That's not really true. Planets can twinkle too, if air turbulence is great enough. They just are much less suceptible to it. Since it was low on the horizon, it also had to go through many more layers of air as well, making it even more likely to twinkle.

But it's gotta be Venus. Most people just can't believe how bright it can get. Mars wouldn't be involved unless it was literally right on top of Venus, which I seriously doubt is the case right now.

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...And that, my liege, is how we know the Earth to be banana-shaped. --Sir Bedevere