The Aristarchus Campaigns: Collaboratively Measuring the Solar System Best Practices Best

The Aristarchus Campaigns: Collaboratively measuring the Solar System Best Practices Best

Jorge I. Zuluaga Juan C. Figueroa Keywords FACom-Instituto de Física-FCEN, Universidad de FACom-Instituto de Física-FCEN, Universidad de Citizen astronomy, lunar orbit, lunar distance, Antioquia & Sociedad Antioqueña de Astronomía Antioquia & Sociedad Antioqueña de Astronomía Moon calculations, speed of light, astronomical Colombia Colombia methods, astrometry, citizen science [email protected]

Summary

Citizen astronomy has proven to be one of the most effective ways to actively involve amateur astronomers in real scientific endeavours. We present here the Aristarchus Campaigns, a citizen astronomy project intended to collaboratively reproduce historical astronomical observations. During the campaign amateur astronomers were invited to use simple optical instruments to gather data about some common astronomical phenomena. This data was used to calculate the value of well-known physical and astronomical quantities such as the speed of light and the distance to, and size of the Moon. We describe the project and the results of the first two Aristarchus Campaigns. We argue that this type of simple campaign may help to engage the public with astronomy in developing counties and prepare their astronomical communities to participate in high-impact observational campaigns.

Introduction using powerful lasers and retro-reflecting Today, the advent of advanced and arrays of mirrors placed on the lunar sur- accessible technological devices such Ancient astronomers devised inventive face by the Apollo astronauts, so that the as smartphones is opening new doors methods to measure the Solar System. distance is now known to within just a few for do-it-yourself astronomy. Many per- Using these methods, which are in princi- centimetres (Tapley, 2004; Dickey, 1994). sonal electronic devices such as smart- ple very simple, we can measure the sizes The diameter of and distance to the Sun phones come with a GPS receiver, fast of the Sun, the Moon and the planets, and have been determined to one part in a internet connections and precise clocks. their distances from us. One of the best billion and one part in a 100 billion respec- This gives us, the science communicators, known of these ancient methods was orig- tively (Schou, 1997; Muhleman, 1969) an incredible opportunity to involve astron- inally proposed by Aristarchus of Samos and the speed of light, which until a few omy enthusiasts, and the wider public, in (ca. 310–230 BCE) who devised proce- decades ago had only been constrained astronomy projects. They allow for in situ dures that used lunar phases and eclipses using astronomical methods, is now reg- measurements that would otherwise be to estimate the relative sizes and distances ularly measured in the laboratory so pre- prohibitively expensive and available only of the Moon and the Sun (Van Helden, cisely that it is known to roughly one part to professional scientific teams. 2010; Heath, 2013). in a billion (Sullivan, 2001). This scientific and sociological phenom- More recently, physical constants have In contrast to the classical methods devised enon is called citizen astronomy, or more attracted the attention of astronomers. by such pioneers as Aristarchus or Rømer, generally, citizen science (Raddick, 2010). Using the huge spatial and temporal most of these modern techniques are far scales natural to astronomy, astronomers from the reach and technological capacity Our citizen astronomy campaigns aimed to have devised ingenious ways to measure of most amateur astronomers. Therefore, reproduce historical astronomical obser- the values of these physical constants. measuring distances in the Solar System, vations and measurements that helped to Take for example the method devised by and constraining the physical constants determine the size of the local Universe. Ole Rømer (1644–1710) who measured the that govern it, today seems to be a mat- Here, we will give a background to the speed of light in vacuum by observing the ter of sophisticated instrumentation and project and the role that citizen astronomy periodic occultation of the moon Io by its advanced scientific capabilities. But, these plays in science outreach; we describe host planet, Jupiter (Cohen, 1940). classical methods have a great deal left the project and the specific campaigns to offer and still find a privileged place in that we have run with the participation of Now, many centuries after the invention astronomy and physics textbooks. They individuals and communities in Colombia of these historical methods, astronomers are used today as educational tools, not and abroad; summarise some the most and physicists have measured these quan- only for teaching science history, but also important scientific results of the cam- tities with exquisite precision using vastly for teaching the methods of astronomy and paigns; and discuss the challenges more elaborate tools and methods. The physics and inspiring new ways of thinking involved when organising and running this distance to the Moon can be determined about the results (Salvador, 2009). kind of initiative.

CAPjournal, No. 17, June 2015 23 The Aristarchus Campaigns: Collaboratively measuring the Solar System

over a geographic area covering not only Colombia but several neighbouring countries.

