Welcome to my fourth “Science Answers” post! If you have a question, you can ask it in the comments here, or ask it in an email. Or find me on Facebook!
Q: (1) How did scientists find elements in the first place? Could there be more undiscovered elements? (2) How did scientists create the periodic table? (3) How do we know that everything is made up of atoms, when atoms are so small that they can’t even reflect light (a necessity for seeing them)? (asked by Mukesh Garbyal)
Really good questions! I was asked these in a comment on my post “Types of Atoms,” and chose to answer them in a post of their own.
Let’s take this apart. I actually want to address the third part of the question first, since it contains a misconception: atoms can reflect light. Their interaction with light is actually why we can see anything in the world.
Albireo is the distinctive double star in the head of the constellation Cygnus. You can find it yourself if you look for the Summer Triangle amid the dusty trail of the Milky Way across the night sky.
The brighter, orange star of Albireo is a K3-class bright giant. That means it’s just a few thousand Kelvins (Celsius degrees plus 273) cooler than the sun. But it’s also larger—70 times the sun’s radius—and that makes it brighter than you would expect.
The blue star, on the other hand, is a B8-class dwarf. It has only about 3.5 times the sun’s radius, although it’s hotter by about 7422 Kelvins.
Neither star in Albireo is particularly unusual. There are doubtless millions, even billions, of other stars similar to each one. But Albireo certainly offers us the most striking contrast. Bright blue and red stars don’t often appear so close together.
But what exactly gives these stars their distinctive colors?
When I was little, I remember hearing the ice cream truck all the time. Just the sound of the opening notes of “Pop Goes the Weasel” were enough to propel me to the door, where I’d beg my parents to let me go out.
Of course, I didn’t always make it out front in time. But one day, my dad found a way to solve that problem—by actually getting in the car and chasing the ice cream truck.
I remember us driving around the neighborhood, following that white truck around. A few times, it slowed and stopped, but when we stopped too, it kept going again. It took a while for the driver to realize we were following him!
Eventually, we caught it, and had a good laugh over it. But the moral of the story is…have you ever noticed that you can tell if something is moving toward you or away from you, just by if it’s getting louder or quieter?
If this quote really is from Cecilia Payne, then she had the right idea—at least for a female astronomer in the 1920s. Women in science back then faced an uphill battle to get recognized for any discoveries they made, and Payne was no different.
What’s so special about Payne, you might ask? Well, she wasn’t just one of the many “unsung heroes” of modern science. She was the one who figured out what stars are made of.
Yeah, that’s right. She sent a probe to the sun, collected a jar of star stuff, and brought it back to her laboratory…
Um, no, not really. It wasn’t that easy.
In fact, it was very difficult. She had far too many roadblocks than were fair. But she wasn’t out for money or recognition. She was just in it for the science. And science was what she got…
Meet the sun: a G2 class star towards the middle of its lifespan.
Wait a second…G2? What does that even mean?
It’s all part of a way astronomers break down the billions of stars in the sky and organize them by temperature. They can use a star’s spectrum to figure out what it’s made of, and that helps them figure out how hot it is.
But really…being able to read stellar spectra (plural for spectrum) is only so helpful. There are billions. It helps to have an organizational system.
That way, if an astronomer sees a stellar spectrum that looks a certain way, they can know immediately that it’s a certain class of star.
How hot would you say this star is? Take a wild guess.
Well…sorry, but I’m going to stop you for a moment just to make sure we’re all using Kelvins. The Kelvin scale is like the Celsius scale, except water freezes at 273 K instead of 0℃. 0 K is absolute zero, which is purely theoretical and doesn’t exist.
Now can you guess this star’s temperature?
I’ll give you another hint. This is a real photograph, so it’s impossible for this star to be any star other than our sun. How hot do you think our sun is?
Okay…I’ll tell you. It’s about 5800 K, which—for those of you unfamiliar with Kelvins—is about 5527℃. Kinda crazy, huh?
Next question. How do we know this? I mean, it’s not like we stuck a thermometer in the sun’s surface and actually measured it, right?
Astronomers know that if white light passes through a prism and is bent, it’s separated out into its component colors—the colors of the rainbow.
Astronomers also know that when light interacts with atoms, the building blocks of the universe, the atoms absorb photons of light and reemit them—but in a different direction.
Put these two bits of knowledge together, and astronomers now have everything they need to understand spectra (the plural for spectrum).
A spectrum is something I’ve covered in previous posts. In astronomy, it means the wavelengths of electromagnetic radiation spread out so we can analyze them individually. And it’s an astronomer’s most valuable tool.
So, what exactly is a spectrum, and how can we use it to analyze radiation from space and learn more about the universe?
Really hot. Hot enough to have energy to spare for their planets. If our star wasn’t hot, we couldn’t live on Earth. And our star isn’t even particularly hot for a star. It’s a middle-aged star of low mass, so it’s relatively cool compared to other stars.
You might also notice that stars aren’t all the same color. There are redder stars and bluer stars and more whitish stars.
We know stars are hot. They’re also bright. And they’re different colors. But how does that all translate to radiation—and how can we see it?
Everything we know about space comes from radiation.
Now wait just a moment here. That statement explains how astronomy is such a successful field of science—it’s based entirely on the information we can glean from radiation, after all. But how does that make sense?
I mean, it’s one thing to study radiation. It’s quite another thing to study matter, the “stuff” in the universe. How does one have anything to do with the other?
Well…that’s where atoms come in. Radiation does, in fact, have a lot to do with the “stuff” it comes from. And if it weren’t for that basic principle, astronomy as a science wouldn’t work.
Thankfully for astronomers, it does. So what’s the secret, then? What does radiation have to do with matter?
I’m going to venture a wild guess and say you haven’t, since scientists have only recently been able to take this kind of image. I learned about it in my biology class this semester, and the professor said that it was a landmark achievement.