Tools for the Night Sky: An Introduction to UT’s Telescope Labs and Planetarium Author: Meagan K. White, David C. McCallister, Sean Lindsay Version 1.0 created [8/27/2019] Learning Goals

In this activity, the student will learn to ● Identify various types of telescopes and mounts. ● Determine the magnification and field of view of a telescope & eyepiece combination ● Calculate the resolving power and limiting magnitude of a telescope based on its

objective diameter. ● Describe the difference between an Alt/Az mount and an equatorial mount for a

telescope. ● Recall the identity and function of parts of the telescopes used on the rooftop

observation deck. ● Use horizontal (alt/az) and equatorial (RA/Dec) coordinates. ● Define light pollution and describe its effect on nighttime observations. ● Describe the effect that an observer’s latitude has on celestial observations. ● Prepare for Telescope Labs

Materials ● UT’s Digitalis planetarium, with Nightshade Legacy operating system ● Classroom demo of 8” Meade LX200 / Losmandy GM8 / Optics kit, other various

telescopes and mounts (reflectors, refractors, dobs, SCTs)

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1. Background 1.1 The Night Sky Astronomy has long been considered the first science. Early humans surely looked to the skies and were able to detect and predict patterns. Ancient Mesopotamians recorded their astronomical observations of the night sky starting 5000 years ago. Though modern astronomy is far more than mapping the positions of stars and planets on the celestial sphere, accurate measurement in the night sky is crucial to answering some of the biggest questions under study today. Two frequently used systems for specifying locations on the celestial sphere are horizontal and equatorial coordinates. 1.1.1 - Horizontal Coordinates A simple system uses the target object’s angular distance above the horizon and heading. These two parameters are called altitude and azimuth, respectively. Beginning by facing north, azimuth is the number of degrees one would rotate clockwise to face the target object. Altitude is the number of degrees between the local horizon and the target object. As this coordinate system is uses the local horizon as a reference, it is attached to the observer’s location and rotates with the earth. Horizontal coordinates are only good for a particular location, at a particular time. The advantage is that it is easier to use than equatorial coordinates. Horizontal coordinates are useful for event viewing, such as a planetary conjunction or to communicate where the Moon is on a particular night. Angular distances can be approximated by using the hand shapes below held at an arm’s length.

A diagram of the horizontal coordinate system.1 Hand positions relay rough angular distances at arm’s length.2

1 Image by TWCarlson [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons 2 Image by B. Ventrudo. One Minute Astronomer. https://oneminuteastronomer.com/860/measuring-sky/

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1.1.2 - Equatorial Coordinates The equatorial coordinate system maps the celestial sphere into lines of right ascension and declination. Comparing the celestial sphere to a globe of the earth results in a helpful and frequently used analogy: right ascension is like longitude, and declination is like latitude. Declination is the number of degrees above or below the celestial equator, which is formed by extending the earth’s equator in a plane out into space. Our “celestial longitude” is divided into 24 hours of right ascension, measured from the Sun’s location during the vernal equinox. The result of all this is a coordinate system that appears to move with the stars, allowing for a set of coordinates that astronomer at any location on Earth can agree upon. These coordinate systems can be difficult to grasp on paper, and challenging for instructors to diagram on a blackboard. As part of this lab, the teaching assistant will demonstrate both coordinate systems in the planetarium, which singularly insightful on this topic. 1.2 Telescopes 1.2.1 From Two Small Pieces of Glass... When the Earth turns away from the Sun, night falls and the Universe opens up. Looking at the dark sky, an observer in a good location can see 4,500 stars with their bare eyes. With a telescope, that same observer could see millions. The larger the telescope is the more light it can gather, revealing ever dimmer stars and galaxies. With the right telescope, the oldest and most complex structures in the Universe are revealed to us. Earth's atmosphere prevents astronomers from observing light in most regions of the electromagnetic spectrum. Even in those regions of the spectrum called atmospheric windows where the light can get through, there is still considerable distortion of the light. To avoid the distortion and observe in the restricted parts of the spectrum, we have launched telescopes into space. Launching observatories into space is in some cases necessary. It provides observers with a unique perspective on the Universe, but it can be prohibitively expensive. For those wavelengths that can be viewed on Earth's surface, astronomers use ground-based telescopes. The largest ground-based telescopes are radio telescopes. The Very Large Array in New Mexico has over 25 dishes each 20 meters in diameter that can be arranged to electronically produce a telescope kilometers across. Most students will be familiar with optical telescopes, like the ones on display in the lab. Optical telescopes can range from foot-long manually operated models available from any store for $50, to the two ten meter-mirrored Keck telescopes pictured below that cost millions of dollars to build and are controlled by an intricate computer system.

