Development of modern calendars

DR DEEPAK RAJ PANT

The calendar is a system of measur ing and recording the passage of time. In ancient times when the clock was not created, humans used the calendar to keep track of time. The motion of stars, the sun and the moon in the heaven played a very important role in calendar making. Stars, planets, the moon and the sun travel on circles or on an ecliptic path in the sky. They rise and set which carry them below the horizon. The people used the rising and setting events of the sun to record a day. Similarly, the interval between two successive full moons was used to remind of a month and the travel of one constellation per month of the sun through the zodiacal constellations (Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer and Leo) was used to note a month. The cycle of seasons was marked as a year, the annual azimuthally journey at the horizon of the sun verified a year, and, the rising and setting incidence of a star documented a year.

Daily and annual migration of the sun: The sun appears to move eastward among the stars in the ecliptic path that is inclined 23.5 degrees with respect to the equator. The annual changes in the declination of the sun cause variations in the suns’ rising and setting directions, times and altitudes at noon. When it is north of the equator, the sun rises in the northeast and daylight lasts for more than half the day for people in the northern hemisphere; whereas when the sun is in south of the equator, the sun rises in the southeast and the day is shorter than the night. The altitude of the sun at noon is highest at the summer solstice (June 21) and lowest at the winter solstice (December 22). Daylight is only a little more than 9 hours at the winter solstice but is 15 hours at the summer solstice. Prehistoric people noticed the annual migration direction of the sunrise and sunset, northward and southward along the horizon and determined when the solstices occurred to keep track of the seasons 

Lunar calendar: Relative to the stars, the moon moves eastward by 13 degrees per day and the times of moonrise and moonset both become later throughout the month. The moon takes 27.32 days to revolve around the earth and this is called a sidereal month. During a sidereal month, the earth orbits around the sun and therefore the moon must travel a greater length to complete its trip around the earth and return to the same phase (the time between successive full moons) and hence a lunar month is 29.53 days. Twelve such months amount to about 354 days for a lunar year. The interval of a lunar year is almost 11 days shorter than the true solar year that has 365 days, 5 hours, 48 minutes and 46 seconds. One solar year is the time the earth takes to complete one revolution around the sun. A lunar year of 13 lunar months would amount to about 383.5 days and would be more than 18 days longer than the solar year. Similarly, a lunar calendar based on 12 lunar months becomes out of step with the seasons. This inconsistency of the lunar year and the solar year explains the confusion over calendar keeping which has been in debate between different clans for thousands of years.

Egyptian calendar: The ancient Egyptians were probably the first to adopt a calendar observing the motion of a star. They developed a calendar of 365 days a year made of 12 months each 30 days long and added an extra five days at the end. It was based on the annual flooding of the Nile River that began soon after the brightest star Sirius in the sky reappeared on the eastern horizon sky just before sunrise with westward motion during the night after months of being out of sight. This re-emergence occurred around June 20 of each year. The earliest date recorded in the Egyptian calendar corresponds to 4236 B.C. The Egyptian calendar has been very useful for scientists to chronicle events in other parts of the ancient world.

Chinese calendar: The ancient Chinese were perhaps the first to adopt a calendar based on the phase of the moon and the legendary emperor Huangdi invented it in year 2637 B.C. Each month begins at the new moon and has 29 or 30 days. A month is repeated seven times during each 19 year cycle. The year starts at the second new moon after the beginning of winter and calculates years in sequence of 60. Chinese years are named after the 10 Chinese constellations and 12 animals (rat, ox, tiger, hare, dragon, snake, horse, sheep, monkey, rooster, dog and pig). The year 2000 was the year of the dragon. The Chinese New Year occurs between January 20 and February 20.

Islamic calendar: This calendar is also based on the motion of the moon and begins with Muhammad’s flight from Mecca to Medina that took place in 622 A.D. It has 12 months (Muharram, Safar, Rabi I, Rabi II, Jumada I, Jumada II, Rajab, Shaban, Ramadan, Shawwal, Zulkadah and Zulhijjah), alternatively 30 and 29 days long. The Islamic year is much shorter than the solar year with only 354 days. The calendar divides time into cycles 30 years long and during each cycle, 19 years have regular 354 days and 11 years have an extra day each.

Gregorian calendar: This is the modern day calendar used by most of the western world and is regulated partly by the sun and partly by the moon. The Julian calendar was prepared in 46 B.C. by Julius Caesar and divides the year into 12 months alternating from 30 to 31 days except in February, which has 29 days. The Gregorian calendar was invented to correct the Julian calendar’s errors and starts at the year of the birth of Jesus Christ. The dates before the birth of Christ, is noted as B.C. and dates after, A.D. (Anno Domini). The calendar has 12 months, 11 with 30 or 31 days. February has 28 days and every fourth year (a leap year) 29 days. To shorten the average year slightly, century years are not leap years unless they can be evenly divided by 400. Thus, 2000 was a leap year, but 1900 was not. The calendar is so accurate that the difference between the calendar and the true solar year is now only about 26 seconds. Furthermore, this difference will increase by 0.53 second every hundred years as the solar year is gradually becoming shorter.

