Pick a destination. Guess how long light takes. Then get roasted by the universe.
Pick a destination, guess how long it takes, then see how close you were.
Light moves at 299,792 km/s. When Mars is closest to Earth — during opposition, about every 26 months — the distance is roughly 54.6 million kilometers. That means a radio signal takes about 3 minutes and 2 seconds. When Mars is on the opposite side of the Sun, the delay stretches to over 22 minutes.
This is why NASA's Perseverance rover had to be completely autonomous. There's no real-time remote control possible. If the rover hit a rock, the signal would take 12 minutes to reach Earth, and another 12 for the command to come back. The rover has to decide for itself.
Alpha Centauri, the nearest star system, is 4.37 light-years away. The light you see tonight left that star system before you graduated high school. If an alien there had a powerful telescope watching Earth, they'd be watching the year 2022 right now.
The universe is big. Really big. And even light — the fastest thing we know — takes time to get anywhere. The Moon is 384,400 km away. Light gets there in 1.28 seconds. That's why Apollo astronauts had about a 2.5-second round-trip delay talking to mission control.
Mars ranges from 54.6 million to 401 million km from Earth, depending on where the planets are in their orbits. Light takes 3 to 22 minutes to make the trip. When NASA talks to a rover on Mars, they're listening to a conversation that started minutes ago. There's no "real time" in space.
The nearest star beyond the Sun is Proxima Centauri, 4.24 light-years away. If a flare happened there today, we wouldn't know for over four years. The Milky Way is 100,000 light-years across. The light from the Andromeda galaxy you see tonight left its source 2.5 million years ago — before humans existed. You're looking at the past every time you look at the sky.
When Mars is closest (~55 million km), light takes ~3 minutes. At farthest (~400 million km), ~22 minutes.
One light-year is the distance light travels in a year: ~9.46 trillion km. Alpha Centauri is 4.3 light-years away.
When you look at stars, you see them as they were years ago. Light from the Andromeda Galaxy left 2.5 million years ago.
Mars is 225 million km away on average. Light travels at 300,000 km/s. 225,000,000 / 300,000 = 750 seconds = 12.5 minutes. That's the average. The actual number changes because both planets are moving.
Voyager 1, launched in 1977, is now about 24 billion km away. A one-way radio signal takes about 22 hours to reach it. It's still sending back data. By the time you read this, it's about 1 million km farther away.
Not with physics as we know it. To accelerate a human to 99% light speed requires enormous energy. Even if we could, time dilation means you'd age slower than people on Earth. The trip to Alpha Centauri would take 4.2 years ship time but 50+ years Earth time at that speed.