In Mongolia, there is a lot of debate about the timing of the traditional holiday “Tsagaan Sar”, or the first day of the 17th ‘Jaran’ (sixty year) of the Wood Snake. Some people are asking whether it will be celebrated on January 29 or March 1, and there are various opinions circulating, such as “The Tsagaan Sar will fall on January 29,” “There is an extra moon this winter, so the first day of the lunar month is off,” and “Astrologers’ calculations are incorrect.” To clarify this, we spoke with B.Javzandolgor, the senior lecturer in the Department of Geology and Geophysics at the School of Natural Sciences of the National University of Mongolia, about how the lunar calendar and the first day of the lunar month are defined in both popular and scientific terms.
There is debate among the public about whether the Tsagaan Sar of this year should be celebrated on January 29 or March 1. Is it possible to explain this from a scientific perspective?
Every year, debates arise about when the Tsagaan Sar holiday will fall, due to the different lunar calendars used by Mongolians. Therefore, it is necessary to first examine how the lunar calendar calculations and algorithms work. Afterward, we should observe which calculation aligns best with the real-world conditions. Generally, the first day of the spring lunar month is determined by nature and the weather, as the signs of spring, like the arrival of warm air, are unmistakable. On the other hand, from a scientific perspective, astronomical observations and mathematical calculations need to be considered.
Thus, it is important to understand the movement of celestial bodies and the physical laws that explain them, using observations and comparisons to ensure accuracy. In particular, it is crucial for young people, especially students, to develop a solid understanding of the natural sciences, particularly astronomy and space science, so they can approach such issues in a scientific manner. As time goes on, the need for this knowledge and approach is becoming more apparent.
Are there cases where the lunar and solar calendars conflict with each other? For example, we use the solar calendar in daily life, but astrologers use the lunar calendar.
It is possible to follow the solar or Gregorian calendar exclusively for daily life, as it is the calendar used globally. However, for traditional celebrations, rituals, and cultural events, a different calendar is often used. The issue is not a conflict between the solar and lunar calendars, but rather how and when each is applied. These calendars do not contradict each other per se; rather, the challenge lies in understanding when and for what purposes each should be used.
How is the first day of the lunar month defined in astronomy?
As a result of the mutual movement of the Sun, Moon, and Earth, the Moon orbits the Earth in about a month, and its appearance changes every night. This phenomenon is named according to the phases of the Moon, such as the new moon (Shiniin negen), waxing moon, full moon (tergel sar), and waning moon (bituun), among others. In astronomy, the visible part of the Moon that is illuminated by the Sun is referred to as the “phase” of the Moon. The Moon’s phase is calculated based on the diameter of the Moon’s illuminated section and the length of the brightest part. In addition, the concept of the Moon’s “age” should be taken into account. The Moon’s age is measured from the time of the astronomical new moon (bituun) to the present moment. At the astronomical new moon, the phase and age of the Moon are both 0.0. The new moon occurs when the Sun, Earth, and Moon are aligned. After the new moon, the Moon gradually moves away from the Sun and becomes visible. About two days later, in the evening, the Moon appears as a crescent with the curved part facing the Sun in the western part of the sky. At this point, the Moon’s phase is approximately 0.10. This is referred to as the “moon of the second day” in Mongolian.
The phenomenon where the Moon does not appear between the new moon and the second day of the lunar month means that the Moon is in alignment between the Earth and the Sun, obscuring the Sun’s light and making it invisible. As the Moon moves eastward and gets farther from the Sun, its visible portion increases. About a week later, the Moon will be approximately 90 degrees away from the Sun. At this point, the Moon’s phase is 0.5, and its age is around 7.4 days. This is the well-known “eighth day” of the lunar month. In this way, the phases of the Moon can be defined up until the new moon. Astronomers highlight eight phases of the Moon, including the new moon, first quarter, full moon, and last quarter.
When does the first day of the spring month occur according to astronomy this year?
As mentioned earlier, from an astronomical perspective, the first day of the lunar month, or the new moon, is a phase of the moon. Therefore, every month there is a new moon, and the first day of the lunar month occurs. However, the concept of the first day of the spring lunar month, or the Tsagaan Sar, should be understood according to the traditional lunar calendar.
Can you explain the concept of an “extra month”? This winter, people are talking about there being an “extra” month, or four months in a year. Under what circumstances does this occur?
First, it is important to briefly discuss the concept of timekeeping. The system of timekeeping used on Earth is based on natural cycles that repeat over specific periods. These include the Earth’s orbit around the Sun, the Moon’s orbit around the Earth, and the Earth’s rotation on its axis. Various timekeeping systems have been developed based on these phenomena, adapted to different cultures, traditions, and geographical locations. Some systems are no longer in use today, while others have been refined and are still in use. For example, the Gregorian calendar, or solar calendar, is widely used around the world, based on Earth's orbit around the Sun. Meanwhile, although not used globally, lunar calendars and lunisolar calendars are still popular, especially in many Asian countries. The lunar calendar primarily tracks the movements of the Moon, while the lunisolar calendar accounts for both the movements of the Sun and the Moon.
In Mongolia, we traditionally use a lunisolar calendar to determine the timing of the first day of the Tsagaan Sar. This is commonly known as the “Mongolian calendar.” The concept of an “extra month” arises from this lunisolar system. From an astronomical standpoint, the Mongolian calendar involves mathematical calculations based on the movements of celestial bodies, similar to the solar calendar.
Let me explain briefly how an extra month occurs. When the Moon returns to the same position relative to the Sun, the period between two new moons is considered a “lunar month.” In other words, it’s the time between one new moon and the next full moon or the subsequent new moon. This period typically lasts between 29.25 and 29.83 days, depending on the irregularities in the Moon’s orbit. On average, a lunar month is 29.5 days. If we assume each month is 29.5 days, the lunar year would have 354 days, which is shorter than the 365-day solar year. During a leap year, the solar calendar has 366 days. The difference between the two calendars is about 11-12 days, which means that roughly every three years, there is an extra month added to the lunar calendar to align it with the solar year.
In the Gregorian calendar, the year begins on January 1, and similarly, to ensure that the start of the year stays in sync with the seasons, an extra month is added in the Mongolian and Tibetan calendars approximately every three years. The main goal is to ensure that the lengths of the solar and lunar years are approximately equal over the long term. As mentioned earlier, to correct the discrepancy, an extra month is added every three years, or roughly every 65 months, to account for the 11 to 12 day difference. This system is similar to the leap year system in the Gregorian calendar, where an extra day is added every four years.
It is said that ancient Mongols used the movement of the Moon and the positions of the stars to measure time and determine festivals and the equinoxes of spring and autumn.
The Mongols have a long history of observing the sky and using the knowledge they gained from it in their daily lives. For example, they divided the stars into over 400 constellations, naming them based on their light, movement, shape, and patterns. In international astronomical terminology, the three stars in the Orion constellation are called “Gurvan Maral” in Mongolian. By observing the positions of these three stars, they would calculate time, such as when dusk would fall, the middle of the night, or the dawn. These examples show how knowledgeable the Mongols were about astronomy. The interest and necessity to understand the patterns of the cosmos, space, and nature has been with humanity for centuries, and it continues to this day. It is continuously evolving.
By D.CHANTSALMAA