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UT’s Physics & Astronomy Department has a fleet of optical telescopes on the roof for student use. One purpose of this lab is to familiarize you with telescopes and prepare you for the night time observations required of all astronomy students. In general, telescopes come in two broad designs: the reflecting telescope (or reflectors for short) and the refracting telescope (or refractors for short). All reflecting telescopes use reflection of light off a curved mirror to focus light, and they are the type of telescopes preferred by professional astronomers due to the ability to easily make large reflecting mirrors. All refracting telescopes use lenses to focus light instead of mirrors. In their most basic forms, both designs are simple, easy to use, and easy to make. More advanced versions of these types of telescopes are created to increase the performance and correct for problems inherent to the simple designs. Here we introduce the designs of the basic types, some of the problems they have, and one of the more advanced reflecting telescope designs, the Cassegrain telescope that attempts to correct for some of the problems of the basic designs. 1.2.2 Simple Refractors Based on rumors of a failed patent attempt by Hans Lippershey, Galileo fashioned his own telescope and demonstrated it for Venetian lawmakers in 1609. It consisted of two glass convex lenses, and was capable of a magnification factor of only about 8 or 9. He refined his design until he had a telescope capable of magnifying about 30 times, and used it to make observations that cemented the idea that the Sun, not the Earth, is the center of the solar system. The basic idea behind a refracting telescope is using a primary lens to gather light, and an eyepiece to magnify the image. One problem with refractors is that glass bends blue light more than red, as demonstrated by a prism. This result causes chromatic aberration, a color distortion that occurs when different colors of light have different focal lengths. Modern refractors can correct this by using multiple lens elements made of different kinds of glass as a primary objective.

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Diagram of a refracting telescope.3 1.2.3 Simple Reflectors Though Galileo had discussed the potential for using a mirror rather than a lens, the first reflecting telescope is credited to Isaac Newton in 1668. This change corrected the color issues that plagued refractors, but introduced a new problem. When a mirror is spherically shaped, not all the light gets reflected back to the same focal point. This is known as spherical aberration. Grinding mirrors to a parabolic shape corrects this, but is difficult and done at a greater expense.

Design of a Newtonian reflector.4

1.2.4 Schmidt-Cassegrains A very popular design for amateur telescopes, and in fact the majority of telescopes used on the roof, are Schmidt-Cassegrain Telescopes (SCTs). The Cassegrain reflector design uses a concave, converging primary mirror, and a convex, diverging secondary mirror. This results in a large focal length in a compact tube. A Schmidt corrector plate allows for the use of inexpensive spherical mirrors. SCTs use both mirrors and lenses to minimize both chromatic and spherical aberrations.

Diagram of a Schmidt-Cassegrain Telescope.5

3 Image by Richard Pogge, Ohio State University. http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit4/telescopes.html 4 Image by Krishnavedala [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], from Wikimedia Commons 5 Image by Griffenjbs [Public domain], from Wikimedia Commons

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1.3 Important Qualities of Telescopes

1.3.1 - The Importance of Aperture By far, the most important attribute of a telescope’s ability to gather light is the area of the primary light-collecting surface (lens or mirror). This is usually stated in terms of the objective diameter (DO), measured in millimeters (mm) for small telescopes and meters (m) for large, professional-grade telescopes. The focal length (fO) of the objective is the distance over which the objective lens or mirror converges incoming light. The images below show how lenses and mirrors can be used to gather light, and demonstrate the focal length in both cases. In the constellation Lyrae there is a star that, upon sufficient magnification, reveals itself to be a double star system. Given a telescope of sufficient objective diameter, and cooperative viewing conditions, additional magnification will show that each star can be resolved into two stars each. Observing the famous “Double Double” Epsilon Lyrae is a great exercise in testing the ability of a telescope to resolve. The resolving power (PR) of a telescope is the smallest separation two objects can have such that the eyepiece will show two different objects. If the separation of the two objects is larger than the resolving power, then two distinct objects will be seen in the eyepiece. It is calculated by an empirical formula: dividing 120 by the diameter of the objective, measured in mm, will yield the resolution in arcseconds (3600 arcseconds = one degree). Equation: Resolving Power6

