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2D1S About


Two Deserts, One Sky


2D1S Project Overview

Learn about Two Deserts, One Sky on the Talking Space podcast.

Learn about Two Deserts, One Sky on the Talking Space podcast.

 Project Overview

The desert sky we see here in Tucson, Arizona, is the same desert sky that Arabs have observed for millennia. Two Deserts, One Sky is intended to bring the richness and depth of astronomy in ancient Arab cultures to modern awareness. This project for the first time presents ancient Arab astronomical traditions within their own cultural contexts instead of fragmented within the confines of Greek-oriented modern astronomy. (See Celestial Complexes, below.) From explaining the meaning and usage of star names in ancient star calendars to examining their continuing impact on modern-day astronomy around the globe, this project is designed to build bridges of understanding and foster greater appreciation for the vast heritage of Arab astronomy.

From the very outset of our journey, I must emphasize the multivalent nature of the materials that we are about to explore. The many star names and asterisms recorded in the writings of 9th to 12th century CE scholars must not be viewed through the lens of cultural unity or consensus. Even though these authors often refer to “the Arabs” as if they were a homogenous collective, in fact scores of diverse Arab tribes interacted with each other in the Arabian Peninsula, each with their own body of sky knowledge. Some of these beliefs were shared widely, and some were unique to specific tribes. The extant books on this subject only rarely identify a specific tribe or region in which a certain belief about the sky was held.

In addition to the above multivalency, each of these tribal societies experienced great changes through time as they first converted to Islam (622 and later) and then were organized under the rules of the Umayyad (661-750) and Abbasid (750-1258) caliphates. Even before the advent of Islam, Arab tribes were not isolated from the cultures of Greece, Rome, Egypt, Mesopotamia, Persia and India and their own astronomical histories. Because of this, it is difficult to identify origins for Arabic star names that existed before the early Abbasid period.

Two Deserts, One Sky is an outreach project funded jointly by NASA, through the Arizona Space Grant Consortium, and by the School of Middle Eastern and North African Studies and the School of Anthropology at the University of Arizona. In addition to this website, outreach activities including live sky talks will be conducted in partnership with Flandrau Planetarium and Science Center and the Mount Lemmon SkyCenter.

2D1S How to Observe

 How to Observe

No equipment needed! All observations should be made with the naked eye, but please do use eyeglasses if you normally require them for long-distance viewing. Telescopes were not in use when the Arab star calendars were made and in use. Therefore, if you have to use binoculars to see a star, you are probably observing too close to the time of sunrise. The only thing you’ll need to follow along with these star calendars is a trusty alarm clock (see below). (However, I won’t discourage you at all from using binoculars or a wide-field telescope to appreciate the majesty of the starfields we’re about to explore!)

Time of night and stellar magnitude. Most of the star calendars of ancient Arabia work by observing stars as they rise or set shortly before the sun rises. (My apologies to the night owls among us!) The star(s) should be almost touching the horizon (within 5-10 angular degrees or so) to be in the proper position. Historically, the rain stars (anwa’ ) and the lunar stations were typically observed at a time of night called ghalas, when the darkness of the night mixes with the light of dawn in the tracts of the horizon. You will find that the period of ghalas occurs between 75 and 45 minutes before sunrise, depending upon your observing latitude. (Note that the time of sunrise will change throughout the year as we progress from fall to winter, spring and summer. Your local times of sunrise throughout the year can be found on a website like The proper mixture of night and dawning light in which the brighter stars are still visible represents a precise period of the night, but not an exact time. Minutes were not in use prior to the European Middle Ages, so don’t get caught up in trying to find an exact time.

In practice, the proper timing for this depends upon the brightness (magnitude) of the star and whether they are rising or setting. The brightest stars are visible just before sunrise, but the dimmer ones may require observation more than an hour before sunrise. Dim stars will also be more difficult to see in locations where city pollution creates a layer of smog low on the horizon. Note that stars that rise in the east before the sun will be in a brighter patch of sky than those setting in the west. Therefore, the same star may require an earlier observation time when it is rising ahead of the sun than when it is setting on the opposite side of the sky.

