How Much Empty Space is There in Space?
The amount of space between the planets is vast, and the distances between the stars are truly incomprehensible. Humans have reached the moon, which is located around 240,000 miles away. This is approximately 10 times the distance around the Earth. This trip took the astronauts 3 days each way.
However, the distance to the sun is around 400 times further than this. Intriguingly, the moon is also about 400 times smaller than the sun, which causes them to appear the same size in the night sky.
The distances between the planets is often measured in astronomical units, which is the distance between the Earth and the sun. Mars is located at around 2.7 astronomical units from the sun, and it gets as close as around 33 million miles or around 0.4 astronomical units to Earth. Thus, it would take astronauts traveling at the speed of the Apollo rockets around a little over a year to reach Mars.
Jupiter and Saturn are significantly further away at 6.2 and 9.5 astronomical units from the sun on average respectively. Uranus is located an average of 19.2 astronomical units from the sun, and Neptune is located at around 30 astronomical units. Astronauts traveling at the speed of the Apollo rockets would take approximately a human lifetime to reach Neptune. Here's a map of the solar system to scale with the moon the size of a single pixel- https://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html
What About Stars Beyond the Solar System?
The start of interstellar space is located at around 120 astronomical units from Earth. This is the distance at which the solar wind is no longer detectable. Voyager 1, Voyager 2 and Pioneer 10 are all past this threshold.
However, the distances to the nearest stars are vastly larger than this. Proxima Centauri is located at slightly over 4.2 light years from Earth or approximately 267,000 astronomical units. It is around 1 billion times further to the nearest star than to travel around the world.
The nearest galaxies are vastly further away still. In fact, Andromeda is located about 2.2 million light years, which is around 500,000 times further than the nearest star. Some galaxies are as distant as approximately 33 billion light years away. This is around 13,000 times the distance to Andromeda.
How Many Stars and Galaxies are There?
There is an estimated 2 trillion galaxies in the universe, and there are between 100 and 400 billion stars in the Milky Way galaxy. So, it is estimated that there may be as many as approximately 1 septillion stars in the universe (e.g. 1,000,000,000,000,000,000,000,000 stars). These stars are separated from one another by vast distances, which are incomprehensible.