𝑃" =120𝐷%

PR - resolving power | DO - objective diameter

Stars are ranked in a magnitude system, the basic idea for which is that higher numbers mean fainter stars. The system is organized such that a difference in 5 levels of magnitude is a factor of 100 times apparent brightness. The limiting magnitude of a telescope is the dimmest star that a telescope can detect under ideal viewing conditions. Note in the equation below that the limiting magnitude is determined solely by the diameter of the objective, once again demonstrating the importance of the size of the telescope’s aperture.

6 This empirical formula requires the objective diameter in mm and will yield the resolving power in arcseconds. It assumes the light being used can be approximated as 480 nm.

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Equation: Limiting Magnitude7

𝐿'() = 2 + 5𝑙𝑜𝑔10(𝐷%) Lmag- limiting magnitude | DO - objective diameter

The focal ratio (fR) is the ratio of the focal length to the objective diameter. This is also referred to as how “fast” a telescope is and is usually written as “f/” followed by the value of the ratio. A smaller focal ratio is caused by a more curved mirror or lens, exacerbating the potential for aberrations. Equation: Focal Ratio

𝑓" =𝑓%𝐷%

fR - focal ratio | fO - objective focal length | DO - objective diameter

Focal Ratio: Comparing an f/5 to an f/10.8 A telescope’s primary function is not to magnify an image, but rather to gather light. The size of the light collecting area makes faint objects brighter than using one’s pupil, but the image produced by the telescope alone is very small. To magnify the telescope’s raw image, we use eyepieces. Two values for each eyepiece are important in producing the image we can see. The focal length of the eyepiece (fe) is conceptually the same definition as the focal length of the objective: it is the distance, measured in mm, over which the eyepiece converges light. The apparent field of view (FOVa) of an eyepiece is angular size of the image produced by the eyepiece, and is measured in degrees.

7 Once again, for the limiting magnitude equation, the objective diameter must be measured in mm. 8 Image by Randy Culp. http://www.rocketmime.com/astronomy/Telescope/telescope_eqn.html

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Magnification is the factor by which an image is larger than the real object’s size to the unaided eye. Magnification is calculated by dividing the focal length of the telescope by the focal length of the eyepiece. By changing the eyepiece, we can change the magnification of the image. It can also be changed by use of a Barlow lens or a focal reducer. The actual field of view (FOV) is the angular size of the sky that is visible in the eyepiece. Equation: Magnification

𝑀 = 𝑓%𝑓3

M - magnification | fO - objective focal length | fe - eyepiece focal length Equation: Actual FOV

𝐹𝑂𝑉 = 𝐹𝑂𝑉(𝑀

FOV - field of view | FOVa - apparent field of view | M - magnification

For Lab Activity 1, students will inspect the telescopes in the lab room, recording the objective diameter, focal length, and focal ratio of each telescope. Then, students will apply the above equations to characterize the view in each telescope using an eyepiece with a 26 mm eyepiece and a 52 degree apparent field of view. 1.4 Cameras

Astrophotography can be as simple as putting camera on a tripod and taking long exposures. Taking photographs using the telescope as your lens is a bit more complicated.9 With patience and the right equipment, anyone can produce fantastic images of celestial objects. As part of this class, you will take pictures through telescopes on the roof during your telescope lab. The computer chip in cameras that records the image is an array of picture elements (pixels) that is called a CCD, which stands for charge coupled device. It operates via the photoelectric effect: when a photon strikes a pixel, an electric signal records the hit. The distribution of these signals is interpreted as an image.

9 Still, the low-tech trick of holding your cell phone up to an eyepiece is doable, and can produce some nice images of brighter solar system objects with a bit of practice.

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The SBIG ST402ME cameras used on the roof are specially made for dark sky astrophotography. Pointing these cameras at bright stars or solar system objects will flood the CCD chip. Since the cameras are finely tuned for dim objects, they take long exposures and are sensitive to stray light and movement on the roof. The slightest touch to the camera, telescope, or tripod will blur the image. When collecting your images, refrain from moving around the telescope and keep stray light to a minimum. The high focal ratio of the LX200 telescopes (f/10) results in a magnification that is a bit too high for many of the objects we photograph on the roof. A focal reducer de-magnifies the image that falls on the CCD chip. ***Warning: The focal reducers that we use are no longer made, and so are not replaceable. Take extreme care not to damage them.*** The format under which the photo will be saved is FITS, which stands for Flexible Image Transport System and is the most commonly used digital image format used in astronomy. One of the goals of the telescope lab is to acquire these images to process during the last lab of the year.

