Sun’s Light Reaches Earth in 8.3 Minutes as Sound Would Need 13.82 Years

Q: Why does the exact moment Earth plunges into darkness change depending on the time of year the Sun disappears?

The moment Earth would go dark is not exactly fixed because Earth is not always the same distance from the Sun. Its orbit is slightly elliptical, so the Sun is closest to Earth at perihelion in early January and farthest at aphelion in early July. That changing distance slightly changes the light-travel time. Near perihelion, the last sunlight would arrive sooner, in about 8 minutes 10.7 seconds. Near aphelion, it would arrive later, in about 8 minutes 27.3 seconds. The average value, based on 1 astronomical unit, is about 8 minutes 19 seconds. So if the Sun somehow vanished instantly, Earth would not plunge into darkness at one universal delay all year long. The delay would shift by about 16.7 seconds between the closest and farthest points in Earth’s orbit. The same timing change would apply to the Sun’s gravitational influence under modern physics, because changes in gravity also propagate at the speed of light. In practical terms, the exact date in the calendar matters only because it tells you whether Earth is a little nearer to or farther from the Sun when the event happens.

Q: If the Sun vanished today, what would happen to the Moon orbiting Earth in the sudden darkness?

The Moon would stay with Earth. If the Sun vanished in this impossible thought experiment, both sunlight and the change in the Sun’s gravity would stop affecting the Earth-Moon system only after about 8 minutes and 19 seconds, because those changes propagate at the speed of light. During that delay, nothing would seem different in the sky except that the last sunlight and moonlight already in transit would still be arriving. After that, the Sun would disappear from view and the Moon would go dark as well, because it shines mainly by reflecting sunlight. You would no longer see the familiar bright Moon, though the Moon itself would still physically be there, orbiting Earth. The key point is that the Moon’s orbit around Earth depends mainly on Earth’s gravity, not the Sun’s. So when the Sun’s pull vanished, Earth and Moon would continue moving together through space rather than the Moon flying off immediately. The pair would keep orbiting their common center of mass while the entire Earth-Moon system left its former solar orbit and traveled on a new path. Over time, the night sky would become much darker, except for stars and planets whose light was already on its way. The Moon could still be detected by instruments or, eventually, by faint reflected starlight and Earth glow, but it would no longer appear as the bright object people know from normal moonlit nights.

1 articles · Updated · spacedaily.com · Aug 30

499 seconds after a hypothetical instant solar disappearance, Earth would lose direct sunlight—the mean one-way light time across 1 astronomical unit, or 149.6 million kilometers.
343 meters per second for sound in air stretches that same distance to 436.1 million seconds, about 13.82 years, making light roughly 874,000 times faster.
The comparison is only arithmetic: interplanetary space is too close to a vacuum to carry an ordinary sound wave, and the exact sound delay changes with the assumed medium and temperature.
Gravity would share the light delay under general relativity, so Earth would keep orbiting normally for about 8 minutes 19 seconds before any change in the Sun’s gravitational field arrived.
Solar oscillations are real, but scientists infer them from Doppler shifts and brightness changes in sunlight; any audible 'roar' is a sonification, not sound transmitted through space.