome has been moved since it was closed, they'll be lined up. [If the shutter doesn't respond, try moving the dome slightly to get better contact on the electrical feed box. If it still doesn't work after several tries, move the contacts off the electrical feed box and use the backup cable. Don't plug in the backup cable with the dome near the feed box -- that can create a short!]

Top off instrument dewar if needed.
This simple procedure probably causes more trouble for novice observers than any other. It's important to understand the pitfalls.

The first principle is that dewars must be kept cold under all circumstances, and cannot be refilled if they're allowed to warm up. Once a dewar warms up, any volatiles remaining boil off into the vacuum, and if you cool the dewar down without first pumping on it, there's a serious risk of getting gunk on the CCD. Only the staff are authorized to re-pump a dewar -- it's a complicated operation which must be done correctly.

The procedure for a routine dewar fill depends on the instrument. If you're filling one of the MDM dewars mounted in an upward-looking position (e.g. for direct work, or the Mark III spectrograph), be sure that the fill tube freezes into place all the way up, that is with the metal in contact with the metal at the top of the dewar, or you'll get a false fill and likely warm the dewar up during the night. Goosing the platform up just a little bit after the rubber hose freezes can ensure the fill tube is touching the top of the dewar.

Assuming the fill tube is properly set, you can tell the dewar is full when it overflows. Before it actually overflows, it may spit some -- don't be fooled! When it's really full, the overflow is a continuous spray of drops almost like a shower.

If the storage dewars are up to pressure, it should take roughly five minutes to fill an MDM dewar which has been sitting for 12 hours. If it takes a lot less than this, it's probably a bad fill, and You Will Pay. It's a good idea to just let the LN2 run for a little bit after you think the dewar is full -- nitrogen is relatively cheap compared to the expense of running the observatory and getting you there, and a warm dewar is a true show-stopper.

In the upward-looking configuration it is especially important to insert and remove the fill tube straight, without pulling or pushing sideways, as this can loosen the internal fitting which holds the LN2 and create a slow leak; your hold times will go down to a couple of hours if that happens.

Yet another caution about the dewars - Do not start the dewar filling and forget about it, thereby emptying the storage dewar. This is an easy mistake to make, since it's easy to wander off and get absorbed in something else during the 5-minute fill time. This error is very much to be avoided; the consequences are: (a) It wastes money, and the observatory budget is tight. (b) It forces the staff to drop whatever they're doing and refill the storage dewar. (c) If it's a weekend and you're out of nitrogen, you are probably out of luck. So don't be a flake--monitor your dewar fill!

Finally, a note on safety. LN2 is not particularly dangerous, but you should avoid getting any in your eyes and getting more than a few drops on your skin (if it's just a few drops it boils instantly and the vapor layer insulates you.) Be aware that LN2 in a sealed container quickly builds up lots of pressure and may cause the container to explode -- the storage dewars all have pressure release valves for this reason. These valves should be free to open. A little hissing from an LN2 dewar is normal, it's the gas escaping from inside. You want it to escape! Finally, in confined spaces the vapor can suffocate you -- it isn't toxic but obviously doesn't have any oxygen in it. Luckily, the domes are big enough, and the amounts of LN2 we handle are small enough, that this has never been a problem for observers.  Close-toed shoes are crucial when filling.  Gloves and other safety equipment are available in the dome.

Open louvers and optionally garage door.
This and the next few items are good short tasks to do while the dewar is filling. Check the dewar frequently as you go about them.

The dome building walls have louvers that you can open to allow ambient air to circulate through the dome. You can also open the garage door by the loading dock. Allowing ambient air to flush through the dome helps the temperature equilibrate and has the potential to greatly improve the seeing.

Open instrument dark hatch.
Near the top of the MIS, on the east side, there's a little knurled handle - pull it down to release it and flip it to its other position. This opens a dark hatch at the top of the instrument. If instead it feels like it's falling and goes "clunk", then you've closed it (the previous observer left it open by mistake!).

Close shades in buildings, go to dim light
Keep the heavy curtains closed at night, and don't forget the shop area and living quarters. It is very bad form to let excessive light spill out from the living quarters -- even if the practical effect is minor, it's noticed with derision elsewhere on the mountain. Personally I also use only incandescent (or better yet, incandescent-matching LED) light at night, since the bright white ceiling fluorescents are very hard on dark adaptation. It's useful to avoid frying your retinas with fluorescents since you'll want to go out and check the sky from time to time, and the fresher your eyes are, the quicker you'll dark adapt. You need to be quite well dark-adapted to see thin cloud on a dark night.

Obviously, you can "rig for silent running" whenever you want to in the sequence, as long as it's before dark.

Verify dome fully open (it can stick!).
In the past the dome has occasionally tended to stop up on various rough spots on the track, and think it's open. At one point there was a particularly insidious bad spot which left about 2 feet of dome in the zenith. Check carefully, with a flashlight if needed, to be sure the dome is open all the way. If it isn't, hit the open button again and it should continue.

Incidentally, note that the telescope beam is occulted slightly near the zenith even when the dome is fully open. See the manual for a tabulation of this zone.

