In January of 1801, astronomer Giuseppe Piazzi made a startling discovery. While charting the positions of the stars across several days, he noticed one of them appeared to move relative to the others. After tracking it for several weeks, he announced to the world that he had discovered a new planet.

He was mostly right. He had discovered Ceres, the first known asteroid. Then, due to a combination of sickness and poor astronomical alignment, Piazzi promptly lost it. The search to find it again required a brilliant mathematician and a brand new kind of math:

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The problem with trying to look at an asteroid like Ceres is that for half of the year, it's on the other side of the sun. Piazzi had just started making observations when he fell ill, and when he finally recovered enough to get back to his telescope Ceres had traveled out of sight.

Piazzi announced his results and triggered a race against the clock to find the new planet. Although Ceres was hidden for most of the year, it would be visible again by December, giving astronomers another chance to see it. But by that point it would have moved along its orbit, which means astronomers needed to figure out where it was going to be.

All they had to work with were Piazzi's few observations, which was not enough for most mathematicians of the time. There simply wasn't enough data, and estimates were wildly inaccurate. In order to really find Ceres again, new mathematics would be necessary.

Fortunately, new mathematics had already been invented. A few years earlier, a mathematician named Carl Friedrich Gauss had secretly developed a new statistical tool called the method of least squares, which made it easy to fit a line to a set of data points. Gauss used his method to estimate the orbit of Ceres very closely, and in December of that year an astronomer named Franz Xaver von Zach used those estimates to find Ceres.

Today, we still use Gauss's method of least squares to calculate the orbits of planets, comets, and asteroids. His technique of least squares lets us determine, from only a few observations, whether an asteroid is likely to collide with the Earth, and whether we need to consider it a threat. So you can sleep safe at night, knowing Gauss is protecting you from killer asteroids.

Source: Ted-Ed

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