NATURAL CYCLE- LUNAR MONTHS, DAYS AND YEAR

NATURAL CYCLE- LUNAR MONTHS, DAYS AND YEAR

1.1 INTRODUCTION

The calendar you certainly use on a day-to-day basis is the Gregorian calendar, which has been the standard system for western nations since 1582. A refinement of the Julian calendar, Pope Gregory XIII introduced the new timekeeping method to stop the drift of seasons that was caused by the inaccuracy of that ancient Roman calendar. He wasn’t a moment too soon either; the old calendar was ten days off by that point, leading to problems in determining the date of Easter.

Easter itself is determined with a lunar calendar, however, as the Catholic Church liked the idea of the calendar’s equinox being closer to what was being observed, the Gregorian calendar is entirely solar in nature. Easter is, in principle, celebrated on the first full moon after the spring equinox. It became vital then that the date of the equinox be correct.

A lunar calendar is a calendar based upon the monthly cycles of the Moon’s phases (synodic months), in contrast to solar calendars, whose annual cycles are based only directly upon the solar year. The most commonly used calendar, the Gregorian calendar, is a solar calendar system that originally evolved out of a lunar calendar system. A purely lunar calendar is also distinguished from a lunisolar calendar, whose lunar months are brought into alignment with the solar year through some process of intercalation. The details of when months begin varies from calendar to calendar, with some using new, full, or crescent moons and others employing detailed calculations.

Since each lunation is approximately ​29 1⁄2 days (29 days, 12 hours, 44 minutes, 3 seconds, or 29.530588 days), it is common for the months of a lunar calendar to alternate between 29 and 30 days. Since the period of twelve such lunations, a lunar year, is only 354 days, 8 hours, 48 minutes, 34 seconds (354.367056 days), purely lunar calendars lose around 11 days per year relative to the Gregorian calendar. In purely lunar calendars like the Islamic calendar, the lack of intercalation causes the lunar months to cycle through all the seasons of the Gregorian year over the course of a 33 lunar-year cycle.

1.2 NATURAL CYCLE

When things happen over and over again, we call it a cycle. For example, we need food, air and water to live. The ways we get food, air and water are part of our life cycle.

All living things depend on each other. Animals need oxygen. They breathe in oxygen. They breathe out carbon dioxide as a waste product. Plants need carbon dioxide to perform photosynthesis…

Photosynthesis is the way plants make their food, which is called carbohydrates. Plants use sunlight for energy and make carbohydrates out of carbon dioxide and water. Oxygen, which animals need to live, is a waste product of photosynthesis, along with tiny drops of water. When the plant releases the waste product, we call this transpiration. So, animals depend on plants for oxygen, and plants depend on animals for carbon dioxide. Animals and plants both have to have water. This exchange is a natural cycle.

When natural cycles are changed, the plants and animals have to change, too. Making a change like this is called adapting.

Sometimes a change in a natural cycle is so big, that the animals and plants don’t have the time to change. Or, they cannot make the changes they need to make. That’s often what happens when our environment becomes polluted. The plants and animals are unable to make changes and either die or are driven off before they can change.

Our earth’s five greatest environmental problems are causing changes that make it hard for animals and plants to adapt: air pollution, acid rain, water pollution, waste disposal and the loss of trees.

The sages of ancient India acknowledged the value of living in harmony with the rhythms of nature. They understood that when our actions are aligned with the rest of the natural world, we experience auspiciousness — the energy of our actions is blessed by the energies of nature.

In determining the most auspicious times for a given activity, the relationship between the sun and moon is considered crucial, since these are the major “lights” in our sky, the two astral bodies most visible from the Earth. The Indian sages have created guidelines to help people align their activities with the phases of the moon and with lunar and solar eclipses.

In the Indian tradition, this guidance is often used when planning travel, weddings, major purchases, and other significant events.

1.3 LUNER MONTHS

A lunar month is the time it takes the Moon to pass through all of the Moon phases, measured from one New Moon to the next New Moon. 12 lunar months make up a lunar year. A lunar month can also be defined as the time the moon takes to pass through each of its phases (new moon, half moon and full moon) and return back to its original position. A lunar month takes 29.5 days, although this varies slightly around this average.

A lunar month comprises all the Moon phases.

A lunar month is also known as a lunation, while the astronomical term for this period is a synodic month, from the Greek term synodos, meaning meeting or conjunction.

We measure the lunar month from the precise moment of a New Moon, when the Sun and Earth are aligned on opposite sides of the Moon, until the next New Moon.

