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Every year we celebrate our birthdays. Hooray! During this entire time, the Earth makes one complete revolution around the Sun. But relative to the center of our Milky Way galaxy, the entire solar system travels about 7 billion km in one Earth year. From childhood, we are presented with a convenient and simple picture. A large yellow sun hangs motionless in the center, and the Earth moves around it in a given elliptical orbit. But if the sun itself is hurtling through the galaxy, what does Earth's path actually look like? This is where those viral 3D animations come from. You've probably seen some of them. The solar system is depicted as a giant vortex, with the sun rushing forward and the planets
trailing behind it in a long spiral. These animations are not entirely fictional. They are based on real fact. The sun is moving, but they combine with the wrong geometry, creating the false impression that our star is physically dragging the planets through some dense medium. To understand how accurate these videos are, it's worth looking at the actual inclination of the orbits and, most importantly, from which frame of reference we are observing them. In physics, it is impossible to describe motion without first answering one question. Regarding what? Imagine a fly circling around a light bulb on the ceiling of a train moving inside the train. Its path is a closed
circle, but from the platform, the train's forward motion stretches this circle into an open wavy line. Both descriptions are correct. They simply use different reference frames. The animation creators we're talking about here are trying to show us the view from the platform, that is, relative to the galaxy. This part is correct, but if we track the Earth in the galactic frame of reference, its closed orbit becomes an open three-dimensional curve. However, its exact shape depends on the orientation of the orbital plane. And this is where these viral videos start to cut corners. Let's take a closer look at this famous spiral. In the animation, the orbital plane is located almost perpendicular
to the direction of the sun's movement. This makes it appear that the planets are trailing straight behind the Sun, like the tail of a comet. In fact, the orientation of our system is completely different. The Earth and most planets rotate in almost the same plane, called the ecliptic. And this plane is tilted relative to the disk of our galaxy by about 60°. By human standards of time, this orientation remains virtually unchanged. So, the solar system is not moving head-on through the galaxy. As the animation suggests, she cuts through it at an angle. Because of this tilt, the planets cannot
remain permanently behind the Sun and form a tail. In the galactic frame of reference, the Earth's trajectory becomes a looped three-dimensional path superimposed on the Sun's journey through the galaxy. Over the course of a year, our planet alternately finds itself either ahead of or slightly behind the Sun along the direction of its galactic motion. Many animations contain another serious simplification. The sun itself supposedly moves in a perfectly straight path. Any system of bodies has a common center of mass. Barycenter. In a gravitationally bound system, all of its objects revolve around this common center of mass. And although the sun accounts for about 99.8% of the
total mass of the solar system, the remaining fractions of a percent are more than enough to influence the star. Our gas giants play a major role here. First of all, Jupiter, because it is really very, very big, more than 300 times more massive than Earth. And Saturn. Their combined mass is enough to constantly shift the center of the solar system. Sometimes the barycenter is deep inside the Sun, and other times it extends beyond the Sun's surface, depending on the location of the giant planets. Because of this, as it moves through the galaxy, the sun is constantly gravitationally oscillating around this invisible point. On the scale of its galactic trajectory, this fluctuation is incredibly small.
By the way, such oscillations in other stars are one of the ways astronomers find exoplanets. They measure periodic tiny shifts in a star's position or its spectral lines. But gravity doesn't just affect the sun. The shape of the Earth's orbit and the orientation of its axis of rotation also slowly change over time. These changes are known as Milankovitch cycles. Over cycles lasting about 100,000 years, Earth's orbit becomes more elongated and then more circular again. The tilt of the Earth's axis changes with a cycle of about 41,000 years. And every 26,000 years, the axis slowly processes, describing a circle under the gravitational influence of the sun and moon. These orbital cycles cannot
freeze the planet immediately, but they gradually change the distribution of solar energy at different latitudes and at different times of the year. Working in tandem with the Earth's own climatic responses, such as the growth of ice sheets or changes in greenhouse gases, these cycles dictate the long natural rhythm of the onset and change of ice ages. And that's just what's happening inside the solar system. But if you look at it on the scale of the Milky Way, things get even stranger. Our entire galaxy rotates, and the solar system races around its center at a speed of about 230 km/s. It takes us about 230 million years to make just one complete revolution around the galaxy. The Sun's orbit around the galactic center is not perfectly
