Posted on 09/11/2018 11:27:07 AM PDT by ETL
Some of the earliest astronomers proposed that we live in a geocentric universe, which means that Earth is at the center of everything. They said the sun rotated around us, which caused sunrises and sunsets — same for the movements of the moon and the planets. But there were certain things that didn't work with this vision. Sometimes, a planet would back up in the sky before resuming its forward motion.
We know now that this motion — which is called retrograde motion — happens when Earth is "catching up" with another planet in its orbit. For example, Mars orbits farther from the sun than Earth. At one point in the respective orbits of Earth and Mars, we catch up to the Red Planet and pass it by. As we pass by it, the planet moves backward in the sky. Then it moves forward again after we have passed.
Another piece of evidence for the sun-centered solar system comes from looking at parallax, or apparent change in the position of the stars with respect to each other. For a simple example of parallax, hold up your index finger in front of your face at arm's length. Look at it with your left eye only, closing your right eye. Then close your right eye, and look at the finger with your left. The finger's apparent position changes. That's because your left and right eyes are looking at the finger with slightly different angles.
The same thing happens on Earth when we look at stars. It takes about 365 days for us to orbit the sun. If we look at a star (located relatively close to us) in the summer, and look at it again in the winter, its apparent position in the sky changes because we are at different points in our orbit. We see the star from different vantage points. With a bit of simple calculation, using parallax we can also figure out the distance to that star.
Earth's spin is constant, but the speed depends on what latitude you are located at. Here's an example. The circumference (distance around the largest part of the Earth) is roughly 24,898 miles (40,070 kilometers), according to NASA. (This area is also called the equator.) If you estimate that a day is 24 hours long, you divide the circumference by the length of the day. This produces a speed at the equator of about 1,037 mph (1,670 km/h).
You won't be moving quite as fast at other latitudes, however. If we move halfway up the globe to 45 degrees in latitude (either north or south), you calculate the speed by using the cosine (a trigonometric function) of the latitude. A good scientific calculator should have a cosine function available if you don't know how to calculate it. The cosine of 45 is 0.707, so the spin speed at 45 degrees is roughly 0.707 x 1037 = 733 mph (1,180 km/h). That speed decreases more as you go farther north or south. By the time you get to the North or South poles, your spin is very slow indeed — it takes an entire day to spin in place.
Space agencies love to take advantage of Earth's spin. If they're sending humans to the International Space Station, for example, the preferred location to do so is close to the equator. That's why cargo missions to the International Space Station, for example, launch from Florida. By doing so and launching in the same direction as Earth's spin, rockets get a speed boost to help them fly into space.
Earth's spin, of course, is not the only motion we have in space. Our orbital speed around the sun is about 67,000 mph (107,000 km/h), according to Cornell. We can calculate that with basic geometry.
First, we have to figure out how far Earth travels. Earth takes about 365 days to orbit the sun. The orbit is an ellipse, but to make the math simpler, let's say it's a circle. So, Earth's orbit is the circumference of a circle. The distance from Earth to the sun — called an astronomical unit— is 92,955,807 miles (149,597,870 kilometers), according to the International Astronomers Union. That is the radius (r). The circumference of a circle is equal to 2 x π x r. So in one year, Earth travels about 584 million miles (940 million km).
Since speed is equal to the distance traveled over the time taken, Earth's speed is calculated by dividing 584 million miles (940 million km) by 365.25 days and dividing that result by 24 hours to get miles per hour or km per hour. So, Earth travels about 1.6 million miles (2.6 million km) a day, or 66,627 mph (107,226 km/h).
The sun has an orbit of its own in the Milky Way. The sun is about 25,000 light-years from the center of the galaxy, and the Milky Way is at least 100,000 light-years across. We are thought to be about halfway out from the center, according to Stanford University. The sun and the solar system appear to be moving at 200 kilometers per second, or at an average speed of 448,000 mph (720,000 km/h). Even at this rapid speed, the solar system would take about 230 million years to travel all the way around the Milky Way.
The Milky Way, too, moves in space relative to other galaxies. In about 4 billion years, the Milky Way will collide with its nearest neighbor, the Andromeda Galaxy. The two are rushing toward each other at about 70 miles per second (112 km per second).
Everything in the universe is, therefore, in motion.
There is no chance that you'll be flung off to space right now, because the Earth's gravity is so strong compared to its spinning motion. (This latter motion is called centripetal acceleration.) At its strongest point, which is at the equator, centripetal acceleration only counteracts Earth's gravity by about 0.3 percent. In other words, you don't even notice it, although you will weigh slightly less at the equator than at the poles.
