observing date and time:
due: April 30 in section

In this lab, we'll introduce you to the 14-inch Celestron telescope on the roof of the astronomy building, and teach you how to use it to observe specific objects in the night sky. There are a variety of mechanical and electronic systems which operate the telescope, but once you are familiar with them, finding your desired targets becomes almost trivial.

Collaboration policy: Observing is inherently a collaborative exercise, but make sure everyone pulls their weight, and the post-observing questions should be your own work also. If you have questions about this lab, please talk to your TA.

I. Observing preparation

Astronomers will often spend days or even weeks preparing for an observing run. Much of that time is spent deciding exactly which sources they will observe during the run, how long they will spend observing each source, and the order in which they will obesrve them, which often requires a delicate balancing act. As we will see later in this lab, observers would prefer to observe sources as close to the time that they are crossing the meridian as possible in order to reduce the negative effects of the atmosphere. However, if two or more sources are near the same RA and therefore crossing the meridian at roughly the same time, the observers must prioritize each source to decide which one to observe during the most favorable observing conditions. Also, especially for faint sources it is very important to make finding charts, which are images of the sky around the source that you are wanting to observe. This way, even though it might take many minutes (or hours) of observing to see your source, you can quickly make sure that you are pointing in the right direction!!! There is a lot of logistics that go into each observing run, and because telescope time is so valuable, astronomers want to be sure to think through their plan of attack and contingencies before the night begins.

This telescope lab is designed to familiarize you with the operation of the Robinson Rooftop Telescope and also to give you a chance to use the telescope to look at various interesting astronomical objects, to see firsthand the rotation of the celestial sphere over the course of a few minutes and to observe the effects of the atmosphere in observing.

Before arriving at the telescope for your observing slot, please make sure that you complete the following:

1. Read through the telescope operation instructions below, so they're not a complete novelty when you arrive at the dome. There's a lot to read, so please be sure to do this before the lab.

2. Use your star maps to locate the bright stars Sirius, Rigel, Betelgeuse, Regulus, and Arcturus. You may need to find them manually with the telescope, so figure out where in the sky they are supposed to be, and where they are relative to familiar constellations. Either the evening before your observing run at about the same time as your run will start the next day, or on your way over to your observing run, try to locate as many of these stars as possible in the sky. Not all of them may be up at the time of your run.

3. Bring a flashlight - the roof of Robinson can get fairly dark at night, so a flashlight will definitely be helpful.

II. Starting up the telescope

1. The first step will be to open the dome using the turning wheel located near the slit in the dome. You should make sure that the cover is on the mirror of the telescope before opening or closing the dome so that dust or other parts of the dome won't fall on the optics! Go ahead and open the dome very early on, as you should wait 5 minutes after opening the dome before removing the cover of the telescope so that any dust will have settled. (As an interesting sidenote, the dome was designed to be a replica of the dome for the Palomar 200-Inch, so if you are coming on the Palomar trip you'll see the same dome but on a MUCH larger scale!)

2. Turn on the power strip that provides power to the computer on the left as you are facing the door to the dome --- this computer will be used to control the telescope. The other computer will be used to control the CCD lab.

3. Boot up the control computer (on left as facing dome door).

4. Boot up the CCD computer (on the right) and start the CCD control program. Turn on the temperature control.
5. Turn on the black Skywalker control box on the telescope pier with the silver toggle switch, and make sure the black slider switch behind that is to the left. The black slider switch must be on the left for the computer to be able to control the telescope.

6. Start The Sky (on the control computer) by double-clicking the icon on the computer desktop, and if it complains about sound files, tell it OK. Shrink it back down with the [_] button at the upper right of the window.

7. Start the Skywalker software in the same way, and hit OK for any warning messages.

8. On the handpaddle, press the SLEW button to turn on the slew light, and then use the 4 motion buttons to steer the telescope around. Tip it over to the east and have a look down the barrel to see the primary mirror, the secondary support, and the Cassegrain tube. Be careful not to tip it over past horizontal. It is also important that you never try to move the telescope by hand. All telescope motion must be done either by using the computer or by using the hand paddle.

