Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.astro.louisville.edu/shared_skies/documents/shared_skies_student_projects.pdf Дата изменения: Mon Oct 17 17:34:03 2011 Дата индексирования: Sat Feb 2 22:58:22 2013 Кодировка: Поисковые слова: comet tail

Shared Skies

Opportunities for Student Research with Robotic Telescopes

John Kielkopf, Karen Collins, Tom Tretter, Chip Davidson University of Louisville

Brad Carter, Rhodes Hart, Kay Lembo University of Southern Queensland

Shared Skies Partnership October 17, 2011

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Contact Information

University of Louisville
Dr. John Kielkopf, Professor, Department of Physics and Astronomy, College of Arts and Sciences, University of Louisville, Louisville, KY 40292, USA, kielkopf@louisville.edu and jkielkopf@gmail.com Dr. Thomas Tretter, Associate Professor, College of Education and Human Development, University of Louisville, Louisville, KY 40292, USA, tom.tretter@louisville.edu Karen Collins, Department of Physics and Astronomy, College of Arts and Scienes, University of Louisville, Louisville, KY 40292, USA, karen.collins@insightbb.com Chip Davidson, Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292, USA, cdweb@me.com

University of Southern Queensland
Dr. Brad Carter, Senior Lecturer (Physics), Faculty of Sciences, Biological and Physical Sciences, University of Southern Queensland, Toowoomba, Australia, brad.carter@usq.edu.au Dr. Rhodes Hart, Research Associate (Physics), Office of Research, University of Southern Queensland, Toowoomba, Australia, rhodes.hart@usq.edu.au Kay Lembo, Academic Liaison Officer, Faculty of Sciences, University of Southern Queensland, Toowoomba, Australia, kay.lembo@usq.edu.au

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Summary
The Shared Skies collaboration between the University of Louisville, and the University of Southern Queensland is developing remotely operated astronomical facilities for research, teaching, citizen science, and open access to education. Telescopes in the southern and northern hemispheres, with a longitude difference that enables students to observe the night sky in daytime classes, are linked by Internet2 to campuses in Louisville, Kentucky, and Toowoomba, Queensland. The very dark sky at Mt. Kent Observatory in Australia offers the center of the Milky Way, the Magellanic Clouds, and transient events not visible from mid-latitudes in the northern hemisphere. Moore Observatory, in a forested nature preserve near Louisville, Kentucky, offers complementary remote services, live images of bright planets and the Moon, and the occasional northern comet and supernova to students in Queensland. Opportunities for student activities include projects for beginning students such as following the Moon at night in one hemisphere from a daytime class on the other side of Earth, projects to use thoughtful analysis such measuring the mass of Jupiter from the motions of its satellites, and projects that challenge our perceptions of space and time such as determining distances across our Milky Way and to nearby galaxies from the properties of stars. We are developing a scaffold to enable students and their teachers to progress from carefully structured exercises to a more open individual research projects. The structure allows students to find a level at which they can work and learn, and it can be adapted to a college preparation curriculum in middle and high schools, science fair research, elementary university classes, and advanced preparation for research by physics and astronomy majors. Here we outline possible projects that would be components of the scaffold.

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Program goals
We are using hands-on activities in live remote astronomy to encourage students interest in science, math and technology, provide them with experience in an observational and experimental physical science, improve their math skills, and develop their ability to pose questions, think critically, and test ideas with new experiments. The program we offer supports teachers and their students through well-defined scripted exercises and leads to mentored independent creative research. It provides an educational scaffold that may be built on: · · · · Physical concepts Operational tasks Instruments and technology Astronomical objects and astrophysical processes

The connections between these goals and curriculum requirements in formal education will be provided in another document.

Scaffold of physical concepts
A conventional theme in astronomy follows a developing perception of space, from your location on Earth and the appearance of the sky, to the edge of the visible universe. As distances increase, time becomes a factor bearing on what we see because of the fixed finite speed of light. Students learn 1. Their location on Earth 2. Earth's motions of rotation on its axis and revolution about the Sun 3. The effect of their location on the appearance of the sky

