Backstaff

A backstaff is a tool used by sailors a long time ago to help them figure out the angle between the sun and the horizon. This was important for navigation because it helped the sailor figure out their position on a map.

So, how does a backstaff work? Well, it has a bunch of different parts. There's a long stick (or "staff") with a mirror at the end, and a smaller mirror on a movable piece that slides along the staff. The sailor would hold the backstaff up to their eye and look at the horizon through the smaller mirror. Then, they would adjust the movable piece until they could see the reflection of the sun in the larger mirror.

Once they had the sun's reflection in the big mirror, they could move the movable piece back and forth until the reflection was on a certain line on the staff. This line was called the index line. Then, they could look at a little scale on the backstaff (kind of like a ruler) and see what angle the movable piece was at. That angle told them how high the sun was in the sky, and that was important for figuring out their position on a map.

Overall, a backstaff was a pretty cool tool that helped sailors navigate the seas a long time ago!