Bart Bear's Blog

In our courtyard there is a funny-looking thing on a concrete pillar. It looks like a couple of almost-rings and an arrow all welded together. Actually, it is an armillary sphere, a type of sundial. The arrow is called the gnomon and it's job is to make a thin shadow that moves along one of the rings as the Sun travels across the sky. The ring has numbers marked on it to tell you what time it is when the shadow is on a mark. Sundials are not really accurate except for four times a year, near equinoxes and solstices. At other times they can be up to 20 minutes fast or slow here in Canberra. Dad has this one set up to read best when we are on Daylight Saving Time, so I have a bit of trouble telling the time from it. First I have to remember what the date is, then how much the shadow is fast or slow, then if it is Daylight Saving or not. I often get it very wrong, small bears are not good at mental arithmetic. It is fun trying though because the only way I can read the thing is to climb up the concrete and into the middle of the sphere where I can see the marks. Any excuse to climb is fine by me.

Labels: astronomy, Canberra, climbing