This evening, be on the lookout for one of the brightest stars in the sky. It is so shiny that each year in northern autumn, people in the Northern Hemisphere ask us about a flashy star, sparkling with red and green flashes. You can spot it low in the north-eastern sky at nighttime or evening hours as seen from mid-northern areas. The star is probably Capella – а golden star.
Moreover, if you could fly to space, you’d notice that Capella is actually two golden stars, each with nearly the same surface temperature as our local star, the sun. However, each one of them is bigger and brighter than our sun.
Capella is in the constellation of Auriga the Charioteer, but it has been called the Goat Star since ancient times. You could spot it by looking northeast from the latitude of the Northern Hemisphere. The best chance for this is the evening hours in October. Capella climbs up in the nighttime. So, this month, a few hours before dawn, it will be high above.
We have a golden beam of light that shines red and green when it’s low in the sky. But the question is, how does that happen?
The truth is, every star in the sky experiences the same process as Capella, creating its vibrant twinkling. Therefore, a star’s light must glow through Earth’s atmosphere before it enters our eyes. Not every star shines as visibly as Capella. The flashes are occurring because, at this time of year, Capella is low in the sky in the evening. So, when you look at an object that is low in the sky, you look at more atmosphere than when the same thing is above.
The atmosphere separates or “refracts” the light of the star, just like the prism breaks the sunlight.
So that’s where the red and green flashes of Capella come from; not from the directly from the star, but from the refraction of the light by our atmosphere. However, when Capella is higher up in the sky, you will not be able to see these red and green flashes.
You may ask yourself, why are these color flashes so visible with Capella? The explanation is that it’s simply a bright star. More precisely, the sixth brightest star in Earth’s sky, not counting our sun.
To sum up: You will be able to see a bright star, which is likely Capella, twinkling with red and green flashes if you live in the Northern Hemisphere of our planet. The best time for this would be October evenings – you will catch it low in the northeastern sky.