The Scale of the Solar System

Although the dimensions of our solar system are quite small when compared with the scale of even nearby stars, distances from one planet to another are difficult to comprehend.

Our close neighbor, the Moon, averages about 385,000 km (239,000 miles) from the Earth. The diameter of the Earth is about 12,900 km so the circumference is 12,900 times pi (3.14159) or about 40,000 km. This means that the Moon is about "10 trips around the Earth" away.

The average Earth-Sun distance is called an astronomical unit (au) and is equal to about 150,000,000 kilometers (93,000,000 miles). At 300,000 km per second, light takes over 8 minutes to travel from the Sun to the Earth (one au). Neptune, which is currently the furthest planet from the Sun at about 30 au, is over four light-hours (the distance light travels in one hour) from the Sun.

To put the solar system dimensions into perspective with inter-stellar dimensions (inter stellar means "between stars"), assume for a moment that the distance between the Earth and Sun is one meter. At this scale, Mercury is about 30 centimeters from the Sun and Neptune is about 30 meters away. The diameter of the Earth is a few thousandths of a millimeter. The entire solar system would fit inside a 60 meter circle.

At this scale of one meter equals one astronomical unit, where would the closest star (other than our star the Sun) Alpha Centauri, which is about 4.3 light years away, be?

So Alpha Centauri is about 41 trillion km (4.3 light years times 9.5 trillion km/light year) from our solar system. If we divide this huge number by one astronomical unit in meters, (150,000,000 km/au * 1000 m/km) we get 271 kilometers, i.e. the number of kilometers to the nearest star at our scale of one meter equals one astronomical unit. To put this into perspective, if our solar system was the size of a small yard (60 meters diameter) our nearest stellar neighbor would be 271 km away! Its almost enough to make you feel lonely.