Verify telescope free
The lift platform must be all the way down or there is serious risk of coming into contact with a slewing telescope. When you're tired or in a hurry, it's easy to make bonehead errors like slewing the telescope with a LN2 dewar still attached. Just check to be sure the space around the telescope is clear of obstructions before you start.

Return to the control room

Verify dome azimuth readout is near 320 degrees. Reset if needed.
To reset the dome encoder, go toTelescope>Initialization>Other Positions tab and set "Dome Position" to 320.  Click "Apply".
Verify BRAKES OFF from TCS Software (Telescope>Misc>Switches tab: "Release Brakes").  If the brakes are ON, there will be indication in one of the status bars near the bottom-right of the Control System software.  If you do have to shut off the brakes, the pads will squeal unless you bang on the calipers.  This causes no damage but can become annoying over time to listen to.

Verify TCS Bridge is running in terminal window on mdm24ws1 machine.  This can be found, typically on workspace 4, in a terminal window called tcsBridge (on hiltner).  To start it, Applications>Telescope Control>tcsBridge.

Incidentally, the observatory computer clocks are set using the network time protocol (NTP), which typically keeps them within a few milliseconds of UTC. If you happen to press a guider camera into service as a science instrument, beware that those machines are not on NTP, and their clocks drift pretty quickly.  Slit Viewer (Andor) machines now query NTP every 15 minutes and set their clocks accordingly.
Silver switches on MDC rack (computer room):

Open mirror covers (Telescope>Misc>Switches tab: "Open mirror doors")
Go out in dome and verify that all four mirror petals are up.  Also, note that mirror pedal status is available via the Control software under Options>Environmental Data/Control>Settings/Status tab.
The mirror petals are driven open by a pneumatic air system. If there's a failure in that (e.g., ice in the lines) they may not come up; also, they barely clear the sky baffle so they sometimes hang on that.

Clearing a hung up mirror cover petal is an intrinsically dangerous operation, but here are the instructions if you wish to try. Firstly, call the Site Manager if possible.  Alert the 1.3m observer and have them come up to watch, or at least tell them that if you don't get back to them in 10 minutes they must come up to summon aid in case you injure yourself. Using the control paddle stored on the west side of the telescope, slew the telescope way over so you can get access to the sky baffle. Get the aluminum ladder and a stick about 5 feet long (e.g., a broomstick). Get up on the ladder. That petal is going to open explosively!!! Look out where it's going to go before you do anything!!!! Once you're sure you won't be knocked off the ladder by the opening petal, gently push on the sky baffle to free the cover. BAM! - the cover opens violently. Stop shaking and climb back down. Tell the 1.3m observer that you're OK.

Check dome lights off, control room window dark shade closed.
Simple stuff but forgettable.

Take sky flats?
If you're working direct, and want to use the twilight sky for flatfield information, now is the time to get the flats. There's only a short time window (about 10 minutes) a little after sunset when the sky is the right brightness for this, so you have to be on the timeline.

You need at least three usable sky flats per filter, so that stars can be medianed out. Don't forget to move the telescope by a field width or so between exposures to make this possible.

Exposure times are problematical, especially since the readout time may be comparable to the timescale over which the sky changes. Note that the JSkyCalc24mGS program computes an estimate of the twilight sky brightness, and auto-updates every 15 seconds or so, so you can simply start the program and read the number off the screen. If you write down the exposure time, filter, average counts and skycalc's computed sky brightness, you can use the information to set the exposure time on other sky flats (in the morning, for instance). For reference, I've found with the Echelle and MDM U filter that I can start with a 2-second exposure when the sun is 3 degrees below the horizon, and skycalc reports 12.3 magnitudes above dark night sky. The U filter will usually be the least sensitive.

Start telescope tracking (Telescope>Rates>Set Sidereal Rate.  Then click Apply.)

Slew to a nearby bright star (choose Nearest Bright Star in JSkyCalc24m on mdm24ws1).

Once telescope has completed the night's initial move, start dome tracking:
If using MIS, configure so guide camera should see bright star: Note that if the telescope is badly out of focus, the star image will appear donut-shaped, because of the secondary mirror obscuration. If you're looking at the star reflected off spectrograph slit jaws, or using OSMOS, you can go ahead and do a crude focus of the telescope by eye at this point. But if you're working direct, you'll want to focus the telescope on the CCD first, which is a more elaborate procedure best deferred for later; see the "focus the telescope as needed" item a little farther along.

Focus telescope as needed
This is instrument-dependent. If you're working direct with the MIS, you'll probably want to get to your first object and run focus frames for your filters. Then, and only then, focus the guider optics so that they are parfocal with the telescope. A similar procedure obtains focus for OSMOS, assuming the instrument is in focus internally (i.e., the slits are focused on the detector); with OSMOS, filters are in a parallel beam so they do not affect the focus. If you're looking at spectrograph slit jaws (CCDS, MkIII, Modspec) the camera you're using should already have been focused on the slit jaws. It suffices then to put a star near the slit jaws and focus by eye. You'll want to use a relatively unsaturated image for this, so a bright star is probably not the best. The focus star should be near the slit jaws since the slit is inclined to the focal plane.

