THE USE OF COLOR IN INTERSTELLAR MESSAGE DESIGN by Kimberly A. Jameson & Jon Lomberg

Communicating with others... reality, there are good reasons for communication gaps with our non-human terrestrial neighbors. onsiderable effort has been devoted to under- Cstanding the consciousness of others, the ways Is anybody out there conscious like us? human consciousness resembles that of other terres- trial species, and what assumptions about others’ con- ike seeking to communicate with non-human earthlings, sciousness are sensible. Aspects of consciousness, Lthere is also a strong desire to communicate with conscious mental experience, and self-awareness have been beings that might reside beyond our planet. Since 1961, deliberated for a range of Earth’s creatures: from the astronomers have been conducting a Search for Extraterrestrial highest forms of mammals–humans, non-human pri- Intelligence (SETI), scanning the skies for radio messages from mates, cetacean1—to the lowly nematode.2 Some believe intelligences possibly sharing our Milky Way galaxy. The belief is that consciousness proper occurs in few species, that if—and it is a big if—intelligent extraterrestrial beings (ETI) whereas others believe it is widespread. Animal behav- are out there, they may be transmitting radio beacons to find iorist Donald R. Griffin has suggested that the other civilizations. Intriguing questions concern what features an ETI radio beacon would have, and how we might devise our own ...belief that mental experiences are a unique messages to be correctly decoded by ETI recipients across vast attribute of a single species is not only interstellar distances. In general, because it seems plausible that, unparsimonious; it is conceited. It seems if they exist, ETIs might inhabit planets revolving around other more likely than not that mental experiences, star systems, then the universal laws of physics and its like many other characters, are widespread, mathematics could be something other intelligent beings might at least among multicellular animals, but share. These universal laws might therefore be an appropriate differ greatly in nature and complexity.3 basis for designing messages between the stars, and information about a star’s electromagnetic spectrum may be a basis for At a minimum, we can assume many non-human primate communicating with ETI beings (a point elaborated below). species experience consciousness, and humans will aim to communicate with these others, and seek out appro- Similar to pursuits of intraterrestrial communications, efforts to priate languages—fundamental units, signs or symbols— communicate with inhabitants of other planets proceed by assum- for communicating our thoughts and ideas with these ing that (i) an extraterrestrial consciousness exists, (ii) some sets different species. Nevertheless, despite consciousness of translation rules can be found to relate human and ETI experi- in other terrestrial animals, the challenges impeding ences, and (iii) that the laws of stellar and planetary physics and shared communication are substantial. This is because its mathematics are a solid basis for communication. although humans share environments with other spe- cies, our perceptions of environmental sounds, sights, Based on these assumptions, several kinds of fundamental units and smells and tastes do not always systematically relate, or ways of messaging have already been developed for human-ETI even greatly overlap, with those of other species. Thus, communication. Here we consider one specific approach, and its although our specific sensory experiences define our particular use of features of solar light that humans experience as volume 2.4 winter 2010 Cosmos 37 grayscale . A color film image of the Grand Tetons (top) with the of the R, G, B components. Image courtesy of Wikipedia Figure 1 Figure R, G, B primary separations of the image shown below as three panels. The VIR used the same approach with twenty color images included in the message, with the exception that the sent as R, G, B, components of each image were three versions member: Mike1024. - - - - Each of 4 for communication, for understand a picture, would could fundamental basis fundamental Still, it is probably unreasonable to assume 4 spacecraft carries identical copies of this record, record, this of copies identical carries spacecraft

Voyager robably because human communication modalities rely heav rely modalities communication human because robably have researchers SETI components, auditory and visual on ily

