Astronomy Stack Exchange
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Questions tagged [observable-universe]

Questions regarding the region of space containing all the objects that we can detect using any method of observation.

The observable universe contains all the objects that we can detect using any method of observation. It currently has a diameter of 46 billion light-years, because cosmological expansion is moving objects apart at enormous speed. The size of the observable universe is constantly changing.

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Objects entering or leaving the observable universe

Have there been any observations of objects entering or leaving the observable universe? When looking at the physical limit of observing something like this I will to assume that the "object" would be an galaxy. I think it would be a good assumption…
fibonatic
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Since the Universe is expanding, is it accurate to say that a galaxy is 5 billion light years away?

Isn't it better to say that the light from the galaxy took 5 billion light years to reach us and it is a very old picture of it? However, if light travelled back to the galaxy at the constant speed and an observer was stationed to record it wouldn't…
signsgeek
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How can the observable universe be so small if there are so many stars in it?

The observable universe has a radius of about 46.5 billion light years. That’s big but I just wonder how that can be big enough to fit in everything we know exists in the universe. There are hundreds of billions of galaxies and each galaxy has…
curious
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How can the JWST telescope detect matter “shortly” after the big bang?

Since space is expanding, and accelerating, with distant locations accelerating at such a high rate that they are receding at greater than the speed of light, how can the Webb detect these distant objects. I have read that the size of the “visible…
Gabe
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How much of the Universe is invisible to us, and how does it affect our theories?

I watched an interview with Neil deGrasse Tyson on The Late Show with Stephen Colbert where he briefly mentioned a disturbing thought. It is something that I have never thought of before, and the idea borders on the eerie. The idea is this (and here…
Yoda
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What is the rarest stable element in the universe?

I am making a hard sci-fi game with a focus on realism, in this game there is a need for a hard element to base money off of. Similar to how gold is used on earth. I know there are lots of elements that only exist for seconds at a time that are…
Dylan Bozarth
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Various stars moving in a line

I from India saw various stars moving in a line from North-West direction to the South-East direction at 5:27 AM on date 13 february 2020... They all are moving rapidly and can be easily seen from the earth's surface.... Wat was it? Any idea? Any…
Priyam
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How has the estimate of the number of stars in the universe changed over time?

Current estimates for the number of stars in the universe are about 10^22. However, that number has changed several times as new observations have come forth. How has the estimate of the number of stars in the universe changed over time? What was…
user27343
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How far out would we need to travel to measure the "constant observer"?

One hypothetical tenet of much astrophysics is that the Universe is uniform on large scales. This actually hinges on many deep theoretical results from astrophysics, since what we actually observe is that the Earth is at the center of the…
Him
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Maximum distance light can travel?

If we assume that there is nothing except the sun in the universe then how far the light can travel ??
Siddhant Sinha
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What defines Universe's Boundary?

We consider Heliopause as our solar system's boundary, Galaxy has its own boundary, certain theories says that there can be lots of universes, only when we define a boundary we can distinguish a universe, then (in generally) what defines our…
Kavin Ishwaran
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