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Gravity & orbits ↗
Why planets do not crash into the Sun.
Solar system · Question
What is an astronomical unit?
An astronomical unit (au) is a defined unit of length: exactly 149,597,870,700 metres (about 150 million km), close to the typical distance between Earth and the Sun. It's a convenient ruler for solar system distances, but hard to picture. Pick a real-world step size and see where every planet would actually be.
Visual model
If 1 AU were this long, where would Neptune be?
cm
Mercury29 cm
Venus54 cm
Earth75 cm
Mars1.1 m
Jupiter3.9 m
Saturn7.2 m
Uranus14.4 m
Neptune22.5 m
Dot positions use a log scale so every planet stays visible; the distances printed above each dot are the real linear numbers at your chosen scale.
Measurable fact
1 AU in a few units.
149,597,870.7 kmExactly 1 au by IAU definition; Earth–Sun distance varies over an orbit.
92.96 million miThe same distance in miles.
~8.3 minutesHow long sunlight takes to reach Earth.
30.05 AUNeptune's average distance from the Sun.
Definition: IAU 2012 Resolution B2 ↗. Approximate distances: NASA Science ↗.
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Why diagrams aren't to scale
See the same distances plotted against true planet sizes.
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Solar system model
Explore all eight planets in the interactive 3D model.