The Moon is the only satellite of the Earth that has a gravitational effect on it, which can be clearly seen in the sea or ocean tides. In turn, the Earth has an even greater impact on the Moon, preventing the satellite from rotating around its axis. The moon always faces our planet with only one side, and because of the elliptical orbit, it can be illuminated both at 100% (with a full moon) and at 0% (with a new moon).
Moon phases
The Moon completes one revolution around the Earth in 27.3 days, and its synodic period lasts 29.5 days (709 hours). During it, the satellite goes through 8 main phases: from the new moon to the full moon, and then to the old moon. The boundary between the illuminated and unilluminated part of the lunar surface is constantly shifting, which is why a satellite from the Earth can look like a perfect circle, month or crescent. And the line separating the illuminated and unlit territory is called the terminator.
The duration of the lunar phase is a variable value and can range from 3 to 4 days. Every month, the earth satellite is illuminated by the Sun for 14.77 days and stays in darkness for 14.77 days. And this applies to the entire area of the Moon, and not just its visible side, turned to the Earth. The far side of the Moon is illuminated with the same frequency, but we cannot observe this phenomenon from the earth's surface.
As for the number of phases of the moon, this is a conditional value that differs in different cultures. For example, in Hawaii, 30 lunar phases were traditionally distinguished - one for each day of the month. But the Western model is generally accepted in the world, dividing the lunar cycle into 8 phases:
- New Moon. The satellite is in line with the Sun and the Earth and is not visible from our planet. The visible side of the Moon is completely obscured, while the far side is completely illuminated.
- The new moon. The satellite begins to be seen in the sky in the form of a thin crescent.
- First quarter. Within 3-4 nights, the Moon appears in the sky in the form of a month, and the illumination of its surface gradually increases to 50%.
- The waxing moon. As the month progresses, the celestial body gradually turns into a perfect circle.
- Full moon. In this phase, the side of the satellite facing the Earth is completely illuminated and is observed in the sky all night.
- The waning moon. The illuminated part begins to decrease - on the opposite side of the one that increased during the first quarter.
- Third quarter. The area of the illuminated lunar surface gradually decreases to 50%.
- Old Moon. The final phase of the cycle, during which the visible side of the satellite is viewed from Earth as a thin crescent, after which it is completely obscured and a new moon occurs again.
In different phases, the ecliptic longitudes of the Sun and Moon differ by 0, 90, 180 and 270 degrees. This corresponds to the four main phases: new moon, waxing moon, full moon and waning moon. Due to the ecliptic orbit of the satellite, its phase changes are observed at different points on the Earth with a slight delay. On average, each main cycle (1 out of 4) lasts 7.38 days or a quarter of a synodic month.
Why do we need a lunar calendar
For many world religions, the lunar calendar is the basis for determining annual holidays, which often fall on different dates. A vivid example is Easter, which is tied to the lunar calendar and is celebrated annually in a wide range of dates: from April 4 to May 8. Moon phases are also widely used in astrology and esotericism, including for writing horoscopes and predictions.
If we talk about the practical significance of the lunar phases, then they are most important for agriculture. The cycle determines at what time it is better to organize sowing, irrigation and harvesting. And this applies to all agricultural crops: cereals, vegetables, and fruits. Finally, the lunar calendar is necessary for launching spacecraft that enter Earth's orbit and beyond. If you launch in an unfavorable phase, the gravity of the satellite will interfere with the flight, and vice versa.
Summing up, we can say that there are only two absolute lunar phases: new moon and full moon. The remaining phases are intermediate and only reflect a gradual transition from zero to one hundred percent illumination of the earth's satellite. According to research, the Moon affects not only the ebb and flow, but also the life of all living beings on Earth. Therefore, the lunar calendar is important not only from an esoteric or religious point of view, but also from a practical point of view!