(The author is a Professor of Astronomy)

Potential of plant tissue culture

Dr Saman Bahadur Rajbhandari

Plant tissue culture is an upcoming technology that has the potential of producing clean and improved planting material for plantation crops. This technology can be used in the country as a powerful tool to eliminate poverty. The importance of this technology is equally important to both developed and developing countries. Despite such a big potential the application of plant tissue culture remains insignificantly low in production of clean planting materials. This is due to the high production cost of tissue culture plants although, to some extent the floriculture industry uses this technology for mass production of clones.

However, the expense of production of such plants has become a hazard towards its development. Below are outlined the reasons for why tissue culture plants are costly: The general technique of producing tissue culture plant involves 5 steps:

1) A small piece of plant is taken from the plant that needs to be multiplied

2) It is kept in multiplying media

3) Small shoots are multiplied every 4 to 10 weeks by subculturing/reculturing

4) Multiplied shoots are rooted in culture media

5) Small plants are acclimatised before transfer to the field.

The steps 1-4 are carried out under sterile conditions but step 4 (rooting) is very costly. This step alone takes up 30 to 70 percent of the production cost of tissue culture plants. Therefore, we have modified this rooting procedure by directly transferring the small shoots in non-sterile sand in an ordinary greenhouse. By doing so we obtained both rooting and acclimatisation. This procedure was published in the early 1980s, however I was really surprised to notice in recent tissue culture publications the use of the same 1-5 steps method. With this conventional procedure, it is practically impossible to apply this technique for crops like potato, strawberry and other vegetative propagated crops because of inherent high production cost. With sand rooting procedure, the price of tissue culture plants is almost less by three times compared to conventional media rooting technique. A comparative chart of the conventional and the sand rooting procedure is presented in the Table.

Commercial tissue culture laboratories are now producing banana and other floricultural crops such as carnation and lily using this approach. The National Potato Development Programme (NPDP) has started producing clean tubers of potato from tissue culture from the last 7 to 8 years. However, their conventional tissue culture production practice has only had a limited effect in generating clean seed tubers. An International NGO, Appropriate Technology International (ATI), USA, using hundreds of farmers in Nepal in 1993, investigated the potential application of simple and cheap procedures of potato tissue culture propagation. They brought out a photo essay of ‘Potato tissue culture application project in Nepal’, which clearly indicated that the farmers can produce tissue culture plants from the small cuttings taken from culture flasks supplied to them. However, an unfortunate reaction by Nepal Agricultural Research Council (NARC) in 1994/95 against the use of MS 42.3 potato variety in the programme resulted into halt of the project. The objection raised was that the MS 42.3 is prone to a wart disease caused by Erwinia. This has seriously impeded the expansion of potato tissue culture in Nepal.

The lack of clean seed tubers is one of the main reasons why potato yield is so low (just merely 8 ton/ha) in our country compared to over 20 ton/ha in developed countries. A conventional breeding programme has increased the yield from 5.6 ton/ha to 8.6 ton/ha in 25 years (1970-1995) but this is a very slow process of increase. Therefore, to have an impact on the yield increase (over 20 ton/ha) in potato, a programme for production of clean seed tubers needs to be launched. At present potato is being cultivated over 100,000 hectares of land which requires 4 billion seed tubers. In order to generate 4 billion tubers of third generation, an annual production of 4 million tissue culture plants is essential. Four million plants will produce forty million tubers of first generation, which in turn will produce 400 million tubers of second generation, and 400 million tubers will produce 4 billion tubers of third generation. We do have mature technology for producing 4 million tissue culture plants annually. A successful production of tissue culture plants followed by the development of a mechanism to produce 4 billion
tubers of third generation will result into ten million rupees worth of economic benefits.

Since tissue culture plants are produced in highly hygienic conditions, their movement from one country to another is rarely restricted. Therefore, this offers an opportunity for Nepal to export tissue culture plants to other countries. The weight of each tissue culture plant is so small that 1 kg of a packed box can hold around 500 tissue culture plants. Sample movement of tissue culture plants are already been carried in different parts of the world. Conventionally produced tissue culture plants cost around 0.25 US dollars and range to as high as one US dollar per banana plant in the world; however, in our country tissue culture banana plants are being sold at around 15 rupees (0.19 US dollars} per plant. Similarly, strawberry tissue culture plants cost around 0.5 US dollar per plant. Therefore, the scope of supplying potato, strawberry and other floricultural plants to developed countries is very high.

In conclusion, I remember an article by I. Roberston in a UNESCO publication (1991) "this world is facing food and fuel wood scarcity and tissue culture is such a tool, which has the potential of greatly alleviating the hunger of the world by substantially increasing the productivity." I quote his words "A busload of dedicated, committed, funded scientists, plus a container of equipments could soon cope with the pressing problems –the crushing poverty and hunger and the intellectual loneliness of the third world." Therefore, for Nepal to gain the benefits from tissue culture export, the scheme needs to be supported by good governance and an enabling policy environment that includes trade, macroeconomic and microeconomic policies.

(The author is one of the pioneers of tissue culture in Nepal)

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