Category: mercury

This One Puzzle Brought Physicists From Special To General Relativity

“With an average speed of 47.36 km/s, Mercury moves very slow compared to the speed of light: at 0.0158% the speed of light in a vacuum. However, it moves at this speed relentlessly, every moment of every day of every year of every century. While the effects of Special Relativity might be small on typical experimental timescales, we’ve been watching the planets move for centuries.

Einstein never thought about this; he never thought to calculate the Special Relativistic effects of Mercury’s rapid motion around the Sun, and how that might impact the precession of its perihelion. But another contemporary scientist, Henri Poincaré, decided to do the calculation for himself. When he factored in length contraction and time dilation both, he found that it led to approximately another 7-to-10 arc-seconds of orbital precession per century.“

Special Relativity was easy enough to discover in a certain sense: the Lorentz transformations, Maxwell’s equations, and the Michelson-Morley experiments had been around for decades before Einstein came along. But to go from Special Relativity to General Relativity, incorporating gravitation and the equations governing motion into the same framework, was a herculean effort. However, it was the simple identification and investigation of one puzzle, the orbit of Mercury around the Sun, that brought about Einstein’s new theory of gravity: General Relativity.

What were the key steps, and how did they help revolutionize our view of the Universe? The history is rich and spectacular, and holds a lesson for those on the frontiers of physics today.

Don’t forget to follow on instagram! -> funophysics

Ask Ethan: Why can’t I see Mercury without a telescope?

“I have been sitting on the coast watching the sun set through the thinnest sliver of clear sky on the horizon. I’m struggling with a question: how can one see Mercury with the naked eye? I know it’s possible, but how can I observe it enough to know it’s a “wandering star”? It’s the only classical planet I’ve never seen. Help!”

Under ideal conditions, Mercury achieves a maximum elongation, or angular separation, from the Sun of 28 degrees. Total darkness is achieved when the Sun dips 18 degrees below the horizon. So for many of us, why is it that we’ve never been able to see the closest planet to the Sun, even when it appears we have ideal conditions? As you may have guessed, there’s more to the equation than that. A huge factor is your latitude, and what angle the Sun rises/sets at with respect to the horizon. If you live closer to one of the poles than the equator, there’s a good chance that you’ll never be able to see Mercury, even at this maximum, ideal elongation, as by time darkness sets in, the world is well below the horizon.

Still, even with that at play, you can still have a chance if you know where/when to look! Find out the tricks on this week’s Ask Ethan!