Astronomy EssentialsToday's Image

Sirius in many colors

View larger. | A sequences of images of the star Sirius, via Amanda Cross.

Amanda Cross in Euxton, Lancs, UK caught the images above of Sirius – the brightest star in Earth’s sky, sometimes called the Dog Star – on December 11, 2017. She wrote:

This is the star Sirius early in the morning. I used a high ISO and 1/320 shutter speed. The colour flashes are picked up by the camera as the atmosphere splits the light from the star. No color enhancements were made to this image. This is how the camera picked up the colors.

Thank you, Amanda!

It’s true. When you see this very bright star low in the sky, it appears to flash in many different colors. These colors aren’t intrinsic to the star, but instead result from refraction, which splits starlight into the colors of the rainbow. Atmospheric refraction causes all kinds of strange optical effects, like bent crescent moons, and flattened suns. And it causes the brightest stars – like Sirius – to shine in many sparkling colors!

When you see Sirius higher in the sky, where you’re looking at it through less atmosphere, this star appears to shine more steadily and with a whiter color.

Read more: Sirius is Dog Star and brightest star

Sirius is part of the constellation Canis Major – the Greater Dog – looking super cute in this photo Tom Wildoner.
How can you be sure you’ve found Sirius? Orion’s Belt always points to it.

Bottom line: Composite image of the star Sirius, shining in many colors.

December 15, 2017
Astronomy Essentials

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