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Why do we see the stars as they were in the past?

Why do we see the stars as they were in the past?

Looking at things in the universe (including stars) does not mean seeing them as they are now. This is why “distance” is not what it seems in the universe

Take a look at any object and it depends on what you see How far is it from you?. In fact, all things (including stars) have existence Specific physical properties:Size, color, brightness, etc. Well, our way of detecting these objects is based on electromagnetic radiation. the light! The light you see now was emitted from this body at some time in the past. When we talk about Cosmic distancewe refer to the time it takes light to travel from that object to our eyes.

Because looking far into space means seeing time in the past

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Image source: NASA, ESA, P. Oesch and B. Robertson (University of California, Santa Cruz), and A. Feild(STScI)

In our daily experience, the way we perceive the reality around us is the same as that of Euclid and Newton. As if the world were defined of some sort of fixed spaceWhere we can select all objects based on their position. If this also applied to the universe, everything would be simple and straightforward when it comes to measuring the cosmic distance of different objects. The problem is that we are in an expanding world What you see changes with your speedchanges over time It changes according to the distribution of mass in the surrounding space.

Imagine the universe as a rising panettone with raisins inside. Eat raisins It’s like a galaxyThe dough expands and expands over time. If you stood on a raisin, what would you see? As the fabric of space expands, the light from other raisins also lengthens in wavelengths Increasingly longer. Longer wavelengths mean redder colors, cooler temperatures, and lower energies.

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NGC 5468 galaxy and stars
Image source: NASA, ESA, CSA, STScI, Adam G. Riess (JHU, STScI)

Have you ever wondered why we see objects (and stars) 32 billion light-years away if they are 13.4 billion years old? This is due to the way distances evolve in the expanding universe. When light was first emitted, The universe was much smaller This body was not even a billion light years away from us. As that light headed toward us, the universe itself expanded. At first the light moved away, but as the rate of expansion slowed, He reached us. Finally today, after a journey that took 13.4 billion years, this light has arrived. But the object itself is farther away, about 32 billion light-years away.

Role model among the stars? The sun is a 8 light minutes from us:Does this mean that it takes 8 minutes for light to travel from our star to Earth? But the moon is far from our planet 1.3 light seconds (And thus we see it as it was 1.3 seconds ago.)

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