2021 HAD Meeting Abstracts

Monday. January 11^th, 12:00-1:30 pm EST

Session Chair: Alan Hirshfeld

 

D. DeVorkin (Smithsonian Institute, National Air and Space Museum)

In his address to the British Association in August 1920, Arthur Stanley Eddington proclaimed that “Probably the greatest need of stellar astronomy at the present day, in order to make sure our theoretical deductions are starting on the right lines, is some means of measuring the apparent angular diameters of stars.” In less than 4 months, his request was answered by astronomers at Mount Wilson working with Albert Abraham Michelson when they measured the angular diameter of Betelgeuse with the new 100-inch reflector on the evening of December 13th, 1920. How they did it is the subject of this talk. We will feature Michelson’s long journey to this end, and how he was aided and abetted by George Ellery Hale, who was a man not averse to taking big risks.

 

V. Trimble (University of California, Irvine)

Michelson's measurement of the diameter of Betelgeuse was a case where a new technology had to be invented to tackle the problem. The measurement of about 7 mas for the diameter of Sirius by Hanbury Brown and Twiss was another (called intensity interferometry). There are some famous cases, like the first measurement of solar neutrinos, of gravitational waves, and of X-rays from neutron stars and black holes. Others are less well known, for instance photographing light scattered by the dust clouds at L4 and L5 of the earth-moon system (Kordylewski clouds) and the confirmation of the prediction of polarization of the light from the Crab Nebula. At least a few of these, for instance observation of the cosmological neutrinos, are still ahead of us (and no, I don't know how to do this either). But Sir William McCrea could think of no way to measure lambda independent of the other cosmological parameters, and you can read about it now as the Alcock-Paczynski test. The presentation will highlight 5 or 6 examples, not all necessarily mentioned here.

 

C. Doran (Harvard University)

Whether using optical or non-optical telescopes, spectroscopy or interferometry, light is intrinsically involved in both the message (the astronomical data observed) and the various instruments used to detect, explore, and interpret that message. Regarding each of these functions, mathematics necessarily enters as an “instrument” without which the aesthetic purpose embedded within such “technological instruments” cannot be realized, nor the observations attain precision of meaning. As the French mathematician Henri Poincaré explained at the first International Congress of Mathematicians in 1897, mathematics must not only aim to provide a “mathematical instrument for the study of nature” (such as his New Methods of Celestial Mechanics); mathematics must also serve the “aesthetic purpose” of aiding philosophers and physicists “to fathom the notions of number, of space, of time,” for only mathematics can “express relations so delicate, so rich, and so precise.” When theoretical and technological advances compelled 20th-century physicists to interrogate a dynamic universe expanding from an initial singularity, cosmologists embraced immense conceptual and material challenges to make light a precise instrument for illuminating its cosmic messages. This talk will analyze several episodes in modern astronomy, relativistic physics, and observational CMB cosmology in which practitioners grappled with unresolved tensions within modern cosmology. We will see that an underexamined and often misunderstood issue is how to overcome the limits of geometric empiricism - an issue first posited in its modern form 130 years ago by Poincaré.

 

Monday, January 11^th,, 1:40-2:40 pm, EST

Session Chair: Alan Hirshfeld

 

Tuesday, January 12^th, 12:00-1:30 pm EST

Session Chair: Kevin Krisciunas

 