1.5 Telescope Mounts Having the perfect telescope does not guarantee high quality observations. If the mount is wobbly, unlevel, on shaky ground or not strong enough to support the weight of the telescope, results will be poor. Choosing the right mount for a telescope is crucial. Telescope mounts can be split into two basic categories, one for each of the major coordinate systems used for locating objects in the night sky. An altazimuth mount (alt/az) is named for the two directions in which it can move. It can point in any direction along the horizon (azimuth) and from 0 (on the horizon) to +90 degrees (straight up) altitude. Two common types of alt/az mounts are fork mounts and Dobsonian mounts. While simple to use, the disadvantage of alt/az mounts is image rotation. The telescope would not keep the same orientation to the sky as the target moves (Earth rotates). Tilting the azimuthal axis of an alt/az mount toward Polaris allows the telescope to hold its orientation to the sky, and gives us an example of the other category of mount, equatorial. Equatorial mounts move the telescope in equatorial coordinate system (sometimes celestial coordinate system), that is in Right Ascension and Declination. The equatorial axis is aligned with Polaris (if one is viewing in the northern hemisphere), keeping the telescope from rotating relative to the sky. Most of the telescope mounts used on the roof are German Equatorial Mounts, or GEMs. Another option is to use a wedge to tilt an alt/az fork mount toward Polaris, forming a polar fork mount.

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When trying to identify what type of mount a telescope is on, determine the two directions in which it moves. 1.6 UT’s Meade LX200R / Losmandy GM8 Telescope and Mount Students should be able to label a photo with the bolded items, and describe function of starred items.

i. Dew shield* - slows the cooling of the corrector plate to delay dew formation ii. Optical Tube iii. Finder scope* - displays a wider-field, lower mag view of the target area with crosshairs. Used

for centering target in the eyepiece. iv. Servo Motors v. Counterweight

vi. Computer vii. Hand Controller

viii. Tripod ix. Power Supply x. Mirror lock

xi. Eyepiece* - magnifies the image for viewing by the user xii. Visual Back

xiii. Diagonal Mirror xiv. Focus knob*- moves the primary mirror to focus the image

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1.7 Introduction to the T-Labs

No practical astronomy experience is complete without getting one’s eye to a telescope eyepiece. As a part of this class, you will complete an evening of telescope labs (known as TLabs) on the roof of the Nielsen Physics Building. Links to online signup sheets are on the Astrolab website. These labs are subject to cancellation due to weather, so it is important that students sign up early and often to ensure that they are able to experience this crucial part of the astronomy lab. The two lab activities described below will be completed on the same night on the roof. The first telescope lab is an exercise in unaided or naked eye observing. Students will be given two star maps - a reference map reflecting what an observer would see from a dark sky site, and a blank star map that the student will fill in based on what they see from the roof. TAs will come around to each group and orient them to the North Star. Later, at home, students will write a short lab report, describing the effect that light pollution had on the observations, comparing the sky they saw on their night to the sky at a different time, and comparing the sky here in Knoxville to other latitudes. Full details and instructions can be found on the astrolab website. For the second telescope lab, students will rotate through telescopes, each one presenting a different target for either looking through an eyepiece or photography. Each station will require students to sketch the object in the view, and fill out some information about the object including a short description of its appearance. At the photography stations, one of the students will collect images from the telescope onto a USB flash drive. It is important that the group members exchange contact information so that the photographs can be shared among the group members. These photos will be processed during the last lab of the year.

Once home, the students will once again write a short lab report, this time profiling 5 targets that they viewed on the roof. Both T-Lab reports will be due at the end of the semester. Again, full details are on the astrolab website. T-Labs are a required part of the course. Attending your T-Lab session is worth 15% of the ASTR 153 and 154 grades. You also will use the T-Lab session to write the two lab reports required for this class. The two T-Lab reports are each worth 7.5% of the lab class grade and are due at the end of the semester. It is imperative that students sign-up early and often to avoid the full signup sheets and potential weather cancellations at the end of the semester. If there are some extenuating circumstances that will make it difficult for a student to complete the T-Labs, that student should speak with their TA about a reasonable accommodation.