4. The motions of the Moon, beginning with as a simple nearly circular orbit,
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adding its rotation, and then refining with the ellipticity of the orbit, the tilt of the orbital plane to the Earth's orbit, and the tilt of the Moon's axis to its own orbital plane 5. The laws of gravity and motion as developed by Newton 6. The speed of light (from Jupiter to Earth is 40 minutes, and its 16 minutes to cross Earth's orbit) 7. The spectrum of light, from the colors of visible light, invisible ultraviolet and infrared, and ultimately x-rays to microwaves as used to explore and explain the universe 8. Optics and how telescopes and electronic cameras work 9. Atomic processes, how atoms have structure, and emit light as photons to be detected one at a time by cameras in our telescopes 10. Nuclear and subatomic processes responsible for energy emitted by stars and their birth and death 11. Space and time on a cosmic scale

Scaffold of operational tasks
Whenever possible we want students to interact with the instruments and use project resources to create their own new knowledge. The Shared Skies program is focused on live remote use of the resources at our observatories. Although we do provide web sites with pretty images and archives of processed data, we offer students the unique opportunity to select a target and make their own observations. Their technical skills develop from the simplest task of clicking a shutter button to download a snapshot of a constellation or of the Moon, to planning a science observation and quantitatively analyzing the data. Progressively they might follow this path:

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1. Identify bright stars and constellations in a wide field of view 2. Point a small telescope or camera at an object of interest 3. Take snapshot images of constellations and the Moon 4. Find a bright planet, Jupiter for example, and capture images of it or the Moon that show changes hour-by-hour or night-to-night with a web-based control 5. Use software that can extract quantitative information from an image such as ImageJ and ds9 6. Use software that simulates the night sky and provides access to astronomical databases such as Stellarium on the desktop, or sky-map.org, Simbad, and Aladin on the web 7. Learn about light, color, telescopes and light sensors from interactive remote instruments and experiments in class or at home 8. Learn about the magnitude scale, star colors, celestial coordinates, and catalogs of astronomical data 9. Plan an observation of something not obviously visible, a particular star cluster for example, decide when it may be seen and what observatory is needed to see it, choose filters and exposure times 10. Correct science images for non-uniform response (flat fielding) and thermal background (dark subtraction) 11. Compare "science" images with prior images and with atlases and catalogs to identify objects and follow their changes in position and brightness 12. Combine images taken through different filters to make color images that are realistic, or that enhance features of interest
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13. Measure images to follow motion: the paths of asteroids, the changes in a comet, the orbits of satellites, the proper motion of stars
14. Measure images to follow changes in signal: variable stars, rotation of satellites and asteroids, the detection of exoplanets when they transit a star

Scaffold of instruments and technology
A benefit of high quality astronomical instruments connected to classrooms through the Internet is that students experience a research environment as if they were present at a remote observatory, even more relevant given that advanced astronomical "observing" today is often done within a control room, and by means of robotic or queue-scheduled observing. Since we have several telescopes at two different observatories we can offer progressive training for skills needed to do more independent work. Skills to use instruments and technologies can be developed in this way: 1. Watch sunset and sunrise in the real sky. This is best done with a classroom teacher who meets students before school starts to watch dawn sunrise, or who arranges an after-school event perhaps with the help of a local public group. For example, the Louisville Astronomical Society promotes public astronomy at its Urban Astronomy Center in an accessible state park, and the University of Southern Queensland and the University of Louisville operate on-campus observatories for their students and visitors. 2. Experience a planetarium. The planetarium emulates a truly dark sky and provides a realistic experience without the mosquitoes or cold. Desktop software (see the following) is an alternative, especially projected in a dark classroom, but a crafted educational opportunity at a planetarium is an ideal second step. 3. Use hands-on simulation software such as Stellarium. This makes the transition from the visual sky to one with celestial coordinates and astronomical databases and is not a passive activity.
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4. Take snapshot images of constellations. We operate webcams that look "up" and show the entire sky in both hemispheres (clouds too!). At Moore Observatory we have a pan-tilt-zoom camera that can be directed at individual constellations and at the Moon. The skill associated with these web-based instruments is to identify patterns and bright stars, follow the changes in the sky during the night, and watch the Moon night-to-night to see its cycle of rising and setting times and places, and of course its phase. 5. Use web-based weather satellites. The geosynchronous satellites provide updates every 30 minutes of the Earth from space in several filter bands. The satellite views can be compared directly with views from our observatories looking up at the sky, and with our weather sensors.

