How Bright Are the Stars?

BY DENNIS MAMMANA

Week of July 16-22, 2023

Much as we measure the intensity of natural phenomena such as earthquakes or tornadoes with a “magnitude,” we also use the term to refer to a star’s brightness. Unfortunately, many beginning stargazers are mystified by this concept.

It was the ancient Greek astronomer Hipparchus who, 21 centuries ago, compiled the first catalog of star brightnesses. In it, he listed the stars around the sky and rated their brightnesses on a scale of 1 to 6. He designated the brightest as first magnitude and the dimmest as sixth.

When astronomers began using modern technology to measure stellar brightnesses, they learned two interesting things. First, they found that each of Hipparchus’ magnitudes is about 2.5 times brighter than the next greater magnitude. In other words, a second-magnitude star is about 2.5 times brighter than one of third magnitude. And, secondly, they found that there were objects brighter than first magnitude, as well as countless objects fainter than sixth. So, they expanded the scale to accommodate these.

For example, stars 2.5 times brighter than first magnitude were termed zero magnitude. Vega, the brightest star now appearing high in the east at dusk, is a good case in point. Stars brighter than this were assigned negative magnitudes, and those stars fainter than naked-eye visibility were assigned larger magnitudes.

Remember that number line you learned in school? Thought you’d never see it again, didn’t you!

The range of celestial brightnesses is impressive. The sun shines at a stunning magnitude of -26, and the full moon appears at -12.5. This week, the planet Venus appearing low in the western sky at dusk shines at -4.7. The faintest objects seen by the largest professional telescopes have been measured to be about 30th magnitude.

BY TRACY BECKERMAN

My husband has never been a coffee drinker. He’ll go for an extremely sweetened cappuccino every now and then that would induce sugar shock in most people, but typically he’s more of a tea kind of guy. Still, he’s always respected our hot drink differences and although he’s suggested I decaf a bit, he’s never sunk to doomsday tactics to get me to give up caffeine. Then he started drinking this health food store green drink that smells like wet grass clippings and makes you want to moo when you drink it. It came with names like Daily Health Greens, Green Goodness and Field of Greens, which neither made me want to drink it nor skip through meadows of it.

Of course, once he discovered his new elixir, he became the poster child of green drink consumption. He extolled

Ancient Greek astronomer Hipparchus created the original system of classifying a star’s magnitude.

Now, throwing around numbers like this can be interesting, but to see how this brightness scale works, go outdoors after dark and look midway up in the northern sky. There, Northern Hemisphere stargazers should spot Polaris, the North Star. It’s not the brightest in the heavens as many beginners think; it’s rather faint -- only a second-magnitude star.

Streaming upward from Polaris after dark this week are the stars of the Little Dipper. This grouping is tough to see from anywhere near the bright lights of a city. From there, you’d be lucky to find Polaris and maybe two additional stars, but drive to a dark site in the wilderness and you’ll have much less trouble locating all seven stars of the Little Dipper.

Once you find it, you’ll discover that each of the Little Dipper’s “bowl” stars shines with a different brightness. The brightest is known as Kochab and