G. Latura (Independent researcher, Trumbull, CT)

In Natural History (Book II, 23, 93-94), the Roman writer Pliny explains: ‘The only place in the whole world where a comet is the object of worship is a temple at Rome. His late Majesty Augustus had deemed this comet very propitious to himself, as it had appeared at the beginning of his rule, at some games which, not long after the decease of his father Caesar... he was celebrating... In fact he made public the joy that it gave him in these words: ‘On the very days of my Games a comet was visible for seven days in the northern part of the sky. It was rising about an hour before sunset, and was a bright star, visible from all lands. The common people believed that this signified the soul of Caesar received among the spirits of the immortal gods...’ This was his public utterance...’ (tr. Rackham, 1938, 237). Coins struck by Augustus in 18 BCE show the comet of Divus Julius and the bust of his heir (Fig. 1, Seaby, 1952, Roman Silver Coins, Vol. 1, 97). The long gap between the purported 44 BCE sighting and the comet on coins of Augustus in 18 BCE has led to questions as to whether such an apparition ever took place (Gurval, 1997). Might the comet of 44 BCE have been Augustus’ invention? Ramsey and Licht (1997) write: ‘The answer to this question must be “surely not” for at least three cogent reasons.’ One, traces of ‘anti-Augustan’ interpretations of the event. Two, comets were usually seen as threatening, but Octavian managed to turn this perception around. ‘This stroke of genius on Augustus’ part has to be regarded as one of the most remarkable examples of “spin” control in the whole of antiquity. Third and lastly, we can be certain that there was a comet in 44 BC because one is attested in our Chinese sources...’ The July cometary outburst reached an apparent magnitude of -4, and the Sidus Iulium appeared repeatedly in Roman literature: Virgil (37 BCE), Ovid (8 CE), Pliny (77 CE), Suetonius (121 CE). Modern discussions of ancient texts and coins include works by Scott (1941) and by Pandey (2013) who shows coins that illustrate the evolution of Caesar’s Comet. What would have qualified Julius Caesar for such a spectacular celestial ascent? Caesar had spent a fortune on bread and games in order to be elected Pontifex Maximus, highest priest of the Roman state religion. Any violence against the body of the Pontifex Maximus was taboo. As he amassed power under his own hand, Caesar must have felt invincible. After Caesar’s demise, Augustus eventually appropriated the office of Pontifex Maximus (Res Gestae), along with the authority of consul and the veto power of tribune. Church and state became one. Caesar’s comet had foretold the birth of the Roman Empire.

 

S. R. Gullberg (College of Professional and Continuing Studies, U. of Oklahoma)

Astronomy in the Andes was well developed by the time the Spaniards arrived in the Inca Empire. This was due in large to the accumulation of knowledge through observations made by the many civilizations preceding the Incas. Astronomy was not simply observing and understanding celestial movement, however, as it was integrally woven into the very fabric of Andean existence throughout myth, cosmology, and culture, playing an important role in daily life. The Incas were a Sun-worshipping people and their emperor was said to be “the son of the Sun.” Their cosmology begins with the primordial rising of the Sun, and also that of the Moon. In their astronomy they were aware of many stars and planets and paid particular attention to the Milky Way and the Pleiades. In a practical sense this knowledge was put to work via horizon astronomy as the Incas marked the passage of sunrises and sunsets on their horizons in order to keep time for agriculture and religion. Ultimately, celestial alignments and effects of light and shadow were integrated into their temples and huacas, as well as with other constructs such as solar pillars built more specifically for astronomical purposes. This presentation will explore aspects of the fascinating astronomy of the Inca Empire.

 

G. Latura (Independent researcher, Trumbull, CT)

In Plato’s Timaeus (35b-36a), the character Timaeus of Locri promulgates a numerical harmonic cosmogony, wherein the Demiurge generates a series of proportions that give seven numbers: 1, 2, 3, 4, 9, 8, 27. At Plato’s Academy, Crantor arranged these numbers in the triangular shape of the letter Lambda, with even numbers down one side (2, 4, 8) and odd numbers down the other (3, 9, 27). These sequences include squares (2x2, 3x3) and cubes (2x2x2, 3x3x3). Plato links these seven numbers to the Circle of the Different (36d) that would indicate the course of the seven Wanderers (38c-e). Plutarch writes, in On The Generation of the Soul in Timaeus (c. 110 CE), about the Platonic numbers: 'Yet certain people look for the prescribed proportions in the velocities of the planetary spheres, certain others rather in their distances...' (tr. Cherniss, LCL 427, 1976: 321). And Macrobius writes, in Commentary on the Dream of Scipio (c. 400 CE): 'Now we must ask ourselves whether these intervals, which in the incorporeal Soul are apprehended only in the mind and not by the senses, govern the distances between the planets poised in the corporeal universe.' (tr. Stahl, 1952: 196). Macrobius gives a correlation between Plato's numbers and planetary distances (Figure 1. Stephenson, The Music of the Heavens: Kepler's Harmonic Astronomy, 1994: 40). Johannes Kepler at first sought to explain planetary orbits through Platonic solids (Mysterium Cosmographicum, 1596), but this was not entirely satisfactory. So Kepler turned to Plato's seven numbers and, in Book 4 of Harmonices Mundi (Linz, 1619), he quotes Proclus' commentary on Euclid: ‘And here we must follow Timaeus, who integrates and completes the whole source and structure from the mathematical types, and locates in it the causes of all things. For those seven terms of all numbers pre-existed in it, as far as cause is concerned.’ (tr. Aiton et al., 1997: 301). In Book 5, Kepler gives his sesquialterate (2:3) power formulation of the Third Law (Aiton, 1997: 411). Then Kepler uses Plato’s harmonic numbers to illustrate his Harmonic Law: ‘Let the periodic times of two planets be 27 and 8. Then the proportion of the mean daily motion of the former to the latter is as 8 to 27. Hence the semidiameters of the orbits will be as 9 to 4. For the cube root of 27 is 3; that of 8 is 2; and the squares of these roots are 9 and 4.’ (tr. Aiton et al., 1997: 413). Ten years after he published his first two Laws, Kepler relates that, when he came upon this correlation, ‘at first I believed I was dreaming.’ (tr. Aiton, 1997: 411). The harmonic cosmic numbers in Plato's Timaeus appear to have inspired Kepler’s Harmonic Third Law.