6. Use a web-based telescope and color camera. At Moore Observatory we have a pair of telescopes on a computer-controlled mount that can be operated through a web site. One provides detailed views at the highest possible resolution suitable for planets, and the other gives a wide field view best for clusters of stars, comets, and tracking asteroids. These both produce full-color images in real time ­ just point, shoot, and after a few seconds the image appears. The remote user may change the target, and the set an exposure time (up to 30 seconds), and gain from drop-down lists on the web control. At the shortest exposures atmospheric turbulence is frozen and images of the Moon and bright planets are recorded with diffractionlimited resolution. Longer exposures capture satellites of the giant planets and stars to 18th magnitude. 7. Participate in assisted observing and video conferencing in remote sessions with the CDK20's. Both observatories have Polycom/Tandberg video conferencing, Skype, and Google video chat capability. We will provide managed observing sessions for classes or groups of students in which the operator at the telescope at night in the other hemisphere will work in real time with the students in their daytime classroom. Students will have immediate access to the unprocessed "raw" images and can make decisions about how to proceed with advice from their classroom teacher and the astronomer at the telescope. In this mode (as with the previous web-based
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science imaging) the image file size is very large, and high quality video conferencing requires bandwidth and possibly special hardware. The best venue may be in a facility where the conference session is managed and the students have access to expert help and interactive technology. Alternatively, the astronomer at the remote telescope can offer a tour and explanation of its use, perhaps take a few images, and prepare students to use the telescopes remotely themselves. 8. Submit queue-scheduled requests on the CDK20's, CDK700, and RC24. We operate 4 large telescopes: at Mt. Kent the CDK20 0.5 meter and the CDK700 0.7 meter (early 2012), and at Moore the CDK20 and RC24 (0.6 meter Ritchie-Chretien) all with similar capability. The CDK20's are idea for imaging and photometry, the RC24 for exoplanet photometry, and the CDK700 for faint object photometry, imaging and spectroscopy. At the present time (October 2011) they require an operator and can run on a queue schedule rather than with remote control if needed for a science goal. 9. Use web-based remote operation of CDK20, CDK700, and RC24 telescopes for imaging, photometry, and spectroscopy. Similar telescopes at Moore and Mt. Kent Observatories provide the workhorses for the Shared Skies program. At the present time (March 2011) the larger telescopes are not available with a web interface. We expect to open the northern CDK20 website late 2011, and a similar interface for the southern CDK20 after installation of a new mount to Australia. Both telescopes are equipped with 16-megapixel scientific imaging CCD's and a set of filters for photometry and narrow spectral band imaging. The system permits a remote user to acquire a target, adjust telescope pointing, select a filter, set the exposure time, and judge based on the image what to do next. 10. Record stellar and nebular spectra with two spectrographs under development. We expect both to be available in 2012. They will provide high spectroscopic resolution at the CDK700 and the RC24 for the determination of the properties of stars and bright nebulae.

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Scaffold of astronomical objects
The concepts addressed here can be developed by targeting objects first in our neighborhood of the solar system, and then at progressively greater distances (and look-back times) to the limit of the instrumental resources.

1. Moon
Moore Observatory operates two instruments suitable for observing the Moon. One allows students to take their own full color 12 megapixel images that show detail down to 1 arcsecond. The other provides an interactive view of the night sky, including the Moon as it would appear to someone at the site in enough detail to see large craters. Images are archived on clear nights for use during the day, and the instruments are available for remote live use by prior arrangement. Possible projects observing the Moon are 1. Phases of the Moon night to night 2. Cycles in the rising, setting and transit of the Moon 3. Apparent size of the Moon, allowing a measurement of the Moon's orbit 4. Libration in longitude, showing the difference in torbital and rotation periods 5. Libration in latitude, showing the tilt of the Moon's axis to its orbital plane 6. Lunar surface features, including crater diameters and depths, heights of mountain ranges, rays from craters, mare, and stratigraphy to find relative ages 7. Subtle colors to identify mineral content variations 8. Occultations of bright stars

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2. Satellites of planets
All of our larger telescopes can record the satellites of the giant planets. Orbital periods are from less than a day to nearly two years. For each planet the satellites obey Kepler's laws, and the observations may be used to find the mass of the planet. 1. Jupiter: The four Galilean satellites can be followed nightly to find their orbital period and the size of their orbits. There are five other satellites of Jupiter that are within reach (Amalthea, Himalia, Elara, Carme and Pasiphae). Their relative magnitudes indicate relative diameters and surface properties. Transit timings compared over a 6 month interval may be used to find the speed of light from the time delay for light to cross Earth's orbit. 2. Saturn: There are 6 satellites, including Titan with a 15.9 day period. The orbital planes are tipped to our line of sight so for Saturn hese nearly circular orbits appear as ellipses. Iapetus varies significantly in brightness depending on where it is in its orbit because of very different surfaces on two hemispheres. 3. Uranus: There are 5 satellites with magnitudes from 13.5 to 15.8 that may be recorded in exposures of 15 seconds. Their orbital periods range from 1.4 to 13.5 days.

