Trips around the Sun

About this video

How old are you? Whatever the answer is, it is also the number of times you have travelled around the Sun.

The Earth spins once a day, and at the same time it travels around the Sun on a path that is almost a circle. That path is called its orbit, and one whole trip around the Sun takes one year. The Earth does both at once, like a spinning top that is also moving around a table: it spins about 365 times during one trip, which is why a year has about 365 days. You can't feel either motion, but the Earth carries you along the whole time.

On each birthday the Earth is back at about the same place in its orbit as on the day you were born. So when someone turns 9, the Earth has carried them around the Sun 9 times, and a cake with 9 candles counts 9 trips.

The trip doesn't take exactly 365 days. It takes about 365 days and 6 hours, a quarter of a day more. A calendar can't have a quarter of a day, so most years get 365 days and the leftover quarters pile up. After four years they make one whole day, which is added to the calendar as 29 February. A year that has it is called a leap year. The real rule is a little cleverer than "every four years", and a later course works it out.

You can act it out at home: put a lamp (the Sun) in the middle of a dark room, hold an orange (the Earth), and walk slowly in a circle around the lamp, turning the orange as you go. One walk around the lamp is a year; each turn of the orange is a day.

Transcript

1. 0:00How old are you?
2. 0:02Whatever the answer, it is also how many times you have travelled around the Sun.
3. 0:09Nine candles, nine trips around the Sun.
4. 0:20While the Earth spins once a day, it also travels around the Sun.
5. 0:25Its path is almost a circle. That path is its orbit.
6. 0:30One whole trip around the Sun takes one year.
7. 0:46It does both at once, like a spinning top that is also moving around a table.
8. 0:53During one trip, the Earth spins about 365 times.
9. 0:58That is why a year has about 365 days.
10. 1:03You can't feel either motion, but the Earth carries you along the whole time.
11. 1:14On each birthday, the Earth is back at about the same place in its orbit as on the day you were born.
12. 1:22So when someone turns nine, the Earth has carried them around the Sun nine times.
13. 1:36But the trip doesn't take exactly 365 days.
14. 1:39It takes about 365 days and 6 hours. A quarter of a day more.
15. 1:44A calendar can't have a quarter of a day. So the quarters pile up.
16. 1:50After four years they make one whole day, added as the twenty-ninth of February.
17. 1:56A year with that extra day is a leap year.
18. 2:00The real rule is a little cleverer, for a later course.
19. 2:04Try it at home. Put a lamp in the middle of a dark room.
20. 2:09Hold an orange, and walk slowly around the lamp, turning the orange as you go.
21. 2:16One walk around the lamp is a year. Each turn of the orange is a day.
22. 2:26Your age is how many trips you have made around the Sun.