 

02.04     Einstein in mid-century: Eclipse tests of General Relativity from 1929 to 1973

D. Kennefick (University of Arkansas)

By the late 1920s most astronomers and physicists were satisfied that the light deflection test conducted by several eclipses expeditions had conclusively falsified Newtonian gravity, leaving Einstein's theory of General Relativity (GR) as the only viable theory of gravity. In the next half-century however, repeated testing would raise some doubts about the accuracy of the confirmation of GR and the emergence of rival theories (such as Brans-Dicke theory) would raise the stakes for new attempts to perform the test. Astronomers from several countries would perform the test at multiple eclipses, all agreeing with Einstein's prediction. At the same time levels of precision of the test failed to improve as logistical challenges associated with the challenges of traveling to eclipses continued to confound even the best prepared expeditions.

 

J. S. Tenn (Sonoma State University) and A. H. Rots (Center for Astrophysics | Harvard & Smithsonian)

The information posted in AstroGen at https://astrogen.aas.org/ may be of use to you. If you are a prospective astronomy graduate student (or advisor to one), you can find which universities are producing Ph.D.s in your field of interest, and you can peruse some of the theses recently completed. The acknowledgments sections of the theses often give an excellent perspective on what it is like to be a graduate student in a particular department. If you are interested in the history or sociology of science, you can gather data on the production of doctorates by year, country, university, advisor, or thesis title words, and you can follow links to more than 19,000 online theses. If you earned a doctorate with an astronomy-related thesis, or supervised one, you should be included. If you are, you can check your entry and provide updates or corrections. If not, you can add yourself to the list. You can add entries for people you know or, if they are already in the database, check on their contents. If you have some available time and interest, you can volunteer to help expand the database. AstroGen is now "nearly complete" for 26 countries, with some 34,000 scientists entered, but there is still much more to be done.

 

202.06   Star and Solar System Maps: A History of Celestial Cartography

N. Kanas (Professor Emeritus, University of California at San Francisco)

Since antiquity, people have observed the night sky in an effort to predict celestial events, help with navigation, coordinate planting activities, and understand their place in the universe. Many cultures viewed the stars as forming fixed heavenly patterns called constellations that reflected issues important to them. The ancient Greeks visualized constellations as allegorical representations of classical heroes, heroines, and monsters from Greek mythology. In contrast, the Chinese saw them as reflections of people and activities on Earth, from the imperial Emperor and his retinue to tradesmen and farm animals. Complicating the fixed order of the heavens were the wandering planets and unexpected events, such as comets and novae. To establish order and predictability, people made maps of the heavens. The mathematical Greeks went so far as to place the stars in a scientific coordinate system that was based on celestial latitude and longitude (today’s declination and right ascension). In time, two kinds of maps emerged: star maps, focusing on stellar placement and constellations, and solar system maps, focusing on planetary locations and, with the advent of the telescope, surface characteristics. But for many centuries, solar system maps were in actuality cosmological diagrams with nested planetary circles centered first on the Earth, then on the Sun, and then expanding into deep space as nebulae and galaxies became identified. Star and solar system maps formed the backbone of stunningly beautiful sky atlases of the 17th to the 19th Centuries. But telescopic and scientific needs called for increased accuracy in star placement using more detailed and enlarged coordinate systems. Constellation images became redundant, and they have largely disappeared in the finely drawn and computer-generated star maps used today. In addition, ever larger telescopes and space probes have allowed us to view the planets and their satellites with stunning accuracy. In this presentation, the history and development of celestial cartography will be discussed using striking images from antiquarian and modern sources.