Telescope focus depends primarily on temperature; a feature on the TCS software compensates for temperature changes once you found optimal focus.  The reference temperature for this system is defaulted to "Center Section".  While this can be user-set, it is recommended to leave as-is.  This is found under Telescope>Misc>Focus tab.  

Take some data! You'll probably spend a little time familiarizing yourself with the guiding and acquisition cameras. Read on for what to do during the night.


During the Night [Terse version.]

Keep an eye on the humidity.
Episodes of high humidity can occur any time of year without warning. The weather widget on the work station is color-coded (green=ok, yellow=approaching limits, red=limits reached, you should be closed already) and updates every minute.  It is very good at grabbing your attention when it changes state.  It should always be set to display on all work spaces.

Step outside from time to time to monitor weather.
This is always good sense, and it makes for a welcome break from the noisy control room.

Go into the dome from time to time to check dome & telescope alignment, cables, etc... .

Some hints for efficient operation ...

Here are a few hints, some in the form of links to the relevant material; some are instrument-specific.


Gotchas! And known bugs. [Terse version.]

"OMG, the dome just went haywire!"
Occasionally, the dome may start rotating for no reason. I call it the dome's "fugue state", after a psychiatric condition marked by aimless wandering and amnesia. This is almost certainly caused by a software bug in the TCS. It has always snapped out of it eventually. In the meantime, you can keep observing using the following procedure:

Note that the procedure above can keep you going even in the event of a more serious failure of the autodome system, as long as you can still rotate the dome manually.

The dome only homes in the CW direction.  If you find yourself slightly east of the 320-degree stow position, this results in the dome going all the way around to stow.  It is often easier to simply home the dome by hand in cases like this.


Closing [Terse version.]

Take sky flats?
See the earlier discussion under Opening for details. If you've written down the exposure data on previous mornings and evenings, it should be possible to get a fairly good exposure the first time.

Shut off tracking.
     Telescope>Rates>Track Rates tab: set H.A. Rate to zero (0).  Click "Apply".  Click "Close".
Set dome to stow.  Homing the dome only goes CW in direction.  So if you find yourself east of 320, it may be worthwhile homing the dome manually.
     Telescope>Misc>Switches tab: Set Dome=On, Dome Mode=Home, Dome Target=Telescope; click "Apply"
Slew to zenith.
     Telescope>Movement>Offset/Zenith tab: Set Zenith Position, click "Apply".  Click "Start Slew".  Click "Close".  You should hear a chime when the telescope reaches zenith.
     Telescope>Misc>Switches tab: Set Dome=Off; click "Apply".
Reset instrument rotator to 0 degrees if needesd.
If you've rotated the instrument, you should set it back to zero, at least on your last night.  Remember that the mirror covers must be open to rotate the instrument!
Close mirror covers (do not move rotator with mirror cover closed).
You should ideally be near the zenith to close the mirror covers, though in an emergency you should just go ahead. To do this:
      Telescope>Misc>Switches tab: Close Mirror Doors

Dome lights on.

Close instrument dark hatch.

Close dome.
  • If dome did not return to contacts, turn AUTO DOME off andmanually align dome with the hand paddle.
  • Dropout must close before main shutter.
Note that the main shutter takes a while to close, so you can get it started first, and then hold down the dropout close button until it slams shut.

If there's a problem getting power to the dome - for example, if the rotation fails and you can't get it on the contacts - there is an emergency cable which can be connected. See the full manual for details.. Note that plugging in the cable with the dome on the contacts will cause a short, so don't do that!!

Top off instrument dewar.
Doing this as the dome is closing is a good habit. Don't forget to mark the time on the whiteboard. See earlier cautions on filling upward-looking dewars and not filling warm dewars.

Close louvers and garage door.

Verify that the dome is fully closed.

Back up the night's data.

If you lose the data, your work and the telescope time are gone! It should be sufficient to copy the data to another computer (e.g. a laptop).

The Linux rsync command is your friend here. For example, if you're using one of the Owl-controlled detectors, you might copy your data onto the workstation by making your own directory, cd-ing into it, and typing something like
 rsync -azvt /data/mdmarc1/mydir/night1 .
This will make a copy of "night1" in your current directory. If "night1" already exists, it will copy only new files or files that have changed.

There's a nice DVD-burning utility on the workstations (physical machine is in the Raritan rack, left-side in the computer room) that you can use to make copies of your data.

Check mirror air conditioning parameters & adjust if needed.
Once the mirror petals are closed, the air conditioner will try to cool the mirror to the user-set temperature, because the seeing goes bad in a hurry if the mirror is more than 1 degree C or so warmer than ambient. The mirror has a long thermal time constant (like 12 hours), and the air conditioner is not particularly effective at cooling the mirror, so if you want to adjust the temperature for the next night, better do it now.

How to decide on a temperature? The A/C control program has a feature which displays the history of the ambient temperature, the mirror temperature, and the temperature set point for the last 2 days or so. Detailed weather forecasts are available on the web; the National Weather Service Tucson office ( has a terrific site which includes very technical details of the forecast. If humidity could be an issue, you'll want to be careful not to overcool the mirror.

