The Moon begins its slow retreat from fullness
A cada 29,5 dias, a Lua completa um ciclo que a humanidade tem observado desde os primórdios da civilização — um relógio celeste que mede o tempo com precisão silenciosa. Neste sábado, 25 de janeiro de 2025, ela se encontra em sua fase minguante, com apenas 21% de sua superfície iluminada, caminhando em direção à lua nova prevista para o dia 29. É um momento de transição, um intervalo entre a plenitude e o recomeço.
- A Lua perde visibilidade a cada hora que passa — apenas 21% de sua face ainda reflete a luz do Sol neste sábado.
- Em quatro dias, no dia 29 de janeiro às 9h37, ela desaparecerá completamente do céu noturno, encerrando o ciclo de janeiro.
- O calendário lunar do mês registrou marcos precisos: crescente no dia 6, lua cheia no dia 13 e início da fase minguante no dia 21.
- O Instituto Nacional de Meteorologia do Brasil acompanha esses eventos, traduzindo movimentos astronômicos em dados que orientam desde marés até o olhar curioso de quem observa o céu.
Neste sábado, 25 de janeiro, a Lua atravessa sua fase minguante com apenas 21% de sua superfície iluminada — uma diminuição gradual que culminará na lua nova do dia 29, às 9h37 da manhã, quando ela se apagará completamente do céu.
O calendário lunar de janeiro conta uma história de ritmo e precisão. No dia 6, a lua crescente surgiu às 20h57, inaugurando a fase de crescimento. Uma semana depois, no dia 13 às 19h27, a lua cheia iluminou o céu em sua máxima expressão. A virada veio no dia 21, às 17h32, quando a fase minguante teve início e a Lua começou seu lento recuo.
Esse ciclo — nova, crescente, cheia, minguante — se repete com exatidão matemática ao longo de 29,5 dias, o que os astrônomos chamam de lunação. Entre as quatro fases principais existem ainda estágios intermediários, como a quarto crescente e a quarto minguante, que compõem ao todo oito fases distintas do mês lunar.
Para quem observa o céu neste janeiro, a lua minguante oferece uma beleza particular: a luz rasante que revela montanhas e crateras em alto relevo, um astro em transição, nem pleno nem ausente, mas a caminho de seu próximo recomeço.
On Saturday, January 25th, the Moon hangs in the sky in its waning phase—a gradual dimming that has been underway for days. At this moment, only 21 percent of its surface catches the sun's light, and that sliver continues to shrink. In four days, on the 29th at 9:37 in the morning, it will disappear entirely into the new moon phase, completing one full cycle.
The lunar calendar for January tells the story of a rhythm that has governed human timekeeping for millennia. The month began on the 6th when the crescent moon emerged at 8:57 in the evening, marking the end of December's new moon and the start of the waxing phase. A week later, on the 13th at 7:27 in the evening, the Moon swelled to its full brightness—the moment when Earth sits directly between the Sun and Moon, and our satellite's entire face glows. Then came the turn toward darkness. On the 21st at 5:32 in the afternoon, the waning phase commenced, the Moon beginning its slow retreat from fullness.
This pattern—new, growing, full, shrinking—repeats with mathematical precision. A lunation, as astronomers call it, spans an average of 29.5 days from one new moon to the next. During that interval, the Moon passes through four primary phases, each lasting roughly seven days. But the cycle is more intricate than that simple division suggests. Between the new moon and full moon lie two intermediate stages: the waxing crescent and the waxing gibbous, each with its own character and duration. Similarly, the descent from full to new encompasses the waning gibbous and the waning crescent. These eight distinct phases, taken together, form the complete lunar month.
The data tracking these celestial events comes from Brazil's National Institute of Meteorology, an institution that monitors not just weather but the heavens themselves. For anyone watching the sky on this January Saturday, the waning moon offers a particular kind of beauty—the light arriving at an angle that casts shadows across the lunar surface, revealing mountains and craters in sharp relief. It is a moon in transition, neither full nor absent, but caught in the long diminishment that will culminate in four days when it vanishes from the evening sky entirely.
Citas Notables
A lunation or lunar cycle spans an average of 29.5 days, during which the Moon passes through four primary phases, each lasting roughly seven days.— National Institute of Meteorology (Inmet)
La Conversación del Hearth Otra perspectiva de la historia
Why does the Moon's phase matter to someone living in a city, where light pollution drowns out most stars anyway?
The phases still govern tides, which affect coastal ecosystems and water systems far inland. But more than that—the lunar cycle is one of the few natural rhythms most people can still observe directly. It's a way of staying tethered to something larger than the built environment.
Four days until the new moon. Is there anything special about that particular moment on the 29th?
The new moon is when the Moon passes between Earth and the Sun, so it's invisible to us. Astronomically, it marks the true beginning of a fresh lunation cycle. Some cultures consider it a time of renewal or intention-setting, though that's more cultural than scientific.
The article mentions these "interfases"—the gibbous phases. Why distinguish them if they're just in-between stages?
Because they're visually and gravitationally distinct. A waxing gibbous moon is almost full but not quite, and it rises later each night. It's useful for navigation, for understanding the Moon's position in the sky, and for anyone tracking lunar phenomena.
So the 29.5-day cycle is an average. Does that mean some months have longer or shorter lunations?
Yes. The actual duration varies slightly depending on the Moon's elliptical orbit and its distance from Earth. But 29.5 days is reliable enough for calendars and predictions across centuries.
What happens after the new moon on the 29th?
The cycle begins again. The crescent reappears in the western sky at dusk, and the waxing phase starts its slow climb toward the next full moon, which will arrive roughly two weeks later.