

Sunshine lights the scene at Holy Rosary School in Duluth Wednesday morning. The sun is 93 million miles away and converts hydrogen in its core to helium (nuclear fusion), creating energy in the process. Photo: Bob King

The sun commands a powerful presence in our lives. Burning hydrogen as fuel, its radiant orb provides the necessary heat to keep our planet warm, alive and thriving. We’re so close to it, relatively speaking, that the sun is much too bright and dangerous to look at directly. Even though we know that all those other tiny dots in the nighttime sky are other suns, we don’t have an intuitive feel for their true brilliance and fierce heat. Our sun stands apart and our lives depend upon its reliability.



An artist’s view of Pluto’s icy surface and its moon Charon. The sun, at upper right, would appear as a brilliant laser-like point of light. Credit: ESO/L. Calcada

That got me to thinking how far you’d have to travel away from the solar system to see the sun’s stature reduced to that of a nighttime star. At first, you might think that buzzing out to the dwarf planet Pluto in the chilly outer burbs would do the trick. At around three billion miles away, the sun would be reduced to a brilliant point of light 1000 times brighter than the full moon. Ever accidentally look into a laser beam — that’s what the sun would look like. That’s plenty bright to illuminate Pluto’s bitter cold landscape of methane ice. While you wouldn’t be able to resolve the sun’s disk with your naked eye, it would appear about as big as Jupiter’s disk does through a small telescope here on Earth. You’d just make out the shape at about 10x magnification.



The sun is similar in size to the two brightest stars in the Alpha Centauri triple star system. Credit: David Benbennick

While Pluto hints at what’s to come, we’ll need to travel further to lose the sun among the starry multitude. Let’s stop at Alpha Centauri , a triple star 4 1/2 light years away and the nearest star beyond the sun. We’re going to assume we can stand on an Earthlike planet there and look up into a clear night sky. When we do, we would notice a bright, new star just to the left of the W of Cassiopeia. A keen-eyed observer might even discern its pale-yellow tint. That’s good old sol!



The sun appears in Cassiopeia in the sky above an imagined planet orbiting Alpha Centauri. Our star would shine a bit fainter (half a magnitude) than Vega, the brightest star in the Summer Triangle. Vega is almost directly overhead at nightfall in early August. Created with Stellarium .

The sun from Alpha Centauri would be almost as bright as Vega in the Summer Triangle and easily make the Alpha Centaurians "Top 50 brightest stars" in the sky list. How about the view through a telescope? Just a point of unresolved light like all the others. No planets would be visible either; all would be too close to the sun and hopelessly lost in its glare. If we continued our journey to Sirius, which is 8.7 light years distant and the brightest star in our earthly sky, the sun would only be as bright as the stars of the Big Dipper. According to the Inverse Square Law , every time you double the distance, a star’s brightness fades by four times.

Writing this is starting to give me the chills, so let’s pull back from deep space and once again enjoy the pleasure of the sun’s company on this fine August day.