20 years after it launched, the NASA spacecraft Cassini ends its mission today. Its 13 years in orbit culminate in one last mission: to dive into the planet’s atmosphere, while still measuring and transmitting data.
Mauna Kea is an enormous, exinct volcano on Hawaii’s Big Island, and one of the best places on Earth to do astronomy (if you ask them, the best one). In fact, the summit of the mountain hosts one of the world’s most renowned observatories. What makes it so special, other than that it looks like this?
Think about it: the idea that the Sun is essentially the same thing as any star doesn’t make any sense. I mean, just look at them, they could hardly be more different!
So how the heck do you go about proving such an outrageous idea?
Well, it’s been quite a long journey, that started from a number of guesses by ancient “scientists”. Granted, some of them turned out relatively correct, but others involved fiery stones hanging from the sky.
The first actually scientific step came only in 1838, when we learned how freaking far way stars are. German astronomer (among other things) Friedrich Bessel measured the distance to a star—now known as 61 Cygni—for the first time, without assuming anything about what the star was like. It turned out to be thousands of time farther than the Sun. Hundreds of thousands of times.
If they’re so far away, people concluded, stars might actually be as big as the Sun, if not bigger (spoiler: they get a lot bigger). But are they the same thing?
Shortly thereafter, we learned to read the chemical composition of a star from its light. Each element inside it, we learned, absorb light in a specific way. So when we look at the light from the star through a prism, we can see the thin black bands the elements leave behind and reverse-engineer what they were.
Then, we figured how to relate the colors (more exactly, the wavelength) of starlight to their temperature. As the video below explains, everything with a temperature—aka everything—glows, and it does in a particular way, depending on how hot it is. Only quantum mechanics explained how and why, but it works: it’s how infrared thermometers operate.
Altogether the Sun turned out about average in size, temperature and composition. Yet, it was a special star: the only one we knew to have planets. That, too, changed. It took a while (until the 1980s), but nowadays we find exoplanets—planets orbiting other stars—by the thousands.
So the Sun is just a star. We’ve thought about the universe and literally just looked at it, and we understood something so violently counterintuitive. No star that we know is home to anything with such remarkable ability. And that, I think, is pretty special.
If you want more
- Nobody measured the distance to a star before Bessel because, at the time, it was really hard. Here’s a wikipedia page on the ingenious method he used.
- Actually, quantum mechanics was born trying to explain how things glow depending on their temperature. This video from PhysicsGirl explains how