The Aristarchus Campaigns

On 15 April 2014 a total lunar eclipse was visible from most of the Americas and the Caribbean. Lunar eclipses are very common phenomena that are spotted, photographed, and even measured by hundreds of millions of observers. They provide well-known opportunities to measure the size of, and distance to, the Moon and the Sun, as recognised over two thousand years ago by Aristarchus of Samos (Heath, 2013).

In 2014, a group of professional astronomers and astronomy undergraduate stu- dents at the University of Antioquia in Medellín, Colombia teamed up with the Sociedad Antioqueña de Astronomía — a regional astronomical association — and launched the Aristarchus Campaign. The campaign was intended to make the Figure 1. Screenshot of the iContact web-based application developed for the 5 July 2014 Aristarchus experience of observing the total lunar Campaign1. eclipse not only an enjoyable recreational activity, but also an opportunity to perform simple measurements using readily avail- The rise of citizen astronomy the past to study the evolution of comets, able astronomical equipment — such as measure the position of near-Earth aster- binoculars, small telescopes and cameras A recent, inadvertent example of the oids or observe the occultation of stars by — and personal electronic devices — like power of citizen astronomy took place Solar System objects (Ortiz, 2011). Projects mobile phones and tablets. on 15 February 2013. On a cold morning like these have led to new discoveries in Siberia, hundreds of thousands of and breakthroughs but, in most cases, The initiative was promoted by local citizens of several large cities around the the people enrolled in these campaigns astronomy clubs and through social net- Chelyabinsk region in Russia witnessed are experienced observers, whether works. An observing guide was written to only the second large asteroid impact professional or amateur. More simple observe and measure the lunar eclipse and ever recorded. Hundreds of pictures and astronomical campaigns, such as those the public in Medellin were encouraged to videos were taken that day by random described here, aim instead to measure submit their measurements and pictures observers and shared almost instantane- or to observe common astronomical phe- for potential scientific use. ously via social networks. The data col- nomena such as lunar and solar eclipses lected by these de facto citizen scien- and occultations, which use simpler and The weather in Colombia on the date of tists allowed professional astronomers more readily available instrumentation the eclipse made it very difficult for many around the world to study the phenome- and methods. These may serve as initial committed enthusiasts to perform most non in unprecedented detail (Brown, 2013; experiences for those who might then go of the measurements. However, despite Zuluaga, 2013). on to participate in more advanced pro- this slow start we were motivated by the jects. Mass participation in these simple enthusiastic response on social networks Another well-known citizen astronomy campaigns from communities in develop- and proposed, in the same year, several project is the Globe at Night project, a ing countries may prepare them for more similar campaigns. successful initiative intended to measure interesting and challenging collaborative light pollution around the world (Barringer, projects. We now call these observational initiatives, 2011). collectively, the Aristarchus Campaigns. In 2014, with all of this in mind, we designed At the time of writing, there have been three Collaborative astronomical observations and launched a new set of citizen astron- Aristarchus Campaigns: that involve many amateur and profes- omy projects in Colombia called the sional astronomers are not new (Meech, Aristarchus Campaigns. The projects 2005). These campaigns have been run in involved amateur astronomers distributed

24 CAPjournal, No. 17, June 2015 CAPjournal, No. 17, June 2015

Campaign 1: The 15 April 2014 campaign centred on the total lunar eclipse.

Campaign 2: The 23 May 2014 campaign associated with the meteor storm of the 209P/Linear comet.

Campaign 3: The 5 July 2014 campaign correspond- ing to an occultation of Mars by the Moon visible in most parts of South America.

Campaign design and preparation

Preparing observations of a simple astronomical phenomenon, such as a lunar eclipse, an occultation or a meteor shower, is a relatively simple task. Finding the most interesting things to observe and measure and devising ways to achieve these measurements with simple and readily available instrumentation, is much more Figure 2. As the Moon rises its distance to an observer on the Earth’s surface of is reduced. Objects are not challenging. shown to scale.

