Saturn is twice as far as Jupiter is from Earth according to a quick Google search. But I needed to understand why do they appear as if they are the same size. I mean as if they are not far apart. For a common man's understanding things that are far should appear smaller than they are, right? What is the reason behind it?

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    $\begingroup$ You cannot say that Saturn must appear to be smaller just because it is astronomically far. $\endgroup$ Dec 23 '20 at 8:08
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    $\begingroup$ Saturn is quite visibly smaller than Jupiter when looking through a telescope. The rings of Saturn make it appear bigger, but there is quite a difference in the size of the planets $\endgroup$
    – MCG
    Dec 23 '20 at 8:32
  • $\begingroup$ You do realize that stars are present many light years away from Earth but all of them appears as twinkling dots. $\endgroup$ Dec 23 '20 at 13:29
  • $\begingroup$ Yes I do, but I am talking about planets here. They don't have their own light source and not light years away. So it's different here $\endgroup$ Dec 23 '20 at 19:19

Our eyes are not good enough to see the difference; Jupiter has an angular diameter of 29.8" to 50.1", while Saturn's is 14.5" to 20.1"; with rings, which are about 2.25 times as wide as the planet, this becomes 32.6" to 45.2". All well within the 60" (1 arcminute) angular resolution of the human eye.

Now, when you use a telescope, you can see the difference in size. Note that the diameters given above are ranges; they depend on the distance of the planets to Earth. In opposition, the diameters are near the upper end and Jupiter is larger. However, right now they are near conjunction (with the Sun, not necessarily with each other) and the diameters are more near the lower end. You see that Saturn (with rings) in conjunction actually appears larger than Jupiter, so if you count the rings, or your telescope is simply not magnifying enough times to separate Saturn's rings from the planet, it may appear as an ellipse whose longest axis is the same size as Jupiter.


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