4. Neptune: One large satellite, Triton, is visible at magnitude 13.5 in a 5.9 day period orbit.
Satellites of Mars are probably out of reach because they are faint and close to the planet. We will try high speed lucky imaging at the next opposition.

3. Phases of Venus
Venus as it appears in the evening or morning sky at sunset or sunrise may be
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followed with the pan-tilt camera at Moore Observatory. The synodic period of Venus allows its sidereal orbital period to be deduced, and with Kepler's third law determines its distance from the Sun. A telescopic observation with any observatory telescope will show a phase that will be a large thin crescent when it disappears from view in the evening sky or reappears in the morning sky, and a smaller full disk when it disappears as a morning star and reappears as an evening star soon thereafter. The Venus cycle is the basis of the Mayan calendar and there is an opportunity to make a connection with archeology and with other cultures in its study.

4. Planetary atmospheres and other details
Venus, Mars, Jupiter, and Saturn have distinctive and different atmospheric features that may be recorded with all of our telescopes. The position of planets and bright asteroids may be recorded to track their orbits. For the planets the widefield cameras attached to the CDK20's are ideal because they show identifiable constellations. 1. Venus: In the ultraviolet the structure of the clouds may be seen, especially when near full. In the infrared (I filter) it may be possible to map surface features. 2. Mars: White clouds sometimes appear. The polar cap size changes can be followed. Dust storms are common at opposition. The rotation period of Mars can be measured by tracking its surface features during a single night, and by comparing images taken several nights apart.

3. Jupiter: Features in the belts can be followed to find the rotation period of the upper atmosphere in just a few hours of observing time. The Giant Red Spot can be followed to measure the rotation, and to confirm that the spot is not locked rigidly to a longitude. Dynamic features such as GRS's junior companion, and changing contrast of the belts and zones, are evident. High speed video can be acquired to allow "lucky imaging" and yield sub-arcsecond image resolution. Shadows of the Galilean satellites in transit can be
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seen on the clouds. 4. Saturn: Some atmospheric structure can be seen and followed over the 10 hour rotation period. The difference in brightness of the polar and equatorial regions is evident, especially in selected filters. The rings, of course, may be recorded in different colors, and the shadow of the rings on the disk may be seen. Saturn will be favorably placed for observation in the spring and early summer of 2011.

5. Dwarf planets
The CDK20 telescopes have a limiting magnitude of about 18 for useful measurements of brightness at an accuracy of around 10 percent. There are five dwarf planets accessible: 1. Ceres at magnitude 6.7 to 9.3 rotates with a 0.4 day period 2. Pluto at magnitude 13.7 to 16.3 rotates with a 6.4 day period 3. Haumea at magnitude 17.3 has a 0.16 day rotation period 4. Makemake at magnitude 16.7 has a 0.32 day rotation period 5. Eris at magnitude 18.7 is probably out of reach, but has a 1.1 day period Nightly motion allows the orbit to be estimated with Kepler's laws (or with precise analysis, a complete orbit to be calculated). The relative magnitudes are determined by their diameters, which may be inferred from a measurement of the brightness. If there is any non-uniformity on the surface, the rotation will modulate the brightness enabling a rotation rate to be determined.

6. Asteroids

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The brightest asteroids are easily followed in short exposures, and their rotations monitored by modulation in their brightnesses. They are close enough that their motion causes them to appear to move with respect to distant stars quickly in a sequence of images over a single night. Accessible asteroids include Pallas, Juno, Vesta, Astraea, and Hebe, all with rotation periods of less than a day. Fainter asteroids are also recorded routinely in images taken for other purposes, and may be found in the data archives. It is possible to determine an orbit given three observations, and to estimate the distance based only on the angular rate of motion between two exposures. When an occasional smaller asteroid makes a close approach to Earth it moves very rapidly and increases in brightness dramatically. For these, even small but potentially hazardous objects may be followed with our telescopes, although there is a limiting window of opportunity for each event that would be further constrained by weather.