message, but they also it considered important to transmit color as humans perceive it. information of color experience are not appropriate for the task of developing of task the for appropriate not are experience color of here, considered are questions These ETI? for intended messages their in pictures employed only not team VIR the because largely environmental objects seems like something every being—animal, every something like seems objects environmental human or ETI—could equally appreciate. Specifically, (1) can any the as serve color of aspect and And, what (2) assumptions what would aspects this require? But But if we assume that ETIs color information add to that understanding? The color of Anthropologists know that isolated groups unfamiliar them with understanding 2-D difficulty have scenes 3-D of representations without training and experience. especially considering the diversity of sense-modes found across found sense-modes of diversity the considering especially be can pictures VIR whether unclear is it Thus, species. terrestrial processed and understood by non-human intelligences. designing interstellar communications? As the VIR team suggests, suggests, team VIR the As communications? interstellar designing this is a very complicated question and is beyond the scope of the present paper. humans— of those parallel that modalities sense possess ETIs that and reviewing those images now—32 years after the satellite launch—still poses interesting questions. For example, are picto rial and photographic images even useful and appropriate for the stars. Earth, from images 120 contains VIR the of portion pictorial The the two the in launched were Both years. billion a is lifetime projected whose between cruise endless an on Pluto beyond far now are and 1977 identify features of human “seeing” and “listening” that might be of human “seeing” features identify con disk copper a is VIR The ETI. to communicated successfully taining music, sounds, speech, and images from Earth. most interstellar messages to the domain of radio waves, but ETI but waves, radio of domain the to messages interstellar most spacecraft NASA some to attached been have artifacts message leaving the solar system. The most ambitious of these was the VIR which was constructed using a science-based approach to grams) we might choose to send. grams) we might choose Financial and other practical considerations have constrained focused focused on developing ways to send pictures using radio signals any reconstruct to ETI allow that ways in data visual encode that images (e.g., of our planet, terrestrial species or scientific dia Communicating across the cosmos? across the Communicating P “color”, that created the most elaborate message artifact yet sent sent yet artifact message elaborate most the created that “color”, Interstellar Record (VIR). namely the Voyager out from Earth, 38 Glimpse www.glimpsejournal.com volume 2.4 winter 2010 Cosmos 39

NASAs modern hi-res 1987 Deutsche Bundespost

A more classic representation 3 (bottom). Figure of absorption lines in the solar spectrum characteristic of the Sun’s G2 star-type between 400 nm and 700 nm (i.e., 4000 to 7000 angstroms). These are known as “Fraunhofer lines” theafter German physicist Joseph von Fraunhofer (1787-1826) who made a very systematic careful study of the lines. Fraunhofer determined that the dark lines are absorbed, missing regions of the spectrum Image courtesy of Wikipedia member: Gebruiker:MaureenV. (below). Unnumbered postage stamp, depicting Fraunhofer lines in the visible spectrum, honoring the 200th anniversary of the birth physicistof Bavarian and optician Joseph von Fraunhofer. Image courtesy of Maiken Naylor, Libraries, http:// Sci-Philately, University at Buffalo ublib.buffalo.edu/libraries/asl/exhibits/stamps/. Figure 2 (opposite page). 2 Figure representation of spectral lines as dark gaps in the solar spectrum. The image shows 50 vertical slices of continua,wavelength each covering 60 angstroms (in 1 nanometer steps from top to bottom), with shorter wavelengths shown at in left blue, and longer wavelengths at right in red, giving a complete spectrum across the visual range from 4,000 to 7,000 Angstroms. Beyond the side left of the solar spectrum continues into the the figure x-raysultraviolet, and gamma rays (at 1/10,000 Angstrom), whereas off the right side the solar spectrum continues as infrared, microwaves, and Dark (through 100 kilometers). radiowaves horizontal dashes or gaps show spectral absorption emissions and the lines. Both the color spectral dark spectral absorption lines shown are constant and specific for each element. Approximately 92 naturally-occurring earthly elements and 72 solar elements exist. Fusion generates both heat and light in the sun’s core, and all 72 solar elements Image each emit unique spectral signatures.. of, N.A.Sharp, NOAO/ adapted from, and courtesy NSO/Kitt Peak FTS/AURA/NSF. - - - atomic atomic Briefly, two design objectives guided 5 was included. Absorption lines within from our Sun was considered useful for visible spectrum based on a transmitted segment of elemental gaps in the absorption lines

survey of all the color images of the VIR would be a lengthy task, task, lengthy a be would VIR the of images color the all of survey and is detailed elsewhere.