If your schedule does not permit observation of these stars during the wee hours of the morning, there is still hope for you! The stars that set in the morning can usually be observed at different parts of the sky earlier in the evening on the same day. In the descriptions for each star or star grouping, I will provide alternate evening observation times. Note that their orientations will be different during the evening observation times.

Time of year, latitude and local horizon. First things first: The Arabs were not trying to calibrate an atomic clock by the movement of the stars. Just as the time of night is specific but not exact, so were the timings of a star’s rising or setting. In fact, many of the star groupings required a small period of time for all of them to go through the process of setting or rising. The point is that the stellar settings and risings designated a time of year, not necessarily a specific day, though the latter was made to be the case as mathematical astronomy developed.

The seasonal timings for the setting or rising of stars during the galas of night are given for the latitude of Tucson, Arizona (32.2°N). Longitude has no bearing on stellar positions, so Tucson sees very nearly the same sky that the northern end of the Arabian Desert sees. (Hence, “Two Deserts, One Sky!”) The sky in Tucson appears like it does in the modern-day locations of some of the early Islamic centers of learning: Cairo (30.0°), Damascus (33.5°), Baghdad (33.3°), Kufa (32.0°), Basra (30.5°), and Isfahan (32.7°).

At latitudes above this (e.g., most of North America and Europe), pre-dawn settings or risings for the same star will come slightly later in the year. How much later depends upon how far away the star is from the celestial equator. Stars on the equator will set on about the same day, whereas stars that are quite far from the celestial equator may set a few weeks later. Conversely, at latitudes below that of Tucson, pre-dawn settings will come slightly earlier in the year. The Arabian Desert stretches some 1300 miles from western Iraq at a latitude of about 33.5 degrees down to Yemen at a latitude of about 15.5 degrees. This means that stars will set for much of the Arabian Desert slightly earlier in the year than they will for our chosen standard location of Tucson. Indeed, many of the recorded timings for the setting stars occur 2-3 weeks earlier than we will experience in this next year, but there is more to the story (see precession, below).

Your local horizons will also affect how you observe the stars in the Arab star calendars. If you can see all the way down to the western (for setting stars) or eastern (for rising stars) horizons, then you are fortunate! Many of us have obstructions like buildings, trees or mountains that lie in the way of our seeing a star’s true moment of setting. The good news is that the requirement of observing during galas (see above) moves the setting and rising positions up the sky a bit due to the horizon glow, about 5-10 angular degrees. (If you hold your hand at arm’s length, 5° is roughly the width of your three middle fingers, and 10° is roughly the width of your fist.) Be aware that if you live in or close to a city that throws lots of light into the sky, you will likely need to make your observation time earlier so the stars are higher in the sky, avoiding the greatest levels of sky glow. This also applies if you live in a dark location, but a large city makes your western horizon glow.

Precession of the equinoxes. The Earth spins like a top about its axis, but its axis also wobbles slowly like a top. This means that the axis of the earth carves out a giant circle when projected against the starry sky. This projection of the Earth’s axis completes a full revolution of this circle once every 25,700 years. Today, the projection of the Earth’s axis onto the sky (the celestial pole) is very close to Polaris, which we know as the North Star. In the early days of Islam, almost 1400 years ago, there was no North Star because the celestial pole was about equidistant between Polaris and Kochab, one of the end stars in the Little Dipper. This shift in the orientation of the Earth against the sky means that most of the recorded timings for the star calendars are about 2-3 weeks earlier than we would observe them today.

Astrophotography. Why not take images of the stellar settings and risings over time to record your observations? All you’ll need is a camera that is capable of longer exposures (up to 30 seconds should be sufficient) and a tripod to keep the image steady. You’ll need to experiment with exposure times to make sure you get the faint star light without being overrun by the dawn light from the sky itself.