7. Comets
There are usually 20 or so known periodic comets returning to the inner solar system every year. Most of them will be faint, perhaps making perhelion when the Earth is in a unfavorable location for us to see them well. However a few will be visible from either the northern or southern telescopes (or both), and may be followed for several months to see the development of a tails or unexpected changes. Occasionally new comets may make a first spectacular appearance. Our telescopes have a wide field of view, and the auxiliary widefield cameras on the C20 will record tails out many degrees. Any image taken with our telescopes should be at least casually inspected for previously undiscovered comets.

8. Exoplanet transits
When a planet crosses the line of sight to its parent star it will slightly diminish the light from the star because it blocks out a part of the star's disk as seen from Earth. Most of the 500+ known exoplanets were discovered by observing this reduction as
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a small increase in the star's apparent magnitude during the transit. These measurements require great attention to detail, and hundreds of images recorded at a rapid cadence during a transit event. Operation of the RC24 at Moore Observatory is presently largely dedicated to measuring transits in search of evidence of planetary atmospheres and unidentified members of the same planetary system. Because very accurate tracking is required to keep the image of the star on the same region of the CCD during the transit, the CDK20's will be equally good at the task when their new precision mounts are installed. The CDK700, soon to be shipped to Mt. Kent, will extend our sensitivity at least one magnitude for stars in the southern hemisphere. Transit measurements combined with knowledge of the star's properties reveal the actual size of the planet, while the orbital period with help from Kepler's third law reveals the size of its orbit.

9. Individual and double stars
Our telescopes can record stars as faint as 18th magnitude in exposures of a few minutes. The exposure times are 100x less for every 5 magnitudes brighter, meaning that through most filters stars brighter than 3 th or 4th magnitude cannot be measured accurately. The widefield color cameras on the CDK20's allow comparisons of bright stars and their colors over entire constellations, and may be used to monitor variability as well as star colors for famous variables such as Algol and Mira. Larger telescopes are suitable for measuring proper motion of faint nearby stars such as Proxima Centauri, Barnard's star, Groombridge 1830, 61 Cygni, and epsilon Indi. These examples have motions through space that carry them past more distant stars at rates greater than 1 arc-second per year, and so would require exposures saved for years to be interesting for a student project. While we currently have archival exposures only of Proxima Centauri, the Digital Sky survey may be used in conjunction with a recent exposure to measure the proper motion of stars when our own archival images are not available. Variable single stars are also interesting, since changes in brightness or stars arise from eclipses in binary systems, and pulsation, or rotation with star spots in single stars. The prototypes of the classical variables such as delta Cephei, beta Lyrae,
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and T Tauri are all accessible, as are many fainter examples. A measurement of the light curve compared to a physical model may be used to constrain diameters, the orbits, and the stellar rotation or variable stars. There are also a few uniquely unusual stars worthy of individual study every year because they vary in unpredicable ways. In this category the most interesting is eta Carinae, an aging unstable supergiant double star in the southern sky. At the other age extreme, the Herbig-Haro objects are the variable nebulae that signal bipolar flows from young stars such as T Tauri in the northern sky.

10. Open clusters
Open or galactic star clusters may be young and nearby such as the Pleiades, or older and more distant such as M67. Typically with hundreds of stars born at the same time from a common protostellar nebula their common origin starts a clock that makes the Hertzsprung-Russell (HR) or color-magnitude diagram an indicator of age. Since the stars of a cluster are all at nearly the same distance (d) from us, simultaneous measurements of the color (B-V or V-R) and apparent magnitude (m) for many members of the cluster will establish the cluster HR diagram and thereby the age of the cluster. Matching HR diagrams made with apparent magnitude to an ideal cluster of the same age on an absolute magnitude (M) scale sets the value of m-M, the so-called distance modulus, and provides the distance to the cluster through m-M = 5 log d ­ 5. When clusters are compared to one another a number of subtle effects appear in analyses such as this ­ the contribution of dust to reddening and dimming of distance stars, and the role of iron and other metals in determining the color-magnitude diagram.