ideas that VIR used. The exercise is also instructive for recognizing just just Below we some recognizing consider ways to for improve the color-coding creative instructive also is exercise The used. VIR that ideas how much our human dependency on considered an color–typically information contained in Figure 4 would communicate information about about information communicate would 4 Figure in contained information (e.g. the blues of sky and ocean). the substances in the pictures spectrum, other triple-imaged photos included the Earth included from photos space, other triple-imaged spectrum, pigmentation, skin varied with humans animals, and plants color landscapes, the that hoped designers VIR The fire. and cities, of lights electric Figure Figure 4 shows the VIR version of Fraunhofer lines, absorption lines marked, and the grayscale R, in G, B components of the color with using is, refraction—that using obtained was spectrum This image. color a glass prism similar to that shown in Figure 5. In addition to this data from our 3). known as Fraunhofer lines (Figure this range are portion of it’s spectrum: the range of humanly visible light. Thus, VIR Thus, light. visible humanly of range the spectrum: it’s of portion absorption spectrum data; rather, to did not include the Sun’s entire convey information about Earth’s humans, only the absorption line Sun’s emission spectrum (e.g., Figure 2). This distinctive pattern of chemical important an and orbit we star of type the identifying simultaneously The key for a naïve ETI recipient to decode our human experience of experience human our decode to recipient ETI naïve a for key The Sun’s our recognize to is images composite multicolored these fingerprint ponent contributions of red, blue and green photographic primaries composite original the reproduce to system visual human the by used 1). image (Figure The use of color in VIR images was limited to 20 of the 120 images depict triples sequenced as VIR the in appeared twenty These sent. com into separated content, image’s each of portions grayscale ing experience, and the ways humans perceive (e.g., in and sunsets flow designs). textile and diagrams anatomy (e.g., color use and ers) was to use physical information from the Sun’s spectrum to (1) point point (1) to spectrum Sun’s the from information physical use to was out the Sun’s star and class, (2) to a define color code for message color human of attributes salient exemplify to used be to construction A aim The message. VIR the of construction the during color of use the Lucid in the sky with color? in the sky Lucid 40 Glimpse www.glimpsejournal.com In other words, observed color is entirely viewer-dependent. Colordependent does on the types of sensors used for detectingentirely are that theperceptions rayscolor produce ofthat light.profile, spectral izable light-bulb) has a quantifiable amount of power and a specific character measurablelightsource (theSun,Aldebaran, compact aflorescent or colorperception ishighly species dependent. Which istosaythat any completelyscientistsvisionunderstand:nowintimateswhat Newton and Power Disposition tostirupasensationofthisorthatcolour certain a than else nothing is there them In coloured. Sir Isaac Newton put it aptly: “For the Rays to speak properly are not human-ETI for as well as Earth, communications. on communication species cross- in use for code tricky a color makes receivers, or senders message of features processing visual the about uncertainty any from apart alone, fact this and color; intrinsic no wavescarry netic Colorless light bathes us curiously. The troublewithcolor experience color human possible. make that radiation solar of attributes fara to and physiology, greater degree physical very the with is it than human specific our with lockstep tied attribute—is physical immutable viewing thewavelength andstrictlyrootedinitsphysiology. not occur in the wavelengths themselves; it is a product of the organism Starlight or sunlight, electromag ” 6 (Figure 6). - - polarized light (which humans do not), nor cichlid cichlid nor not), do humans (which light polarized discriminate that oceans our from etc.) cuttlefish, octopodes, (e.g., cephalopods neither Moreover, magnetic spectrumare detected. electro the of ranges similar largely when even wavelengths. And “seeing” is done in different ways nm ~700 to nm ~400 detect humans) (e.g., others registerultraviolet infrared,some featureslight, of creatures Some humans. of those from differ that experiences color non-human of examples for 8 ronmental needs and purposes—see endnotes 7 and envi individual their to specific manner a in (light) to process environmental electromagnetic radiation own specialized sets of “detectors” that allow them their have species “seeing” Earth’s of all fact, In ais ln te evn eprtr sae il be will scale temperature Kelvin the along varies it as locus Planck’s on colors visible the perature, tem physical on depends only radiator the black-body of mathematics and physics the while Thus, astronomical spectroscopy (Figure in 7,following page). used scale radiator black-body a example, for from, temperatures with associated colors viewing when experience humans that ena register), would experience the same color phenom not do we (that ultravioletlight of range a to tive Greatthe from fish arethat Africa in Lakes sensi at CornellUniversity, NewYork Astronomy andIonosphere Center(NAIC) depicted are courtesy of the National perceive it. The VIR solar spectra image as human observers would would need to reconstruct the color included to suggest the primaries one the red, green and blue components were separate grayscaleimagesrepresenting is not easily apparent. The three high definition), the subtle color gradient 1970’s (when color resolution was not of was photographed and processed in the refraction, and because, in part, the image absorption lines was produced by color spectrum showing the three color imageare shown.Thecontinuous the separateR,G,Bcomponentsof arrows. Below it the grayscale images of lines with absorption lines marked by VIR color image version of Fraunhofer visible range.Thetoppanelshowsthe our G2-class star within that narrow and (b) the signature absorption lines of netic radiation visible to the human eye, both (a)therangeofsolarelectromag Fraunhofer lines (Figure 3) to convey Record (VIR) used the concept of Figure 4(left). The Voyager Interstellar ------Figure 5 (right). Sir Isaac Newton in 1666 used a small aperture and a glass prism to collect a narrow beam of sunlight, and separated the beam using refraction into its component parts.[6] Refracted spectra, like the one depicted, produce color scales that are non-linear with respect to wavelength. Image courtesy of Kimberly A. Jameson.

