THE ONSET OF WINTER: SUHAIL AND THE SEPTEMBER EQUINOX

THE ONSET OF WINTER: SUHAIL AND THE SEPTEMBER EQUINOX

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Canopus (Suhail) observed from Al Sadeem Observatory using RC8 telescope and ZWO1600MC-cool camera (Image Credit: Al Sadeem Astronomy)

The most pleasant season for the UAE is about to come. The air temperatures being experienced across the UAE are slowly getting cooler compared to the previous very hot and uncomfortable temperatures in which we tend to stay much of our time indoors without switching off our air conditioning units.

Before the development of modern and advanced weather and climate forecasting techniques, ancient people rely on the heavenly bodies to determine what will be the upcoming weather condition to persist within a certain area in a given period.  In particular, the ancient Arabs, knowing the fact that they are also pioneers in the study of the cosmos, look up for indications in the sky through keeping track of the positions and motions of numerous celestial objects like stars and planets which were then used for navigation and time-keeping. This article will tackle about the pre historic method used by the ancient Arabs and the contemporary knowledge in telling the onset of winter in the Middle East.

A bright star seen in the southern sky coordinate was used by ancient Arabs as reference star in determining the onset of the winter season in the Arabian Peninsula. This star is named Suhail. In old astronomy tradition, four stars were designated as Suhail. First is the bright star now commonly called Canopus in the constellation of Carina (the keel), and three other dimmer stars Lambda Velorum (al Suhail al Wazn), Gamma Velorum (al Suhail al Muhlif); and Zeta Puppis (Suhail Hadar). Yet, this is particularly referring to Canopus.

Southern sky at twilight featuring Canopus sighted low on the horizon from Al Sadeem Observatory. Image taken with unmodified Canon EOS 1D Mark IV and Tamron 10-24mm wideangle lens (Image Credit: Al Sadeem Astronomy)

Suhail (Lambda Velorum) observed from Al Sadeem Observatory using Meade LX850 16″ SCT and SBIG STT-8300MM CCD camera. (Image Credit: Al Sadeem Astronomy)

Virtual Sky Simulation of Suhail Rising on the Southern Sky on the September 22 Equinox as seen from much of the UAE (Graphics Credit: Stellarium)

Whenever Suhail is sighted at the southern portion of the sky rising before dawn, this indicates the end of the scorching hot summer season in the Arabian Peninsula and gradual decrease in temperatures shall take place all the way towards the winter season. Also, daytime duration shall get shorter which in turn making night times longer. Ancient Arabs found out water on their wells start to cool down the day after Suhail came out in the sky for it is usually hot during the summer. The seasonal sighting of Suhail was the basis for the farmer’s droror calendar, an agricultural calendar consisting of 10-13 day units known as dirs, divided into 36 sections. In between the 70th and 80th day of the calendar, camels start to eat grass, as well as commencing palm pollination, ripening of fruits, cultivating crops, and studding in fields.  Unfortunately, this old prediction methodology is not exactly applicable nowadays due to such radical changes in weather and climate through the years.

Camel Grazing and Palm Pollination (Image Credit: trekearth.com, texasriviera.com)

Suhail is visible in the skies of areas up to 37°18′ north latitude and much of the Southern Hemisphere skies from late August at dawn can be seen throughout the night of the winter months, until mid-April when it sets early in the evening. It also signifies the beginning of the hunter season for huntsmen traveling through the desert. Despite the fact that it is not really the southern star, Suhail was also used by the ancient Arabs as a navigational tool when heading south; for instance heading the Islamic Holy City Mecca for prayer practices.

In modern day astronomy, the phenomenon responsible for the changes in seasons is the occurrences of equinoxes and solstices primarily due to the orientation of the Earth’s axial tilt (about 23.5°) with respect to the Sun. For this case, the onset of the winter season in the Northern Hemisphere begins on the September Equinox, more commonly known as autumn or fall season. For the Southern Hemisphere, it is the direct opposite, meaning it is springtime there and then transitions into summer. The term equinox is derived from Latin words aequus (equal) and nox (night). At the time of the equinox, the Earth’s axis will be oriented straight up with respect to the Sun; having both sides and hemispheres of the Earth receive equal amounts of sunlight leading to the same duration of day and night. The September equinox falls either on September 22 or 23 or on rare occasions on the 21st or 24th, depending on location, time zone, and such date deviations in the Gregorian calendar. After the equinox, daytime will slowly become shorter (longer) and night time will be longer (shorter) which also leads to a gradual decrease (increase) in temperatures in the Northern (Southern) Hemisphere.

Earth-Sun Model Illustration of the Seasons (Source: learner.org)

Timelapse Animation of the Transition of the Earth’s Seasons as seen from Space (Source: EUMETSAT, NASA APOD)

As the winter season on its way, better start preparing your warm-up clothing, heater, dried-up wood and matches or lighters for body protection from the imminent cold weather in the next few months. Also, do not forget to gaze up the night sky with a different set of stars to witness its beauty while having a peace and quiet relaxation.

References

Al Khan, M. N. (2012, August 24). Star of Suhail to signal end of summer heat. Retrieved from The National: https://www.thenational.ae/uae/star-of-suhail-to-signal-end-of-summer-heat-1.361259

When and What is the September Equinox. (n.d.). Retrieved from timeanddate.com: https://www.timeanddate.com/calendar/september-equinox.html

Zacharias, A. (2012, July 29). Farmers reach for the stars to sow perfect dates. Retrieved from The National: https://www.thenational.ae/uae/farmers-reach-for-the-stars-to-sow-perfect-dates-1.396710

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