Section 1.1: Understanding Lunar Phases

The Moon has a diameter of approximately 3,474 kilometers, roughly a quarter of the Earth's size. Each phase of the Moon arises from the varying portions illuminated by the Sun and visible from our planet:

• New Moon: The Moon is positioned between Earth and the Sun, rendering it invisible from our vantage point.
• Waxing Crescent: A small crescent becomes visible shortly after sunset, gradually increasing in size.
• First Quarter: About a week post-new moon, half of the Moon is illuminated, becoming clearly visible in the northern hemisphere.
• Waxing Gibbous: More than half of the Moon’s surface is illuminated as it approaches full brightness.
• Full Moon: The Moon is fully illuminated, with Earth situated between it and the Sun, creating a bright disk.
• Waning Gibbous: Following the full moon, the illumination begins to wane, yet more than half remains visible.
• Last Quarter: Approximately three weeks after the new moon, half of the Moon is again visible, but now the left side in the northern hemisphere.
• Waning Crescent: The Moon continues to shrink, becoming a thin crescent until it is almost entirely obscured, marking the end of the lunar cycle.

Section 1.2: The Moon’s Impact on Earth

The gravitational force exerted by the Moon is about one-sixth that of Earth, meaning a person weighing 60 kg on Earth would only weigh around 10 kg on the Moon. The Moon's phases influence various Earthly phenomena, most notably tides. The gravitational pull of the Moon affects ocean tides, with extreme tides known as spring tides occurring during the full and new moons when the Sun, Moon, and Earth align. Conversely, during the first and last quarters, when the Moon and Sun form a right angle with Earth, the resulting tides are less pronounced, referred to as neap tides.

The Moon also plays a crucial role in the reproductive behaviors of certain species. For example, many coral species synchronize their spawning with the full moon, while some fish, like the California grunion, lay their eggs during spring tides. Nocturnal animals often exhibit heightened activity during the full moon due to increased illumination.

The impact of the Moon on human behavior, often referred to as the "lunar effect," remains a topic of scientific debate. While some anecdotal evidence suggests increased agitation during full moons, consistent scientific findings have yet to substantiate these claims. Nevertheless, lunar calendars significantly influence the lives of billions worldwide.

A lunar year, consisting of 12 lunar months averaging 29.5 days, is shorter than a solar year by about 11 days. To reconcile this discrepancy, some lunar calendars, such as the Islamic calendar, allow dates to drift through solar seasons over a 33-year cycle. In contrast, lunisolar calendars, like the Hebrew and Chinese calendars, occasionally add a thirteenth month to stay aligned with the solar cycle, underscoring their cultural and religious significance.