Why the Moon will turn blood-red in September

As September approaches, stargazers and astrophotographers are in for a rare spectacle as the Moon will turn blood red. On the night of September 7-8, 2025, stargazers across much of the globe will witness a breathtaking celestial event, a total lunar eclipse that will turn the Moon a deep blood red.
This dramatic transformation, often called a Blood Moon, occurs due to a unique alignment between the Sun, Earth, and Moon, coupled with intriguing atmospheric optics.
During a total lunar eclipse, the Earth moves directly between the Sun and the full Moon, casting its darkest shadow, known as the umbra, across the Moon’s surface.
Unlike a solar eclipse where the Sun is blocked from view, the Moon doesn’t go completely dark during totality. Instead, it is bathed in a reddish glow caused by sunlight bending, or refracting, through Earth’s atmosphere onto the lunar surface.
This red colouration results from a phenomenon called Rayleigh scattering, the same reason sunsets appear red or orange.
Sunlight passing through the Earth’s atmosphere is scattered by air molecules and particles.
Shorter wavelengths of light, such as blue and violet, scatter out first and in various directions, leaving the longer red and orange wavelengths to pass through and reach the Moon. Because this refracted light filters through Earth’s atmospheric layers, some of the blue light is removed, causing the Moon to glow with hues of red, copper, or orange during the total eclipse.
The upcoming eclipse on September 7, 2025, is especially notable because of its long duration, with totality lasting approximately 82 minutes, one of the longest total lunar eclipses in recent memory. The eclipse will be visible across Asia, Australia, Africa, and Europe, with nearly 87% of the world’s population having some view of the event.
While these “Blood Moons” have fascinated humanity for centuries and made their way into cultural and spiritual lore, astronomically, they hold no extraordinary significance beyond their rarity and beauty.
Total lunar eclipses happen about once every 2.5 years on average, but eclipses with such a long totality phase and wide visibility are less common, making this event a rare and valuable opportunity for observers worldwide.