Figure 6 (below). Newton’s Opticks6 first published in 1704, although the results existed in 1672, and some experiments were done in 1666.

varying if different (or more, or fewer) visual detectors are used to view colors cor- related with temperature. To use “color” as a basis for communication, it is important to appreciate that terrestrial animals would not have our human color experiences—or experience the color gradient seen in Figure 7 (following page). Their perceptions of this physically based temperature scale would simply be different.

More generally then, if ETIs visually process electromagnetic radiation like many birds, reptiles or insects, they would not be expected to have a correlated color temperature scale analogous to what humans experience. Indeed, a worst-case scenario could be that no range of electromagnetic radiation sensitivities that any terrestrial species (including humans) experiences coincides with the range(s) of spectra that are “visible” to an ETI recipient.

Does this invalidate the use of the Sun’s spectrum as a basis for ETI communication? In some ways, yes, it definitely does. In other ways, however, maybe not, if one pro- ceeds carefully (as elaborated below).

Sending our Sun’s spectrum... which one? Aside from the abovementioned dif- ficulties inherent in communicating “color” as a physically-based experience, there is the question of which solar spectrum to use. This difficulty has two components: (i) where and when the solar spectrum is sampled, and (ii) the pro- duction method used to produce the continuous spectrum.

Where and when to sample. Two particular things affect spectral measurements: First, if solar data is measured in a standardized identical way from (a) the surface of Earth, (b) outside the Earth’s Atmosphere, or (c) outside the Earth’s magneto- sphere, then three very different measures are obtained. The reasons for this include that these all filter the Sun’s spectrum to varying degrees. The VIR elec- tromagnetic spectrum was measured at the Earth’s surface, filtered by Earth’s 42 Glimpse www.glimpsejournal.com theory suggeststhatcolorsofablack-bodyradiator in colorspaceknowas looks white.Thistemperature gradientforms aline 1000 Kelvin,anovenlooksred; at6000Kelvin,it temperature, likeanoven,isobservedtoglow.At the principlethatanobjectatsomefixed temperature scale.Colortemperature isbasedon heated black-bodyradiatorontheKelvin Figure 7(left). of NASA. wavelengths tomicrowavelengths. Imagecourtesy radio from spectrum, electromagnetic entire the covering range wide a involves Sun the by emitted radiation the because important is This different. very appear would filters other and magnetosphere and atmosphere Earth’s the by unfiltered space, surface. Thesolarspectrummeasured indeep Earth’s the at made measurements spectral any from areabsent but fingerprint, atomic Sun’s our of part substantial area panel) bottom the in shown Sun’s spectrumthatare filtered (i.e.,thetanareas the of portions the that Note atmosphere. Earth’s the by achieved filtering radiation electromagnetic Figure 8(below) . courtesy ofWikipediamember:Eyrian would differfromtheoneshownhere. Image gradients ofcolorappearancewithinthescale Planck’s lawofblack-bodyradiation,theirown ture; andwhiletobesure theywouldbebasedon appearance scalescorrelated withcolortempera would eachhave theirown,different, color possessing different visualprocessingsystems 10000K portionofthescale.Moreover, organisms color gradientthantheoneshownin7000Kto tobacco smoke)mayexperienceaslightlydifferent (due to,for example,alonghistoryofexposure to any observerwithhighlyyellowedopticallenses gradient between 1000Kto5000K.And,ingeneral, confusions) mayperceiveaslightlydifferent color confusions (i.e.,protanopicanddeuteranopic deficiencies involvingreddish-yellowish-greenish between about3000Kand10000K.Otherswith perceive adifferent gradientofappearances and bluishcolors(i.e.,tritanopicconfusions) will that giverisetocolorconfusions amongyellowish some humanobserverswithcolorvisionanomalies experience thecolorgradientshownhere. However, wavelengths. Ingeneral,mosthumanobserverswill distribution ofenergyamongthedifferent light atdifferent temperatures hasadifferent only dependonsuchtemperatures, implyingthat

