: Why are other planets and stars and all that colourful galaxy not visible in the sky the same way we see the moon and sun in our everyday mundane lives with naked eyes?
They are. As in, they really are.
But smog and light pollution are making this a real challenge to see in an urban area. If you go wilderness camping, at night, look up, and you’ll see a lot of that stuff you didn’t think you could see.
Now, the “size” part is important, too. It’s one thing to be able to see Mars in the sky, but to you, it’s likely a dot with a bit of a red-ish hue. This is because despite being a neighbor planet, and bigger than the Earth, it’s a lot farther away than you realize, so you won’t see it moon-sized in the sky, unless something somewhere went exceptionally wrong.
The galaxy *is* visible in the sky. In a very dark sky at midsummer, it appears as a band of light that stretches all the way across the sky from one side of the horizon to the other. In fact, the word *galaxy* comes from the Greek word for *milky* because the Greeks thought it looked like milk (specifically, in Greek myth, the goddess Hera’s breastmilk) strewn across the sky. It’s etymologically related to the modern English words “lactate” (to produce milk) or “lactose” (a sugar found in milk): the *lac* in those words and the *lax* in “galaxy” are the same root. And of course, we still call our galaxy the “Milky Way” for this appearance.
Some stars are, of course, also visible. You see them every night, even in a light-polluted sky.
The reason they don’t look like the Moon or the Sun is that the Moon and Sun are very close to us. They’re big enough for us to make out details. But other stars and planets outside of our Solar System are *extremely* far away, too far away for your eye to discern any detail. Your eyes don’t quite have a “resolution” in the same way that a TV screen does, but they kinda-sorta do (more specifically, they have a minimum size they can *resolve*), and you might say that stars in the sky take up much less than a “pixel” of your vision.
Others have given good answers. All those things are visible in the sky. Our own galaxy is visible; it’s the Milky Way, and in August, the night sky is facing the center of it. If you take a picture of the sky with a fisheye lens in an area with no light pollution on a dark August night, our galaxy appears with the central bulge and all, stretched from horizon to horizon. Here’s an example: http://www.atscope.com.au/newsky/fisheyegx.jpg
The reason you don’t see colors in night sky objects is because you have two kinds of receptors in your eyes. One kind called “cones” can sense colors, and the other kind called “rods” can sense brightness. The color receptors don’t work well at low light levels, so you don’t see colors well at night. The colors appear in photographs, however, because camera film (and nowadays digital sensors) respond to colors of any brightness.
If you’re including the planets of our solar system then they are very visible in the night sky. Venus, Jupiter and Mars are generally the 3rd-, 4th-, and 5th-brightest objects in the sky after only the sun and moon. Knowing where they are helps but you can often recognise them in the sky once you’re familiar with them. They follow a similar path to the sun and moon. Mercury and Saturn aren’t much harder to see.
If you know exactly where to look, you can even see Venus in the day.
Id say its similar to how car headlights look really dim from far away then get brighter the closer you get. Except instead of being about a mile away they are ridiculously far away so you need special tools to be able to see it