Have fun! There is something special about connecting with the sky using just your “naked” eyes. Naked-eye astronomical observation is something of a lost art these days because many people want to see greater detail through binoculars or a telescope. Get outside a little bit earlier than your expected observation window so you can get comfortable and let your eyes adjust to the darkness. Locate the stars identified in the blog post for that week, and try to see those stars through the eyes of an Arabian nomad, or perhaps a goat herder or poet.

When you’ve had some time to get in the mood, watch closely. For setting stars, note the last time you can see the star or star grouping before it is swallowed up by the light of dawn. Does the star reach the horizon before it is lost in the light? Does is set before it is consumed by the light? Try to pin down the day when it is just barely visible in the light of dawn at the moment it sets. For rising stars, what is the first day when you can see the star rising just before it gets swallowed up by the sun’s light? Were you able to see enough of the surrounding stars to make sure you saw the right star from the calendar?

You can make a modern star calendar of your own, too! Is there a star that sets or rises when your favorite holiday begins? When your school year begins or ends? When sports playoffs occur? Have fun adapting these star calendars to your modern life!

2D1S Celestial Complexes

 Celestial Complexes

Star names in ancient Arabia were often overlapping and multivalent themselves. The same star or pair of stars might be called different terms in different contexts, even by the same person. Existing surveys of Arabic star names tend to work through the sky spatially by star, or sometimes alphabetically by name. This tends to make culturally bound groups of stars invisible, or at best fragmented.

My solution to this problem is to present these stars in their “celestial complexes,” a term that I am using to designate a grouping of stars that share a certain kind of cultural significance. Some stars are culturally bound to each other because they factor into a story that is told about them. Others together make a picture in the sky, whether large or small. These kinds of groupings, bound by the shared beliefs or stories of a community, I shall call a folkloric celestial complex. The other major type of celestial complex is the calendrical celestial complex, an association of stars or star groupings that together delineate a period of time, most commonly the solar or sidereal year, or the lunar month. By presenting the Arab stars within their celestial complexes, my hope is to make visible these cultural meanings and their multivalency.

One more concept that I wish to introduce is the “celestial chronotope.” The word “chronotope” was first coined by Mikhail Bakhtin (1937, “Forms of Time and of the Chronotope in the Novel”) to describe the interconnectedness of time and space within distinct literary genres. This word was later applied by anthropologist Keith Basso (1984, “Stalking with Stories: Names, Places, and Moral Narratives among the Western Apache”) to describe geographic features that embody moral teachings connected to a tribe’s history, in this case the Western Apache.

In relation to the stars, a celestial chronotope is a star or star grouping whose position in the sky at a certain time of night evokes a season and the cultural significance attached to it. Having grown up in New Jersey, I distinctly remember the sight of the Big Dipper’s bowl resting squarely on the horizon in the early evening shortly before Halloween. For myself, it is a strong emotional memory; if my community shared this sentiment as well, it would qualify as a celestial chronotope. We will see that celestial chronotopes are strongly evidenced through both pre-Islamic and early Islamic Arabic poetry.

Folkloric ComplexesFolkloric Complexes
Rain Stars (anwa')Rain Stars (anwa')
Lunar Stations (manazil al-qamar)Lunar Stations (manazil al-qamar)

Folkloric celestial complexes among the Arabs range from asterisms of just a few stars to enormous megaconstellations that spanned as much as 130 angular degrees in the sky. The Bucket (ad-dalw) and its components, described in our first star calendar post, is an example of a folkloric celestial complex composed of just a few stars. The Lion (al-asad) and the Camel (an-naqa) are examples of very large folkloric complexes.

Much has been written by grammarians concerning the nature and origins of the term naw’ (singular), anwa’ (plural). Generally, most agree that a naw’ is a star whose rising or setting shortly before sunrise signals the onset of rains, a season or some other culturally significant event. Poetry and early star calendars tend to treat naw’ as a setting star, while rhymed prose and later calendars tend to identify it as a rising star. Initially, a star was considered a naw’ only if its setting (or rising) came with rain. Later, its definition widened to include the stars associated with the lunar stations (see below).

