Sparkling world, Grid north and the Sun as a 24-hour clock

I woke up today at about midnight, stepped outside into the cold air and exceptionally bright daylight to walk the few meters to the bathroom for a sorely needed shower. It is difficult to describe how bright it is here when the sky is clear. What was striking about today was all the microscopic ice crystals floating in the air, reflecting the bright sunlight such that everywhere you looked the air was sparkling like the face of an adolescent girl who just discovered glitter make-up. Even when looking at my feet (which is all I could do as I didn’t bring my goggles or sunglasses with me for the short walk) the air was glistening. I looked up and covered the sun with my hand and could see two sun dogs on either side of the sun. I could only look for a split second since even those sun dogs were too bright to look at for any length of time. Unfortunately I didn’t have my camera and by the time I got back to my Jamesway, the clear sky had become overcast enough so that the sparkling ice crystals and sun dogs were gone.

One of the reasons why the sun was so bright was that it was directly in front of me as I stepped out of the Jamesway. This made sense as it was close to grid north which corresponds to it being near midnight here (where we keep New Zealand time). How’s that you ask? Good question. First let me go back to when I was on the C-17 flying south from Christchurch to McMurdo station. I happened to be up in the cockpit talking to the pilots when we crossed 60° south latitude. They joked about how there was going be a big flash and the plane was going to start flying backwards. What they were talking about is that a different navigation system is used at latitudes higher then 60° (closer to the poles). A grid system where the direction towards the prime meridian is considered north, or grid north, and the direction towards the international dateline is grid south. This meant that we would go from flying due south from New Zealand (which is relatively close to the international dateline) to flying grid north without ever changing direction.

Still doesn’t make sense? How about thinking about it in terms of the Sun being a clock…

The sun never sets here at the south pole in the summer time it just circles over your head. Of course the Sun isn’t moving, it is the Earth which is rolling under it presenting the part of the world where it is noon up to the Sun. So at the South Pole the sun is pointing to wherever it is noon on the Earth at “normal” latitudes (and ignoring all that messy daylight savings time stuff). Since we are keeping New Zealand time here, at noon the sun is pointing towards New Zealand. Further, since New Zealand is pretty close to the International Data line, it is also pointing grid south. And so at midnight here, the Sun will be in grid north. One thing to keep in mind here is that if the sky is a clock and the Sun is the hour-hand, it is a 24-hour clock, with one revolution per day, and not the 12-hour we are used to looking at.

Ok, so there you have it – an entry without any pictures and full of pseudo-technical talk. Check out my flickr and youtube sites for photos…


One Response to “Sparkling world, Grid north and the Sun as a 24-hour clock”

  1. t' Says:

    hey keith,

    the lack of pics and pseudo-technical talk was no biggy, since i’ve never heard of sun dogs before your blog and now i not only know what it is, i also know what it looks like!

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