Record any messages for staff (e.g., filter changes) on whiteboard, or better yet, send email!
If you have any requests which will require timely action by the staff, please be certain to write them out legibly on the whiteboard. You cannot expect to wake up at 3 PM, saunter out of bed, and tell the staff to drop whatever they're doing and swap out all your filters. In this, and everything else, try to think ahead, both to assure that your requests can be handled and to minimize the strain on our very small staff. Be sure to also alert the staff in your nightly observing report (next item).

Fill out the Observer's Nightly Report Form.
MDM requires that all observers fill out a brief report of the night's activities. To make this as painless as possible, a simple web form has been created that is accessed from the mountain web server.. Even if you did not observe, you should fill out a report saying why.

Nightly observing reports are stored on the mountaintop server, and emailed to a short list of recipients that includes the observatory directory, site manager, and the MDM consortium representatives from each member institution. Report data are used to track how much observing time is lost to weather, problems, etc., as well as to keep a permanent record of activities.

If you encountered any problems at all, even ones you fixed yourself (i.e., not common mistakes but real problems that required you to take some special action to continue working), also fill out a Trouble Report Form. There is no such thing as a "minor" trouble report. Often a big problem starts as lots of little problems or quirky annoyances. If we can see a pattern develop in the trouble logs, we might be able to head off bigger problems later. Remember, the run you save could be your own!

Some problems occur when using the data-acquisition software or other computer systems. It will greatly help diagnosis and solve a problem if you can include the verbatim text of any error messages printed when the problem occurred.

Go to bed!
Your program may call for instantaneous data reduction - if so, bring a collaborator or automate it so you can get enough sleep. It's important not to get too tired!


At the end of your run ... [Terse version.]

Check with staff about whether to fill dewar.
    Sometimes the staff may want the dewar to run low because it makes it more convenient for them to change the instruments.

Make arrangements to get off mountain if needed.
If you're using the Kitt Peak shuttle you'll have to reserve a spot; the schedules are kept in the Admin building on the summit. MDM pays an annual fee so that observers may use the shuttle; we are not charged by the passenger. In circumstances where an MDM user has schedued for shuttle use in advance, but no one else signs up for the shuttle, the MDM user can drive NOAO vehicles.  If planning to use the NOAO shuttle system, it makes sense to read through the appropriate section of the MDM Visitor's Guide as well as file the appropriate NOAO form

If you're using an MDM vehicle to get off the mountain, you'll have to arrange it ahead of time with the staff. Be sure to give the staff plenty of advance notice!
If you're driving yourself off the mountain, be very careful not to overextend yourself to the point where you're really sleepy while driving. Driving through the open desert can be hypnotic, even when fully awake -- don't put yourself in a position where this is a danger.

Plan to depart as soon as practical.  Keep staff informed, especially if using an MDM vehicle.
Accomodations at the Obsevatory are very limited, and the next observer should not have to work around you as they set up and settle in. Accordingly, observers are required to leave the mountain as soon as they can, ideally by the early afternoon of the day after their last run. Please keep the staff informed of your plans. If you intend to sleep for a while after your final night, be sure the staff knows when you intend to get up and leave, or they have no idea what to tell the next observer about bedroom availability and so on. The instant-departure rule can be relaxed when there is a very good reason (e.g., packing up a complicated user instrument at the end of a run), but exceptions must be cleared with all concerned!

Pay your Kitt Peak meal bill, if you have one (ideally on the afternoon of the last business day before your departure.)

If you've taken any meals at the Kitt Peak cafeteria, you're to pay for them before you leave. This is done at the main office of the Admin building on the summit. If it's after hours or the weekend, you can go to the admin building and fill out a form with a credit card number -- they'll charge you and send you a receipt.

Pay your vehicle and OSMOS slit mask fees, if applicable.

MDM no longer levies a $40/night usage charge. We do still assess fees for vehicle use, as well as custom cut slit masks for OSMOS, as needed.  Observers pay $50 ($25 for one-way travel) if they transport themselves to and from the mountain in an MDM vehicle.  Custom slit masks for OSMOS cost $187/mask.  A PayPal account is available for these fees. Checks are accepted, but you'll get a handwritten receipt that university cashiers may regard with suspicion.

Be sure all your data are properly backed up.
Typically, staff wipe data from observatory computers approximately two weeks after you've gone (though if you ask they can sometimes be persuaded to leave your data alone until you verify your copy is legible at home). It's therefore a good idea to write more than one copy of your data. There are many possibilities for this -- transferring the data to a laptop, writing a DVD, bringing your own USB-pluggable disk drive, etc. The observatory internet service is now fast enough that modest-size data sets (e.g., single-chip detectors) can be shipped home, but given that the network can sometimes go down you shouldn't depend on this exclusively! It's a good idea to leave a backup at the observatory in case something gets wrecked on the way home.

Be sure to allow sufficient time to back up your data. You should plan any backups carefully so that you're finished early enough to allow the staff to start instrument changes when they arrive at 8 AM. As noted earlier, you should be backing up your data as you go along anyway.

