Before that, the Earth, the Sun and the rest of the Solar System were part of a giant molecular cloud of hydrogen, helium, and other heavier elements. As the cloud collapsed down, the momentum of all the particles set the cloud spinning. The current rotation period of the Earth is the result of this initial rotation and other factors, including tidal friction and the hypothetical impact of Theia — a collision with a Mars-sized object that is thought to have taken place approx.
This special shape of our planet means that points along the equator are actually further from the center of the Earth than at the poles. In ancient times, astronomers naturally believed that the Earth was a fixed body in the cosmos, and that the Sun, the Moon, the planets and stars all rotating around it.
By classical antiquity, this became formalized into cosmological systems by philosophers and astronomers like Aristotle and Ptolemy — which later came to be known as the Ptolemaic Model or Geocentric Model of the universe. However, there were those during Antiquity that questioned this convention. One point of contention was the fact that the Earth was not only fixed in place, but that it did not rotate. For instance, Aristarchus of Samos ca.
According to Archimedes, Aristarchus espoused that the Earth revolved around the Sun and that the universe was many times greater than previously thought. And then there was Seleucis of Seleucia ca. The geocentric model of the universe would also be challenged by medieval Islamic and Indian scholars. For instance, In CE, Indian astronomer Aaryabhata published his magnum opus Aryabhatiya , in which he proposed a model where the Earth was spinning on its axis and the periods of the planets were given with respect to the Sun.
At about the same time, Abu Rayhan Biruni — discussed the possibility of Earth rotating about its own axis and around the Sun — though he considered this a philosophical issue and not a mathematical one.
At the Maragha and the Ulugh Beg aka. However, the time it takes Earth to complete one full rotation on its axis with respect to distant stars is actually 23 hours 56 minutes 4. At the equator, its circumference is roughly 40, kilometres, so dividing this by the length of day means that, at the equator, Earth spins at about kilometres per hour. As you move north or south, the circumference of Earth gets smaller, so the speed of spin reduces until it reaches its slowest at both poles.
And all of this is nothing compared with the , kilometres per hour at which Earth orbits the sun. Your instincts are right, it's a trap! The answer may surprise you. How long is a day on Earth? Or more specifically, how long does it take for the Earth to turn once on its axis?
For all the stars to move through the sky and return to their original position? Go ahead, and yell your answer answer at the screen… 24 hours? It only takes 23 hours, 56 minutes and 4. Unless that's what you said. In which case, congratulations! I'm sure you're now stumbling around in an incoherent state, trying to understand how you could have possibly messed this up.
Were you reprogrammed by the hidden chronology conspiracy? Have time travellers been setting back all your clocks every day by 4 minutes? How was your whole life a lie? Here's the deal. When you consider a day, you're probably thinking of your trusty clock, or maybe that smartphone lock screen that clearly measures 24 hours.
What you have come to understand as a "day" is classified by astronomers as a solar day. It's the amount of time it takes for the sun to move through the sky and return to roughly the same spot. This is different from the amount of time it takes for the Earth to turn once on its axis — the 23 hours, 56 minutes. Also known as a sidereal day. Why are these two numbers different? Imagine the Earth orbiting the sun, taking a full days, 5 hours, 48 minutes and 46 seconds to complete the entire journey.
At the same time, the Earth is spinning on its axis. Each day that goes by, the Earth needs to turn a little further for the sun to return to the same place in the sky. If we only measured sidereal days, the position of the sun would slip back, day after day. For half of the year, the sun would be up between 12am and 12pm, and for the other half, it would be between 12pm and 12am.
There would be no connection between what time it is, and whether or not the sun is in the sky. The same thing happens on Earth when we look at stars. It takes about 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, miles 40, 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.
Related: Check out some stunning images of Earth from space. 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.
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.
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