Years and orbiting the Sun

Two of my eldest son's interests at the moment are space and trying to figure out how time works. He's always asking about when things will happen, trying to read clocks and getting his head around days of the week by repeatedly asking questions about which day comes next and we have been helping him to remember which of the 7 days of the week comes next. He's been interested in the days of the month too after we counted the days to Christmas with our home-made Advent calendar. I've been trying to explain that a new year started when the month of December ended and January began. He's not quite got his head around it all yet, but he's starting to piece it all together and ask lots of questions (sometimes repetitively...).

I thought I'd throw a bit of science into our discussions about time and try to explain how years and days link to how planet Earth moves given his current interests. To try and make it a bit less abstract, I got out some pom poms and drew some roughly elliptical dotted line 'orbits' on a large sheet of paper. It's not to scale, but I drew orbits for the four planets closest to the Sun (Mercury, Venus, Earth and Mars) and wrote on them the length of time taken to orbit the Sun. 

When he found it on the table, my son was interested in what it was. I explained briefly, and showed him how he could move the planets around the Sun. He had a go and wanted to know which planet the pink pom pom was. When I told him it was Mercury, I was informed that it isn't pink (we have previously made some planets for his bedroom wall), but he was happy to continue playing with them for a few minutes despite my poor choice of pom pom!

We had a chat about how long it took to move each planet once around the Sun, and I explained that Earth took 365-and-a-quarter days to orbit. I told him that most years have 365 days, but that some years - like 2020 - have an extra day and are called leap years. We did a bit of leaping around the room after this, and I'm not sure quite what information he picked up, but he seemed to have fun! 

We also talked about how years have 12 months, and that the next month is called January. I tried to explain that months are slightly different lengths, but didn't get very far with this as we had moved away from talking about things I could demonstrate with the pom poms and it was getting a bit abstract and incomprehensible (and he had better toys to play with after Christmas!). I decided to try asking instead about whether he thought a year for Mars was longer or shorter than Earth and he confidently predicted that it was longer, after moving both the model Earth and Mars once around their orbits. He's correct, as a year on Mars is the length of 687 Earth days (which given he's only just getting to grips with numbers larger than 100 I described as 'a bit less than twice as long as our year on Earth').

Pom pom 'planets' orbiting a (not to scale) Sun 

The appeal of his Christmas presents was too great and he wanted to go and play with them instead of doing any more with the pretend planets. For an older child, you might want to talk about the length of a year on Mercury (88 Earth days) or Venus (227 Earth days) or you could extend your Solar system model to include planets further from the Sun - if you go all the way out to Neptune, the year is 165 times longer than our year on Earth.  I might try this another time when there are fewer exciting new toys to play with.