Tidy up control room.
Gather up all your charts, scratch paper, whatever, and leave a neat workspace for the next observer.

Throw away uneaten food and wash your dishes.
There's a tiny refrigerator and cooler in the kitchenette -- space is very limited, so don't leave behind anything which could go bad. There are vermin at the observatory, so you should never let dishes pile up or allow messes to linger.

Strip your bed.
Stuff your used linens and towels into one of your pillowcases and leave by linen closet.

Leave your bedroom tidy.
There's no chambermaid. Behave accordingly.  Clean up any spills and messes, especially in the bathroom.  No need however to empty the waste basket (unless you want to!).

Be certain: bedroom windows closed, heater and lights off, no water leaks.
As noted earlier, water and electrical power are extremely expensive on the mountain. No one else is going to check your room to be sure you've turned things off, so be especially careful that you do. Be absolutely sure that (a) the heater is off and (b) the toilet isn't running!

Look around to be sure you haven't forgotten anything.


Acculturation for New Observers ...

I trained as an observer at Lick in the 1970s. At that time new observers were walked through procedures by seasoned staff observers. This certainly got the job done - we learned the equipment - but in the long run, the most important lessons we learned from this were not about which buttons to push, or how to develop plates. They were instead lessons about the experience of observing, and the attitude to bring to the telescope. As an old curmudgeon I think some of these lessons have atrophied over the intervening years, as overworked faculty pack students off to observe with minimal preparation. Here's a distillation of some of that acculturation, as refined through many hundreds of nights of observing experience since then, most of them at MDM.


Computer System Overview

This little blurb isn't complete but might help get you started.

There are two main computers at each telescope. These, along with most of the other aspects of data acquisition and scientific instrument control, are interfaced through a Linux-based workstation.  At the 2.4-meter telescope, the main computers are:

mdm24ws1 (and mdm24ws2):
This is the workstation used for almost all telescope-related functions (instrument control, JSkyCalc, etc.)

This is the main Observing Workstation where the observer logs in for most things. It is a Linux box.
This is the newest machine at the 2.4m, and the only user-system with Win10 for the operating system.  Through it, telescope and guider control are performed. 

In addition, there are specialty machines for the instruments; the facility CCDs are run by mdmarc1, and the Ohio State instruments (OSMOS, CCDS, and TIFKAM) that are run by Prospero have their own machines. Refer to the individual instrument manuals for details.

mdm24ws1 and mdm24ws2 run the K windowing environment, and have been set up to have a common look and feel which will be familiar to most observers. The window system has four desktops available - there's a little cartoon in one corner showing them all.

On all machines, you login to a visitor account named obs24m. Logging onto hiltner as obs24m puts you into the directory /lhome/obs24m. The data all go to directories under /data, where the next item in the path is the machine name (e.g., hiltner or mdmarc1), followed by the user name (obs24m), followed by whatever you want to put there. The /data directories are transparently visible to all the machines. The telescope and the MIS (Multiple Instrument System) are controlled from windows on the workstation.  There's one terminal window called bridge, which links  the telescope control software with instrument software, and another called xmis2, which runs the MIS. These controls are thoughtfully designed and should be fairly intuitive. The web-based manual has sample displays of these windows, in color.

The facility MDM CCDs (Echelle, Templeton, Nellie) are run by a program called Owl, which runs on the mdmarc1 machine, but still, is brought up through the workstation. Here is a manual for Owl.

It's probably a good idea to use mdm24ws2 for any heavy reduction, as this keeps mdm24ws1 free for observing.


How the Telescope Works

The official manual contains a lot of detailed information on the workings of the telescope. Here's a short overview which may be helpful but which is necessarily very general. (Note also the gotchas listed elsewhere, all of which are known telescope bugs.)

The telescope is generally configured as an f/7.5 Ritchey-Chretian.  An f/13.5 secondary has not been used in decades and should be considered decommisioned. It has an equatorial fork mount, built by DFM engineering in the early 80s. The drives are unusual in that they do not have worm gears - rather, the telescope is driven by large steel wheels with smaller driving wheels pressed up against them (friction drive systems).

The Telescope Control System, or TCS, is a PC containing a fair amount of custom hardware. In particular, it a galil-based system that receives signals from the telescope via absolute (HA, dec & focus) and incremental (dome AZ & rotator position) encoders and input from the user via the telescope control software. These in turn send power to the stepper motors which run almost everything. The TCS was upgraded from a 1995-based Lovell system back to a DFM system in October of 2017.

The user interface for computer control of the telescope is through a program on the DFM control PC called TCS. This is fairly easy to use once you are familiar with the step-through procedures. As noted earlier, a program on mdm24ws1 called bridge interfaces things like instrument control and JSkyCalc to the TCS program.  Observations can be made more efficiently by putting your target list into JSkyCalc ahead of time. The TCS program also allows users to reset the encoders for the rotator and dome AZ, adjust track rates, control and monitor mirror AC systems and so on.  When the TCS computer program is running normally, the TCS computer's monitor displays the status of the telescope as well as temperature and humidity information from various points within the dome.I'd recommend that you peruse the monitor display carefully on your first day - you'll be looking at it a lot, so you'll want to understand what you're seeing and where to locate the most critical features.

