Do planets twinkle like stars?

You know that stars “twinkle” in our night sky, by which we mean that they appear to move slightly or shimmer. But this twinkling is actually a phenomenon of Earth’s atmosphere, not of the stars themselves. You can see the idea by putting a coin at the bottom of a cup of water and stirring the water gently. Even if the coin remains stationary at the bottom, the stirring of the water will make it look like the coin is moving or shimmering. The twinkling of stars occurs for the same reason, except it is the constant movement of air in our atmosphere (rather than stirred water) that makes them twinkle.

The fact that twinkling is caused by our air means it must also affect planets. However, planets tend to twinkle a bit less than stars (though they shimmer quite noticeably when viewed through binoculars or telescopes). The reason is that while stars are so far away that they appear as single points of light even to powerful telescopes, the planets are close enough that they appear as tiny disks even through relatively small telescopes. This means that when you look at a planet by eye, you are actually seeing many rays of light at once, and so the twinkling of any one ray is often counteracted by that of another ray, making the planet appear to twinkle less.