Theclassiccolorgradientofa . Schematicdepictionofthe Planck’s locus

. Planck’s - case it is inherent in any solar spectrum measures, and there and measures, spectrum solar any in inherent is it case regarding In were either taken). the which measurements under incomplete conditions is information when difficult class star Sun’s our recognizing makes it (i.e., feature a bad be might it or was sent) a when specify it help transmission could (i.e., feature a good be might This time-dependent. are also samples spectra Cretaceous period—say 145 million years ago. The the point is, during solar observed have might astronomer ETI an what considerably from differs today surface Earth’s at spectrum Sun’s The planet. the on arose life since significantly changed have and are in flux, atmosphere of Earth’s features filtering Second, (Figure 8). of what one would detect if measuring from across distant space perspective of the solar spectrum, but it is very unrepresentative geocentric a conveying of advantage the has This atmosphere. diffraction respect to wavelength. Producing a continuous solar spectrum with with linear is that scale a on resolutions spectral high very at tra troscopy uses high-dispersion diffraction gratings to observe spec Refracted versus diffracted spectra. page). facing 9, (Figure atmosphere Earth’s the of composition the showing diagram a included VIR the that Note not. or filtered whether origins, data’s the communicate accurately to needed is mation infor additional whether to given be should foreconsideration gives but a hint of their class diversity and physical properties. The 10 Thereareuncountablean numberstars ofspace—estimatedin at recipients.message the by achieved be not might linesspectral regions of the spectrum sent, then accurate recognition of our Sun’s some compressedin is scale the if becausenon-trivialquestion a is Thisuse?would ETIassume refraction;weshould whatbut using formed spectrum a used wavelength. VIR to respect with linear not are that spectra produces Refraction 5). (Figure prism 11 stars multiplied by 10 differs from that produced using produced that from differs 11 galaxies—and Figure10 (following page) Typically, astronomical spec refraction via a glass a via - - - - volume 2.4 winter 2010 Cosmos 43 - - - 9 It is essential to study the entire spectrum rather than just limited regions of it. Relying on the radiation that recitalpiano listeninga like tois Earth’s reaches surface with only a few of the piano’s keys working. (1) Communicate the sun’s unfiltered spectrum as measured from measured as spectrum unfiltered sun’s the Communicate (1) deep space. dynam and diversely is it as spectrum sun’s the Communicate (2) by the Earth’s atmosphere. ically filtered (3) Communicate the most stable (over time and atmospheric our distinguish uniquely that those or spectrum, the in gaps flux) sun from other stars. this. Sending the full solar spectrum NASA’s advice on Earthly astronomical spectroscopy: is also consistent with provide should we then spectrum, entire the send don’t we if And more information about the portion we do send—how it was easier fil made task (a on so and important, is portion this why tered, by assuming that ETIs actually reside on planets with and stars). spheres atmo we Here suggest certain to features consider when constructing interstellar messages:

Voyager

Voyager Record #13 of 120, depicting an orbital view of Earth. This was one of the twenty images sent in color, of Earth. This was one of the twenty images sent in color, Voyager Record #13 of 120, depicting an orbital view he question is whether in three decades since the launch, we can imagine ways to improve upon the Voyager

