- 3248 - EARTH - distance orbits around the Sun? Earth orbits the sun at an average of 92,955,807 miles. The distance from Earth to the sun is also called an “astronomical unit“, or AU, which is used to measure distances throughout the solar system.
------------------ 3248 - EARTH - distance orbits around the Sun?
- The AU is the average distance from the Earth to the sun. Earth makes a complete revolution around the sun every 365.25 days, one year.
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- However, Earth's orbit is not a perfect circle; it is shaped more like an oval, or an ellipse. Over the course of a year, Earth moves sometimes closer to the sun and sometimes farther away from the sun.
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- Earth's closest approach to the sun, called “perihelion“, comes in early January and is about 91 million miles, shy of 1 AU. The farthest from the sun Earth gets is called “aphelion“. It comes in early July and is about 94.5 million miles, just over 1 AU.
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- Historically, the first person to measure the distance to the sun was the Greek astronomer Aristarchus around the year 250 B.C. He used the phases of the moon to measure the sizes and distances of the sun and moon.
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- During a half moon, the three celestial bodies should form a right angle. By measuring the angle at Earth between the sun and moon, he determined the sun was 19 times as far from the planet as the moon, and thus 19 times as big. In fact, the sun is about 400 times larger than the moon, so his calculation needed some refinement.
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- Although imprecise, Aristarchus provided a simple understanding of the sizes and distances of the three bodies, which led him to conclude that the Earth goes around the sun, about 1,700 years before Nicolaus Copernicus proposed his heliocentric model of the solar system. Remember this was 250 B.C.
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- In 1653, astronomer Christiaan Huygens calculated the distance from Earth to the sun. He used the phases of Venus to find the angles in a Venus-Earth-sun triangle. For example, when Venus appears half illuminated by the sun, the three bodies form a right triangle from Earth's perspective.
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- Guessing the size of Venus, Huygens was able to determine the distance from Venus to Earth, and knowing that distance, plus the angles made by the triangle, he was able to measure the distance to the sun.
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- In 1672, Giovanni Cassini used a method involving parallax, or angular difference, to find the distance to Mars and at the same time figured out the distance to the sun. He sent a colleague, Jean Richer, to French Guiana while he stayed in Paris.
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- They took measurements of the position of Mars relative to background stars, and triangulated those measurements with the known distance between Paris and French Guiana. Once they had the distance to Mars, they could also calculate the distance to the sun.
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- Expressing distances in the “astronomical unit” allowed astronomers to overcome the difficulty of measuring distances in some physical unit. Such a practice was useful for many years, because astronomers were not able to make distance measurements in the solar system as precisely as they could measure angles."
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- With the advent of spacecraft and radar, more precise methods emerged for making a direct measure of the distance between the Earth and the sun. The definition of AU had been "the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass, moving with a mean motion of 0.01720209895 radians per day (known as the Gaussian constant).
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- That definition actually didn't work with general relativity. Using the old definition, the value of AU would change depending on an observer's location in the solar system. If an observer on Jupiter used the old definition to calculate the distance between the Earth and the sun, the measurement would vary from one made on Earth by about 1,000 meters (3,280 feet).
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- The “Gaussian constant” depends on the mass of the sun, and because the sun loses mass as it radiates energy, the value of AU was changing along with it.
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- The International Astronomical Union voted in August 2012 to change the definition of the astronomical unit to a plain old number: 149,597,870,700 meters. The measurement is based on the speed of light, a fixed distance that has nothing to do with the sun's mass. A meter is defined as the distance traveled by light in a vacuum in 1 / 299,792,458 of a second. 93 million miles is a lot easier to remember.
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- The sun is at the heart of the solar system. All of the bodies in the solar system, planets, asteroids, comets, etc. revolve around it at various distances.
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- Mercury, the planet closest to the sun, gets as close as 29 million miles in its elliptical orbit, while objects in the Oort Cloud, the solar system's icy shell, are thought to lie as far as 9.3 trillion miles. 29,000,000 miles to 9,300,000,000 miles is the spread of our planetary system.
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- Everything else falls in between. Jupiter, for example, is 5.2 AU from the sun. Neptune is 30.07 AU from the sun.
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- The distance to the nearest star, Proxima Centauri, is about 268,770 AU.
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- To measure longer distances, astronomers use light-years, or the distance that light travels in a single Earth-year, which is equal to 63,239 AU.
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- Proxima Centauri our nearest other star is about 4.25 light-years away.
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- August 14, 2021 EARTH - distance orbits around the Sun? 3248
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