A brief of History of Lunar Month (About 29.5 Days)

In the period from 1600 to 2600, an average lunar month lasts 29.530575 days or 29 days, 12 hours, 44 minutes, and 2 seconds. The shortest lunar month ended July 17, 1708 and lasted 29.271819 days (29 days, 6 hours, 31 minutes, and 25 seconds), while the longest was the one that ended on January 14, 1611 and lasted 29.832568 days (29 days, 19 hours, 58 minutes, and 54 seconds). The exact length varies slightly, due to the elliptical shape of the Moon’s orbit.

Synodic vs. Sidereal Month

The time it takes the Moon to complete one orbit around Earth is called a sidereal month. Sidereal refers to the Latin word for stars and sidereal month means that the Moon returns to the same point under the stars. This takes, on average, 27.3 days.

If Earth stood still, the synodic (lunar) month would be the same as the sidereal month. However, at the same time as the Moon is orbiting Earth, our planet also continues its annual orbit around the Sun in the same direction. So, after completing a sidereal month, the Moon has to move a little further to catch up to the same alignment with the Sun and Earth as at the previous New Moon. This is why a synodic (lunar) month is around 2.2 days longer than a sidereal month.

Lunation Number

In astronomy, it is most common to use the Brown lunation number system for lunar months. This system was invented by Professor Ernest W. Brown and presented in the book Planetary Theory from 1933, which Brown co-wrote with Assistant Professor Clarence A. Shook.

Brown starts his count with lunation number 1 at the first New Moon of 1923, which was on January 17. This is why the lunation numbers in the table on our Moon Phase pages are currently in the 1100s. And, for the same reason, lunation numbers listed for years before 1923, are negative.

There are also other lunation cycles in use, such as Herman Goldstine’s Lunation Number, Jean Meeus’s Lunation Number, and the Hebrew Lunation Number, which counts lunations in the Hebrew calendar.

Primary and Intermediate Moon Phases

In Western Culture, we divide the lunar month into four primary and four intermediate Moon phases.

The primary phases are the New Moon, the First Quarter Moon, the Full Moon, and the Third Quarter Moon. Technically, the primary Moon phases occur at a specific moment in time, and the intermediate Moon phases take up the time in between.

The average time between each primary Moon phase is around 7.38 days (just over 7 days and 9 hours) which is considered the origin for the 7-day week.

The intermediate Moon phases are the Waxing Crescent Moon, the Waxing Gibbous Moon, the Waning Gibbous Moon, and the Waning Crescent Moon.

Lunar Calendars

Some of the oldest calendars we know of are lunar calendars, such as the Roman calendar, based on the lunar month. The word month is even derived from the word Moon.

The 12 months of the year

Today, most countries use the Gregorian calendar, which is based on Earth’s revolutions around the Sun. However, the current months September, October, November, and December are still named after their original place in the ancient Roman calendar.

Start of the lunar month

Lunar and lunisolar calendars differ as to which day is the first day of the month. In some lunisolar calendars, such as the Chinese calendar, the first day of a month is the day when an astronomical new moon occurs in a particular time zone. In others, such as some Hindu calendars, each month begins on the day after the full moon or the new moon. Others were based in the past on the first sighting of a lunar crescent, such as the Hebrew calendar and the Hijri calendar.

Length of the lunar month

The length of each lunar cycle varies slightly from the average value. In addition, observations are subject to uncertainty and weather conditions. Thus to avoid uncertainty about the calendar, there have been attempts to create fixed arithmetical rules to determine the start of each calendar month.

The average length of the synodic month is 29.530587981 days. Thus it is convenient if months generally alternate between 29 and 30 days (sometimes termed respectively “hollow” and “full”). The distribution of hollow and full months can be determined using continued fractions, and examining successive approximations for the length of the month in terms of fractions of a day. In the list below, after the number of days listed in the numerator, an integer number of months as listed in the denominator have been completed:

Fraction Approximate duration

29/1 1 day after about 2 months

30/1 1 day after about 2 months

59/2 1 day after about 2.6 years

443/15 1 day after about 30 years

502/17 1 day after about 70 years

945/32 1 day after about 122 years

1447/49 1 day after about 3 millennia

25101/850 Not accurate due to the multi-millenial change of the synodic month length.

These fractions can be used to construct a lunar calendar, or in combination with a solar calendar to produce a lunisolar calendar. A 49 month cycle was proposed as the basis of an alternative Easter computation by Isaac Newton around 1700. The tabular Islamic calendar’s 360 month cycle is equivalent to 24×15 months, minus a correction of one day.

1.4 LUNER DAY

A lunar day is the period of time for Earth’s Moon to complete one rotation on its axis with respect to the Sun. Due to tidal locking, it is also the time the Moon takes to complete one orbit around Earth and return to the same phase. A lunar month is the period between two new moons and lasts about 29.5 solar days on earth.

