THE MOON
The Moon is Earth's only natural satellite and the fifth largest satellite in the Solar System. It is about one-quarter of Earth's diameter, making it the largest natural satellite relative to its planet in the Solar System. The Moon's presence has been a source of wonder, inspiration, and scientific study throughout human history.
Our Moon orbits Earth at an average distance of 384,400 kilometers (238,855 miles), completing a full orbit approximately every 27.3 days (a sidereal month). From Earth, we witness a complete lunar cycle roughly every 29.5 days (a synodic month) as the Moon goes through its phases. This cycle occurs as the Moon's position changes relative to the Earth and Sun, revealing different portions of the illuminated lunar surface.
Throughout its phases, the Moon appears to change shape, but what we're actually seeing is different amounts of the illuminated side of the Moon from our vantage point on Earth. This cycle has been used for millennia as a basis for calendar systems and has significant cultural importance across various civilizations.
LUNAR PHASES
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OCTOBER 2025
MOON PHASES THIS MONTH
LUNAR & LUNISOLAR CALENDARS
Throughout human history, the regular cycling of the Moon's phases provided one of the most reliable and visible ways to measure the passing of time. Lunar calendars, based solely on the Moon's orbit around Earth, typically define a month as the time between two identical Moon phases (usually new moons).
A pure lunar calendar consists of 12 lunar months, totaling approximately 354 days—about 11 days shorter than the solar year. This discrepancy means that lunar calendars drift relative to the seasons. The Islamic calendar is a prominent example of a purely lunar calendar still in use today.
To address this seasonal drift, many civilizations developed lunisolar calendars, which incorporate both lunar phases and solar years. These calendars add leap months periodically to realign with the solar year. The traditional Chinese, Hindu, and Hebrew calendars are examples of lunisolar systems that remain in use.
LUNATION
A lunation, or synodic month, is the average period of the Moon's orbit with respect to the line joining the Sun and Earth. This is the period of the complete lunar phase cycle, from one new moon to the next, averaging 29.53 days. This differs slightly from the sidereal month (27.32 days), which is the time it takes the Moon to orbit Earth relative to the fixed stars.
The difference between these two periods occurs because Earth orbits the Sun, meaning the Sun-Earth line changes direction during the Moon's orbit. As a result, the Moon must travel slightly further than 360° to reach the same phase alignment with the Sun and Earth.
ECLIPSES
Lunar and solar eclipses are dramatic celestial events that occur when the Earth, Moon, and Sun align precisely. A lunar eclipse happens when Earth passes between the Sun and Moon, casting a shadow on the lunar surface during a full moon. Depending on the alignment precision, this can result in total, partial, or penumbral lunar eclipses.
Solar eclipses occur during new moons when the Moon passes between Earth and the Sun, blocking the Sun's light from reaching certain areas on Earth. The type of solar eclipse—total, partial, annular, or hybrid—depends on the Moon's distance from Earth and the precise alignment of the three bodies.
Eclipses don't happen every month because the Moon's orbit is tilted about 5 degrees relative to Earth's orbit around the Sun. Eclipses only occur when the Moon crosses Earth's orbital plane (at points called nodes) at the same time it's in the correct phase—new moon for solar eclipses, full moon for lunar eclipses.
LUNAR EFFECT
The lunar effect refers to the link between different phases of the Moon's 29.5-day cycle and changes in behaviour or physiology among living organisms, including humans. Over the years, researchers have explored the lunar phases' influence inhuman activity, including mental health, crime rates, and birth patterns. By the late 1980s, at least 40 studies had examined the connection between lunar cycles and human behaviour, while around 20 focused on its possible impact on birth rates.
Certain corals, such as Dipsastraea speciosa, synchronize their spawning around the last quarter moon, using periods of darkness between sunset and moonrise as a trigger. These corals contain cryptochromes, light-sensitive proteins that help regulate their biological responses to changing lunar light levels. Similarly, the bristle worm (Platynereis dumerilii) spawns a few days after a full moon, guided by specialized proteins with light-absorbing flavin structures that distinguish between moonlight and sunlight. This species has become a key model for studying how marine organisms adapt to lunar cycles.
TIDAL EFFECT
The Moon plays a crucial role in shaping Earth's tides through its gravitational pull. As the Moon orbits our planet, its gravity draws ocean waters toward it, creating a bulge on the side of Earth facing the Moon. At the same time, a second bulge forms on the opposite side due to the centrifugal force caused by Earth's rotation and the Moon's gravitational influence. These bulges result in high tides, while the areas perpendicular to them experience low tides. Since Earth rotates beneath these tidal bulges, most coastal areas experience two high tides and two low tides within a roughly 24-hour period.
The intensity of tides varies depending on the Moon's phase and its alignment with the Sun. During new moons and full moons, when the Sun, Moon, and Earth align, their combined gravitational forces produce spring tides, which result in higher high tides and lower low tides. Conversely, during first and third quarter moons, when the Sun and Moon form a right angle relative to Earth, their gravitational forces partially cancel each other out, leading to neap tides, which have a smaller tidal range. Additionally, the Moon's elliptical orbit causes slight variations in tidal strength, with particularly strong tides occurring when the Moon is at its closest point to Earth, or perigee. This constant interplay between the Moon's gravity, Earth's rotation, and the Sun's influence keeps our planet's oceans in a rhythmic, ever-changing motion.