Alley in Pisa, Italy

by Lars Kotthoff

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I was wondering by seeing the photos of Milky way galaxy, that how exciting it would be if we could see all those colors and stars like in those photographs (eg. below).

enter image description here

source: http://www.flickr.com/photos/bala_/4766723931/

Why can't we see all those details of milky way in naked eye? Is it because quick exposure time of eye as light has to travel from some thousand light years? or What else can be the reason?

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If anyone is interested, the answer to this question provides details from the photographer of how that image was actually shot: photo.stackexchange.com/questions/19936/… –  Matt Grum Aug 10 '12 at 12:50
    
Note that the milky way was known to ancient people, although they probably couldn't see it as clearly as the example picture you have. –  David Rouse Aug 13 '12 at 12:37

3 Answers 3

In fact, if you spend the night in a remote enough place with clear, moon-free sky you will see most of the colors. The sad truth is that most of us live in cities where light polution and smog do not let us see anything except the brightest stars.

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You don't even need to live in a city. They cause so much light pollution that they effect your view of the sky from miles and miles and miles away. –  Dan Wolfgang Aug 10 '12 at 10:50
    
Please cast some light on how light pollution affects this? –  vivek_jonam Aug 10 '12 at 12:34
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Even without light pollution you will see more colour information from a camera that is able to collect light over a longer period of time than our eyes can. –  Matt Grum Aug 10 '12 at 12:52
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@vivek_jonam light pollution raises the brightness of the background sky; as a result there's no longer enough contrast for the eye to perceive the difference between stars and the sky. Higher sensitivity (>50% vs IIRC 1-2%), longer exposure times (the eye maxes out at ~1/10th second), and larger aperture sizes (the pupil tops out at 7mm) allow a camera to collect more light and lift more detail above the noise floor. You can however get better images with a camera from a dark location than one that's badly light polluted. –  Dan Neely Aug 10 '12 at 15:12
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@floqui: You'll see color, but not as much and not in this much detail. If you let your eyes properly adjust (which can take over an hour), and observe the night sky at high altitudes and far from artificial light pollution on a moonless night, you can certainly see color. It will have a cooler tone (blue shift), as our eyes have blue cones in a much larger area of our retina than red and green cones (10° foveal region for blue cones, vs. roughly 2° foveal region for red and green cones.) You can see a fair amount of detail as well...but there are definite limitations. –  jrista Aug 10 '12 at 18:04

Camera is better at seeing than our eyes. According to http://www.cambridgeincolour.com/tutorials/cameras-vs-human-eye.htm astrophotographers have estimated that human eyes have a ISO rating of 500-1000 after being properly acclimated to dark conditions. The example photograph has used something like ISO 3200.

Cameras can also take longer exposure (=gather more light) than human eye. Our eyes don't see any more details after staring at a subject 10-15 seconds.

Some astrophotographs can have over 24h worth of light collected (usually in 2-15 minute exposures stacked together to make one image), our eyes can't compete with that...

Light pollution is also a major drawback. Light polluted sky is too "bright" to see faint object. Cameras can overcome light pollution by using different kinds of filters to filter it out (f. ex these are all taken from middle of a light polluted city http://www.astroanarchy.blogspot.fi/).

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You can't see the colours in the milky way (or other stars for that matter) as the light coming from the milky way is too dim to be picked up by the cone cells in our eyes which distinguish colour. Instead the light only trips the more sensitive rod cells (which are usually used for detecting motion) hence we see the brightness but not the colour of the stars in the milky way.

The camera is able to collect light over a much longer period of time, and thus has a stronger signal to work with when determining colour.

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Especially when you have poor crappy cones such as the ones in my color blind eyes :( –  dpollitt Aug 10 '12 at 15:49

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