The Short Answer: Planet Day Length When you think of a day, you normally think of one cycle of daytime to nighttime. That is called a solar day. On Earth, a solar day is around 24 hours. However, Earth’s orbit is elliptical, meaning it’s not a perfect circle. That means some solar days on Earth are a few minutes longer than 24 hours and some are a few minutes shorter. Another way to measure a day is to count the amount of time it takes for a planet to completely spin around and make one full rotation. This is called a sidereal day. On Earth, a sidereal day is almost exactly 23 hours and 56 minutes. We know how long an Earth day is, but how about the other planets in our solar system? How long does it take for those planets to spin one full rotation? And what is the best way to show the answer to this question? Let’s look at a few options. We can write a paragraph about how long days last on other planets. On Mercury a day lasts 1,408 hours, and on Venus it lasts 5,832 hours. On Earth and Mars it’s very similar. Earth takes 24 hours to complete one spin, and Mars takes 25 hours. The gas giants rotate really fast. Jupiter takes just 10 hours to complete one rotation. Saturn takes 11 hours, Uranus takes 17 hours, and Neptune takes 16 hours.Mercury 1,408 hours Venus 5,832 hours Earth 24 hours Mars 25 hours Jupiter 10 hours Saturn 11 hours Uranus 17 hours Neptune 16 hours 
Option 1: A Paragraph
Reading that paragraph took a while, and it’s hard to find all the numbers. Let’s see how it looks if we put it in a table.
Option 2: A Table
Planet | Day Length |
| Mercury | 1,408 hours |
| Venus | 5,832 hours |
| Earth | 24 hours |
| Mars | 25 hours |
| Jupiter | 10 hours |
| Saturn | 11 hours |
| Uranus | 17 hours |
| Neptune | 16 hours |
That’s a little bit better. We can look up and down at the numbers and can compare them more easily. But wouldn’t it be nice if we could see how big those differences are?
Let’s make a graph with these numbers!
Option 3: A Graph
To start, make a number line that starts at 0 and goes to the highest number you need to include. This first graph will only have Earth, Mars, Jupiter, Saturn, Uranus, and Neptune on it. We’ll save Mercury and Venus for later. You'll see why in a minute.
The longest day among those planets is 25 hours. That means our number line will go up to 25.
Label the number line so you remember it represents hours. And write what information the graph will have at the top.
Along the bottom, write the names of the planets.
Make a dot above the name of the planet next to the number of hours its day takes.
Our graph is coming together!
What do we do now? Color in the area below the dot to make a bar graph.
Now we can easily see which planet has the longest day, the shortest day, and everything in between. This is much easier than reading a list of numbers, don’t you think?
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But what do we do about Mercury and Venus? Their days are thousands of hours long. How do we make a graph for those?
We make a number line, but instead of numbers 1, 2, 3… we will use 1,000, 2,000, 3,000…
Make a number line that goes all the way up to 6,000. Along the bottom, write Mercury and Venus. Above Mercury, mark a dot a little less than halfway between 1,000 and 2,000. It’s not going to be perfect, but that’s okay. Now make a dot a little under 6,000 for Venus.
Do you think we can include Earth, Mars, Jupiter, Saturn, Uranus, and Neptune on here? Their dots would be so close to 0 it would be hard to tell the difference between them. Graphs work best when the numbers are similar in size, usually with the same number of digits.
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Now that you know how to make a graph, you can show all kinds of information this way. You can graph the time it takes to get to school each day, the number of pieces of pizza your friends can eat, and how many people like the color blue or green. Go on and get graphing!
