During a solar eclipse, the moon passes directly between Earth and the sun, casting a shadow that can darken the sky in the middle of the day. During a lunar eclipse, Earth itself blocks sunlight from reaching the moon, turning it a deep red. Both events trigger a cascade of changes to the sky, the atmosphere, the temperature, animal behavior, and even radio signals. Here’s what actually happens, step by step.
How Solar and Lunar Eclipses Work
A solar eclipse occurs when the moon lines up precisely between Earth and the sun. The moon’s shadow races across Earth’s surface, and anyone standing in that shadow sees the sun partially or fully blocked. Total solar eclipses happen when the moon is close enough in its orbit to completely cover the sun’s disk. The longest totality during the April 2024 eclipse lasted 4 minutes and 28 seconds near Torreón, Mexico.
Because the moon’s orbit isn’t a perfect circle, sometimes it’s farther from Earth and appears slightly smaller than the sun. When an eclipse happens during that phase, the moon can’t fully cover the sun, leaving a bright ring of light around the edges. These are called annular eclipses, sometimes described as a “ring of fire.”
A lunar eclipse is the reverse arrangement. Earth passes between the sun and the moon, and our planet’s shadow falls across the lunar surface. The moon doesn’t disappear, though. Earth’s atmosphere bends sunlight around the planet’s edges, filtering out shorter blue wavelengths and letting longer red wavelengths pass through. This is the same scattering process that makes sunsets red. The light that reaches the moon during totality has traveled through the thickest, densest part of Earth’s atmosphere, so it arrives deeply reddened. The exact shade depends on atmospheric conditions: dust, volcanic ash, or heavy cloud cover can make the moon appear darker or more copper-colored.
What You See in the Sky
In the minutes before totality during a solar eclipse, the landscape takes on an eerie, flat quality as sunlight dims but doesn’t disappear all at once. Shadows sharpen because the sun has narrowed to a thin crescent, acting almost like a point source of light. Just before and after totality, you may notice shadow bands: faint, rippling lines of light and dark racing across the ground and light-colored surfaces. These ghostly bands are caused by atmospheric turbulence. Pockets of air at slightly different densities bend the narrow beam of light from the crescent sun, creating a shimmering, wave-like effect similar to the way stars twinkle at night.
Once totality arrives, the sun’s outer atmosphere, called the corona, becomes visible as a glowing white halo around the dark disk of the moon. Stars and bright planets appear in the daytime sky. The horizon in every direction may glow with sunset-like colors, because areas 50 or 100 miles away are still receiving sunlight. The entire experience of totality lasts only a few minutes at most before the moon continues its orbit and sunlight returns.
Temperature and Weather Shifts
The sudden loss of solar radiation during a total eclipse produces a noticeable temperature drop. The National Weather Service recorded temperatures falling as much as 10°F (about 5.5°C) during the period surrounding totality. The cooling isn’t instant. It builds as more of the sun is covered and typically bottoms out a few minutes after totality ends, similar to how the coldest part of the day comes after sunset rather than at sunset itself.
This rapid cooling also affects wind. As the ground cools under the moon’s shadow, it can weaken local wind patterns like sea breezes or slope-driven mountain winds. Some observers have reported sudden gusts or shifts in wind direction, a phenomenon sometimes called the “eclipse wind.” Researchers have linked these changes to a small, temporary low-pressure system that forms under the cooling shadow, along with shifts in how air mixes between layers of the atmosphere. The effect is subtle compared to normal weather, but it’s measurable with instruments and sometimes noticeable to people standing outside.
How Animals React
Animals respond to an eclipse the way they respond to nightfall, which makes sense: the cues they rely on (light level, temperature) are changing in exactly the same way. During totality, diurnal birds have been observed descending to their roosts and going quiet. In one well-documented case during an eclipse over Kansas, great egrets, cattle egrets, snowy egrets, and little blue herons all began their evening routines as the sky darkened. Weather radar data has confirmed broad decreases in bird flight activity during totality, suggesting this isn’t just isolated behavior but a widespread response.
The reaction extends well beyond birds. A study at a zoo during a total eclipse found that gorillas, elephants, lorikeets, cockatoos, and Komodo dragons all shifted to evening behaviors. Flamingos clustered protectively around their young and became more vigilant. Lorikeets called loudly before swooping in unison across their enclosure, a synchronized display that researchers had never seen from them under normal conditions. Dogs have been recorded falling silent, while horses clustered together and shook their heads and tails.
Nocturnal animals do the opposite. Tawny frogmouths, which are normally active at dusk and night, stirred from their daytime roosts and became active during totality. Night herons observed during an eclipse in India abandoned their daytime perches and began flying as if it were evening. Once sunlight returns, daytime animals resume their normal activity within minutes, apparently unaffected by the brief interruption.
Effects on the Upper Atmosphere
One of the less visible but more consequential effects of a solar eclipse happens high above the ground, in the ionosphere. This layer of charged particles, sitting roughly 37 to 56 miles up, is created and maintained by solar radiation stripping electrons from atoms. When the moon blocks that radiation, the ionosphere temporarily loses its energy source. Electron density drops, and the layer cools.
This matters because the ionosphere is what reflects and bends radio waves, making long-distance shortwave radio communication possible. As the layer weakens during an eclipse, high-frequency radio signals can fade, get absorbed, or take unexpected paths. GPS signals, which pass through the ionosphere on their way from satellites to your phone, can also be affected. Researchers have observed temporary “holes” or depletions in the ionosphere during eclipses, and these anomalies can degrade the accuracy of navigation systems over the affected area. The effects are temporary, resolving as solar radiation resumes after the eclipse passes.
Why Looking at an Eclipse Can Damage Your Eyes
Staring at the sun during a partial eclipse is more dangerous than staring at it on a normal day, not because the light is different, but because the dimmer conditions trick your pupils into staying wider. Your eyes focus incoming sunlight onto a tiny spot on the retina, the light-sensitive tissue at the back of your eye. That concentrated energy triggers a photochemical reaction that damages the cells responsible for your sharpest central vision. Blue light wavelengths are especially harmful, breaking down proteins and fats in the retinal cells through a process called peroxidation.
The damage, known as solar retinopathy, typically affects both eyes and produces symptoms like blurred central vision, blind spots, sensitivity to light, and distorted or wavy vision. These symptoms can appear within hours of exposure. In many cases, vision partially recovers over weeks or months, but some people are left with permanent blind spots.
Safe solar viewers are certified under a standard called ISO 12312-2, which limits the amount of visible, ultraviolet, and infrared light that passes through to your eyes. Certified eclipse glasses transmit no more light than a shade 12 welding filter. The American Astronomical Society emphasizes that these viewers must be non-magnifying and free of scratches, pinholes, or damage. Regular sunglasses, even very dark ones, do not come close to meeting this standard. During totality itself, when the sun is completely covered, it is safe to look with unaided eyes. The moment any sliver of the sun reappears, you need protection again.