What Does 97% Eclipse Coverage Actually Look Like?
Many people who have never experienced a deep partial eclipse underestimate how dramatic 97% coverage can be. At this level of coverage, the visual and environmental effects become genuinely striking, particularly in combination with Porto's sunset geometry.
The thin solar crescent
Through ISO-certified eclipse glasses, the Sun will appear as an incredibly thin arc — a crescent so narrow it looks like the waxing crescent Moon at its thinnest, but rendered in brilliant white against a black sky. This is the residual 3% of the solar disk: the thin rim that the Moon cannot cover. The sharpness of the lunar limb cutting across the Sun is one of the most beautiful sights in observational astronomy, and at 10x magnification through solar binoculars it is breathtaking.
Sky darkening and horizon colours
At 97% coverage, the illuminance at ground level falls to approximately 3–5% of full sunshine — similar to the light level 15 minutes after sunset, or the interior of a room lit by a single candle. The sky will noticeably darken toward the west and northwest. The horizon may develop a 360-degree "sunset-like" redness as the outer edge of the Moon's shadow creates a false twilight in all directions simultaneously. This is a phenomenon that can genuinely be mistaken for an approaching storm by those who are unaware of the eclipse.
Temperature drop
The sudden loss of solar radiation causes a measurable temperature drop during deep partial eclipses. At 97% coverage, surface temperatures in Porto may fall by 2–5°C during the eclipse maximum. Given that Porto in August averages 25–30°C, this cooling will be perceptible but not dramatic. The drop will feel sudden and unexpected if you are not prepared for it — bring a light layer.
Animal and bird behaviour
At 97% coverage, animal behaviour changes are frequently reported. Birds may roost, returning to trees as if evening has arrived. Insects that are active during daylight hours may cease activity. Nocturnal insects may begin chirping. Domesticated animals such as dogs and cats may become confused and agitated. If you are watching from a park or coastal area, keep a close eye on the behaviour of wildlife around you — it is one of the most memorable aspects of a deep partial eclipse.
Planets and bright stars
During the 97% maximum, the sky darkening may be sufficient for bright planets to become visible. Venus, if above the horizon, can sometimes be seen with the naked eye during very deep partials. Jupiter and Saturn, if present in the sky, may be detectable with binoculars. Check a planetarium app for the positions of bright planets on August 12, 2026, in case any are visible during maximum.