The campaign preparations began by selecting a phenomenon that could be that was to provide contact times for a technical instructions, intended for more observed from a wide geographic area. given location inside the occultation area1. advanced observers. Lunar and solar eclipses, lunar occul- A snapshot of the website we designed tations and meteor showers make ideal and created for this campaign is shown The guides from all the campaigns can be targets. and described in Figure 1. downloaded from the official website of the project2. Once the phenomenon was identified, The selection of specific quantities to be details of where in the sky the phenome- measured or objects to be photographed non would be visible for the specific geo- is the next step in the preparation process. Call for participation graphic area covered by the campaign had Since the campaigns are intended to repro- to be prepared. In the case of an eclipse this duce historic astronomical measurements, It is important that the local institutions meant calculating the contact times of the it is good to start from the methods and and groups that normally act as sources of Moon with the shadow of the Earth and the quantities that were selected by astrono- astronomy information for the public be fully magnitude of the eclipse, and for meteor mers in the past. involved in the marketing of the campaign. showers the position of the radiant — the For the first Aristarchus Campaign we were point in the sky where the meteors appear We prepared and distributed a short supported by Medellin’s planetarium and to originate for a ground-based observer observing guide featuring information the local science museum, as well as by — and an estimate of the meteor-sighting on the campaign and the observations. the astronomy clubs. rate had to be calculated. A guide of this type should be engaging, short and very easy to read and follow. Social networks, Facebook, Twitter, email Occultations are far more challenging as It should also include a clear description lists, blogs and other astronomy-related contact times depend much more strongly of the goals and scope of the campaign websites allowed us to reach communi- on geographic position. In this case it is and more importantly, a statement about ties in other regions of Colombia and other important to provide access to astronomi- the precise usage of the data provided by countries. cal tools giving the occultation information participants. For the purpose of the call for specific locations. These tools should for participants it is very important that the be user-friendly and be accessible without guide is easily downloadable. Gathering the campaign any advanced astronomical or computa- measurements tional skills. Depending on the complexity of the observations, we additionally prepared and dis- For gathering the data and images For our occultation campaign we devel- tributed detailed guides containing further obtained by the participants in the cam- oped a simple web-based application paigns we use three basic methods:

The Aristarchus Campaigns: Collaboratively measuring the Solar System 25 The Aristarchus Campaigns: Collaboratively measuring the Solar System

Social networks One of the biggest challenges when tions. In most citizen astronomy projects Social networks such as Facebook and dealing with information provided by a this process is performed by researchers, Twitter are the simplest method for gath- large community of observers, is the but in the Aristarchus Campaigns we have ering the data. Social media is especially diversity of data formats that has to be always tried to actively involve some of the suitable for providing information that can dealt with. Differences in equipment, time participants. Additionally, all the analytical be summarised in a few words, for exam- zones, observational experience and even tools, such as numerical methods, formu- ple, contact times of occultations or equip- operating systems, can make the analysis lae and computer codes, have been made ment specifications. of this information potpourri a very chal- publicly available to allow other experts, lenging task. and amateur astronomers, to reproduce Email the results. When the information to be provided is Our second and larger campaign taught more complex, we ask participants to send us that it is very important to instruct For each campaign we prepare a technical emails to the campaign organiser with their observers in advance on how to deal with report describing the campaign itself, its images or data files attached. the data they are gathering. For instance, scientific goals, the data provided by the it is important to warn participants that citizen astronomers and the full results of Upload repository pictures should not be modified after being the data analysis. Two technical reports If the amount of data to be provided is digitally extracted from the cameras as it is have been written so far, the first on the very large and cannot be sent using the important to preserve the EXIF data stored 15 April 2014 lunar eclipse (Zuluaga, 2014) two previous methods, participants may by the devices as this contains key infor- and the second on the 5 July 2014 occul- upload pictures and files to a public repos- mation needed for analysis. These data tation of Mars by the Moon3. itory especially prepared for this purpose. manipulation tips are the kinds of best practices that astronomy or science citizen We have not yet designed a specific web campaigns can use to improve the skills of Results of the campaigns interface to gather the campaign data, as the community before they participate in has been done in other citizen science pro- advanced or global projects. In the following paragraphs we summarise jects, as there are significant differences the two successful Aristarchus Campaigns between the data requirements for each we have already concluded. campaign, making it harder to design a Analysis of the observations and universally applicable platform. For one publication of the results campaign we may primarily need pictures or videos, whilst for another we may just The last part of the campaign was the need positions and times. compilation and analysis of the observa-

Figure 4. Locations of the observers who contributed Figure 3. Best fit of the measured apparent sizes (data points) of the Moon compared to the theoretical model to the 5 July 2014 Aristarchus Campaign for the (continuous line). The shaded region corresponds to solutions statistically compatible with the observed appar- occultation of Mars by the Moon. The shaded areas ent sizes at a 95% confidence level. correspond to the region where the occultation was visible.