repetitive, linear-sequenced configuration of a broadcast beacon repetitive, accomplished to way the be might artifact message a than rather if sent from an ETI perspective—the unfiltered solar spectrum correctly ETI of chances space–the deep from measured as data decoding our Sun’s unique signature would be optimized. The One suggestion is to transmit the full data of the Sun’s spectrum. spectrum. Sun’s the of data full the transmit to is suggestion One senders, the us, to interesting less be may content such Although Furthermore, recipients. the about assumptions fewer requires it ETI ability to interpret 2-D representations of 3-D such scenes, and avoid to best it’s feel We representations. numeric or graphic assumptions, because these capacities may not be universal. be used as a basis for and human-ETI pictures, sending in inherent communication.assumptions some noted merely Above we an require images pictorial VIR all But further. elaborating avoided T Interstellar Record, and find color processing universals that can our Sun. ETI communiqué Designing a better lines found in some sampled section of another star-class. Thus, a Thus, star-class. another of section sampled some in found lines as originating be interpreted might spectra of transmitted section as such star class G2 a from than different very somewhere from possibility possibility exists that an under-sampled rendering of non-linear spectral of segment a resemble closely more may lines absorption Figure 9. Figure composition of each. understanding about the chemical facilitate in hopes that the colors of land, cloud, and water would defined by a symbols were (These proportions in Earth’s atmosphere. and their relative gases The symbols identify Diagram by Jon Lomberg. diagrammatic dictionary earlier in the VIR sequence.) Figure 10. This Hertzsprung-Russell diagram plots luminosity (absolute magnitude) against the color of the stars ranging from the high-temperature blue-white stars on the left side of the diagram to the low temperature red stars on the right side. Stars are classified into spectral types based on the temperature of a star’s atmosphere. These are typically listed from hottest to coldest by classes O, B, A, F, G, K and M. The spectral classes O through M are subdivided by Arabic numerals (0 – 9). For example, “A0” denotes the hottest stars in the “A” class and “A9” denotes the coolest ones. The Sun is classified as “G2”. The central band of stars that runs from the upper left corner to the lower right of the plot is called the main sequence. This figure shows about 60 random stars illustrating that there are many stars in each group, with 20 well-known stars also shown in their proper place. It illustrates the correct ratio of large stars to small, blue stars to red. The Sun is circled and central to the yellow grouping of G2 type stars. Only an infinitesimally small fraction of existing stars is depicted. Diagram by Jon Lomberg.

(4) Do not attempt to communicate idiosyncratic color Endnotes appearance information (unless other subjective per- 1. Griffin, D.R., “Prospects for a cognitive ethology,” Behavioral and ceptions or data are also intended) or use color appear- Brain Sciences 4: 527-538 (1978). ance as a basis for a code. 2. Margulis, L. and Sagan, D., What is life? (New York: Simon and Schuster, 1995). And finally, 3. Griffin, D.R., The Question of Animal Awareness: Evolutionary Continuity of Mental Experience (2nd edition), (New York: Rockefeller (5) Strive for redundancy in the content. If sending the University Press, 1981). solar spectrum, send a spectrum as measured from space 4. Sagan, C., Drake, F.D., Druyan, A., Ferris, T., Lomberg, J. and to convey star-level information; send spectra filtered by Salzman-Sagan, L., Murmurs of Earth: The Voyager Interstellar atmosphere to convey planet-level information; and send Record, (New York: Random House, 1978) 76-78. portions of spectra used by humans to convey species- 5. Lomberg, J., “Pictures of Earth,” Chapter 3 in Sagan, C., Drake, level information. These levels of transmitted spectra F.D., Druyan, A., Ferris, T., Lomberg, J. and Salzman-Sagan, L., should be logically organized as three levels of informa- Murmurs of Earth: The Voyager Interstellar Record, (New York: tion, while still recognizable as addressing our star’s emis- Random House, 1978) 71-121. sion spectrum. 6. Newton, I., Sir, Opticks: Or a Treatise of the Reflections, Refractions, Inflections, and colours of light, (London, 1704) 124-125. Summary 7. Jameson, K.A. “Human potential for tetrachromacy,” Glimpse: the art + science of seeing: 2.3: 82-91 (2009). olor is an unreliable carrier of information for ETI 8. Bielmeier, C. M. “Fluorescence in the garden,” Glimpse: the art + Cmessaging, and color experience—a chief delight of science of seeing: 2.3: 10-14 (2009). human sensory processing—is as idiosyncratic as gus- 9. NASA teaching source available at http://er.jsc.nasa.gov/SEH/ tatory preferences. Other biological intelligences have Space_Astronomy_Teacher_Guide_Part_2.pdf, p. 9. different sensory worlds. Which aspects of these sen- sory worlds overlap is one of the great mysteries of This work was supported in part by the National Science Foundation under SETI. These caveats notwithstanding, careful use of award number 07724228 from the Methodology, Measurement, and universal features of our Sun’s spectrum may serve to Statistics (MMS) Program of the Division of Social and Economic Sciences (SES). Any opinions, findings and conclusions or recommendations signal distant ETI astronomers that some lonely car- expressed in this material are those of the author(s) and do not necessarily bon-based life forms reside near a certain kind of star reflect those of the National Science Foundation. and imagine they are not entirely alone in space. w