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Note: T-Labs are not the same as the rooftop observations sessions for lecture extra credit offered by Paul Lewis. 1.8 The University of Tennessee Earth and Space Sciences Theater Just as modern telescopes have evolved past two simple lenses, the modern digital planetarium has come a long way from its crude optical-mechanical origins. The planetarium is a useful tool for showing the night sky free of atmospheric interference, but also for showing how the night sky changes over time and over the surface of the Earth. The TA will lead the class in a demonstration of the planetarium’s capabilities, including a lesson on coordinate systems.

2. Lab Activity 1 Observe the telescopes in the room. Identify the type of each telescope and the type of mount it is on. Record the Objective Diameter, Focal Length and Focal Ratio for each telescope in Table 4.2.1. (Knowing any two will allow you to calculate the third.) The TA can move the telescope if asked to help students identify the type of mount. Type: Refractor or Reflector. If Reflector is it a Cassegrain or Newtonian (See Section 1.2) Mount: Equatorial or Horizontal

3. Lab Activity 2 3.1 - The Planetarium Instructions for the teaching assistant (TA) are in blue, bolded, and italicized. Make no mistake, there is no substitute for looking at the real sky, and looking through an actual telescope, on a clear night. However, for the frequent occasions that East Tennessee weather fails to cooperate, The University of Tennessee Earth and Space Sciences Theatre (TUTESST) can provide students with an unobstructed view of the night sky. In the planetarium, the class can observe the sky from anywhere in the solar system. Light pollution can be turned off, and the sky can be changed to match any date and time in the past or future for many thousands of years. Even the atmosphere can be turned off to allow for daytime stellar observations. The planetarium is another amazing tool that can be used to augment understanding of the night sky.

The TA will have the planetarium running with the atmosphere and horizon on. As you first see the dome sky, you may notice that our Planetarium is oriented differently from the cardinal directions of the outside world. Traditionally, planetariums with unidirectional seating are

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oriented so that the chairs, and therefore the viewing angle, face the Southern sky. This is because from our latitude, the sun, moon and planets are visible in the southern half of the sky. 3.2 Viewing Conditions Now the TA will explicitly turn off the Horizon, and atmosphere.

The next thing you will likely notice is that this sky is vibrant with stars. In fact, it may be totally unrecognizable from the night sky outside. A clear night in Knoxville may show 25 or so stars on a good, clear night. The planetarium can simulate ideal viewing conditions from any location. So under the planetarium dome, you may see thousands of stars. To be clear, all the stars that you are used to seeing are still visible on the planetarium dome, they may just be difficult to find, because they are lost in the crowd. Set the visible star magnitude (found in Tools, 6.Effects, 6.1 Light Pollution Limiting Magnitude) to 7.

So why can an observer in Knoxville see 25 stars, but an observer at Big South Fork10 or Pickett State Park11 see over a thousand? The answer is primarily light pollution, but other factors can play a big role. Light pollution is the term used to describe the effect that artificial light has upon the apparent darkness of the night sky. A city like Knoxville has so much artificial light at night from street lamps, field lights, and building display lights, that the dome created by this artificial light goes up nearly to the observer's zenith inside the city. It is very difficult to see shooting stars inside the city or even comets! As an observer leaves a city, the light-dome created by this artificial light becomes even more apparent. From the interstate, you can watch as the dome recedes from view at night. Set the visible star magnitude to 6.5 (Big South Fork), then 3 (Knoxville).

The additional factors affecting night sky observing are air quality, turbulence, and cloud cover. Air Quality in this case refers to the amount of particulate matter in the air. Air quality affects not only the breathability of our air, but also, like being surrounded in fog, can limit seeing. Turbulence refers to massive air motion as air currents flow from hot to cold high above. This effect can be seen on a smaller scale on the air above asphalt on a hot day. The distortions seen by the hot air moving quickly are small examples of turbulence in the sky. Cloud cover seems like an obvious effect on observing, but not all clouds are dense, close to the ground, or fluffy. High up in the atmosphere cirrus clouds, thin willowy clouds, form that can dramatically change the transparency (or ability to see dim objects from a distance) of the night sky. Set the visible star magnitude to 7 again. Bring up the altitude & azimuth grid.

