There is no astronomical cycle which would alter the rising- and setting-times to the extent that you describe them. There are, however, very long-term cycles - involving, for example, axial precession (in an approximately 26000-year cycle ... but eventually causing large changes in the position of our north celestial pole), or the (much smaller) effects of axial tilt over a 41000-year cycle > https://en.wikipedia.org/wiki/Axial_tilt

Nutation of Earth's axis consists of extremely tiny fluctuations over an 18.6-year cycle > https://en.wikipedia.org/wiki/Astronomical_nutation.

So, in order to explain what you are asking about, we might have to appeal to variations in local weather.

Rising- and setting-times are of course dependent on the calendar date (governed by a gradual day-by-day drift), but those dates will be the same from one year to the next (because leap-year effects are not significant).

Dear David,

Thanks for your answer. I thought so too. Are there any cycles with regard to Thuraya and the moon or planets? If people link rainfall to this cluster of stars, there must be some cycle somewhere with a length between 2 and 100 years (otherwise it is not meaningful for living memory). What people seem to be talking about is shifts of several weeks from year to year, so it must be something other than rising or setting times.

I read something about a four year cycle with the moon.somewhere , and about a 52 year cycle. Both of these make sense (there are fluctuations of about 4 and 60 years in rainfall in this region), but i don't know what the story is precisely.

Kind regards,

Timmo

I would be cautious about jumping to conclusions. I am not familiar with the lunar cycles you refer to. Even if they are real, linking them to rainfall patterns would be far from straightforward.

Absolutely. It's not about any causality but co-occurrence. Which is a freak coincidence but which would be very interesting nonetheless. I just had a long discussion with a colleague who himself farms along the Nile north of Khartoum, and he told me that in his area the seasonal calendar begins with 'the falling of Thuraya'. Apparently somewhere between 17 and 24 May the observed position of the Pleiades experiences a drop. Cannot think of any other explanation than that a sudden inflow of moisture in the sky optically changes the position of stars low above the horizon due to atmospheric refraction. From this day, people count a number of days in which they expect a haze in the sky (hence my inference of moisture-induced optical illusion), after which the first part of the rainy season starts with showers of low intensity and long duration (which is when farmers prepare the landwith long intervals (5-7 days between them). This is the season for land preparation. The second part of the season is when there are low-intensity showers of long duration, which is when planting happens. This rain is gentle on the young crops. The third part of the season has high-intensity heavy rainstorms, which are good for the big crops, but not so good for young crops (so you don't want to plant too late!). The fourth part has small showers with long intervals. This is when the crop matures and dries in preparation for the harvest.

This seasonal description fits perfectly well with the movement of the ITCZ in the area. It just happens to coincide with (and possibly cause) 'the falling of Thuraya'. In ancient times before people had watches, radio, phones, etc., 'the 'falling of Thuraya' would have been a very clear indicator that the rains are going to come (after a seemingly endless, exhausting and very hot spring period), and that the season for preparing the land is at hand.

Now what i'm still trying to figure out is what the length of the cycle is of this event between early and late observations in May, and back to the beginning of the cycle. If the 'falling of Thuraya' is caused by moisture-induced changes in atmospheric refraction, its cycle does not only coincide with, but is actually caused by cycles in atmospheric moisture content, and therefore could truly be an indicator of cyclical patterns in rainfall.

From the Netherlands, where i grew up, linking stars and rainfall would be interpreted as new-age gibberish. But here, i think there is a historical pattern that has a genuine phyisical origin.

In my Masters thesis

Wade, R P. 2009. A Systematics for Interpreting Past Structures with Possible Cosmic References in Sub-Saharan Africa. MSc Thesis. University of Pretoria. http://upetd.up.ac.za/thesis/available/etd-05052009-174557/

I made infereces in relation to Pleiades being used to predict the rain season -

"The star lore of Africans spanning the continent focus on the constellations visible in their sky. As one travels from North Africa to South Africa Polaris, the Big Dipper and the Pleiades give way to Orion, Sirius, Canopus, the Magellanic Clouds, and the Southern Cross. Thus the star lore of North Africa differs from the star lore of southern Africa. Instead of telling the star lore of the various African peoples, I summarize a few of the regions/peoples and those celestial bodies that are important to them. The Pleiades and Sirius figure largely in the star lore of the peoples of Mali (Bass 1990) and Ethiopia (Lynch & Robbins 1983, Aveni 1993), and Sirius, and Canopus appear in the star lore of South Africa and Botswana (Snedegar 1997, Cuff 1997). Physically Sirius, Canopus, the constellation Orion, and the star cluster the Pleiades are bright distinctive objects in the night sky, this is most likely the reason for their distinction in African star lore. The Milky Way which spans the sky and Venus which is bright and remains close to the Sun are focused on all over Africa (Senkintu 1956, Aveni 1993, Doyle 1997). While the Southern Cross is important to the Zulu, Sotho, and Tswana of southern Africa and is recognized as a navigation constellation (Cuff 1997, Snedegar 1997)" page 180.

I also mention how the Pleiades acts as the stars announcing time to plough see page 53:

"Two constellations of particular importance to the BaVenda-BaSena that are used to reckon the time to begin ploughing, and so mark the beginning of each year’s activities are Tuda (giraffe) containing the two brightest stars of the Southern Cross ( and  Crucis) called nsadzi (female), with the two pointers to the Southern Cross ( and  centauri) called ndona (male) and Makhali (rhinoceros or three pigs - Nguruve) containing the belt and sword of Orion ( Orionis). “The time for ploughing is when nsadzi is not visible, and ndona is just visible over the horizon soon after sunset; at this time tshilimela (Pleiades) is low on the horizon. These constellations are in these positions at the end of October (called the month of Tshimedzi). Tshimedzi, the month in which ploughing begins, is really the first month of the Venda Year. The moon that appears when the two lower stars of the constellation Tuda are just below the horizon and the two upper stars just visible is the Tshimedzi moon”.93

On this particular evening, at the same time, as the setting Tuda (south west) conjuncts with the setting new moon (west), another very important asterism ascends, namely – Makhali with the three stars – Saiph ( Orionis), Alnilam ( Orionis) and Bellatrix ( Orionis), appearing in line on the horizon, in the east".

