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Monday, May 27, 2024

Earthsky Tonight—March 10: Is Sirius the most luminous star in the sky?

Courtesy of EarthSky
A Clear Voice for Science

Sirius in Canis Major

Look south at nightfall and early evening, and you can’t miss Sirius, the brightest star in the nighttime sky. Mia asks, “Isn’t there a brighter star in absolute magnitude which appears dimmer because of its distance?”

Yes, Mia, you are right. Sirius looks extraordinarily bright in Earth’s sky because it is only 8.6 light-years away. Many stars on the sky’s dome are intrinsically more luminous than Sirius, but appear fainter because they lie farther away. Apparent visual magnitude refers to a star’s brightness as seen by the eye from Earth and absolute visual magnitude measures the star’s brightness as it would appear to the eye at 32.6 light-years away.

At least three stars in the constellation Canis Major are thought to be thousands of times more luminous than Sirius: Aludra, Wezen and Omicron 2. Although the distances to these faraway stars are not known with precision, Aludra and Omicron 2 reside an estimated 3,000 light-years distant, and Wezen at 2,000 light-years.

At 32.6 light-years away, our sun would barely be visible as a speck of light, but Aludra, Wezen and Omicron 2 would outshine Sirius by some one hundred to two hundred times. At 32.6 light-years, Sirius would be about the same brightness as the Gemini star Castor.


The Stellar Magnitude System by Alan M. MacRobert

Written by Bruce Mcclure

Other Links:

Sky and Telescope

National Geographic

Space Com

Amazing Space

The York County Astronomical Society

Scope City

James S McDonnell Planitarium

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