DiameterHow big are the planets? Before we can answer that question, we must make sure we know just what we mean by "big". There are more than one way to measure the size of something. One of these ways is look at the diameter of an object. We measure the size from one side to the other.
The Earth is 7926 miles across. That's a pretty big number. The next time you ride to school, measure the distance from your home to school using the car's odometer. Compare the distance to school with the diameter of the Earth.
Astronomers have used telescopes to measure the diameters of the other planets. Let's compare. The table below lists the diameter for each planet. Because measuring the planets' diameters in miles gives such huge numbers, we'll use the Earth itself as our measuring stick. | Mercury | Venus | Earth | Mars | Jupiter | Saturn | Uranus | Neptune | Pluto | | 0.38 | 0.95 | 1.0 | 0.53 | 11.21 | 9.46 | 4.01 | 3.88 | 0.18 | From this table we can see that Uranus is about 4 Earths across. If you could line up 4 Earths right next to each other in a straight line, that's nearly how wide Uranus would be! We can also see that some planets are smaller than the Earth; their diameter is only a fraction of the Earth's. Check it out!
Look at the table of diameters. Which planet has the largest diameter? Click your answer below.
| Intro | Diameter | Volume | Mass |
| Surface Gravity | And Beyond... | NASA Ames Educator Resource Center Content and Web Development: Brian H. Day
Responsible NASA Official: Donald James |