3 More Numerical Fun Facts About Pluto
How big does the Sun look from Pluto? How bright would it be? And, if you could travel to Pluto, what would the sky look like? Keep on reading to find out!
As you’ve probably heard, after nearly 10 years en route, our intrepid piano-sized, space-exploring robotic friend, New Horizons, successfully made it to (and then sped on by) the dwarf planet Pluto. And the pictures we’ve received thus far have been nothing short of incredible. Those of us who have grown up knowing Pluto as little more than a faint smudge in the sky (which is all of us) have been introduced to a lovely and surprisingly interesting new world.
In anticipation of this historic arrival, last week we took a look at 5 numerical fun facts about the famous dwarf planet Pluto. And now, in celebration of New Horizons’ success, we’re going to take a look at 3 more. Namely, how big is the Sun from Pluto’s perspective? How bright does it appear? And, if you could travel to Pluto, what would the sky look like? Those questions—and their numerical fun fact answers—are exactly what we’ll be talking about today.
Fact #1: How Big Does the Sun Look from Pluto?
As you’ve probably noticed, the further away something is from you, the smaller it looks—trees look really big when you’re standing right next to them, but really small when they’re perched atop a distant mountain peak. As we learned last time, Pluto is currently about 33 times farther away from the Sun than the typical distance between the Earth and the Sun. So, given that things look smaller the farther away they are, and that the Sun is much farther away from Pluto than it is from the Earth, you might wonder: How big would the Sun look from Pluto?
From Pluto the Sun would look roughly 33 times smaller than it does from Earth.
The short answer is that, from Pluto, the Sun would look roughly 33 times smaller than it does from Earth. And that’s because the angular size of something—that’s the angle that the object appears to span from the perspective of the observer—is inversely proportional to the observer’s distance from it. So if one person is twice as far away from something as another, the person who’s farther away will see the object as being half as big in angular extent.
What would the Sun look like if it was 1/33 its current size (as it would from the surface of Pluto)? Well, the Sun and Moon are roughly the same angular size from our perspective, so we can answer this by thinking about what the full Moon would look like if its apparent angular size was shrunk down 33 times. The answer is that the Moon would appear to be right around the same size as the smallest details on the actual full Moon that we can currently just make out. In other words, the Moon would look like a point on the sky without any detail to it. Which is exactly how the Sun would look from Pluto—a point on the sky … just as the other stars appear to us.
Fact #2: How Bright Does the Sun Look from Pluto?
Since the brightness of a light source—whether it’s a firefly, a lightbulb, a traffic light, the Sun, or even an entire galaxy—gets dimmer and dimmer the farther away it gets, you might expect that the Sun would also appear much dimmer from Pluto than it does from Earth. And you’d be right. Given that the Sun appears to be only a point of light in the sky from Pluto’s perspective, you might wonder if it’d look just like one of the other thousands of stars in the sky.
From Pluto’s perspective, the Sun would appear to be about 1,089 times fainter than it is from Earth.
The cool thing about math and science is that we don’t have to be stuck wondering … we can actually do the calculation and figure it out. The key thing to know is that the brightness of a central light source (like the Sun in our solar system) decreases with the square of the distance from it. So if you double the distance between you and the Sun, the amount of light you see will drop 2×2=4 times. From Pluto’s perspective out at a distance of 33 times the typical Earth-Sun distance, the Sun would appear to be about 33×33=1,089 times fainter than it is from Earth.
How bright is that? Well, from our perspective here on Earth the daytime Sun is something like 400,000 times brighter than the full Moon, which means that, from Pluto, the Sun appears to be 400,000 / 1,089 or roughly 370 times brighter than the full Moon does to us. Take a minute to appreciate this, because it’s kind of wild. From Pluto, the Sun appears to be a point in the sky just like every other star. But, unlike those other stars, the Sun appears to be 370 times brighter than our full Moon!
Fact #3: What Would the Night Sky Look Like from Pluto?
Besides this impressively small and bright Sun, you might wonder what else you might see in the sky on your future vacation to ski the peaks of Pluto. Of course, you’d see lots and lots of other stars just as we do from Earth, and they’d look pretty much the same. And you’d also see Pluto’s (at least) 5 moons.
Most spectacular of these moons would be Charon. If you’ve been watching the New Horizons images coming in, you’ll have noticed that Charon is kind of the co-star in this whole affair. And that’s because Charon isn’t like the other comparatively small moons that we find throughout the solar system, Charon is relatively big compared to the object it’s orbiting. In fact, Charon’s diameter is about half that of Pluto’s. And a bit of fairly simple geometry will tell you that from Pluto’s surface, Charon would appear to be between 7 and 8 times as big in the sky as our moon does from Earth. If you were to extend your arm out in front of you while standing on Pluto, Charon would appear to be almost as wide as your fist—it would be a spectacular sight!
Wrap Up
OK, that’s all the Pluto-inspired numerical fun facts we have time for today.
For more fun with math, please check out my book, The Math Dude’s Quick and Dirty Guide to Algebra. And remember to become a fan of The Math Dude on Facebook, where you’ll find lots of great math posted throughout the week. If you’re on Twitter, please follow me there, too.
Until next time, this is Jason Marshall with The Math Dude’s Quick and Dirty Tips to Make Math Easier. Thanks for reading, math fans!
Image credit: NASA
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About the Author
Jason Marshall is the author of The Math Dude’s Quick and Dirty Guide to Algebra. He provides clear explanations of math terms and principles, and his simple tricks for solving basic algebra problems will have even the most math-phobic person looking forward to working out whatever math problem comes their way.