10 Big South Fork National River and Recreation Area, Oneida, TN. 11 Pickett CCC Memorial State Park and Pogue Creek Canyon State Natural Area, Jamestown, TN. In 2015, due to the efforts of Ranger Monique Johnson with help from UT’s own Paul Lewis, Pickett/Pogue earned a Silver-tier International Dark Sky Park designation. It became the first state park in the Southeast to gain this prestigious recognition.

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3.3 Lines of Reference Now we move on to astronomical coordinate systems. The lines currently on the dome are the horizontal coordinate system, consisting of lines of altitude and azimuth. Altitude is the angular distance above the horizon, and azimuth is the heading one should face to see the object. This coordinate system is oriented so that the lines meet at the top center of the dome, the zenith of the night sky. Starting by facing north, the azimuth is the number of degrees one would rotate clockwise to face the object. As the sky moves with time, the alt/az coordinates remain stationary since the coordinate system is attached to the viewing location on Earth. This coordinate system is useful for quickly finding objects in the night sky, particularly those objects that move rapidly relative to the background stars. This is a good system to use when finding a transitory object at a certain time referenced from your location. Fast-forward time to set the sky in motion and follow the path of a bright star on the dome. Point out that the altitude and azimuth lines remain fixed to the observer. Push play to resume the normal sidereal motion of the sky. Ask for the alt/az coordinates of a bright object in the eastern sky at one point, then fast forward to 6 hours later to see if it has changed. Remove the altitude & azimuth grid and bring up the right ascension & declination grid. The coordinate system now projected on the dome sky is the equatorial coordinate system, consisting of lines of right ascension and declination. Lines of right ascension are measured in hours, and declination in degrees. You will notice that RA & Dec. are tilted so that Polaris is at the North Celestial pole (+90° declination), and the Celestial Equator (0° declination) is a projection of our equator. The celestial prime meridian (0 hrs R.A.) is arbitrarily placed at the position of the sun on the celestial sphere at the moment of the vernal equinox. As time moves forward, the projected coordinate system moves with the night sky. This is so that every position on the night sky can be given a fixed RA & Dec. coordinate. Fast-forward time to set the sky in motion and follow the path of a bright star on the dome. The students should see that the stars are moving with the grid. Point to bright stars with the laser and follow their motion. Ask for the RA and Dec of a star near grid lines at one point, then again pause the sky's motion 6 hours later and ask again. Then turn off the RA & Dec grid. In addition to the coordinate systems, there are a few celestial lines that are useful for reference on the night sky. You will see in later exercises that these reference lines make organizing celestial objects, and referencing them in the night sky, easier. Turn on the celestial meridian line.

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The celestial meridian is the great circle passing through the local Zenith and celestial poles. When a star crosses this line moving east to west, it is at its highest point in the sky that it will be. At this time the airmass is at its lowest, meaning the light travelling from the star to the telescope will go through a minimum amount of the Earth’s atmosphere. Therefore, the time when an object is nearest the celestial meridian is the optimal time to view or photograph that object. Turn off the celestial meridian. Turn on the celestial equator. The celestial equator is the projection of Earth's equator onto the celestial sphere. Turn off the celestial equator. Turn on the precession circle. The precession circle is the circle around which the north celestial pole appears to move over a period of 26,000 years. Turn off the precession circle, turn on the ecliptic, then the orbits of the planets. Advance time by a day or week at a time to show the motion of the sun and planets relative to the background stars. The ecliptic is the apparent path of the Sun across the sky, which corresponds to Earth's orbital plane around the Sun. The planets never stray too far from the ecliptic. Turn the celestial equator back on. What is special about the places that the ecliptic and the celestial equator intersect? What about where they are farthest apart? Clear all reference lines from the dome. 3.4 The Effect of Viewing Location The apparent sky and its motion change with an observer's location on Earth. An observer in the Southern Hemisphere sees a a very different sky than those in the Northern Hemisphere. We are going to observe the sky from the North Pole, and from the equator. Change the location to be at the North Pole (Tools, 1. Set Location, 1.1 Latitude = 90), set the sky in motion. Have students point out their observations. Note the altitude of Polaris.

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Now we move to the Equator. Change the location to be at the Equator, (Tools, 1. Set Location, 1.1 Latitude = 0). Again ask students to point out their observations. When finished, reset the dome to default (Tools, 8. Administration, 8.1 Load Default Configuration). We will now complete Table 4.2.2 as a class.

