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Western Slope Skies: The Wonder of a Twinkling Star

If you’re anything like my two and a half year old daughter, you picked up this melody at an early age. The lyrics communicate the child-like wonder that one feels when looking at a twinkling star. While gazing at that mystical point of light, time and space seem to disappear, if only for a moment. Even us older stargazers can still find plenty to wonder about when it comes to twinkling stars.

To start, we might ask: are these glittering stars actually twinkling? Put another way, is the light emanating from these stars fluctuating? In short, no! Starlight is constant. What then causes the perceived variation in light and even color? The culprit is the Earth’s atmosphere.

The atmosphere is composed of a variety of different gasses, all held around Earth by our planet’s gravity. These gasses vary in density and temperature, causing them to rise, fall, and swirl around as atmospheric conditions change. When starlight shoots through this moving air, it bends and bounces around rather than maintaining a straight line. This irregular light path causes stars to appear to twinkle, and light refraction (or bending) can even cause that light to change color. Astronomers call this effect “atmospheric scintillation.” You could compare it to looking across the landscape on a hot summer day and seeing a distant tree appear to wiggle as hot air ripples up from the ground.

Stars near the horizon often twinkle more than stars directly overhead because starlight at the horizon passes through even more of the atmosphere than the stars that are directly above you. While stars flicker and change color due to this effect, planets do not. This is because stars are much farther away from us than planets. Thus, starlight enters our atmosphere as an unstable pinpoint of light, while the light that planets reflect from the sun enters as a wider and more stable beam.

Though the real reasons for star twinkling are atmospheric scintillation and light refraction, you can see why such terms didn’t make it into the Twinkle Twinkle Little Star lyrics that we know so well. Apart from containing too many syllables and sounding quite technical, these words ultimately fail to sufficiently express the awe we feel while watching stars flicker on a dark night. For that, perhaps another stanza of the song, originally published as a poem by Jane Taylor in 1806, would be more appropriate:

'Tis your bright and tiny spark,
Lights the trav'ller in the dark:
Tho' I know not what you are,
Twinkle, twinkle, little star.

Western Slope Skies is produced by the Black Canyon Astronomical Society and KVNF Community Radio. This feature was written and voiced by Gina Loewen.