How does Earth move through the Universe?

KayleeSep 25, 20241 Comment

The Earth is a moving object in space; it is never at rest.

NASA’s MESSENGER spacecraft, which had to make flybys of Earth and Venus in order to lose enough energy to reach its final destination: Mercury, is responsible for providing us with this image of Earth. It is indisputable that the Earth is round and rotates, as this rotation explains why the planet has distinct equatorial and polar diameters, is compressed at the poles, and bulges at its core. (Source: MESSENGER, NASA)

The Earth completes a full 360° rotation on its axis every day.

A pendulum revolving at 45 degrees North latitude and the effects of the Coriolis force. It should be noted that at this specific latitude, the pendulum requires two full rotations of the Earth to complete one rotation; the rotation angle is dependent on latitude, much as the speed at the Earth’s surface. (Source: http://cleonis.nl/ Cleon Teunissen)

This results in a speed at the equator of roughly 1700 km/hr, which decreases as you move toward the poles.

The Earth seems to form a closed, stable, elliptical orbit as it revolves on its axis and moves in its orbit around the Sun. However, if we search with sufficient accuracy, we will discover that our planet truly precesses in its orbit on timescales tens of thousands of years, and spirals away from the Sun at a rate of around 1.5 centimeter each year.
(Source:Larry McNish and RASC Calgary)

Simultaneously, Earth orbits the Sun at speeds between 29.29 km/s and 30.29 km/s.

The winter solstice and perihelion lined up only 800 years ago. They are gradually moving apart as a result of Earth’s orbit precession, which completes a full cycle every 21,000 years. The eccentricity changes, the precession period lengthens, and the Earth moves a little bit away from the Sun over time. (Credit: Greg Benson/Wikimedia Commons)

The fastest speeds occur in early January at perihelion, while the slowest are in July at aphelion.

With only a small percentage of variation even among the most eccentric planets, all of the major planets orbit the Sun in ellipses that are almost exactly circles. Any planet’s orbital speed is far faster than its rotational speed, yet the Solar System’s travel across the galaxy is faster than the planets’ orbital speeds combined. This animation depicts our anticipated gravitational collision with asteroid 99942 Apophis in 2029. (Credit: ESA/NEO Coordination Centre)

Beyond that, the Solar System itself moves through the Milky Way.

Like every other star in our galaxy, the Sun travels at hundreds of kilometers per second around the galactic center. The main uncertainty component in our cumulative motion calculation is the speed of the Sun and other stars near the galactic center, which is estimated to be roughly ~10%, or ~20 km/s, in our neighborhood. (Credit: NASA; credit: Jon Lomberg)

Our speed relative to the Sun is between 200 and 220 km/s, inclined at about 60° to the plane of the planets.

The Sun revolves around 25,000–27,000 light years around the Milky Way’s plane, although the planets in our Solar System are not at all aligned with the galaxy’s orbit. To the best of our knowledge, the planets’ orbital planes arise arbitrarily inside a solar system; they are frequently aligned with the rotational plane of the central star but can also be arbitrarily aligned with the Milky Way’s plane. (Source: Science Minus Specifics)

This motion isn’t a vortex but simply the sum of these velocities.

A precise representation of the planets’ orbits around the Sun, which travels through the galaxy in a distinct direction. The velocity of the Solar System through the Milky Way galaxy is mostly determined by other factors than the motions of the planets around the Sun. Mercury’s revolution around the Sun accounts for just around 20% of the system’s total motion in our galaxy. (Source: Rhys Taylor.)

On a larger scale, the Milky Way and Andromeda galaxies are moving toward each other at 109 km/s.

a sequence of stills depicting the Milky Way-Andromeda merger and how Earth’s view of the sky will change throughout the event. It is absolutely expected that the supermassive black holes in these two galaxies would unite as well. Currently, the Milky Way and Andromeda are traveling at a relative velocity of about 109 km/s. (A. Mellinger, NASA; T. Hallas; R. van der Marel and Z. Levay, STScI)

Gravitational forces from both dense and less dense regions influence the motion of our Local Group.

This graphical depiction of the Virgo supercluster, which includes our Local Group consisting of the Milky Way, Andromeda, Triangulum, and roughly sixty other galaxies, covers an area of almost 100 million light-years. In comparison to the average cosmic pull, the regions of below-average density effectively reject us, while the overdense regions gravitationally attract us. (Source: Andrew Z. Colvin on Wikipedia)

Altogether, we are moving at 627 ± 22 km/s relative to the universe’s average.

Not only do the underdense regions affect our motions gravitationally, but also the overdense regions do, because matter is spread very uniformly throughout the universe. Our Local Group moves differently from other things in the Universe, which could be explained by a property recently identified called the dipole repeller, as shown above. (source: Nature Astronomy, 2017, Y. Hoffman et al.)

However, the leftover photons from the Big Bang provide a unique cosmic frame of reference.

Any viewer will encounter a consistent “bath” of omnidirectional radiation that originated at the Big Bang at any point in our cosmic history. Since it is currently only 2.725 K above absolute zero from our point of view, it is known as the cosmic microwave background and peaks in microwave frequencies. (Credit: NASA/BlueEarth for Earth; ESO/S. Brunier for the Milky Way; NASA/WMAP for the CMB)

The Sun moves at a total speed of 368 km/s relative to the Cosmic Microwave Background (CMB).

There are 1-part-in-800 variances in one specific direction of the cosmic microwave background, despite the fact that it is roughly the same temperature everywhere. This is consistent with our velocity across the universe. At an overall magnitude of 1-part-in-800 for the CMB’s amplitude, this translates to around 1-part-in-800 light-speed, or ~368 km/s. (Source: A&A, 2013; J. Delabrouille et al.)

There is an uncertainty of ± 2 km/s due to not knowing the exact magnitude of the CMB dipole.

Even though we are able to measure temperature variations on all angular scales throughout the sky, we are unable to distinguish between the intrinsic dipole in the cosmic microwave background because the dipole we see from our motion through the universe is larger than the primordial value by more than a factor of ~100. We can’t tell how much of this parameter’s value is intrinsic and how much is a result of our motion when we can only measure its value at one place; tens of thousands of such measurements are needed to bring the uncertainties down to their current levels. (Source: the Planck Collaboration, A&A, 2020; NASA/ESA and the COBE, WMAP, and Planck teams)

Given our location within the Milky Way, we can only speculate about taking these kinds of measurements.

The temperature and density fluctuations that appear in the cosmic microwave background and that seed the current large-scale structure are caused by the initial fluctuations that were imprinted on our observable universe during inflation, even though they may only be active at a level of ~0.003%. The only practical means of distinguishing the intrinsic dipole of the CMB from that caused by our speed through the Universe would be to measure the CMB at multiple cosmic locations. (Source: Sam Moorfield and Chris Blake.)

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Dave

3 months ago

It’s the Earth’s south pole that points toward the center of the Milky Way.
You have it backwards in your main photo at the top of the page.

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