johnnydeep wrote: ↑Sat Dec 12, 2020 4:19 pm
So, assuming the left-most planet images are the oldest and the right-most the newest, it looks like Jupiter and Saturn ended up farther
apart on Aug 28 than they were on June 19. Yet they will apparently get closer
together from Aug 28 to Dec 21?
Yes, this is correct. It didn't bother me all summer that they did not seem to be converging until I heard that they'd be in conjunction on Dec 21. At that point, probably in early August, I started watching for them to get closer, and it seemed to me that they were not making near enough progress to get there by Dec 21. Then it finally occurred to me why this is. (I'm elaborating on De58te's description with some visual aids.)
Click to enlarge
I have the following, which is very approximate, taken from solarsystemscope.com
In the first image, on June 21, 2020, you can see that Jupiter and Saturn are near opposition from the Sun, viewed from Earth. And it looks like they should be pretty close in the sky. Then, if you look at the positions each month following, you can see that Jupiter is slowly "catching up" to Saturn. Throughout the next 6 months, it slowly slides between Saturn and the Sun (Saturn comes into opposition as viewed from Jupiter). But the motion of the Earth during this time is much more dramatic and is having the most significant effect on the alignment of the two giant planets from our viewpoint. Indeed, it looks as though some time in early November, we reached our maximum elongation (from the view of the giant planets). This would have increased the angle between them that we saw, even as Jupiter's progress was trying to reduce it. But then, finally, as the Earth began to get to the far side of the Sun from the giant planets, our own position will finally help us to see them lined up. We're not fully around to the opposite side from them, but we reach a point very close to being on a line drawn through Saturn and Jupiter on Dec 21.
One unfortunate thing that this shows is that as they've come into conjunction, they're quite a bit farther away from us now than they were in the summer. So they're going to appear quite a bit smaller in a telescope on Dec 21 than they did last summer.
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