What if a solar eclipse lasted all day?

Sometimes the Moon slides right in front of the Sun. The sky goes dark like evening, in the middle of the day!

Then the Sun comes back. What if it stayed dark all day?

A total solar eclipse happens when the Moon passes between the Sun and Earth and completely blocks the Sun's face. NASA says the sky darkens as if it were dawn or dusk, and people can see the Sun's glowing outer atmosphere, the corona.

But it's over in minutes. So what if a total eclipse lasted all day? Why are real ones so short, and what would animals do? This is a thought experiment. Choose a path to follow the Moon's racing shadow, find out why totality is brief, and see how animals respond.

During a total solar eclipse, observers inside the Moon's umbra see the Sun's disk fully covered and the corona revealed; outside it, in the penumbra, the eclipse is partial. NASA notes eclipses occur only during eclipse seasons, about twice a year, because the Moon's orbit is tilted relative to Earth's.

This thought experiment stretches totality from minutes to a whole day. The evidence comes from NASA's measurements of the 2017 and 2024 eclipses and from observations of animal behavior. An all-day totality cannot happen with the real Sun, Moon and Earth; its effects are ideas, not predictions.

On April 8, 2024, the Moon covered the Sun. It happened over parts of Mexico, the United States and Canada.

In each place, the sky stayed dark for just a few minutes.

On April 8, 2024, the Moon's shadow crossed Mexico, the United States and Canada. NASA says the longest totality, the time when the Sun is completely covered, was 4 minutes and 28 seconds, near Torreón, Mexico. Most places on the center line got between 3.5 and 4 minutes.

In 2017, the longest totality in the United States was only 2 minutes and 42 seconds. During totality, NASA says, the temperature can drop about 5 °C.

The April 8, 2024 eclipse's longest totality was 4 min 28 s, about 25 minutes northwest of Torreón; most centerline locations saw 3.5 to 4 minutes, and Canada up to 3 min 21 s. In 2017 the maximum was 2 min 42 s near Carbondale, Illinois.

The Moon was also a little closer to Earth in 2024, which NASA says made the path wider: 108 to 122 miles (about 174 to 196 km) across North America, against 62 to 71 miles in 2017. NASA notes air temperature can drop about 5 °C during totality, depending on humidity and cloud.

Imagine the dark staying and staying. It might feel like evening all day long.

Birds might stay quiet, and crickets might keep chirping!

Imagine the Moon's shadow parked over your town all day. The sky might stay as dark as dusk, and the air might keep cooling. NASA says that during short eclipses, birds stop singing, crickets start chirping and bees return to their hives, fooled by the false dusk. In an all-day eclipse, animals might act as if evening had come and never ended.

That could never happen with our real Moon, because its shadow moves too fast to stay in one place. These are ideas about an imaginary eclipse, not predictions.

Holding the umbra over one place for a day would require the Moon's shadow to stay fixed on Earth's rotating surface, which the real orbit and rotation do not allow. Within the thought experiment, the observed short-term responses suggest possibilities: continued cooling beyond the roughly 5 °C NASA cites for minutes of totality, and animals keeping their dusk behaviors.

None of this is modeled. Whether animals would settle into night routines, or how far temperatures would fall, are open ideas; the real eclipse record covers only minutes, and NASA notes the effects of eclipses on plants and animals are not fully understood.

The Moon's shadow moves very fast across Earth. It zooms past each place.

So the dark part only lasts a few minutes.

The Moon is always moving along its orbit, so its shadow sweeps across Earth's surface. NASA's visualization shows the darkest part of the shadow, the umbra, crossing the 2024 path at more than 2,400 kilometers per hour. Earth spins the same way, and NASA says the shadow would move even faster if it didn't.

The shadow also only just reaches Earth, and NASA explains that it narrows as it stretches away from the Moon, so the dark spot on the ground is small: in 2024 the path was less than 200 kilometers wide. Small spot plus fast motion means short totality.

NASA's Scientific Visualization Studio notes the Moon's umbral cone is roughly 30 Earth diameters long, barely enough to reach Earth. On April 8, 2024, the umbra swept the path of totality at more than 1,500 miles (2,400 km) per hour, tracking the Moon's west-to-east orbital motion; it would move even faster if Earth were not rotating in the same direction.

With a path roughly 174 to 196 km wide and a shadow moving that fast, any fixed observer stays inside the umbra for only minutes. The umbra spent just an hour and forty minutes over land before leaving across the North Atlantic.

Scientists flew jets to chase the Moon's shadow. That made the eclipse last longer for them!

Other people recorded the sounds of animals during the eclipse.

If the shadow moves too fast, what if you chase it? In 2017, NASA-funded scientists did just that, flying two WB-57F jet planes one after the other along the Moon's shadow. NASA said most viewers on the ground would get less than two and a half minutes of totality. Each jet saw about four minutes, and together the two kept totality in view for about seven and a half minutes without a break.

In 2024, NASA's Eclipse Soundscapes Project asked people to record animal sounds during the eclipse. It repeats a study by scientist William Wheeler after a 1932 eclipse, which gathered almost 500 observations from the public.

Moving with the umbra extends totality. During the August 21, 2017 eclipse, a NASA-funded team flew two retrofitted WB-57F jets in tandem along the path at about 750 km/h. Each plane saw about 240 s of totality, against about 160 s for a stationary observer near greatest duration, and together they recorded 457 s, about 7.5 minutes, of continuous totality (Caspi et al., 2020). Before the flight, NASA noted that most ground viewers would get less than two and a half minutes.

Animal responses are being studied systematically. NASA's Eclipse Soundscapes Project invited the public to collect sound recordings and multisensory observations during the October 14, 2023 annular and April 8, 2024 total eclipses, replicating William M. Wheeler's study of the 1932 eclipse, which drew almost 500 public observations. The project was especially interested in crickets, and in whether nocturnal and daytime animals respond differently.