Twinkle, Twinkle, Little Star

Twinkle, twinkle, little star. Just a children’s song, right? It turns out this memorable melody has a lot more truth than you might think. On most nights, the stars appear to flicker as a result of minor refractive shifts in color as the starlight passes through the different layers of atmosphere.

If you look closely, however, you’ll notice that the planets appear bright and steady, no flicker whatsoever. Why is this? Stars are so far away from Earth that to the eye they only appear as bright pinpoints of light even with high magnification, with no resolvable surface area. The light that reaches your eye is coming from such a narrow beam of light that even minor disturbances or refraction in the atmosphere cause visible shifts that our eyes detect as flicker.

Planets on the other hand are much closer to us, which makes them appear much larger in the sky, relatively. With moderate magnification surface features are visible and the planets’ discs have a clear width, unlike a star which will appear as still just a point, though brighter than without magnification. This visual surface area makes planets less susceptible to atmospheric effects as there is more angular surface area to spread the atmospheric effects over, minimizing the effect.

A good field “sanity check” to confirm that you are indeed looking at a planet and not just a background star is to check for flicker: planets are still, stars twinkle.

This episode of StarTalk covers more on this topic:

Don’t forget to view Mars in the eastern sky after twilight, having just passed opposition it will remain prominent for the coming weeks and visible the rest of the year.

Join us Wednesday Oct. 21 @ 6:00 PM for our free program: “Tour of the Cosmos” where we’ll explore the night sky in steps moving out from Earth to the edges of the known universe. Email Register@StandleyLakeStargazing.com to sign up!

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Stay well, and clear skies!