In practice, the telescope points to about 30 arcsec rms. The position as displayed has been corrected using a model of the telescope errors. The position displayed is also corrected for refraction, nutation, aberration, and precession, so it should approximate the mean coordinates for the specified equinox. 

Note that the telescope has some pointing limits. It can't get extremely close to the horizon, or various hard and soft limits are triggered (see the comprehensive manual for where these limits are and how to back out of them if you get into them). The RA is limited to +/-6 hours to avoid cable wrap problems. Observing under the pole is not really supported, though I hear it's been done.

There are manual control paddles to move the telescope. These have directional buttons NSEW, and two buttons labeled SET and SLEW. The actions of these buttons are quite standard. Holding a directional button down moves the telescope very slowly in GUIDE rate (typically one or two arcsec per second of time - the guide rate can be adjusted). Holding down the SET button results in a much faster rate, about 1 arcmin per second. Finally, the SLEW rate is full-speed, around 1 degree per second, used for major repositioning of the telescope. If you need to slew manually, you must keep an eye on the telescope to be sure you know what it's up to.

Here are a few more aspects of the telescope you'll want to know about:

The focus control: The telescope is focused by holding down the IN and OUT buttons on the paddle. This moves the focus rather slowly. If you also hold down the SET button, the focus moves much more quickly. Conversely, you can control focus from the TCS program (Telescope>Misc>Focus tab): enter a target position and hit "Apply".  Once focus has been found, the software will maintain proper separation between the primary and secondary mirrors to continue to remain at optimal focus.  This is transparent to the user.  Note that the focus value on the TCS display will not change as this routine adjusts secondary mirror positioning.  This is normal and to be expected.  It is also worth noting that this compensartion does not take into account any change in focus due to filter changes that may not be parfocal.  If changing filters, it is worthwhile to verify focus (OSMOS filters should in theory be parfocal).

The Instrument Rotator: There is an instrument rotator at the back of the telescope. It has its own encoder.  While it is stressed that the user should consult with MDM staff prior to updating this readout, you can set the encoder using the TCS program (Telescope>Initialization>Other Positions tab)--this should not be necessary under typical circumstances. A monitor that echoes the TCS program display is located in the dome so you can watch rotator position as you move the unit via hand paddle.  Remember:

  1. You must have the mirror covers open to rotate the instrument. The mirror covers bear upon a moving part of the instrument rotator! Metal shavings and paint flakes don't do much good for the mirror!

  2. The rotator paddle is in the dome, located along the north wall, west of the monitor and below the dome shutter controls.

  3. While rotating the instrument, use a flashlight to watch carefully for any cables which might be hanging up. It's a helluva thing to have a cable catch on some critical switch or knob, pull it, and then get ripped out ... ruins your whole night.

  4. To avoid problems with cable hangup, the rotator angle should be kept within +/-90 degrees.

  5. In 2011, the rotator controls were reworked, and much improved, to enable the very fine control needed by OSMOS in multiple object mode. A GUI on Hiltner, accessed through the workstation, allows you to execute very fine moves, but only if they're smaller than four degrees. Gross rotations must still be done in the dome because they must be monitored carefully for cable snags and the like.

What's the "slit angle"? : If you do slit spectroscopy away from the zenith, your data suffer from atmospheric dispersion - the star is smeared into a little spectrum in a direction perpendicular to the horizon. You can capture all the wavelengths in the slit by orienting the slit perpendicular to the horizon. (The importance of doing this was all emphasized in a paper by Alex Filippenko very early in his career.) The position angle of an arc connecting a given point to the zenith is called the parallactic angle, because it's (anti)parallel to the direction of topocentric parallax displacements. With the rotator angle at zero, the MDM spectrographs are oriented with their slits north-south, so that they're on the parallactic angle for any object crossing the meridian. Once you're far away from the meridian, you want to rotate the slit to the parallactic angle, but keep the rotator angle within +/-90 degrees. Because the slit is indifferent to 180-degree rotations, but the rotator isn't, the "slit angle" is the rotator angle which, for the present position of the telescope, will put the slit on the parallactic angle and keep the rotator within its travel. For instance, if the parallactic angle is -150 degrees, the "slit angle" will be +30 degrees. It's important not to interpret the "slit angle" as an actual readout of the rotator position. The rotator position readout is the "Rotator Angle", displayed near the bottom-left of the TCS monitor.

If you intend to track an object over a large range of hour angle, you will want to check out the Parallactic... button on JSkyCalc24mGS. This computes the optimal rotator setting over a range of time for your object and gives a graph showing how badly you do if you're off on either side. The "cross-slit refraction factor" given there is a "badness parameter", computed as the tangent of the zenith distance times the sine of the mismatch of the slit away from the parallactic angle. How much effect this has depends on a host of factors, but it you keep the absolute value less than 0.5 or so you should have minimal effects with most setups.


