APOD: Sunrise, Moonrise (2011 Jan 06)

[Chris Peterson]

Alright, it is almost always smaller near the horizon. <g>

Exactly. Your image shows what the Sun looks like in most cases when it's near the horizon- quite a bit smaller in area than it is when higher.

[eaglekepr]

I suspect that the zoom lens shifted (or was misadjusted) slightly between exposures, resulting in the actual Sun images being made at something other than exactly the same focal lengths.

Agreed... although I wouldn't try to use an artistic compilation of manipulated images taken with an imprecise consumer kit lens (aka "cheap" Canon EF-S 18-55mm by the look of it) to make factual scientific judgments on measurements in any case

[Chris Peterson]

Agreed... although I wouldn't try to use an artistic compilation of manipulated images taken with an imprecise consumer kit lens (aka "cheap" Canon EF-S 18-55mm by the look of it) to make factual scientific judgments on measurements in any case :lol:

Right. Actually, this case is just the opposite: we know on solid scientific grounds that the Sun's apparent diameter isn't changing. We can therefore use the Sun as a scale reference, and make some deductions about the equipment and method used to produce the image. What we know about the Sun and atmospheric optics informs us about the image, not the other way around.