 

Tuesday, January 12^th, 4:10-5:40 pm EST

Session Chair: Jay Pasachoff

 

222.01   History of Astronomy: The Voyager Golden Record in Intellectual History

J. Pasachoff (Williams College)

In this session cosponsored by the American Astronomical Society's History of Astronomy Division, we discuss especially the Golden Record of music, greetings, photographs, and more organized by Jon Lomberg working for Carl Sagan in spring 1977, shortly before the Voyagers' launches. Emer Reynolds will discuss the 2019 documentary - The Farthest - that she directed; we have separately arranged for those attending the meeting to stream the two-hour theatrical version. Sarah May will discuss the legacy of the Golden Record in intellectual history. Nick Oberg will discuss the trajectory of the Voyager spacecraft in the distant future. Supplementally, as three nations' missions travel from Earth to Mars this fall, Lomberg will discuss the disk of greetings and more that was sent to Mars on NASA's Phoenix lander in 2008.

 

J. Lomberg (Galaxy Garden Enterprises, Honaunau, HI)

The golden records carried aboard each Voyager spacecraft are 43 years into their billion year journey to the stars. Their message from Earth will last until they are eroded away by interstellar dust. The Design Director of this unique project reconsiders it four decades after he helped make it.MEMORIES OF VIKING by Jon LombergA look back at the first successful landing on Mars by a human spacecraft, seen through the lens of the Visions of Mars DVD.This disk, a gift to future human colonists, is now on Mars aboard NASA's Phoenix lander. It contains a recording of the night we landed on Mars as well as greetings from Carl Sagan and others. This retrospective is narrated by a reporter who covered the mission and a composer who has worked with scientists to imagine how Mars might sound.

 

S. May (Swansea University, Cardiff, UK)

Expressing the essence of contemporary humanity to an unknown audience sounds like an extraordinary, unprecedented undertaking. Indeed, the 'golden record' like the space programme it formed part of, was remarkably ambitious. But it also formed part of a long tradition of 'intentional heritage' in which societies select elements, images and stories to represent themselves to the future. Statues and monuments may be considered part of this tradition which flourished in the 20th century with the development of time capsules. The golden record represented a leap, both in imagined audience and in methods of communication. The tradition has continued and communication with unknown audiences has diversified and become individualised, even commonplace. All of these undertakings do more than communicate with future audiences, they tell us about ourselves. The arrangements, decisions and choices reveal the workings of our communities in the present day. This paper will explore the place of the golden record in this tradition of intentional heritage and consider its legacy in the present day.

 

E. Reynolds (Writer/Director, “The Farthest,” Dublin, Ireland)

In an interview with Jon Lomberg, as Writer and Director of The Farthest (2017), I will reflect on the film and the enduring and unique appeal of the extraordinary and era-defining Voyager mission. We will discuss the film that we endeavoured to make in detail - in terms of approach, tone, cinematic scale, reach, etc. About the core Voyager mission team whom we were so fortunate to meet and interview for the film; the worldwide response to the film, and what that response illuminates about the enduring love and pride that this mission evokes. Many of the major scientists involved then and now appear. (https://www.imdb.com/title/tt6223974/fullcredits). The film will be available for viewing during the whole week of the meeting.

 

N. Oberg (Kapteyn Astronomical Institute, Groningen)

The Voyager spacecraft are on solar escape trajectories into the interstellar medium. Each Voyager carries a phonograph record encoded with depictions of life and culture on Earth, intended as a ‘message in a bottle’ to distant epochs. Due to the benign environment of interstellar space the records may be preserved after other cultural/technological artifacts are erased from the Earth’s surface. It is thus of anthropological interest to investigate the trajectory and fate of the spacecraft that may carry some of the final evidence of human civilization. We evaluate the eventual degradation of the records from interaction with interstellar matter. We find that after traveling for 5 Gyr in a smooth axisymmetric galactic potential, Voyager 1 is ~99% likely to suffer damage rendering the exterior-facing side of the record indecipherable, while Voyager 2 is only ~20% likely to suffer similar damage. We find that the spacecraft-facing side of both records will likely survive until the merger of the Milky Way and M31 in ~5 Gyr, after which it becomes possible that the spacecraft are ejected into the intergalactic medium and erosion rates reduce accordingly.