About the MIS

All the commonly used instruments are mounted on an adapter called the MIS (Multiple Instrument System). This provides a number of commonly-needed utilities. Some useful diagrams can be found in the manual.

There are three parts to the MIS. Working downward from the telescope they are

The finder unit:
This is a gold-anodized box about two feet square and 10 inches deep. It contains a prism that can slide in and out of the beam to feed an Apogee CCD camera called RETROCAM, so called because it was retrofitted to the MIS by Chris Morgan of OSU. The finder unit also houses a set of comparison lamps - an incandescent flat bulb, and Ne, Hg, Ar, and Xe discharge lamps - for calibrating spectra. The prism that feeds the RETROCAM also diverts the comparison lamp light downward to the instrument, and the optics are arranged so that they provide an approximate f/7.5 beam to match the telescope. Note that you can either see comparison lamps or the sky, but not both at the same time, as they call for different positions of the RETROCAM (FINDER) prism. To summarize:

  • FINDER out: The main science instrument sees the sky.
  • FINDER in: The main science instrument is blocked. Comparison lamp light gets to the science instrument, and RETROCAM can see the sky.

The guider unit:
This is about 5 inches deep; it bolts to the back of the finder unit. It has a pickoff mirror which feeds optics leading to a CCD camera. The pickoff mirror (which I'll call the guide probe can be moved around on a precision XY stage. The camera fed from this mirror is used for offset guiding; one acquires a guide star by moving the guide probe, and then starts the autoguider to keep the telescope locked in position. The guide camera has a fairly small field (about one arcminute). The CCDS, Mark III, and Modspec spectrographs use a separate CCD camera to view the slit, so one can see the slit and offset-guide at the same time. OSMOS does not use a slit-viewer; you acquire targets by taking direct images with the disperser and slit out of the beam.

The filter wheel:
The "Buckeye" filter wheel (built at Ohio State and Ohio University) is used only for direct imaging. It has 12 positions and takes 4-inch filters. A limited number of 2-inch inserts are available for mounting smaller filters. The Buckeye filter wheel has been very reliable and positions filters with near-perfect reproducibility.
The MIS is operated using the xmis2 program on hiltner opened on mdm24ws1. This issues commands to the MIS controller box. The controls are fairly straightforward to operate. There are a number of preset positions for the guide stage (slit, center, etc). You can also type in an X or Y coordinate for the guide stage and hit return to send them. You can also get relative steps using the "Delta X" or "Delta Y" fields. Other buttons or menus allow you to turn comparison lamps on or off, move the FINDER prism in or out, and so on.

One can also move the guide probe using the JSkyCalc24mGS program. Read on for details.

There are a number of things to be aware of when using the guide probe.

  1. The JSkyCalc24mGS program running makes it almost criminally easy to pre-select guide stars for your target, using the recent and very accurate UCAC3 star catalog as a database. The full explanation is given a little later in the document. This is highly recommended, even if you're working at low latitude where guide stars are plentiful, since the software flags positions in which the guide probe might obscure the field center (see the next item on the list). Also, pre-setting the guide star can greatly expedite field acquisition and centering; JSkyCalc24mGS actually makes it possible to do this with a mouse click. There is also a newer, very complete manual that describes these guide-probe centering tricks in detail.

  2. It's important to note that there's nothing to stop you from blocking the telescope beam with the guide probe. You must keep the guide probe away from the science field! The JSkyCalc24mGS program indicates rough boundaries for the "safe" positions, but if you have a big detector and you choose a star close to the boundary, you may see some shadowing at the edge of your field.

  3. The guide probe camera needs to be focused so that when the telescope is in focus, the guide probe is also. The guide probe focus is controlled by a GUI located on the TCS PC (Guider_Focus.exe). If you run all the way to the end of the focus travel, and the star is out of focus, try guiding anyway -- Maxim DL does an amazing job on truly terrible images. The guider focus sometimes slips; if this happens, try slipping it back by changing the telescope position. If you happen to be using Modspec or Mark III, it is theoretically possible to adjust the guide stage by hand -- have the staff show you how to do this -- but with the Buckeye filter wheel and OSMOS, the relevant port is covered and it can't be done.

  4. If the guide probe is driven past the end of its travel, it loses track of where it is. I've also seen it lose track when it gets close to the end of its travel in Y, say at 10000 or greater. In any case, it takes only a minute or so to reset the coordinates, by selecting Origin in xmis. This drives the probe back to its zero position and resets the counters.

  5. The guide probe travel is larger than the unvignetted field of the telescope. The outer red circle in the JSkyCalc24mGS diagram shows this.