11. Planetary nebulae
Color images of planetary nebulae are some of the most beautiful taken with large telescopes. They reveal subtle shades of light emitted by different atomic species in
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the gas expelled from an aging central star. These nebulae are common, but transient, and about 100 are known in our own galaxy. Student research opportunities would include constructing meaningful color images in which the mapping of colors consistently distinguishes similar physical conditions in different planetary nebulae. The three-dimensional shape of the nebulae is not always obvious from their appearance projected on the sky, and there is an opportunity to create 3D structures that account for the observed images. The central stars of the nebulae are on a path to becoming white dwarf stars are are interesting in their own right. Planetary nebulae are also ideal targets for spectroscopic study since the relative strength of lines is a diagnostic of the density and temperature in the nebula, and Doppler shifts due to gas motions may be distinguished.

12. Globular clusters
The globular clusters are typically quite distant by comparison to the galactic clusters, ranging from M4 at 7000 light years to M3 34,000 light years away. Given a limiting magnitude for our telescopes of 18, the color-magnitude diagrams from the nearest clusters are accessible up to the tip of the red giant branch, the faint cool stars in transition from normal main sequence stars to white dwarfs. The tip of the RGB is faint at 19th magnitude for M3, but bright enough to detect in closer M4. The asymptotic branch, which includes RR Lyrae variable stars, is detectable in almost all globular clusters. When these stars can be identified from their short period variability, their known absolute magnitude allows a simple calculation of the distance of the cluster. Exposure times of a few minutes for a well-tracked and focused image will reach these variables, and can be used to find their distance. Alternatively, if exposures are taken in different filters, a color-magnitude diagram based on apparent magnitude can be compared with one for a standard cluster in absolute magnitude to make independent distance measurement. The ages of the globular clusters are typically billions of years, and the point on the main sequence at which stars have just now started on a track to become red giants (called the turnoff point) may be used to find their age by comparison to theories of stellar structure.
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Color-magnitude diagrams reveal the history of star formation in star clusters, and may be evidence of their past interactions with the galaxy. When the distance to a cluster is known, and its direction from Earth is found from its celestial coordinates, the cluster can be located within our galaxy. If enough clusters are measured in this way then the center of their distribution should be statistically close to the center of the Milky Way galaxy. There is an opportunity to repeat an historically significant first measurement of the location of the center of our galaxy from the spatial distribution of the globular clusters. Of course, when the distance is known the physical size of the cluster may be calculated, and this allows a comparison of clusters with one another. The two largest globular star clusters are Omega Centauri and 47 Tucanae, both nearly 16,000 light years away. These are close enough that our Mt. Kent telescopes can record HR diagrams that capture the tip of the red giant branch, which allows comparison to stellar structure models that set the age and distance to the clusters.

13. Large and Small Magellanic Clouds and M31
The Large and Small Magellanic Clouds (LMC and SMC) are two companions of the Milky Way visible in the southern sky. They are relatively nearby on an intergalactic scale, at distances at 157,000 and 197,000 light years. Because they are individual galaxies with stars all at nearly the same distance, they are a laboratory for the study of stellar evolution. Cepheid variables (delta Cephei in the Milky Way is the prototype) are calibrated based on their magnitudes in the LMC and are the standard stars for measuring distances out to the Virgo Cluster of galaxies. M31, the "Great Nebula" in Andromeda is a galaxy similar to our Milky Way and just visible in the northern sky to our unaided eye. Its largest galactic star clusters and very brightest stars can just be distinguished in images of M31 taken with our telescopes, and its spiral structure is evident.

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14. Galaxies
The Virgo cluster, 54 million light years from us, includes about 1500 galaxies of all types. It is observable from both Mt. Kent and Moore observatories. The importance of the Virgo cluster to astronomy is that Cepheid variables in some of its galaxies have been measured with the Hubble Space Telescope to make a very precise determination of its distance. Students can use it to study the variety of elliptical and spiral galaxies in a large cluster, to see galaxies interacting in a mutual collision, and to measure the jet from a black hole in M87. Occasionally there is a supernova in the Virgo cluster, or other nearby clusters, that can be imaged with our telescopes. Usually there are a few each year within reach. The maximum brightness of a supernova and the decay of its light curve allow us to find its estimate its distance and to infer the distance of the host galaxy. Automated patrol images usually recognize nearby supernovae promptly, and our telescopes can follow the light curves from soon after their discovery.

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