How long does it take for the earth to make one complete spin on its axis?  I thought it was 24 hours or pretty close to it.  I was wrong, it takes 23 hours and 56minutes.  Thats 4 minutes out!  Some of you might think it is close but 4 minutes is a lot when it builds up; nearly half an hour a week.  It turns out that the value we use as 24 hours is a solar day which is the apparent motion of the sun.  This is not 23 hours and 56 minutes because of our motion around the sun.  This is all very geeky and has been prompted by me picking up The Natural Navigator by Tristen Gooley.  If you are in any way interested in navigation then this book is a must read.  Belfast had a few copies of this last week but they are all sold out now.  Not sure why they sold out so fast, I don’t think it is the typical choice for mother’s day.

It has a section on star navigation and it mentions briefly how the night sky has been used be the mars rovers Spirit and Opportunity.  It turns out that the spacecrafts that delivered the rovers also relied on looking up at the stars for navigation.  It’s amazing to think that this ancient method is still so very real in this age of GPS.

This image was taken by one of the mars rovers.  You can see the three stars of Orion’s belt at the bottom.

On this theme, here is a picture of sunrise from mars taken by one of our lonely little robots so many millions of miles away.

These amazing little robots have worked harder than they were designed to do, but they are never coming home.

xkcd

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