 

Wednesday, January 13^th, 12:00-1:30 pm EST

Session Chair: Steven Gullberg

 

B. E. Schaefer (Louisiana State University) and J. Stamm (Berea College)

The Picture Rocks Sun Dagger is a spiral petroglyph on a hillside northwest of Tucson that shows sun dagger events at both the summer solstices and the equinoxes. On each of these dates, a wedge-shaped sunbeam with opening angles of 20°-30° touches the center of the spiral, with both of these being confidently intentionally constructed by peoples of the Hohokam culture, c. 800-1300 AD. More generally, for claimed sun daggers throughout the American Southwest, the critical question is whether the ancient indigenous peoples intentionally placed the petroglyph so as to create a sun marker. The confident starting point for proving the intentionality of sun daggers in general is a historgram measured by the Prestons showing highly significant peaks for indicated declinations within 2° of -23.4°, 0.0°, and +23.4°, with this being not by chance. In a review of solsticial and equinoctal sun daggers, we find that they all have beams of light shaped like a long-thin triangle with an apex opening angle of 40° or less that touches the center of the petroglyph symbol. The majority of the sun daggers use a spiral petroglyph, with circles and other symbols being used. We find that from one-to-five light wedges appear on flat rock panels during any one hour interval of searching on just one side of the small hill, so false alarms must be common, and it is easy to find a place for a petroglyph so as to create an intentional sun dagger. Further, where a spiral or circular petroglyph has a coincidental light/shadow display, the false alarm rate is measured to be 20% to 33%. Sun daggers that have indicated declinations other than ±23.4° or 0.0° are false alarms, including claims for alignments to cross-quarter days and lunar standstills, which are certainly wrong. Intentional sun daggers are not related to any form or calendric regulation, astronomical tools, or public ceremony. Rather, abundant ethnographic evidence shows that the sun daggers are a part of sites, called Sun Shrines, where a local Sun watcher would have lone vigils, with offerings and prayers to the gods on the solstices and equinoxes.

 

C. L. Mudd (Mudd Law, Chicago)

History, if we allow it, can serve as a guide for the future. This precept applies to more than we often consider. In the context of space, a history exists with respect to the manner in which the world addressed orbital or space debris. Over the course of nearly thirty years, national and international governmental bodies grew into regulations designed to mitigate orbital debris. This comes none too early. In fact, some argue it has come too late. Others contend substantial movement must yet occur to avoid the Kessler Syndrome and other catastrophic developments in Earth’s orbital environment. And yet, change did occur. Within the United States, the issue grew from a glancing examination to efforts by the Federal Communications Commission (“FCC”) to impose restrictive metrics on satellites and satellite mega-constellations. In fact, the regime likely to be implemented by the time this will be presented reflects a coherent approach to the issue. As such, the current regulatory scheme provides a model by which other aspects of space may be regulated on, ideally, a shorter time scale. In the context of satellite mega-constellations and the light pollution emanating therefrom, an urgency exists even more pronounced than orbital debris. Observations, modeling, and simulations demonstrate the adverse effects on astronomy caused by satellite light pollution (“SLP”). The harm exists and, absent efforts to mitigate such effects, will only increase in severity and breadth. Indeed, in the United States, the FCC approved and licensed at least two mega-constellations. As such, there exists no governmental impediment to launch the thousands of authorized satellites. And, although certain industry actors such as SpaceX have engaged with the astronomy community to mitigate SLP, there exists no legal compulsion to do so. Consequently, the immediate need for regulatory parameters could not be more paramount. Astronomy and our dark skies simply cannot wait three decades for significant policy development. This presentation reviews the history behind efforts to address orbital debris and highlights the existing paradigm. It then applies this historical analysis to SLM by adapting the regulatory framework for orbital debris. In this manner, efforts to attain a viable regulatory regime for SLM can bypass decades of development and the deterioration of our dark skies that would otherwise occur.

 

N. Vasquez, R. Caiza, D. Domínguez, C. Erazo (Physics, ESCUELA POLITECNICA NACIONAL, Quito, ECUADOR), and R. Puebla (Centro de Física, Universidad Central del Ecuador, Quito, ECUADOR)

Coaque, a fishermen village in north coast of Ecuador where the Equator first meets the South American land, it is an iconic place where astronomy and archaeology converge and can show the geodesic and astronomical history of Ecuador. 16th Century ethnohistorical data is rich on descriptions about the abundance of wealth and land fertility within Equinoctial zones. This awoke the curiosity of Europeans of the geodesic position. Two centuries past until La Condamine and Bouguer of the French-Hispanic Geodesic Mission, first measured the zero degrees latitude at Punta Palmar, just south of Coaque. In this study, we present the transit of emblematic stars of the equinoctial sky and we emphasize in the detectability of high energy galactic sources as the Crab in the TeV range. Due to the geography of Ecuador, we determine the fluence of secondary particles of the Crab pulsar at ground level from altitudes from 4000 m.a.s.l. to sea level taking into account the influence of the South Atlantic Anomaly in the production on extensive air showers from gamma and cosmic rays. This study aims to contribute to the astronomical studies for the creation of the astronomical and archaeological museum in the coast of Ecuador.

