Happy Aphelion Day, everybody!
July 6, 2018, marks the point on Earth’s orbit where we are the farthest from the Sun. Orbits are elliptical, not circular, and ours is no exception. The degree to which an orbit deviates from circular is called its eccentricity, and that ranges from the very low, almost circular (like ours), to the very high, extremely elongated (like a long-period comet).
Today, we are 1.0167 AU, or astronomical units, from the Sun. One AU is conveniently defined as the average orbital distance from Earth to the Sun, so we are a whopping 1.67% farther away than average, and also moving at our slowest along our orbital path – not unlike how a baseball slows down at the top of its arc before accelerating back toward the ground, we’ve reached the apex of our flight. Today, the Sun’s apparent size is at its smallest, and I’m sure we can all feel the chill of the extra distance! (Kidding, though we are seeing less solar radiation today, on average, than during the rest of the year).
This little tidbit is another mystery of the observable universe that was solved, and understood, by people who did nothing more than make very careful observations. I hope you appreciate knowing it!
Get Out There