Twinkle, Twinkle, Little Star ...

Dennis Mammana
Mon, 05 Jan 2026 21:00:00 -0800
Lifestyle

Week of January 11-17, 2026

We on planet Earth thrive under a thick atmosphere of oxygen, nitrogen and other gasses; it not only sustains life on our planet but affects everything we astronomers see beyond.

Stargazers rarely think about this, but we must always be aware. Sure, it's easy to know when weather disrupts our observations, but there's much more to the story.
Updated: Tue Jan 06, 2026

Week of January 11-17, 2026

We on planet Earth thrive under a thick atmosphere of oxygen, nitrogen and other gasses; it not only sustains life on our planet but affects everything we astronomers see beyond.

Stargazers rarely think about this, but we must always be aware. Sure, it's easy to know when weather disrupts our observations, but there's much more to the story.

For example, dust, moisture and other particulate matter can become suspended in the atmosphere and reduce its transparency. We notice this on a hazy day when distant mountains don't appear quite as clear as they might otherwise.

The atmosphere also tends to redden the colors of all light coming from space. Just as the air separates the sun's bluish light from its spectrum and gives our star a more yellowish cast (just check any child's drawing of the sun!), it does the same with the stars. With faint starlight, it's very subtle, but watch the moon rise or the sun set some evening — you'll see the effect easily.

One of the most astronomically disturbing features of the atmosphere is that it's so turbulent. Weather systems come and go, the jet-stream swirls overhead, and more. As starlight travels through the vacuum of space, its path is straight, but once it hits our thick, turbulent atmosphere, it is bounced around thousands of times each second, causing the star to twinkle or, in astronomer-speak, "scintillate."

The amount of twinkling a star displays depends on the steadiness of the air through which its light must pass, and the more turbulence there is, the more a star will appear to twinkle. That's why a star low in the sky seems to flicker and flash more than one overhead; its light must pass through a much longer column of turbulent air on its way to our eyes.

Nowhere in the sky is this effect more obvious this week than low in the southeastern sky, as the bright star Sirius appears to twinkle wildly after dark. You may also notice that the star appears to fire off colorful sparks as well.

This is a perfectly natural phenomenon. The star's light is actually a blending of every color of the spectrum, and each is bent rapidly in different directions at different times by moving air currents. Because of this, Sirius seems to become a dramatic and colorful sparkler! For an even more dramatic effect, check it out with binoculars or a telescope thrown slightly out of focus.

Wait a while for the Earth to rotate and the star to rise higher in our sky, however, and Sirius will appear brighter and whiter, and will twinkle much less dramatically.

You might wonder why this effect does not occur with the planets or the moon. It does, but since these bodies are much closer and appear larger in our sky, they seem to shimmer rather than twinkle when seen through a telescope.

All this bouncing light makes it difficult for astronomers to get sharp views or images, and it's why we send telescopes into space. Despite these issues, however, twinkling stars are still fun to watch.

Check out Sirius this week, and you'll see what I mean!

The Earth's thick atmosphere causes the scintillation, or "twinkling," we see when we look at stars.