circular. Our star undergoes vertical oscillations, periodically rising and falling relative to the mean plane of the galactic disk. The cause of these oscillations is the gravity of the Milky Way itself. The bulk of the stars and gas is concentrated in the disk. As the solar system rises above this plane, the combined gravity of the disk begins to pull it back down. The sun picks up speed, then passes right through the midplane, drops below it, and then gravity starts pulling it up again. If we mentally unfold the Sun's galactic orbit into a straight line, this trajectory will look like a wave. A full cycle of these vertical
oscillations takes about 60-70 million years. Some researchers suggest that passing through the densest parts of the galactic plane enhances the gravitational pull of the Oort cloud, that hypothetical spherical reservoir of icy bodies on the far outskirts of the solar system. The idea is that this could direct more comets into the inner solar system. But researchers have never conclusively linked this cycle to mass extinctions on Earth, so for now it remains just a hypothesis. However, Earth's orbital motion also gives physicists something more practical, a possible way to search for dark matter. Our Milky Way galaxy is believed to be surrounded by a vast halo of dark matter, roughly spherical in shape. As
the direction of Earth's orbital velocity changes throughout the year, our velocity relative to this hypothetical dark matter halo also changes. The Earth moves in its orbit at a speed of about 30 km/s. At the beginning of each June, Earth's orbital velocity has its largest component, pointing in the same direction as the motion of the solar system relative to the galaxy. In early December, this component is directed in the opposite direction. Imagine you are driving a car in heavy rain. The faster you drive, the more raindrops fall on your windshield every second. This is the so-called dark matter wind. It works on the same basic idea. To block the main cosmic rays, physicists place
ultrasensitive detectors deep underground. In Damalibre's experiments, 112 ultrapure crystals of sodium iodide, a type of crystalline salt, but definitely not the kind you add to French fries, serve as the sensitive material. The logic is simple. If dark matter consists of hypothetical particles, such as so- called WIMPs or weakly interacting massive particles, then they should pass through the Earth almost completely unhindered. However, it is extremely rare that such a particle can, or at least could or should, crash into an atomic nucleus inside a salt crystal. The collision would create a tiny flash of light that could then be registered by a detector. At least that's the idea. According to the
standard Halo model, these detectors should record slightly more collisions in June than in December. The Dama Libra experiment in Italy claimed for years to have detected this particular seasonal modulation, but the combined results of the Co 100 and Anes 112 experiments could not reproduce this modulation, raising serious doubts that the dama is detecting dark matter. However, what causes the lady signal still remains unclear. But the Chemai Way galaxy itself is also moving. Our galaxy, along with Andromeda and the rest of the Local Group, moves through space under the gravitational influence of huge clumps of matter far beyond our galaxy. One of the most famous such regions is what you may have
heard of called the Great Attractor. It is part of a much larger network of galaxy clusters and superclusters. Their combined gravity is so powerful that it controls the motion of galaxies within a radius of hundreds of millions of light years. It may seem that all we need to do now is add up all these motions: the Earth's orbit and the Sun's oscillation around the barocenter, its vertical motion through the galactic disk, and its drift in the direction of the big tractor to get our true velocity. But no such single number exists. First, you have to ask again, as I said, regarding what. Since there is no universal fixed coordinate grid in the universe, any velocity must be measured relative to something else. One of the
most convenient cosmological reference frames is provided by the CMB. A microwave echo left over from the big bang that almost uniformly fills the entire visible universe. Due to the Doppler effect, this ancient background radiation appears slightly hotter, or blue-shifted, when viewed in the direction we are flying, and slightly cooler, or red-shifted, behind us. By measuring this temperature difference, scientists were able to determine our speed and direction relative to the cosmic microwave background radiation. In this frame of reference, the entire solar system moves at a speed of about 370 km per second. So, if the textbook diagram only shows the simplest reference system, why is it still used? The school model is not wrong, it just works only at the
local level. For any calculations, you choose the reference system that makes the problem easiest to solve. When calculating the probe's trajectory to Mars, engineers don't need to consider the overall motion of the solar system through the galaxy or its speed relative to cosmic microwave background radiation. The spacecraft, the Earth, Mars, they all share the same general motion through the galaxy. Therefore, everything else is ignored when we calculate their positions relative to each other. So, the Earth does not have any one true trajectory. Relative to the Sun, it is almost a closed ellipse. Relative to the center of the galaxy, it describes a complex three-dimensional path.
Regarding the cosmic microwave background, this is another, even more complicated path. None of these descriptions contradict the others. Each of them is correct in its own frame of reference. If this analysis helped you look at a familiar model of the solar system in a new light, please like the video and, of course, subscribe. on the channel. Write in the comments what other popular model we should analyze next. See you at the new coordinates.