NASA says the probability for Earth stopping its spin is "practically zero" for the next few billion years. Theoretically, however, if the Earth did stop moving suddenly, there would be an awful effect. The atmosphere would still be moving at the original speed of the Earth's rotation. This means that everything would be swept off of land, including people, buildings and even trees, topsoil and rocks, NASA added.
What if the process was more gradual? This is the more likely scenario over billions of years, NASA said, because the sun and the moon are tugging on Earth's spin. That would give plenty of time for humans, animals and plants to get used to the change. By the laws of physics, the slowest the Earth could slow its spin would be 1 rotation every 365 days. That situation is called "sun synchronous" and would force one side of our planet to always face the sun, and the other side to permanently face away. By comparison: Earth's moon is already in an Earth-synchronous rotation where one side of the moon always faces us, and the other side opposite to us.
But back to the no-spin scenario for a second: There would be some other weird effects if the Earth stopped spinning completely, NASA said. For one, the magnetic field would presumably disappear because it is thought to be generated in part by a spin. We'd lose our colorful auroras, and the Van Allen radiation belts surrounding Earth would probably disappear, too. Then Earth would be naked against the fury of the sun. Every time it sent a coronal mass ejection (charged particles) toward Earth, it would hit the surface and bathe everything in radiation. "This is a significant biohazard," NASA said.
Monty Python says it best.
https://www.youtube.com/watch?v=buqtdpuZxvk
All motion is relative, since there is no absolute reference frame.
Zero.
This doesn’t seem to match the flat earth theory.
“All motion is relative, since there is no absolute reference frame.”
But not all frames of reference are relative at once.
Once one frame is referenced, all others are measurable.
67,000 mph. Give or take. lol
That is why ‘Time Travel’ is impractical.
Even if you perfected a Time Machine, just going back ONE SECOND in TIME would leave you stranded in the middle of a very cold dead space.......................
I thought the ballpark, relative to some sort of “background”, is an average of 1.3 million MPH.
Average, because the various speed components may be additive or subtractive, depending on their direction at the moment.
How come we can tell what motion we have with respect to the CMB? Doesn’t this mean there’s an absolute frame of reference?
The theory of special relativity is based on the principle that there are no preferred reference frames. In other words, the whole of Einstein’s theory rests on the assumption that physics works the same irrespective of what speed and direction you have. So the fact that there is a frame of reference in which there is no motion through the CMB would appear to violate special relativity!
However, the crucial assumption of Einstein’s theory is not that there are no special frames, but that there are no special frames where the laws of physics are different. There clearly is a frame where the CMB is at rest, and so this is, in some sense, the rest frame of the Universe.
But for doing any physics experiment, any other frame is as good as this one. So the only difference is that in the CMB rest frame you measure no velocity with respect to the CMB photons, but that does not imply any fundamental difference in the laws of physics.
How Fast Is Earth Moving?
With respect to what? We are moving at a significant fraction of the speed of light wrt the most distant galaxies in the observable universe. WRT the most distant galaxies beyond the edge of the observable universe? Your guess is as good as mine. Maybe greater than c, since the expansion of space can be faster than c.
“The cosmic microwave background (CMB, CMBR) is electromagnetic radiation as a remnant from an early stage of the universe in Big Bang cosmology. In older literature, the CMB is also variously known as cosmic microwave background radiation (CMBR) or “relic radiation”.
The CMB is a faint cosmic background radiation filling all space that is an important source of data on the early universe because it is the oldest electromagnetic radiation in the universe, dating to the epoch of recombination. ...”
https://en.wikipedia.org/wiki/Cosmic_microwave_background
We are in fact travelling about 600 kilometers per second with respect to the cosmic microwave background, which means we are moving about 600 kps relative to the Big Bang. The Big Bang itself represents the universe’s reference frame. However, it is just as valid to say we are stationary while the universe is moving as to say we are moving while the universe is stationary.
With respect to what?
The article clearly refers to motion with 'respict' to axis spin and orbits around the sun and galaxy. Beyond that there is motion within the "Local Group" and larger super cluster galaxy groupings.
Thanks! Looks interesting. Will check out later.
The title doesn't make it clear that that's all they're talking about. And as you say, they go beyond those two cases themselves. So I did, too.
Any good intro astronomy course will cover all the types of motion in space and there are a LOT more than two of them... I'm a little disappointed in space.com on this one. Not criticizing you. Please don't take it that way. Cheers!
self ping
I watched a youtube video that made some interesting claims last weekend.
1) The cosmic background radiation has some cold spot patterns that basically make a giant x that intersects where Earth is. Verified by 3 differnent scopes/methods. Indicating the earth may be the center of the Universe.
2) According to relativity, whether the earth rotates around the sun or the sun rotates around the earth along with the entire universe, is simply a matter of perspective.
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