26 CAPjournal, No. 17, June 2015 CAPjournal, No. 17, June 2015

A simple method to measure tacts and the fourth was to photograph the amount of time to reach us. For bodies with the distance to the Moon partial eclipse with the shape and size of a substantial apparent motion, like Solar the Earth’s shadow clearly visible. System objects, whose position on the sky Although our perception seems to indicate changes from day to day, the effect of this that the Moon is larger, and thus closer, The fifth and last task was to take a picture light travel time is a detectable difference when it is just above the horizon, the reality of the Moon and include in the same field between the position predicted without tak- is actually the opposite. The distance from of view as the star Spica and the planet ing the light travel time into account and the the Moon to any observer on the surface of Mars. observed position of the object in the sky. the Earth decreases as the Moon rises in the sky, although the distance from the Moon From the pictures that were taken and the During the occultation on 5 July 2014, light to the centre of the Earth remains approx- measurements that were made we were took approximately 8.5 minutes to reach us imately constant. In Figure 2 we show the able to determine the distance to the Moon from Mars. On the same date the appar- cause of this nightly observer-Moon dis- with a fractional precision of 3% (ie to three ent motion of Mars was one arcsecond tance variation. Measuring the angular size parts in a hundred; see Figure 3), finding a per minute and the apparent motion of the of the Moon as a function of elevation pro- value of 386 000 kilometres, fairly accurate Moon was approximately 21 arcseconds vides an estimate of the lunar distance to when compared to the accepted value of per minute. To put the arcsecond unit into the centre of the Earth. 384 400 kilometres. (Zuluaga, 2014) context, the Moon has an angular size of about 1800 arcseconds, or, in other Five specific observations and measure- We discovered that the only informa- words, it extends up 1800 arcseconds ments were proposed for this campaign, to tion required to achieve this precision is across the sky. Due to the time taken for be executed during the lunar eclipse. The the angular size of the lunar disc and the the light from Mars to arrive at the Earth, first — actually unrelated to the eclipse precise time when the disc size is meas- its apparent position on the sky was almost itself — invited people to take pictures of ured. This constitutes the most simple and 8.5 arcseconds off from the position calcu- the full Moon from rising to culmination, affordable way to measure the lunar dis- lated assuming that the light had arrived when the Moon reaches its highest alti- tance and radius devised so far. The only instantaneously (as shown in Figure 5) and tude in the sky. The aim of these measure- instrument required to achieve this is a the occultation took place 24 seconds later ments was to detect the subtle variation in good camera. than expected. Using simple mathematics the lunar disc size due to changes in the this meant that, by working out the differ- lunar distance that result from observa- ence between when we could expect the tions taken from different locations on the Measuring the speed of light with an occultation to take place if the light travel Earth’s surface as the Moon rises, rather occultation of Mars by the Moon time were zero, and when it was actually than at the centre of the Earth. observed to take place, the speed of light On 5 July 2014 we had an occultation of could be calculated. For the Aristarchus The second task involved taking pictures Mars by the Moon that was visible from Campaign we exploited this effect to of the Moon before it entered the Earth’s the northern part of South America (see measure the speed of light in a vacuum. shadow and after it was completely Figure 4). This phenomenon provided Although this is a novel method it was eclipsed. The aim of this measurement a perfect opportunity for setting up an inspired by the original method devised by was to evaluate the properties of the light Aristarchus Campaign. Ole Rømer to measure the speed of light by refracted through the Earth’s atmosphere. looking at variations in the predicted times It is well known that when we observe an for the transits of Jupiter’s moon Io. The third task was to measure, as precisely object in the sky, we see the object as as possible, the times of the eclipse con- it was in the past as light takes a finite For the campaign we asked participants to measure visually or photographically the contact times of the occultations in different locations across a wide geographic area. We gathered results from at least nine groups and individuals from Colombia, Venezuela and the north of Chile (see Figure 4). The joint analysis of the data provided by these groups, allowed us to determine the speed of light in vacuum as 320 180 kilometres per second, a value that, although inaccurate, is just 7% different from the value measured with more sophisticated methods. We show in Figure 6 the contact time delays meas- Figure 5. Illustration comparing the positions of Mars and the Moon in the sky assuming an infinite speed of ured by the participants and the theoreti- light (c) (dashed lines and photographic representations) and a finite speed of light (solid lines). The contact cal delay expected for different values of times for an infinite or finite speed of light are different. The solid lines show what we would observe. Sizes and the speed of light. apparent motion were exaggerated for illustration purposes.