The lunar stations, sometimes translated as lunar mansions, is a complex of 28 individual stars or small groups of stars that largely parallel the path that the moon takes through the sky. Each night, the moon rests (“stations”) near one of these star groupings. Since the lunar month is approximately 29.5 days, the phase of the moon when it stops at one of the lunar stations changes sightly from month to month. The Arab lunar stations as a system developed after the translation of Hindi sources that described the Indian lunar mansions (nakshatra). This new system assimilated star names that already existed to form the 28 stations.

2D1S Sources


Information about early Arab astronomical traditions is scattered throughout collections of poetry, rhymed prose, celestial almanacs and even Qur’anic commentaries. With the onset of the Abbasid period of Islam (750 CE), there arose an abiding interest in translating foreign sciences into Arabic. The influx of these new materials brought about a need to record many of the earlier Arab traditions and cultural knowledge. The genre of anwa’ books takes up the subject of seasonal forecasting on the basis of setting or rising stars. More than 50 authors composed an anwa’ book during the period 750-1050 CE, but only a small number of these are extant and complete.

Qutrub (d. 821 CE)Qutrub (d. 821 CE)
Ibn Qutayba (d. 889 CE)Ibn Qutayba (d. 889 CE)
As-Sufi (d. 986 CE)As-Sufi (d. 986 CE)
The earliest complete extant work of the anwa’ genre is Kitab al-azmina wa talbiyat al-jahiliya (The Book of Seasons and the Consecrating Prayers of the Age of Ignorance) by Abu ‘Ali Muhammad b. al-Mustanir, known in his time as Qutrub. (d. 821 CE). Qutrub was a philologist and Qur’anic commentator of Persian origin, and in his anwa’ book, his focus is to explain the meanings of numerous astronomical and meteorological terms. As one of the earliest works of this kind, Kitab al-azmina wa talbiyat al-jahiliya includes multiple star calendars that demonstrate the multivalent conceptions of these systems in Qutrub’s day.

By far, the most extensive surviving work of the anwa’ genre is the Kitab al-anwa’ (The Book of Rain Stars) of Abu Muhammad ‘Abdallah b. Muslim al-Dinawari, known as Ibn Qutayba (d. 889). Also a Persian, Ibn Qutayba was a reknowned philologist and grammarian whose intent in his book is to demonstrate the completeness of Arab astronomical knowledge without the need for adopting foreign (especially Greek) sciences. With this intent, Kitab al-anwa’ includes hundreds of references to poetry and rhymed prose to attest to the long usage of astronomical and meteorological terms among the Arabs even prior to the advent of Islam.

The astronomer Abu’l-Husayn ‘Abd al-Rahman b. ‘Umar as-Sufi (d. 986) composed the first extant astronomical work in Arabic in which star maps appear, Kitab suwar al-kawakib ath-thamaniya wa’l-arba’in (The Book of the 48 Images of the Constellations). This book as a whole does not actually fall within the realm of the anwa’ genre, as it is not at all concerned with seasonal timings. As-Sufi wrote his book to correct the record of stellar magnitudes within Ptolemy’s Almagest, but in doing so he records both contemporary and ancient Arabic names for the stars within the bounds of each Greek constellation and therefore does contain a lot of information concerning the anwa’.

2D1S Transliteration

Arabic Transliteration Conventions

The Arabic language has a number of consonants that are not found in the English alphabet, and it distinguishes its vowels by length (short vs. long). In academic texts, these characters are often represented by dots below Latin-scripted consonants and macrons above lengthened vowels. For ease of pronunciation among a general audience, I do not include these markings, nor doubled consonants in most cases. Additionally, sun letters that elide with a foregoing alif-lam are presented as elided in the transliteration. The name of one of our astronomers under study demonstrates the above conventions:

Arabic text: الصوفي
Academic transliteration: Al-Ṣūfī
Transliteration on this site: As-Sufi