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What’s that flashing star?

Northern Hemisphere autumn – across the month of October – is when folks most frequently ask us:

What’s that brilliant star twinkling with purple and inexperienced flashes?

There are three brilliant stars you would possibly discover flashing or twinkling fiercely on an October night time. You would possibly discover glints of shade from all of those stars. They’re: Capella in Auriga, Arcturus in Boötes and Sirius in Canis Main.

Capella is brilliant. It shines at magnitude 0.24, making it the Sixth-brightest star in Earth’s sky, not together with our solar. And it’s low within the sky, within the northeast route, at dusk or early night as seen from mid-northern places right now of yr. Simply step outdoors this night and look northeast. See a flashy star? It’s in all probability Capella.

If you happen to may journey to this star in area, you’d discover that Capella is absolutely two golden suns, each with roughly the identical floor temperature as our solar, however each bigger and brighter than our solar. Capella is the brightest star within the constellation Auriga the Charioteer. However since antiquity it’s carried the title Goat Star. You would possibly decide it out simply by gazing northeastward from a Northern Hemisphere latitude in the course of the night hours in October. To make sure you’ve discovered Capella, search for slightly triangle of stars close by, an asterism known as The Children.

Why do stars flash colours?

The fact is that each star within the sky undergoes the identical course of as Capella to provide its colourful twinkling. That’s, each star’s gentle should shine via Earth’s environment earlier than reaching our eyes. However not each star flashes as noticeably as Capella. The flashes occur as a result of Capella is low within the sky within the night right now of yr. And, while you take a look at an object low within the sky, you’re trying via extra environment than when the identical object is overhead. The environment splits or “refracts” the star’s gentle, simply as a prism splits daylight.

In order that’s the supply of Capella’s purple and inexperienced flashes. Simply know that they’re not from the star itself. The refraction of its gentle in Earth’s environment causes them. Once you see Capella greater within the sky, you’ll discover that these glints of purple and inexperienced will disappear. Why are these flashes of shade so noticeable with Capella? The reason being merely that it’s a brilliant star.

Now right here’s one other brilliant flashy star you would possibly discover in October:

Arcturus is a flashing star, too

Arcturus is within the constellation Boötes the Herdsman. It’s an orange-colored star, within the northwest (from northerly latitudes) within the night in October. You possibly can at all times inform you’ve discovered Arcturus should you discover the Massive Dipper close by. The arc of the Massive Dipper’s deal with might be prolonged outward to Arcturus. See the chart above.

Arcturus is about the identical brightness as Capella, however it’s not as noticeable for one massive cause. On October evenings, Capella is ascending within the sky. Arcturus is descending. So Capella shines a lot of the night time, whereas Arcturus units not lengthy after the solar.

And at last, our nomination for third flashiest star of October is …

Sirius is legendary for its twinkling

Sirius within the constellation Canis Main the Larger Canine is the brightest star within the night time sky. And this star is legendary for twinkling in several colours. Sirius is now within the south earlier than daybreak, as seen from the Northern Hemisphere (greater within the sky earlier than daybreak for the Southern Hemisphere).

For instance, Paula wrote in October:

This morning two of us bought up early. We discovered a pulsing star straight down the sky under Orion’s Belt. It was pulsing the colours of inexperienced, yellow, blue and purple like a strobe gentle. I’ll seek for it each morning because it was so enchanting.

Questions on a flashing star

We get many, many questions each autumn a couple of multicolored star twinkling within the southeastern to southern sky after midnight. Sirius seems to flash totally different colours when it’s low within the sky. Actually, all the celebs are flashing totally different colours, as a result of gentle consists of all the colours of a rainbow, and the journey via our environment breaks starlight into its element colours through refraction. However you don’t discover the colours of the opposite stars a lot, as a result of they’re not as brilliant as Sirius (or Capella or Arcturus).

Since our environment is inflicting the sunshine to interrupt into its colours, and since Sirius is commonly seen low within the sky now (the place you’re peering at it via a thicker layer of environment than when it’s overhead), the flashing colours of Sirius are very apparent. When Sirius is greater within the sky – which it’s near daybreak within the month of October – or within the night sky in January and February – you’ll discover that Sirius shines with a steadier, whiter gentle.

Need a particular view out of your location on the globe? Go to Stellarium and enter your location.

Backside line: We get many questions on brilliant, colourful, twinkling stars on these October nights. There are three stars we hear about most frequently: Capella, Arcturus and Sirius.