The Aristarchus Campaigns: Collaboratively measuring the Solar System 27 The Aristarchus Campaigns: Collaboratively measuring the Solar System

Acknowledgements Heath, T. 2013, Aristarchus of Samos, the Zuluaga, Jorge I. et al. 2013, Submitted to Ancient Copernicus: A History of Greek Earth and Planetary Science Letters (EPSL) We want to thank all the friends and col- Astronomy to Aristarchus. (Cambridge: (arXiv:1303.1796) leagues who supported the Aristarchus Cambridge University Press) Zuluaga, Jorge I. et al. 2014, submitted to Campaigns by sharing information about Meech, K. J. et al. 2005, Science, 310, 265 American Journal of Physics the project via social networks and by Muhleman, Duane O. 1969, Monthly Notices of (arXiv:1405.4580) encouraging people to participate in the the Royal Astronomical Society 144, 151 observational campaign. We also thank Ortiz, J. L. et al. 2011, The stellar occultation by our co-authors in the technical reports for Make on 2011 April 23, EPSC-DPS Joint Notes sharing some of the results and figures Meeting 2011, held 2–7 October 2011 in presented in this paper. The Campaign Nantes, France, 704. (Available online from: is a project of the Sociedad Antioqueña http://meetings.copernicus.org/epsc- 1 The simple web-based application devel- de Astronomía (SAA) and the University dps2011) oped to provide contact times for a given of Antioquia. We thank both organisa- Raddick, M. Jordan et al. 2010, AGB Stars and location inside the Mars occultation area is now publicly available at: tions for promoting and supporting these Related Phenomenastro 2010: The Astron- http://github.com/facom/iContact public initiatives. Jorge I. Zuluaga is funded omy and Astrophysics Decadal Survey, 46P, 2 The official website of the project: by El Programa de Sostenibilidad de la (Available online from: https://www.zotero. org/groups/creative_action_lab/items/ http://saastronomia.org/campana-aristarco Vicerrectoría de Docencia de la Universidad itemKey/3MBC8ZXQ?fullsite=1 3 de Antioquia 2014-2015 and El Comité Further details about the campaigns and the analysis or their results can be found in para el Desarrollo de la Investigación de la Salvador G. et al. 2009, Latin-American Journal of Physics Education, 3, 2, 329 the technical reports available in the arXiv Universidad de Antioquia. Schou, J. et al. 1997, The Astrophysical e-print repository: Journal Letters 489, 2, 197 http://arxiv.org/abs/1405.4580 and: http://arxiv.org/abs/1506.00346 References Sullivan, D. B. 2001, A Century of Excellence in Measurements, Standards, and Technology, Barringer, D. et al. 2011, Earth and Space Sci- (Florida: CRC Press) 191–193 ence: Making Connections in Education and Tapley, B. D. et al. 2004, Science 305, 503 Public Outreach, 443, 373 Van Helden, A. 2010, Measuring the universe: cosmic dimensions from Aristarchus to to Brown, P. G. et al. 2013, Nature, 503, 238 Biography Cohen, B. 1940, Isis, 31, 327 Halley, (Chicago: University of Chicago Press) Dickey, J. et al. 1994, Science 265, 482 Jorge I. Zuluaga is an associate professor at the Institute of Physics at the University of Antioquia, Colombia and a collaborator of the Harvard–Smithsonian Centre for Astro- physics. He is the founder of the undergraduate programme in astronomy at the University of Antioquia, the first of its kind in Colombia and the Andean region. Jorge has more than fifteen years of experience as a university lec- turer in physics and astronomy and as a science communicator. His public talks have appeared on local television networks and his contributions to the development of astronomy in Colombia was recently recognised by the International Astronomical Union by nam- ing asteroid 347940 with his name.

Juan C. Figueroa is a computer scientist with a bachelor’s degree in Engineering from the Universidad EAFIT (jointly, the Escuela de Administración y Finanzas [School of Admin- istration and Finance], or EAF and the Instituto Tecnológico [Institute of Technology] or IT) and is currently an undergraduate student of astronomy at the University of Antioquia. He recently completed the Diploma Course in Astronomy, a three-semester programme offered by the same University. Juan has fifteen years of experience as a software developer and ten years as a teacher of programming languages. His passion for astrophotography Figure 6. The difference between the contact times measured at each location and the value expected if the led him to participate actively as a contributor speed of light was infinite. Dashed lines correspond to the expected contact time difference if the speed of light to the Aristarchus Campaigns and design of was (from bottom to top) 200 000; 250 000; 350 000 and 400 000 kilometres per second. The solid black line some of its experiments. corresponds to the actual speed of light; 300 000 kilometres per second. The solid red line is the best-fit value obtained after excluding the most problematic measurements.

28 CAPjournal, No. 17, June 2015