Looking at a photo of our nearest galaxy, why is our sky so black at night when we are inside a galazy?

Answer 1

Our galaxy is just as bright as those others, or rather those others are just as dim as ours. Those photos of our nearest galaxy that look so bright are very long exposures. The camera shutter was held open for many seconds, minutes, or maybe even hours, to make the photograph look far brighter than your eye could ever see. This is commonly done for all kinds of astronomical photographs. These objects would not look like the photographs at all if you simply looked at them through a telescope with your eye. I know, I have done so. Galaxies are extremely disappointing, dim and lacking in any interesting detail, when viewed visually through even a large telescope.

There are long exposure photographs of the night sky showing the milky way as a bright band of light in the sky, and the source below is one of them.

Answer 2

Mr Olbers, even without a photo, wondered about the same thing. That became known as the Olbers Paradox:

Olbers' paradox, described by the German astronomer Heinrich Wilhelm Olbers in 1823 (and then reformulated in 1826) and earlier by Johannes Kepler in 1610 and Halley and Cheseaux in the 18th century, is the paradoxical observation that the night sky is dark, when in a static infinite universe the night sky ought to be bright. It is one of the pieces of evidence for a non-static Universe such as the current Big Bang model. This paradox is sometimes also known as the "dark night sky paradox".

The explanation of the paradox which is generally accepted by the scientific community points to the finite speed at which light travels through space. Given its finite speed, the light from the most distant star cannot have travelled a further distance, measured in light years, than the star itself is old.

The most widely accepted model for the Big Bang would make the universe approximately 13.7 billion years old, so the furthest expanse that light could have possibly travelled since its creation is an equal number of light years. Thus, even if every infinite trajectory into space from the earth eventually passes through a star in the farthest regions of the universe, the light of all such stars beyond the maximum distance in which light has travelled since the origin of the universe will remain beyond visibility from earth. In reality this does not explain the dark sky, as the light from the Big Bang was incredibly intense, and was emitted in all directions.However the emission from the Big Bang is redshifted to microwave wavelengths due to general relativity, where it forms the cosmic microwave background radiation. So in reality the explanation for the dark night sky results from the redshifting of all light from distant objects, and not directly from the finite age of the Universe (although the redshifting process and the age of the universe are connected in most theories).

Answer 3

Because even here, in a galaxy with billions of stars, the space between the stars is so massive that the sky appears as blank as it does... which really isn't that blank. Also remember that there are many stars that are too far away for your eyes to pick out the points of light that come from them, because they are too faint or small. A cat, eagle, or owl might see more stars than you.

As well, our atmosphere is not completely clear, and some of the stars that you maybe still could see are dimmed by the atmosphere.

As well, some stars main form of electromagnetic output isn't in light waves, but in UV rays, or Microwaves, or Radio waves, or X Rays.... etc. Your eyes can't percieve these types of "light", and so where there may be a star you see empty space.


Tiger Striped Dog MD

Answer 4

I completely agree with your question. When you look at M113 (andromeda, which can be seen quite clearly just using a spotting scope), all you can see is this massive amount of light eminating from all the stars that are in this galaxy. M113 seems like a very bright galaxy. But also notice all the space in between the stars when you look at M113, and ask yourself, how much space exactly is there inbetween those stars. Then notice our planets possition in this galaxy relative to our closest stars. All but the sun are very very far away. Think of light bulb hanging from a tree at night time in the woods. Standing next to the bulb you can see that it luminates the surounding area, how much illumination it has depends on its wattage, just like stars. Now start to move away from the bulb and notice that you start to loose sight of what the bulb is iluminating as you increase your didstance from the bulb, pretty soon the only thing you can see is just the bulb hanging there in total darkness. Space is the same way.

Answer 5

Have you ever really seen the Milky way?

I hadn't until a few years ago, when I was on holiday in the Alps. There is a lot less light pollution and the air is thinner.

You can see a distinctive band of "cloud" made up of millions of stars. This is our galaxy.

So the simple answer is that the sky isn't as black as you think, you're just looking from the wrong place.

Answer 6

Well the next star nr to use in are galaxy is around about billion light years way get me. Some of the star in the sky may not exist anymore but there light from the star is still on its way to earth and could keep shining for another 100,000 years!

Answer 7

there are hundreds of images of galaxies that are billions of light years away. The Hubble Telescope and other space-based and surface-based telescopes have imaged objects as far away 780 million light years (some quasars), and the Hubble Ultra Deep Field survey images galaxies 13 billion light years away. Other closer galaxies and clusters (like the Virgo Cluster) have been imaged by Hubble and the Keck I and Keck II telescopes in Hawaii. But to your question - the stars you see at night are just that - stars in our own galaxy. But there are also 3 galaxies visible to the naked eye on Earth. The Andromeda Galaxy is 2.5 million light years away, but is visible in the night sky in the Andromeda constellation as a hazy patch of light about the size of the full moon. The Large Magellanic Cloud and the Small Magellanic Cloud are 2 smaller satellite galaxies of our own Milky Way, and are visible in the southern hemisphere (they are named such because they were first seen and reported by the explorer Magellan on his circumnavigation of the earth).

Answer 8

With all the stars that give off light, we could see this light if it were reflected off of something. Look at the milky way in the sky and look at the way it seems to have all light blend in together. This is just from the mass collectioon of stars as we are looking at the middle of our galaxy, and not the edges.

Answer 9

Light pollutuion from cities, etc. blot out stars.
Stars themselves are very far away the closest is Proxima Centauri in the Southern hemisphere or Sirius in the North.
The average distance between stars in the galaxy is 3 LY but Sirius is over 8 LY away.

Answer 10

That is the famous Olbers' Paradox. If there is an infinite number of stars why the sky is so dark at night?

There are a number of possible explanations for this. But you better read the reference link.