How old is sunlight when it reaches earth

The photons are born in a nuclear fusion, when hydrogen cores smash together to make helium. As a byproduct of this reaction, a huge amount of energy is released in the form of photons. But those are not visible light photons, not the kind of light our eyes can see, but high energy gamma-ray photons. The Sun is composed of different layers, like an onion.

The hottest and the densest part of the Sun is the core. This is where all the nuclear fusion magic happens. Surrounding the core is the radiative zone.

It extends from 0. As we move through the radiative zone, the temperature drops by about an order of magnitude, from 15 million degrees C in the core to to 2 million degrees C on the outer edge of the radiative zone.

The density drops too. Further out is the convective zone. It extends all the way to the visible surface. My questions are. How long does it take for the light from the sun to reach the Earth, and other planets in the Milky Way? How far does the sun's light travel beyond our solar system? How much larger is the sun compared to the planets in our solar system?

Thank you for your time. The sun's light takes about 8. The time it takes for light to reach planets in our Solar System not the Milky Way, which is our galaxy varies from about 3 minutes for Mercury, to about 4. There is nothing out in space to prevent the sun's light from going infinitely far, in principle. In practice, the sun is only 4. But there's nothing to stop that light from propagating outwards forever, as time goes on. The sun's radius is about times that of the Earth, meaning that about 1.

If it takes just over 8 minutes for the Sun's light to reach Earth, then if the sun were to suddenly extinguish, would we not know it until just over 8 minutes later? This is correct. There's no reason for the Sun to suddenly turn off, but more generally, the light from flares or other stellar "weather" also takes 8 minutes to reach us. Dave was the founder of Ask an Astronomer. There he runs his own version of Ask the Astronomer. The Sun is more than 8 light-minutes away.

For example, the galaxy M is located about If aliens lived in those galaxies, and had strong enough telescopes, they would see the Earth as it looked in the past. They might even see dinosaurs walking on the surface. We have written many articles about the Sun for Universe Today.

Source: NASA. Originally born as energetic gamma rays, after billions of collisions with matter, this radiation reaches the surface and escapes into space. How old is sunlight by the time it reaches the surface? Most textbooks say that it takes light between , years and 50 million years to escape. You would be surprised to know that this simple, and very popular, question seems to be without a firm answer! The reason has a lot to do with the assumptions that textbook authors use in making the calculation.

Most astronomers are also not particularly interested in a high-accuracy answer, so they tend not to bother doing the tedious calculation exactly. It is actually a very complex problem in physics! Because the density of the sun decreases by tens of thousands of times from its lead-dense core to its tenuous photosphere, the typical distance a photon can travel between charged particles changes from 0.

As a comparison, most back-of-the-envelope estimates assume that the sun's interior has a constant density and that the 'free path' distance for the photon is about one centimeter.