If you’re fortunate enough to live somewhere where the stars are visible, those of us who live in cities hope that you’re taking advantage of it. Sure, we can see the moon when it’s out — maybe an occasion planet if it’s bright enough — but not much beyond that. Then there are the moments when it looks like we can see a star — realise that it’s moving, hoping it might even be a shooting star — only to realise it’s an aeroplane.
But not every blinking object in the sky is a plane. In fact, there’s one star in particular that flashes red and green this time of the year. Here’s how to spot it.
How to find the Capella star
Each autumn, those in the Northern Hemisphere have the opportunity to see the Capella star low in the northeastern sky at nightfall or early evening. According to EarthSky, it’s a golden star — actually, two golden stars — both larger and brighter than the sun, and roughly the same temperature.
Capella’s most notable feature is that it appears to flash red and green, like a single celestial holiday light bulb. It rises in the sky throughout the night, ending up directly overhead early in the morning, but your best chances of seeing the red and green blinking light is early evening.
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Why does it flash green and red?
Turns out, all stars visible from Earth go through the same process, per EarthSky:
Every star’s light must shine through Earth’s atmosphere before reaching our eyes. But not every star flashes as noticeably as Capella. The flashes are happening because Capella is low in the sky in the evening at this time of year. And, when you look at an object low in the sky, you’re looking through more atmosphere than when the same object is overhead. The atmosphere splits or “refracts” the star’s light, just as a prism splits sunlight.
Though we can’t see this happening with other stars, Capella’s massive size simply makes it easier for us to spot.