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Watch for Sirius, sky’s brightest star

Is October 4, 2017 the Harvest Moon? Click here to find out!

Also, be sure to watch for Mars and Venus during their close conjunction on the morning of October 5. Click here for more info. And know that you can see these two worlds – still close – throughout this weekend.

And – if you’re up early watching for Venus and Mars – take a moment to see the sky’s brightest star, Sirius, on these October mornings. This star is so brilliant that you can easily see it on a moonlit night in from a light-polluted city. Click here to find out when Sirius will rise tonight from your part of the world.

Andy wrote:

Early this morning, looking southeast, I saw a beautiful star, bright and multicolored … Can you identify it for me?

And Paula wrote:

This morning two of us got up early. We found a pulsing star straight down the sky below Orion’s Belt. It was pulsing the colors of green, yellow, blue and red like a strobe light. I will search for it every morning as it was so enchanting.

This star is enchanting, so much so that – every year, beginning in Northern Hemisphere autumn – we get many, many questions about a multicolored star twinkling in the southeastern to southern sky after midnight. This star typically turns out to be Sirius, which is in the constellation Canis Major the Greater Dog and is sometimes called the Dog Star.

Sirius is now rising in the southeast in the hours after midnight and can be found in the south at dawn. Notice that a line from Orion’s Belt points to Sirius.

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View larger. | Brightest star Sirius on left, with constellation Orion. See how three stars of Orion’s Belt point to Sirius? This photo from EarthSky Facebook friend Susan Jensen in Odessa, Washington. Thank you, Susan!

Sirius appears to flash different colors when it’s low in the sky. Really, all the stars are flashing different colors, because light is composed of all the colors of a rainbow, and the journey through our atmosphere breaks starlight into its component colors via refraction. But you don’t notice the colors of the other stars much, because they’re not as bright as Sirius, which is the brightest star visible from anywhere on Earth.

Since our atmosphere is causing the light to break into its colors, and since Sirius is often seen low in the sky now (where you are peering at it through a thicker layer of atmosphere than when it’s overhead), the flashing colors of Sirius are very obvious. When Sirius is higher in the sky – which it is close to dawn in the month of October – or in the evening sky in January and February – you’ll find that Sirius shines with a steadier, whiter light.

So, on these October mornings, watch as Sirius winks at you in the wee hours before dawn!

More about Sirius: Dog Star and brightest star

Bottom line: We get many questions about a bright, colorful, twinkling star on these October mornings. It’s the star Sirius in the constellation Canis Major, brightest star in the sky. The bright planet Venus is also up before dawn now. But you’ll know Sirius, because Orion’s Belt always points to it.

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Deborah Byrd

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