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Astronomy 301 LAB 2 ---- Mizar, Alcor, and Learning to Use the SFSU Telescopes Fall 2014

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Astronomy 301 LAB 2 ---- Mizar, Alcor, and Learning to Use the SFSU Telescopes Fall 2014 Astronomy 301 LAB 2 ---- Mizar, Alcor, and learning to use the SFSU telescopes Fall 2014 In this lab introduces the basic concepts and techniques needed to operate the SFSU telescopes. You will learn how to attach dew caps, how to align finder telescopes, and something about how to choose eyepieces. An important skill for using telescopes (and binoculars) is to be able to translate what you see in an atlas to what you see on the sky, and vice versa. As a first step toward this, you will make observations that will allow you to estimate the field of view through the finder telescope, the main telescope, and through binoculars. The results of this lab will be written up in a lab report after we have discussed them in class. Materials * Tirion Atlases; Golden Guides; copper wire for “loops”; Burnham’s on Mizar and Alcor In-class preparations (record all measurements, sketches, and calculations in log book) (1) Big Dipper Find the Tirion Atlas chart that includes Ursa Major. Notice proper names, Bayer designations, and Flamsteed designations for the stars in the Big Dipper. Use the plastic overlay to estimate the magnitudes of each of the stars in the Big Dipper. Then use it to measure the angular separation between various pairs of adjacent stars in the Big Dipper. Also estimate the separation between Mizar and Alcor. Finally, make a sketch of the Big Dipper in your log book and label it carefully, including proper names, Bayer designations, and angular separations. (2) Hand angular measures Measure the angular size of your palm (including thumb) at arm’s length using the markings on the blackboard. What part of your hand (at arm’s length) spans about 1 degree? (3) Field of view of binoculars and/or finder telescope Use the degree markings on the blackboard to measure the field of view of binoculars and finder telescopes we will have set up in the classroom (4) Angular size of the Moon Calculate the current angular size of the Moon in degrees and in arcminutes. The Moon’s diameter is about 3470 km. Its distance from Earth varies from about 363,000 km at perigee to 407,000 km at apogee. The current distance can be found here: http://time.unitarium.com/moon/where.html In the Observatory Please note: Be sure to always make note of which telescope and what eyepiece (focal length) you used for each observation you make and record. You will need this information for lab reports! (1) Attach a dew cap to your telescope All Meade telescopes (Schmitt-Cassegrain design) should have a dew cap attached before you begin. One of the instructors will show you how to do this. (2) Align your finder telescope(s) The first step in using any of the telescopes is to align the finder telescope with the main telescope. To do this, use the paddle to point the telescope at a bright star or planet (not the Moon). Place the object on the crosshair in the finder as accurately as you can. Then look through the main telescope. If the object is in the middle of the telescope’s field of view, then the finder is aligned. If not, center the object in the telescope and then ask your instructor to show you how to align the finder. Important: set screws on finders should be adjusted in pairs---you loosen one while tightening the other. Never loosen two at once! (3) The Moon If the Moon is up, attach a 40 mm eyepiece to your telescope. This will provide the lowest magnification and largest field of view. The group using the 16-inch Meade should use the large (2-inch diameter) 55 mm eyepiece instead. If the phase is gibbous or full, you may want to attach a “neutral-density” (grey) filter to the back of the eyepiece before attaching it to the telescope. The instructor can help you with this. (i) Observe the Moon through the finder. What fraction of the finder field of view does it take up? Use this to estimate the finder’s field of view. (ii) Observe the Moon through the main telescope. What fraction of the field of view does it take up? Use this to estimate the telescope’s field of view with a 40 mm eyepiece. (iii) Try a shorter focal-length eyepiece (e.g. 20-26 mm). How much of the field does the Moon fill now? (iv) Now try a pair of binoculars. What fraction of the field of view does it take up? Use this to estimate the field of view of the binoculars. Compare your result to the estimate you made in the classroom. (4) Finder field of view Pick a pair of Dipper stars to observe through the telescope’s finder. Can you get both stars into the finder? If not, consult your sketch to see if there is another pair that is closer together. How far apart do the two stars appear in the finder (e.g., do they span ½ of the field of view, ¾ of the field of view, etc)? Use this information to refine your estimate of the finder’s field of view. (5) Mizar and Alcor Mizar, the middle star in the handle of the Big Dipper, is a famous visual binary star 25 pc from Earth. The two components, Mizar A and B, are each spectroscopic binaries. Mizar is thus a quadruple star system. Alcor, a fainter star about 12 arcminutes away, is also a binary star. Measurements suggest that it is gravitationally bound to the Mizar quadruple, making this a stellar sextuplet (!) (i) Look at Mizar with your unaided eye. Can you see a faint neighboring star? Try averted vision if you don’t see it at first. Using a clock analogy, with Mizar as the center of the clock, and Alcor being the hour hand, what “o’clock” is Alcor at? Compare notes with your lab partners to see if you are really seeing it. If you see it, make a sketch in your lab book. If you don’t see it, make a note of that in your lab book. (ii) Look at Mizar with binoculars. Now what do you see? Make a sketch in your lab book showing the field of view of the binoculars along with whatever you see in the field. Label Mizar and Alcor. If you are not sure which stars they are, talk to the lab instructor. (iii) Point your telescope at Mizar using the paddle or joystick. Start with a 40 mm eyepiece, and make a careful sketch of what you see. Carefully label Mizar (a binary star with a 15˝ separation) and Alcor. If you are not sure what’s what, talk to your instructor before moving on to the next part. (iv) Look at Mizar and Alcor in the Tirion Atlas. Now that you’ve observed it with unaided eyes, binoculars, and a telescope, can you make sense of why it looks the way it does in the Atlas? .
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