And on page 159:

"The ‘ploughing stars’ or Pleiades star cluster, shows that the time for ploughing has arrived and there is a proverb that goes “If the Digging Stars set in sunny weather, they rise in rain; if they set in rain, they rise in sunny weather”, and exactly at the first appearance of the new moon when the ‘female’ (Giraffe) is not visible, and ‘male’ (Giraffe) is just visible over the horizon soon after sunset with the Pleiades low on the horizon around the end of October, then it is the time to call for rain and is the start of the ‘Wet month’ and a very special time begins."

And,

Page 85:

"The rainmaking ceremonies performed by rainmakers at the breaking of the drought link the descendents of the builders of Great Zimbabwe with the pre-Islamic practice of the anwã system, where the weather is predicted or foretold by counting and naming certain stars and providing use of the stars as markers to determine seasons, winds and rain or the correct time for planting.

The concept of naw’ (plural anwã) represents potential times of rain linked with the risings and a naw’ is generally defined as the dawn setting of a star or asterism in the west at the same time as an opposite star rises with the sun in the east as well as with winds and temperature.99

Amongst the terrace cultivators of southern Highlanders of Yemen, the verb to plough - ‘talama’, associated with one of the earliest references in the tenth century literature with the growing of sorghum (dhurah) by al-Hamdani100, is the root word used in the Yemenite concept of ‘agricultural marker stars’ – ‘ma‘ãlim al-zirã‘ah’ 101, with the emphasis being the root - ‘lim’ or ‘lam’.

The use of agricultural marker stars (ma‘ãlim al-zirã‘ah) throughout Yemen involves the use of variations of the classical Arab science of using an astronomical reckoning system of lunar stations (manãzil al-qamar)102.

The idea of substituting locally important stars or asterisms for the classic stations extends back at least to the Rasulid times, and probably to the tenth century. There are variations from region to region and era to era. Another system for planting sorghum amongst the terrace cultivators “in al-Ahjur is a local shadow scheme. As the sun rises in the morning, the top of the plateau of Husn al-‘Arus (located east of the valley) casts a shadow (ghawm) on the western side of the valley wall in al-Ahjur. This shadow appears to migrate as the sun moves along the ecliptic during the course of the year. By observing where the shadow falls at dawn, it is possible to construct a simple seasonal calendar. A landmark (ma‘lam) is fixed to mark the time when sorghum should be planted” 103.

The ‘Ndzalama’ rock, usually chosen from nature or fashioned and found central to a Tsonga-Shangaan settlement, may be named after the shadow-rock used to indicate the ploughing or ‘talama’ period.

Other words like isiLimela (Pleiades - Zulu) and tshilimela (Pleiades - Venda) are associated with the pre-Islamic Yemenite word -ma‘ãlim al-zirã‘ah (agricultural marker stars) 104 and are found in words like abeLimi (farmers - Zulu) to Lima (plough - Zulu), Limpopo (one of the first river valleys to be characterized by ploughing), Lemba (traders who sold the ploughs/hoes) and the possible origin of the people described as Limiin by Ibn Battuta in 1331 105

Rainmakers use a similar process to the anwã in that before rain can be foretold, the stars are counted and named according to a very secret incantation – known only to the Rain Queen.106 A seemingly magical use therefore, of using the stars as markers to determine seasons, winds and rain based on the astronomy practices shared since pre-Islamic times.

The Karanga/Shona term used to describe how the ‘stars call the weather’ is, coincidentally -‘chando chinodanwa’ 107 and the Makhali asterism conjuntion with the new moon of Tshimedzi is a possible example of a naw’".

In my PhD thesis I elaborate and summarise the preceding thesis - see

Wade, R.P. 2015. Southern African Cosmogenics and Geomythology of the Great Zimbabwe Cultural Complex since the Mediaeval Trade Network Era. PhD Thesis. University of Pretoria. http://upetd.up.ac.za/thesis

see page 30, page 182 and page 202 -

"The naming of the Pleiades – ‘isilimela’ (Zulu), ‘tshilimela’ (Venda), ‘kilimela’ (kikuyu) may draw etymological comparisons with ‘ploughing’(lima) and ‘ma‘ãlim al-zirã‘ah’ (agricultural marker stars), together with many other instances, to the pre-Islamic anwã system and therefore the trader origins and directions. Amongst the earliest traded crops were ‘dhurah’ (sorghum) and so too an idea of the origin of the method for planting this crop such as the use of terraces and ‘al-‘ashr al-mukhtãrah’ (ten select days) in the Yemenite and pre-Islamic period.

These agricultural practices, together with the rain-maker traditions of ‘counting and naming’ of stars, ‘Mademba-Ndikuteme’ sacrificial rituals, Tshimedzi Moon related structural marker at the Great Enclosure, ‘divination’ bowls - ultimately determine a rich legacy of trader and external cosmogenic influence on the southern African indigenous astronomical knowledge system that was eventually epitomised by the Great Zimbabwe Cultural Complex."

Awesome!

Richard - I tried to send you a message through ResearchGate - did it arrive? May I write to you by e-mail? ... Regards, David Mc