How Does Earth Move Through Space? Now We Know, On Every Scale

An accurate model of how the planets orbit the Sun, which then moves through the galaxy in a different direction-of-motion. Image credit: Rhys Taylor of http://www.rhysy.net/, via his blog at http://astrorhysy.blogspot.co.uk/2013/12/and-yet-it-moves-but-not-like-that.html.

by Ethan Siegel, Contributor
On the largest scales, it isn't just the Earth and the Sun that move, but the entire galaxy and local group, as the invisible forces from gravitation in intergalactic space must all be added up together.

NASA, ESA; Acknowledgements: Ming Sun (UAH), and Serge Meunier

On the largest scales, it isn’t just the Earth and the Sun that move, but the entire galaxy and local group, as the invisible forces from gravitation in intergalactic space must all be added up together.

Ask a scientist for our cosmic address, and you’ll get quite a mouthful. Here we are, on planet Earth, which spins on its axis and revolves around the Sun, which orbits in an ellipse around the center of the Milky Way, which is being pulled towards Andromeda within our local group, which is being pushed around inside our cosmic supercluster, Laniakea, by galactic groups, clusters, and cosmic voids, which itself lies in the KBC void amidst the large-scale structure of the Universe. After decades of research, science has finally put together the complete picture, and can quantify exactly how fast we’re moving through space, on every scale.

Within the Solar System, Earth's rotation plays an important role in causing the equator to bulge, in creating night-and-day, and in helping power our magnetic field that protects us from cosmic rays and the solar wind.

Steele Hill / NASA

Within the Solar System, Earth’s rotation plays an important role in causing the equator to bulge, in creating night-and-day, and in helping power our magnetic field that protects us from cosmic rays and the solar wind.

Most likely, as you’re reading this right now, you’re sitting down, perceiving yourself as stationary. Yet we know — at a cosmic level — we’re not so stationary after all. For one, the Earth rotates on its axis, hurtling us through space at nearly 1700 km/hr for someone on the equator. That might sound like a big number, but relative to the other contributions to our motion through the Universe, it’s barely a blip on the cosmic radar. That’s not really all that fast, if we switch to thinking about it in terms of kilometers per second instead. The Earth spinning on its axis gives us a speed of just 0.5 km/s, or less than 0.001% the speed of light. But there are other motions that matter more.

The speed at which planets revolve around the Sun far exceeds the rotation speeds of any of them, even for the fastest ones like Jupiter and Saturn.

NASA / JPL

The speed at which planets revolve around the Sun far exceeds the rotation speeds of any of them, even for the fastest ones like Jupiter and Saturn.

Much like all the planets in our Solar System, Earth orbits the Sun at a much speedier clip than its rotational speed. In order to keep us in our stable orbit where we are, we need to move at right around 30 km/s. The inner planets — Mercury and Venus — move faster, while the outer worlds like Mars (and beyond) move slower than this. As the planets orbit in the plane of the solar system, they change their direction-of-motion continuously, with Earth returning to its starting point after 365 days. Well, almost to its same exact starting point.

Because even the Sun itself isn’t stationary. Our Milky Way galaxy is huge, massive, and most importantly, is in motion. All the stars, planets, gas clouds, dust grains, black holes, dark matter and more move around inside of it, contributing to and affected by its net gravity. From our vantage point, some 25,000 light years from the galactic center, the Sun speeds around in an ellipse, making a complete revolution once every 220–250 million years or so. It’s estimated that our Sun’s speed is around 200–220 km/s along this journey, which is quite a large number compared both Earth’s rotation speed and its speed-of-revolution around the Sun, which are both inclined at an angle to the Sun’s plane-of-motion around the galaxy.

But the galaxy itself isn’t stationary, but rather moves due to the gravitational attraction of all the overdense matter clumps and, equally, due to the lack of gravitational attraction from all of the underdense regions. Within our local group, we can measure our speed towards the largest, massive galaxy in our cosmic backyard: Andromeda. It appears to be moving towards our Sun at a speed of 301 km/s, which means —when we factor in the motion of the Sun through the Milky Way — that the local group’s two most massive galaxies, Andromeda and the Milky Way, are headed towards each other at a speed of around 109 km/s…

more…

https://www.forbes.com/sites/startswithabang/2017/06/16/how-does-earth-move-through-space-now-we-know-on-every-scale/#2cf72ac7861f

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