Cosmic Quiz Question: Why do stars twinkle?

Seth Jarvis

Thanks to all of you who submitted questions to the Clark Planetarium, KUTV-2 Cosmic Quiz. Our first week’s winner, William Whetstone, asked us, “Why do Stars twinkle?”

Stars “twinkle” because of turbulence in Earth’s atmosphere. The atmosphere acts like a big, imperfectly formed sheet of glass through which starlight has to pass before it arrives at your eyes.

Starlight, even from the brightest stars, is a point source of light, which means they have no visible diameter. Because they’re a point source the slightest change in the optical properties of our atmosphere makes stars look like they’re jittering around slightly in space – what we call “twinkle.”

Because the atmosphere is turbulent the density of the air between you and the starlight is always changing a little bit. These shifting densities are constantly changing the direction and the amount of bending of starlight on its way down through the air to your eyes.

Planets don’t generally twinkle because instead of being point sources of light they actually have a visible diameter. The planet’s diameter may appear to be tiny to you, but it’s still big enough to average-out most of the small changes in the refraction of light due to atmospheric turbulence.

Hubble Telescope - NO TWINKLING!

Hubble Telescope - NO TWINKLING!

Astronomers put the Hubble Space Telescope in space above Earth’s atmosphere in order to eliminate the twinkling of starlight. Hundreds of miles overhead, out of our atmosphere, it sees space with a clarity that only a generation ago would have been difficult to even imagine.

Today, ground-based telescopes shoot lasers into the atmosphere to identify exactly what kind of twinkling is going on overhead. This information allows astronomers to use computers and mirrors that can rapidly wiggle themselves to cancel out twinkling (called “adaptive optics”) to see distant objects in space almost as well as the Hubble Space Telescope.

Adaptive Optics Laser

Adaptive Optics Laser

If you would like to have your astronomy questions answered, submit them on our website for a chance to win four tickets to Clark Planetarium!

One thought on “Cosmic Quiz Question: Why do stars twinkle?

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