by Chris Peterson » Fri Aug 24, 2012 10:11 pm
revloren wrote:OK, is it just me or does the line that the pair traces curve slightly upwards? :?:
Last time I checked, the earth rotates smoothly and regularly, therefore the track should be perfectly straight. Is the earth's rotation now suddenly wobbling? :!:
It is perfectly straight. But you normally can't project a straight line on the inside of a sphere to the flat plane of an image. Think about star trails- they appear to curve, and the closer they are to the pole, the greater the apparent curvature. But their paths are all straight, depending on how you define that, and what coordinate system you're using. And in this image, Venus has to come around to the same place the next morning (ignoring its slight shift due to its orbit). If the path was truly straight in the sense I expect you mean, that would be impossible. So its probably best to see each of these objects moving in a circle around the poles, since that's really how they show up in images.
[quote="revloren"]OK, is it just me or does the line that the pair traces curve slightly upwards? :?:
Last time I checked, the earth rotates smoothly and regularly, therefore the track should be perfectly straight. Is the earth's rotation now suddenly wobbling? :!:[/quote]
It is perfectly straight. But you normally can't project a straight line on the inside of a sphere to the flat plane of an image. Think about star trails- they appear to curve, and the closer they are to the pole, the greater the apparent curvature. But their paths are all straight, depending on how you define that, and what coordinate system you're using. And in this image, Venus has to come around to the same place the next morning (ignoring its slight shift due to its orbit). If the path was truly straight in the sense I expect you mean, that would be impossible. So its probably best to see each of these objects moving in a circle around the poles, since that's really how they show up in images.