- A gamma ray photon is created at the core of the Sun at 27 F million degrees and 250 billion atmospheres.
- As gamma rays are "dangerous," it is fortunate that this high energy photon has to pass through 432,000 (Brill says 400,000) miles to the surface of the Sun.
- The first 300,000 miles is plasma denser than lead.
- This gamma ray photon collides with mostly hydrogen molecules (really, the proton portion), bounces around, and loses energy.
- It takes around 100,000 years for this photon to finally reach 100,000 miles from the surface of the Sun, and is now only one ten-millionth of its original energy as an X-ray photon.
- The final 120,000 miles is "only" turbulent plasma (mostly ionized hydrogen), so this X-ray photon only takes a week more to get to the surface of the Sun, which is at around 10,000 F.
- This photon is now only one-millionth as energetic, or one ten-trillionth of what it originally was.
- Thus, this benign photon, called sunlight, takes a final 8 minutes and 20 seconds to reach the surface of Planet Earth.
- The whole journey took about 100,00 years + one week + 8 minutes +20 seconds, or around 100,000 years to reach us. However, Brill says in the first paragraph 120,000 years, so I suspect he meant that it takes 120,000 years, not 100,000 years, to reach a point 100,000 miles from the surface. In any case, 100,000 years or 120,000 years is a long time and it doesn't matter much if scientifically accurate.
Homo habilis (right) lived, and way before the Neanderthals (first appeared 400,000 years ago), where the earliest version of Homo sapiens, us, only came, perhaps, 250,000 years ago. In other words, if any signal is detected from that galaxy, if we respond, it will take another 2.5 million years to get there.
Incidentally, while it might be true that our Sun should be good for maybe another 5 billion years, it turns out that our Milky Way and Andromeda will begin to merge in 4 billion years. With Andromeda to the left, here is what this collision will look like from Planet Earth:
Andromeda has a trillion stars, while at most, the Milky Way might have 400 million, so we will lose this battle. But, we are only two of 225 billion galaxies that can be detected (there are more). Inter-galactic travel? There are suggested ways. But dream on.