9. The computer does not retain a knowledge of where the telescope is pointing after the power has been turned off to the computer and Skywalker. Therefore, we need to tell the computer where the telescope is pointing. In order to calibrate the control system -- to "teach" it where and when it is, it's easiest to point the scope at a known bright star.
   • Go outside and identify a bright star in a convenient location -- southwards is best.
   • Slew the telescope to the vicinity of your selected calibration star. You may have to use the red controller to rotate the dome into position.
   • Turn off slew, and move the telescope slowly to point at the star. Use the Telrad sight that's piggybacked on the telescope tube to line it up -- put the star inside the innermost circle.
   • Use the CCD software in focus mode to center the target star in the field of view, and focus until it looks like a nice sharp point. In order to focus, use the red colored knob on the telescope tube, located to the west of the eyepiece mount. Turn this knob back and forth, adjusting the focus until you are pleased with the result.

10. Now tell the control software where you are. In the control window, select Celestial in the Modes section. The control program should indicate a link has been established with the telescope and you should hear the tracking motors firing. Now switch to The Sky program.
    
    Under the telescope tab, select "establish link." Then in the star chart window, click on the star you've centered the telescope on. A new window appears. Click on the telescope tab and then click on sync. This aligns the telescope and computer.

    If you find that during the night the telescope is not exactly pointing to where The Sky believes it is pointing, you can repeat this sync procedure. Center a star on the eyepiece, click on the same star on the screen and then hit Sync under the Telescope tab to realign the software and the telescope.

11. Okay, time for some action. Choose another star near the current location, and click on it to bring up the info window. Among the buttons along the bottom of the info window is a green telescope icon. Click it and stand back! The telescope should now move to the position of the star that you selected.

12. Check the Telrad and the eyepiece. Are you there? The pointing won't be perfect, but for short slews, it should put it inside the eyepiece FOV.

III. Observing

The scope is all calibrated and awaiting your command. Let's go see some stuff.

1. If it is still up in the sky by the time you get to the telescope you might want to try to observe the Orion Nebula. Use The Sky to select the Orion Nebula and move to that source (your TA will know whether it is too far down in the sky to observe). Have a look. You should be able to see the Trapezium (4 stars in a parallelogram) surrounded by a faint green nebulosity. In a long-exposure photograph,this glowing gas extends many eyepiece FOVs, and shows intricate structure.

2. Find a bright star near the horizon. What does it look like at high magnification? Record the altitude of the star, and note any peculiar phenomena that you see in the eyepiece. Compare it to the stars you observe at high elevation.

3. Observe as many of the following targets as you can in the time available. Have everyone take their turn maneuvering the telescope.
   • open clusters: Pleiades (03h 47m, +24d), M41 (06h 47m, -21d), M50 (07h 03m, -08d), M93 (07h 45m, -24d), M48 (08h 13m, -06d), M44 (08h 40m +20d)
   • globular clusters: M3 (13h 42m, +28d), M13 (16h 41m, +36d)
   • double stars: Sigma 1695 (12h 56m, +54d), Mizar (13h 24m, +55d), Kappa Boo (14h 14m, +52d), Sigma 1829 (14h 16m, +50d), Sigma 1882 AB (14h 44m, +61d)
   • anything else that occurs to you...if you have a chance to play around with The Sky or other similar programs before you come to observe, make a list of a target or two that you would like to observe!

4. Save any images that you like. We'll put them on the webpage...

5. Most Importantly: Have fun!!!

IV. Shutdown

Your run is not over until the telescope has been properly put to bed.

1. Point the telescope toward the zenith (doesn't have to be perfect) and put the cover back on.

2. Turn off the CDD software and shut down the CCD computer
3. Quit The Sky and Skywalker, and power off the Skywalker box.

4. Shut down the control computer and turn off the power strip.

5. Crank the dome slit closed, and rotate it so the wheel is to the west.

6. Exit the dome and head back down the stairs, being extremely careful of your footing.

V. Post-observing analysis

Let's go back to Section III, step 2.

1. What is the angular size (diameter) of the CCD field of view? Express in degrees, arcminutes, and arcseconds.

    

    

2. How did the star viewed at the horizon compare to those that you observed at higher elevations?

    

    

3. What affects the view of stars near the horizon?

    

    

4. Let's assume the earth is flat, and that the atmosphere is a homogenous horizontal layer that goes up 30 miles (50 km) and then stops. If you look straight up at the zenith, what's the elevation angle? How much air are you looking through? Okay, now what about an elevation angle of 45 deg -- how much air? 30 deg? Derive an analytic formula for the amount of air as a function of elevation angle.

    

    

    

5. How much air distance were you looking through when observing your horizon star, compared to if it were straight overhead?

    

    

6. Why are many observatories built on top of mountains?