  6. Easy pre-selection of guide stars! The program JSkyCalc24mGS is available on hiltner. This is a 2.4-meter specific version of JSkyCalc that lets you select guide stars for your target, and is also aware of where the telescope is pointing. Users report that it is a great convenience. The program has its own help facilities; for instructions as to how to start it, see the short document linked here, or for a more comprehensive view refer to this more recent and detailed manual.
  7. Fast target acquisition using the guide probe. The guider XY stage is very accurate, and so is the UCAC3 catalog used in JSkyCalc24mGS (positions are even updated for proper motion). Therefore centering the preselected guide star in the appropriate location on the guide camera should put you very close to your target, provided of course that you're setting on the right star! This can save enormous amounts of time. To develop this procedure, start with a target you can set up accurately. Select a guide star using the program (described immediately above), set up the guide probe at the XY coordinates predicted by the program (JSkyCalc24mGS lets you push the guide probe directly), aim the telescope accurately at your target, and note where the guide star lands on the guide camera. If you keep the fiducial guide position in the same place as you set up on new fields, and center the (correct!) guide star in the box, you should be within a few arcseconds of the target. Be careful of a HUGE GOTCHA here, explained a little farther up: the guide probe can lose track of where it is when it is driven to Y-values greater than about 10000. It does this silently -- no error message is printed, and it all looks fine, but the numbers are all wrong. Just reset the probe coordinates by sending the probe to the preset "Origin" if this happens. Also, you'll want to be sure you know the rotator angle accurately. As noted earlier, this more recent and detailed manual explains all this more comprehensively.
  8. You should almost never need to "hunt and peck" for guide stars, but if you need to for some reason, here's how to do it.
    • Center up on the object
    • Be sure guide camera is on and updating.
    • Set the guide probe to X = 0, Y = 2000
    • Set Delta-Y to 1000
    • Repeatedly hit carriage return and watch the camera output to look for guide stars
    • Stop when Y = 10000; if you drive beyond that, the guider will silently lose track of its Y-coordinate.
    • At the top of the Y travel, set X = 1000 and Delta-Y = -1000, then step back down ...
    and so on, raster scanning until you have a guide star. In principle you can scan across the low Y range and up the far side of X without vignetting the chip, but this is seldom necessary. The field maps produced by the skycalc tool give an idea of the useful field.

Guiding and acquisition cameras

In order to do science, you obviously need to find targets and keep the telescope pointed at them accurately as they track across the sky. The telescope position readouts are nowhere near accurate enough to do this -- you need to be able to acquire and guide on targets. This requires the use of sensitive cameras.

Because every observer needs to know how to autoguide new observers should be sure to READ THE MANUAL that describes how to do this.

Mark III and Modspec users will also want to read the manual for the Andor cameras. 

Note that CCDS has its own slit-viewing camera, an SBIG. The Andor cameras are much better than this, but as of this writing the slit-viewer on CCDS has not been mated to an Andor.  However, work is being persued to replace the SBIG with one of the FLI cameras, which should prove much more sensitive.


CCDCOM is gone! About Owl ...

Until mid-2011, the facility MDM CCDs, which are workhorse direct imagers and the only detectors that work on the Mark III and Modspec spectrographs, were run by a program called CCDCOM. (The Ohio State instruments OSMOS, CCDS, and TIFKAM are run using an entirely separate progam called Prospero). CCDCOM was tied to old Sun Sparcstation computers that were unmaintainable, so over the summer of 2011 we shipped the controllers and detectors to Bob Leach at Astronomical Research Cameras (ARC) in San Diego. Detectors have been converted to run with ARC Gen III controllers.  The change is not reversible -- the old controllers and computers could not be revived even if we wanted to.

At present (and probably indefinitely), the new system is controlled using ARC's in-house software, called Owl. The Manual for Owl explains the details. Be sure to have a look at this if you're intending to use a facility CCD. Even if you're familiar with the old commands, be advised that this is completely different.

At present the system is a little primitive, but it does get the job done and it is not especially difficult to use. It does at least capture the telescope and MIS configuration information and populate the FITS header keywords automatically. As of this writing there is only one automated script written for Owl, a multiple-exposure "step-and-shoot" script for focusing direct images. There is, unfortunately, no easy way to generate observing scripts "on the fly", but one can at least take a series of identical exposures without any difficulty.


What time should I start?

OK, so the weather's great -- low humidity, photometrically clear, and the wind is a gentle zephyr. So you can open. But when should you plan to start observing? Here are a few remarks on that.

It obviously depends on what time it gets dark. Java skycalc, and its 2.4 m version JSkyCalc24mGS, both have a "Nightly Almanac" button, which pops up a window with the information you want. If you can do it, it's a good idea to open the dome maybe 15-20 minutes before sunset so you can have your dewar topped off and ready to go by the time the sun actually sets (that way you can enjoy the sunset and see the green flash!). There are constructive uses for twilight time. If you're doing direct imaging in the optical, sky flats can start in the U band shortly after sunset, within 5 minutes or so, and the window of opportunity for well-exposed sky flats is pretty short. Bright stars can be found almost in bright twilight to verify telescope pointing. Certain kinds of spectroscopic standards can be done in quite a bright sky -- e.g. 10-th magnitude flux standards should be do-able within 20 minutes after sunset. The limiting factor will be when the sky saturates the guide camera in a very short exposure.

A word about the python-based skycalc GUI ...

There's an older python-based GUI skycalc, which was the prototype of the Java version and resembles it closely. The python version has several useful tools not implemented in JSkyCalc24mGS. These include:

You have (at least) two ways to get at this program: