Light seconds, years and centuries: how to measure long distances

Looking at the sky, we see a flat two-dimensional picture. How, then, astronomers measure the distance from the Earth to the stars and galaxies? Ting Yuan-Saint explains how the trigonometric parallax, standard candles, and much more to help us determine the distance to objects located several billion light-years away.

version Light - fastest object known to us. His speed is so great that we are measuring long distances, expressing them through the time during which the light overcomes them. In one year, light travels about nine and a half trillion kilometers, or in other words, one light-year. For comparison, the moon, to which the mission astronauts "Apollo" flew four days, only one light-second away from us. The nearest star to the Sun - Proxima Centauri - four twenty-four hundredths of light years away. Our Milky Way galaxy is across a hundred thousand light-years. The nearest galaxy to us - Andromeda - two and a half million light-years. Space unimaginably huge.

But wait, how do we know the distance to the stars and galaxies? Looking at the sky, we see a flat two-dimensional picture. If you put your finger on one of the stars, you do not get to determine how far it is. So how does this happen in astrophysics?

For close objects we use a method called trigonometric parallax. The meaning is quite simple. Let's do an experiment. Pull out his hand with a protruding thumb and close your left eye. Now open the left and close the right. It seems as if the finger has shifted, while objects in the background are still in place. With the stars of the same. But the distance to them is much greater than the length of your hand. And the earth is not so great. Even located on the equator facing each other telescopes could not determine the offset position of the star. Therefore, we conduct surveillance for six months, as during this time the Earth passes half of its orbit around the sun. Measurement of provisions stars in winter and summer, the same as the observation of the object is left, then the right eye. Near the stars look bumped against the background of more distant stars and galaxies. But this method is only suitable for distances of more than a few thousand light-years. Objects outside our galaxy so far and parallax is so small that even our most sensitive technique is not able to fix it.
In this case we rely on other techniques, using landmarks called "standard candles." Standard candles - are objects whose constant brightness, or luminosity, we know well. For example, if you know the luminosity of the light bulb and ask your friend to take it and move away from you, the amount of light received by you will be reduced in proportion to the square of the distance. Thus, comparing the amount of light received at a constant brightness of the bulb, we can determine the distance to your friend. In astronomy, the role played by the star light bulb of a special type, called Cepheids. They are intrinsically unstable, like constantly inflates and deflates the balloon. And as ripples change their brightness, we calculate their luminosity by measuring the cycle. And the brighter the star, the longer the cycle. Comparing the observed light of these stars with their luminosity obtained by said measurements, we can determine the distance to them.

This, unfortunately, is not the end of history. The maximum distance at which we can still distinguish individual stars, is about forty million light-years. After that, they become too blurred. But, fortunately, we have another type of standard candle - the famous `type 'A A' (Eng. Ia). Supernovae - giant star flash - this is one of the variants of the death of stars. These bursts are so bright that dwarf galaxies in which they occur. So even if we can not distinguish individual stars in a certain galaxy, we are still able to see the explosion of a supernova. It SNe One and the approach to the role of standard candles because brighter supernovae decay more slowly than the less bright.

Due to the relationship between the brightness and the speed of extinction, we can use these supernovae to determine the distances of up to several billion light years.

And why was it so important to look at distant objects? Remember how fast light travels. For example, the light emitted by the sun reaches the earth in eight minutes, which means that we see the sun just as it was eight minutes ago. When looking at the Big Dipper you see it for what it was eighty years ago. And those are difficult galaxies are millions of light years away. Their light took millions of years to reach us. Thus, the whole universe is in some sense itself is a time machine. The more we look, the more we see the young universe.

Astrophysicists are trying to read the history of the universe and to understand how and where we came from. The universe is constantly sending information to us in the form of light. We are required only to decipher it.

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