 

A. Rots (Center for Astrophysics | Harvard & Smithsonian) and J. Tenn (Sonoma State University)

After eight years of development and data gathering, the Astronomy Genealogy Project (AstroGen: https://astrogen.aas.org) went online 25 July 2020, the 159th anniversary of the first astronomical doctorate awarded in the USA. AstroGen, a project of the AAS Historical Astronomy Division (HAD), is a database of astronomy-related doctoral dissertations hosted online by the AAS. AstroGen clearly struck a chord in the community, as many reactions, additions, and corrections came flowing in immediately afterward. When it went online, it contained 33,000 dissertations and more are being added every day. Clearly, AstroGen can never be finished: the team will continue working to update the database with new theses, while also augmenting, and correcting, the historical record and expanding the database to include more countries. AstroGen serves also as a historical database of astronomers and allows the reader to follow links from an astronomer to his or her academic parent (thesis advisor) and children (doctoral students). Eventually it will allow the extraction of the number of astronomy-related doctorates granted over any time period and by any university or country, thus enabling a wide range of studies in the history and sociology of modern astronomy. We encourage you to check your own entry, correct it if necessary, or add it if it is missing. You can add entries for people you know or, if they are already in the database, check on their contents. And we continue to seek more participants for the team, including people who can gather data from countries not yet explored, especially in Asia. We gratefully acknowledge the financial support of the AAS and the HAD.

 

301.05   Ten Historic (Non-academic) US Observatories and Their Likelihood of Preservation

T. A. Hockey (University of Northern Iowa)

The USA is rich in optical observatories of historical significance. A partial list is included here. With one exception, each of these remains a working observatory, with a primary instrument greater than 20 inches in aperture. Academic observatories (colleges, universities) deserve their own list, which I will compile on a later occasion.

    I visited each of the private and government observatories below. My assessment of preservation likelihood is based upon inspection, legal ownership, and level of recognition. (City name = that closest to observatory.)

    ⁂ Chamberlin Observatory. Denver, CO. First major observatory established in the Rocky Mountains. Denver Astronomical Society*. Preservation likelihood = good.

    ⁂ Keck Observatory. Hilo, HI. Built in the 1990s, the twin 10-m reflectors represent the maturation of new, turning-point, telescope-building technology that evolved in the 1960s. California Association for Research in Astronomy. Preservation likelihood = excellent.

    ⁂ Kitt Peak National Observatory. Tucson, AZ. First observatory in the United States to offer state-of-the-art instrumentation to all observers on a competitive basis. Association of Universities for Research in Astronomy. Preservation likelihood = excellent.

    ⁂ Kuiper Airborne Observatory. Mountainview, CA. The original, airliner-size, flying observatory housed a 36-inch reflector. National Aeronautics and Space Administration. Preservation likelihood = poor.

    ⁂ Lowell Observatory. Flagstaff, AZ. Last significant observatory financed completely by an individual. Lowell Observatory Corporation. Preservation likelihood = good.

    ⁂ Mount Wilson Observatory. Pasadena, CA. The first high-altitude astrophysical observatory is home to the 100-inch Hooker reflector—one of the most productive telescopes of all time. Mount Wilson Institute. Preservation likelihood = fair.

    ⁂ Palomar Observatory. San Diego, CA. The 5-m Hale reflector was the largest telescope in the world for 27 years. Caltech Optical Observatories. Preservation likelihood = good.

    ⁂ Sunspot Solar Observatory. Cloudcroft, NM. Site of the first observatory consisting of instrumentation exclusively designed for studying the Sun. Sunspot Solar Observatory Consortium. Likelihood of preservation = good.

    ⁂ United States Naval Observatory. Washington, DC. Served as a de facto national observatory for well over a century. Naval Meteorology and Oceanography Command. Likelihood of preservation = excellent.

    ⁂ Yerkes Observatory. Lake Geneva, WI. First of George Hale’s Great Observatories. Yerkes Future Foundation. Likelihood of preservation = fair.