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Tools for the Night Sky Name: _ Student Responses 4. Analysis and Summary Exercises

4.1 Pre - Lab Questions – [Total pts for additional questions]

4.1.1 - What is the difference between a reflector and a refractor?

4.1.2 - What two lab exercises in this course will be completed outside of class?

4.2 In-class Lab Questions – [Total pts for additional questions] 4.2.1 - Record the telescope type, mount type, objective diameter, focal length and focal ratio for each example telescope. Focal Ratio Equation:

𝑓" =𝑓%𝐷%

fR - focal ratio | fO - objective focal length | DO - objective diameter

Table 4.2.1

Telescope Type Mount

Objective Diameter (mm)

D0

Focal Length (mm)

f0

Focal Ratio

fR

A Cassegrain GEM 203.2 2000 f/10

B C D E

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4.2.2 - As a class, fill in the table below using observations from the planetarium. For the columns with a delta (𝛥), write Y or N to indicate if the preceding coordinates changed for that object after 2 hours.

Table 4.2.2

Date Time Object Alt Az 𝛥 RA Dec 𝛥

8/21/2013 10:00 PM

16° 107°

9/15/2013 11:00 PM

Uranus

9/15/2013 11:00 PM

20° 154°

9/16/2013 5:00 AM

Mars

9/16/2013 5:00 AM 7h 10m 22°

8/21/2017 2:35 PM

62 211

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4.3 Student Worksheet – [Total pts for additional questions]

4.3.1 Calculate the resolving power and limiting magnitude of each telescope. Determine the magnification and field of view of each of the telescopes if an eyepiece with a 26mm focal length and a 52 degree apparent FOV is used on them. (16 points)

Equation Bank for Table 4.3.1.

𝑃" =120𝐷%

𝐿'() = 2 + 5 log=>(𝐷%) 𝑀 = 𝑓%𝑓3

𝐹𝑂𝑉 = 𝐹𝑂𝑉(𝑀

PR - resolving power |DO - objective diameter | Lmag- limiting magnitude | M - magnification | fO - objective focal length | fe - eyepiece focal length | FOV - field of view | FOVa - apparent field of view

Table 4.3.1

Telescope Objective Diameter

(mm)

Resolving Power (arcsec)

Limiting Magnitude

Focal Length (mm)

Magnification Actual FOV (degrees)

A 203.2 2000 B C D E

4.3.2 - What quality of a telescope most impacts its ability to gather light?

4.3.3 - What is the finder scope and how is it different from the eyepiece?

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4.3.4 - What is the goal of the nighttime telescope labs? What should you make sure you have after its completion?

4.3.5 - What type of objects should be imaged, and why can't the cameras be used to take pictures of bright solar system objects?

4.3.6 - What is the celestial analogue of latitude? Longitude? Specify which!

4.3.7 - Moving 17,500 miles per hour and orbiting over 300 miles above Earth’s surface, the International Space Station can reflect sunlight off its massive solar panels allowing it to be seen from Earth. Viewing opportunities involve looking at a particular part of the sky, at a particular time, from a particular location. Which coordinate system should be used in this case? Why?

4.3.8 - What is light pollution? What effect does it have on observations?

4.3.9 - How does the motion of the sky change with position on the Earth?

4.3.10 - When does the Sun cross the celestial equator? When is the Sun farthest in the sky from the celestial equator?

4.3.11 - Keep the camera as still as possible while it is taking pictures to prevent

__________________.

4.3.12 - During the night time telescope lab, astroimages will be saved as ____________ files.

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4.3.13 - At the T-labs, every group member will need a copy of all _____________________ to do the last in-class lab of the semester.

4.3.15 - List and describe the two kinds of aberrations in telescope design discussed in this lab.

4.3.16 - Describe the function of the following parts of the telescope:

Dew Shield

Finder Scope

Eyepiece

Focus Knob

4.3.17 - A student observes the moon due east, about a “fist held at arm’s length” above the horizon. What is the altitude and azimuth of the moon?

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4.3.18 - Label the following parts of the telescope in this photo of our 8” LX200 / GM8 setup.

Dew Shield, Optical Tube, Finder Scope, Counterweight, Hand Controller, Power Supply,Eyepiece, Focus Knob