why does venus flicker?

  • I was watching Venus with the naked eye yesterday at about 7 pm and I noticed that it was flickering, almost like a star.

    I have always learned that planets don't flicker to the naked eye, only stars (indeed, every other time I've seen a planet it wasn't flickering), so I was rather confused. I even checked Stellarium to make sure that what I was seeing was, in fact, Venus.

    Does anybody have an explanation for that behaviour?

    Thank you all.

    Personally I've seen Mars scintillate almost every time I've watched it, so I can tell you that planets are capable of flickering. In Mars' case it's more of a change in color than a change in brightness; I'm not sure why. I've never seen Venus scintillate, but then I don't go looking for Venus very much at all. I've never seen Jupiter or Saturn scintillate though, probably because I only notice them when they're high in the sky at night.

  • Because planets actually do twinkle. Most people were told that the major difference between stars and planets is that only the former twinkle - but that's an oversimplification. Given the right conditions, planets will twinkle too, it just happens more rarely.

    Several factors that contribute to it:

    • lots of air turbulence; or, as astronomers call it, "bad seeing"

    • closeness to horizon; if the planets are high in the sky, the air column is shorter so there's less chance they will twinkle; but when they are low, their light goes through more air and so it is perturbed to a larger degree

    The observation you've made, Venus twinkling, is not very unusual. Many stargazers are used to seeing that once in a while. I've seen Venus scintillate several times in the past, always at sunset when it was about to drop below horizon; I would presume you could see the same behavior very early in the morning as Venus has just risen.

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Content dated before 7/24/2021 11:53 AM