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The Relative Distances in the Solar System

The size of the Solar System consists of all the planets and other astronomical objects, such as asteroids and comets, which are orbiting the Sun, captured by its gravity. It is almost hard to understand on a human scale. It took Apollo 11 four days to reach the moon, but almost half a year for the Spirit and Opportunity rovers to get to Mars, covering about half the distance between the Earth and the Sun.

Sun to Earth
- The distances inside the solar system are usually measured in Astronomical Units (AU), which is the average distance between the Earth and the Sun. Since the Earth's orbit is elliptical, the distance from the Sun varies. An AU is about 92,957,130 miles. It takes eight minutes for light to travel from the Sun to the Earth. By comparison, it takes light two seconds to travel to the moon.
Inner Solar System
- If the Sun were a bowling ball, the Earth would be a peppercorn. Mercury, the first planet from the Sun, would be a pinhead, at 10 paces distance from the Sun. Venus, which is the second planet from the Sun, would be a peppercorn as well. It would be 19 paces from the bowling ball Sun. Earth is a further 7 paces away. Mars is another pinhead, 14 further paces away. It is actually an average of 1.5 AU from the Sun.
Outer Solar System
- After Mars come the gas giant planets. From Mars, it is 95 paces to Jupiter in the scale model where the Sun is a bowling ball. It is the size of a chestnut. Saturn is somewhat larger, and 112 paces farther out. Uranus is yet 249 paces further away, Neptune another 281 paces, and the Oort cloud begins somewhere inside Pluto's orbit, another 242 paces away. Jupiter is 5 AU from the Sun, Saturn 10 AU, Uranus 19, and Neptune 30.
Oort Cloud
- The Oort Cloud surrounds the solar system with comets and objects like Pluto (which is no longer classified as a planet). It is between 5,000 and 100,000 astronomical units away from the Sun. The Oort Cloud is even more sparsely populated with astronomical bodies than the Solar System.
Orbital Variations
- The distances between the planets and the Sun are not fixed. All planets move in elliptical orbits. Since they also move at different speeds in their orbits, this means that one planet may be farthest from the Sun at the same time as it is on the other side of it, seen from the Earth. When two planets are close in their orbits, and the orbits are close to the Sun, launches of spacecraft to those planets are economical, relative to the case when they are far away from each other. This is what astronomers call the launch window.

Astronomy