You Gotta See This: Mercury’s Solar Transit

mercury

Yesterday, you probably heard a lot about Mercury’s solar transit, but you might be asking yourself ‘what does that mean?’

On Monday, Mercury crossed the face of the sun (also known as a transit). The entire trip took 7 1/2 hours.

Why is this transit such a big deal? Because we’re not space experts, here’s how TIME magazine described the transit in layman’s terms:

“Earth takes 365 days to make one circuit of the sun—which is how we measure our year. Mars, one slot out on the planetary race track, takes 687 days. If you lived on Neptune, your year would be nearly 165 Earth years. Mercury, by contrast, zips around the sun once every 88 Earth days.

That’s more than four revolutions for every one Earth makes—which means that we ought see at least four Mercury transits a year, as the planet laps us again and again. But speed isn’t the only thing, inclination counts too.

The Earth orbits the sun more or less in the flat, staying roughly in the sun’s equatorial plane. Mercury’s orbit is tilted seven degrees relative to Earth’s, which means that most of the times it passes the sun, it appears to us to be moving above or below it as well—which eliminates the transit effect. It is only when Mercury’s orbital plane intersects Earth’s orbital plane that a transit becomes visible to us—which is what’s happening now.

So why does it matter? First, because Mercury itself matters. It’s a remarkable little warrior world, one that got clobbered early in its lifetime by a passing planetesimal, unleashing an explosive energy equivalent to one trillion 1-megaton bombs. And yet it survived. It has spent the entirety of its life being blowtorched by the close-up fires of the sun—losing much of its exterior layers and winding up as a sort of planetary shot put, with its iron core making up 75% of its volume. And yet it survived.”

This transit also provides scientists with a great opportunity to study Mercury. “Mercury has been visited only twice: a flyby by the Mariner 10 spacecraft in 1973, and an orbital mission by the MESSENGER probe, which circled the planet from 2011 to 2015,” added TIME.

See the Facebook video below posted by NASA of Mercury’s solar transit

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