Star Flashing Red, Green and Blue? Why Bright Stars Twinkle
A bright star low in the sky can flash red, green and blue and seem to dance about. This is twinkling: the starlight passes through a lot of turbulent air near the horizon, which bends and splits it. Sirius, the brightest star in the night sky, is the most common culprit.
What it looks like
- A single point flashing several colours quickly.
- Low in the sky, often in the south or near the horizon.
- Seeming to jitter or wobble but never actually travelling across the sky.
- Still there, in the same place, for hours.
How to check
- Our sky checker lists the brightest stars above the horizon at your time and place.
- Watch it against a fixed object like a chimney: over an hour it moves slowly with all the other stars.
- Higher in the sky, the same star twinkles much less.
Questions
Why do stars twinkle but planets don’t as much?
Stars are so far away they are effectively single points, so the atmosphere disturbs their light easily. Planets are tiny discs, which smooths the effect out.
Which star flashes colours?
Sirius is the most famous because it is the brightest, but any bright star low in the sky can do it.