Earth takes 24 hours to complete one rotation, right?
It actually takes slightly less than that.
You can test out how much less by studying the movement of the stars to work out the length of time it takes Earth to spin once on its axis.
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How to do it
Observing a favourite star and a bit of maths will prove Earth’s spin takes less than 24 hours.
- Position yourself so you can see a bright star disappear behind a chimney pot.
- Note the exact time it vanishes.
- Repeat this with the same star, from the same position, over the next few nights, noting how many minutes difference there is.
- After a week, you’ll have six values.
- Add them, divide the total by six to get the average, and convert them to seconds.
Watching Vega we saw a difference of four minutes and five seconds (245 seconds).
The published figure is three minutes 56 seconds (236 seconds) short of 24 hours: that’s one rotation every 23 hours, 56 minutes and four seconds.
Try it your self. What do you get?Let us know by emailing us at contactus@skyatnightmagazine.com.