Relative to the fixed stars on the celestial sphere, the Moon takes 27 Earth days, 7 hours, 43 minutes, and 12 seconds to complete one orbit; however, since the Earth–Moon system advances around the Sun at the same time, the Moon must travel further to return to the same phase. On average, this synodic period lasts 29 days, 12 hours, 44 minutes, and 3 seconds. This is the mean figure since the speed of the Earth–Moon system around the Sun varies slightly during a year due to the eccentricity of its elliptical orbit, variances in orbital velocity, and a number of other periodic and evolving variations about its observed, relative, mean values, which are influenced by the gravitational perturbations of the Sun and other bodies in the Solar System.

As a result, daylight at a given point on the Moon would last approximately two weeks from beginning to end, followed by approximately two weeks of night.

The term lunar day may also refer to the period between moonrises or high moon in a particular location on Earth. This period is typically about 50 minutes longer than a 24-hour Earth day, as the Moon orbits the Earth in the same direction as the Earth’s axial rotation.

The term lunar day is also used in the context of night and day, i.e., opposite to the lunar night. This is common in discussions of the huge difference in temperatures, such as discussion about the lunar rovers “Soviet Union’s Luna missions, were designed to survive one lunar day (two Earth weeks)

1.5 THE LUNER YEAR

Scientists define a solar year based on the movements of the sun, but use the movements of the moon to define a lunar year. Unlike the lunar calendar, most places across the globe use the solar calendar to track the passage of the year. Solar years have a different length to lunar years, and the term “epact” describes this time difference. One epact is 11 days.

The Definition of a Lunar and Solar Year

12 lunar months make up a lunar year. A lunar month can also be defined as the time the moon takes to pass through each of its phases (new moon, half moon and full moon) and return back to its original position. A lunar month takes 29.5 days, although this varies slightly around this average.

We call the time period required for Earth to complete one revolution around the sun a solar year. A solar month means one twelfth of a solar year. Calendar months differ from this, but in practice the differences are minor and exist so we can have a whole number of days in each month.

The Time Period of Lunar and Solar Years

A lunar year has approximately 354 days. A solar year has 365 days. This leaves an 11-day difference between one solar year and one lunar year, resulting from the difference in their definitions. The term epact describes this specific time difference. Over the course of 33 years, there will be a lag of one year between solar and lunar calendars because of the successive expacts.

Lunar and Solar Calendar Conventions

Most places around the world use a solar calendar rather than a lunar one. However, Muslims and Jews follow a lunar calendar. Islamic calendars, otherwise known as Hijri calendars, are based on the lunar cycle, and its year consists of 12 lunar months. The Hijri calendar plays an important role for religious purposes and the Muslim religious festivals are based on this calendar. A Jewish calendar uses primarily lunar definitions, and each month begins on the new moon, but the years are based on solar years. Chinese calendars are a type of lunisolar calendar, a combination of a lunar calendar and a solar calendar.

Leap Years and Leap Months

Because there is an 11-day difference between a solar year and a lunar year, people using a lunar calendar insert an extra (13th) month into it every three years. In the solar calendar, people add a leap day to the month of February every four years.

1.6 CONCLUSION

The moon, the sun, and the Earth work together as a team to bring us the phases of the moon and the lunar and solar eclipses. The sun illuminates the moon so that we can see it and depending on what angle the moon is at depends on what phase of the moon we see. The moon phases and the eclipses would not be the same without one of the teammates.

Calendar reforms, however, are not something of the distant past. For example in the late 18th and early 19th century, there was a calendar reform following the French Revolution this calendar was based on a 10-day week aimed to remove any trace of religion from the calendar, as well as bringing it into line with the broader decimilisation of measurements. A new calendar marking a new regime is not uncommon, for example in China with each new Emperor a new calendar would be produced these include calendars produced byLuoxia Hong and Zu Chongzhi.

1.7 REFERENCE

Nancy Owano, Scotland lunar-calendar find sparks Stone Age rethink, Phys.org, 27 July 2013 Archived 9 August 2013 at the Wayback Machine.

James Elkins, Our beautiful, dry, and distant texts (1998) 63ff.

“Oldest lunar calendar identified”. BBC News. 2000-10-16. Retrieved 2013-03-14.

R.H.Codrington. The Melanesians: Their anthropology and folklore (1891) Oxford, Clarendon Press

Reform of the Julian Calendar as Envisioned by Isaac Newton by Ari Belenkiy and Eduardo Vila Echagüe (pdf); Notes and Records of the Royal Society of London (vol. 59, no. 3, pp. 223-254).