Moon phase today: September Lunar calendar reveals transition to waning Moon with 55% visibility

On the morning of this Sunday, September 14, 2025, a significant change occurred in the sky: the moon, which until then was in its full phase, began its transition to the waning phase at exactly 7:32 AM, with a 55% visibility for terrestrial observers. The meta-description, present at the beginning of this text, informs that the September moon is transitioning to its waning phase, an event that marks the advance of the lunar cycle and the gradual decrease of its illuminated portion, with exact data provided by the National Institute of Meteorology (Inmet).

The astronomical event, which is part of the natural 29.5-day cycle, reflects the complex dance between Earth, the moon, and the sun, and explains the satellite’s appearance in the sky. The phase change is a phenomenon that has intrigued and guided various human activities for centuries, from agriculture to navigation.

Why does the moon change phases? The detailed cosmic dance

The phase change of our natural satellite is not an isolated event, but rather the direct result of the gravitational and positional interaction with Earth and the Sun. The brightness we perceive on the moon is not generated by itself, but is the reflection of sunlight on its surface. Lunar phases occur as the moon completes its orbit around the Earth, causing the portion illuminated by the Sun, as seen from our planet, to constantly change. This variation in perspective is what creates the different phases, from the invisible new moon to the full moon, where the face facing us is fully illuminated.

The cycle repeats every 29.5 days, and the transition between each of the eight phases—the four main ones (New, Waxing Crescent, Full, and Waning Crescent) and the four intermediate ones (First Quarter, Waxing Gibbous, Waning Gibbous, and Last Quarter)—happens gradually. For the current phase, the change from Full to Waning, the illuminated portion begins to progressively decrease. This specific transition, which occurred today, will be followed by the new moon on September 21.

Some important details about the lunar phase cycle for September are:

• The full moon began on the 7th, at 3:08 PM, reaching its fullness.
• The waning phase started this Sunday, September 14, at 7:32 AM, with reduced visibility.
• The next event, the new moon, is scheduled for the 21st, at 4:54 PM.
• The last phase of the month, the waxing crescent, will begin on September 29, at 8:53 PM.

The mechanics behind the phases and their visibility

The moon’s orbit is the main factor that determines its visibility. In the case of the new moon, for example, it is not apparent in the sky because its illuminated face is turned towards the Sun and, consequently, opposite to Earth. The full moon occurs when Earth is positioned between the Sun and the moon, allowing sunlight to completely illuminate the face facing us, making it entirely visible. The waning phase, which began this Sunday, is the opposite of the waxing phase, meaning the illuminated part we can see begins to shrink day by day until it becomes a thin sliver, before disappearing completely in the new phase.

This transition to the waning phase is a gradual process that makes the visible portion of the satellite constantly shrink. The Waning Gibbous and the Last Quarter are the phases that precede the full Waning moon, while the Waxing Gibbous and the First Quarter precede the Full moon. Each stage has its own particularity and is a key piece in the lunar cycle. The movement around Earth and the Sun is not just a visual spectacle, but a force that affects, for example, the ocean tides. The variation in lunar brightness has direct effects on various ecosystems and even in popular culture and ancestral practices that associate each phase with different natural and spiritual events.

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The Waning phenomenon, which marks the decline of the moon’s visible portion, is one of the most awaited by astronomers and astronomy enthusiasts, who take advantage of the satellite’s lower brightness to observe stars and other celestial bodies with greater clarity.

• The waxing crescent moon is the period between the new and full phases, where the illuminated portion seen from Earth gradually increases.
• The full moon, on the other hand, is the point of greatest visibility, where the face facing us is completely illuminated.
• The waning crescent moon is the phase in which the visible portion decreases until it disappears.

Astronomical impact of the change and its influence on daily life

The transition between moon phases is an event of extreme importance for astronomy and for understanding celestial movements. In addition to being a guide for calendars and navigation, the lunar cycle has a direct effect on Earth’s tides. The moon’s gravitational pull is the main cause of this phenomenon, and the intensity of the tides varies depending on the moon’s phase. During the full and new moons, for example, the combined gravitational pull of the sun and moon is stronger, resulting in higher tides. In the waxing and waning phases, the force is smaller, which leads to milder tides.

The study of lunar phases is not limited to science; it permeates human culture in various ways, being used as a basis for agricultural calendars, religious festivities, and even in legends and superstitions. The ability to predict the moon’s phase is ancient knowledge that has been refined over time and today allows us to accurately understand the satellite’s position and its consequences for our planet.

The waning phase, specifically, has a symbolic role in many cultures. It is often associated with a period of reflection, decrease, and letting go, in contrast to the fullness and expansion of the full moon. This variation in symbolism shows how the satellite’s influence goes beyond its physical effect and manifests in the collective imagination.

The September lunar cycle and the next astronomical events

The month of September is particularly interesting for moon observers, as the transition from Full to Waning is one of several events that can be followed. The sequence of phases throughout the month demonstrates the constancy and regularity of celestial movements. The next major event, the New Moon on the 21st, will be a time of less brightness, ideal for observing other celestial bodies, such as planets and nebulae, which become more visible without the intense brightness of our satellite.

Despite being a routine phenomenon, the lunar cycle is a constant reminder of the universe’s complexity and beauty. The understanding of the mechanisms behind the moon’s phases is a pillar of astronomy and continues to fascinate scientists and laypeople alike. The constant movement and changing visibility are reflections of the dynamics between celestial bodies, a cosmic choreography that unfolds in space and directly affects us. The Waning phase, which now dominates the sky, is a passage to the next stage, renewing the cycle and the opportunity for new observations.