This is directly following on from the earlier Midday is almost never 12:00 post.
You may have noticed that if you look at where the Sun is, in the sky, at the same time of the day it appears to change. Particularly over a gap of a week or a month.
Well, it sure does. This took a while, but I used the free Stellarium astronomy software to show the position of the Sun, from here at Williamstown, looking due North at 12:00 local time. I captured one image per week, then merged the 52 images into a Video and edited that.
Stellarium automatically takes into account Daylight Savings, so if you look carefully, it ‘jumps’ to 1:00pm, which is still 12:00 ‘sun’ time. I’ve also added the meridian line, as mentioned in the earlier Midday post. You’ll see that the Sun never seems to touch nor cross it.
So here’s the video:
If you look carefully, it’s a distorted figure 8. You can learn more about the shape at this Wikipedia article. To paraphrase it:
- The North-South change is due to the Earth’s tilt relative to the Sun
- The East-West change is due to the Earth’s tilt and that our orbit of the Sun is NOT a circle. It’s slightly elongated, into an ellipse.
How stars appear to move through the sky, in terms of time here on Earth, is very interesting and has a big surprise. It will certainly get a good working out in the future on this here Blog.
Maths Extra and Behind The Scenes
There are a few sites that show how the (relatively simple) maths & graphs of how the above items (tilt, ellipse) merge to create the figure 8 shape. The one I was thinking of doesn’t work any more, but this one is a start.
As for how I did this, well it took a while. I’m sure that Stellarium can automate tasks, in fact I know it can. BUT by the time I taught myself how to do it, I could have captured the 52 screenshots multiple times 🙂 It was simple: “]” to jump forward 7 days, then “Ctrl-S” to capture the screen shot.
The free and excellent video/audio toolkit ffmpeg was used to merge the 50+ images into a video. It was one command, repeat, one. And on Windows.
The last step was to use the free and magical DaVinci Resolve video editor to tidy things up, add the second copy of the video (to annotate with months), then finish up by adding the text & music.