![]() Light years also provide some helpful perspective on solar system distances: the Sun is about 8 light minutes from Earth. That's a more manageable number than 25 trillion miles, 40 trillion kilometers or 272,000 AU. For example, the nearest star system to ours is the triple star system of Alpha Centauri, at about 4.3 light years away. (By the way, you can't travel at the speed of light, as far as we know, but that's a whole other story.) Like AU, light years make astronomical distances more manageable. Put another way, a light year is how far you'd travel in a year if you could travel at the speed of light, which is 186,000 miles (300,000 kilometers) per second. A light year is the distance a photon of light travels in one year, which is about 6 trillion miles (9 trillion kilometers, or 63,000 AU). ![]() Credit: NASA-JPL-Caltechįor much greater distances - interstellar distances - astronomers use light years. This animated video illustrates how far a light second, minute and year are. (This is because, technically, you're expressing every distance as a ratio of the distance from Earth to the Sun. They make it easy to see that Jupiter orbits five times farther from the Sun than Earth, and that Saturn is twice as far from the Sun as Jupiter. So astronomical units are a great way to compress truly astronomical numbers to a more manageable size.Īstronomical units also make it easy to think about distances between solar system objects. When measured in astronomical units, the 886,000,000-mile (1,400,000,000-kilometer) distance from the Sun to Saturn's orbit, is a much more manageable 9.5 AU. One AU is the distance from the Sun to Earth's orbit, which is about 93 million miles (150 million kilometers). So for cosmic distances, we switch to whole other types of units: astronomical units, light years and parsecs.Īstronomical units, abbreviated AU, are a useful unit of measure within our solar system. ![]() Distances between the planets, and especially between the stars, can become so big when expressed in miles and kilometers that they're unwieldy. The space beyond Earth is so incredibly vast that units of measure which are convenient for us in our everyday lives can become GIGANTIC. And the star we see is just what the star appeared like a million years ago, not how it looks like today.Your browser does not support the audio element. Hence it took the light of the star 1 million years to get here, and the light we see was created 1 million years ago. ![]() At the speed of light the light from that star has moved to reach us. Let's presume a star is only one million light years ahead. $ \Rightarrow $ 1 light year = $\dfrac$ parsecĪge can be measured using a light year. One parsec is defined as the distance to an object whose parallax angle is equal to one arcsecond.Ī parsec is equal to 3.26 light years and because a light year the distance light travels 9.4 trillion km in one year, 1 parsec is equal to 30.8 trillion km. is approximately equal to 150 million kms. One Astronomical unit (A.U.) is defined as the mean distance between the planet Earth and the sun. Therefore, 186,000 miles (300,000 kilometres) is a light second. Light flies at an altitude of 186,000 miles per second (300,000 km per second). So people use a device called a light-year to calculate very long distances. Nobody wants to write or speak about numbers with 20 digits in them. When you start talking about these kinds of distances, it's just not a realistic unit to use a mile or kilometer because the numbers get too high. There are stars which are larger than that by billions of times. ![]() (It travels about 25 percent slower in water, for example.) Most of the universe is a near-perfect vacuum, so astronomers can generally assume that light is moving at its highest speed.Īs astronomers look at stars using their telescopes things are different. Specifying a vacuum is critical, since light slows as it passes through any form of matter. Then, we will mention the relation between the unit parsec and light years.Ī light-year is the distance one light beam travels in one year in a vacuum. Then, we will write down the requirement of this unit of measuring distance. Hint: Here, we will proceed defining the term light year. ![]()
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