Sky appears blue because of reflection of the light (blue wave) from atmosphere,,,,so if the atm. were fully transparent,,,,,our sky would have been pitch dark.....then what would the effect on day and night ?????????
Will there be not any day ????????????
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An interesting outcome, but your statement is somehwat ambiguous. Are we specifing night and day as the colour of the sky, or the time periods of one day (day being 6:00AM to 6:00PM and night being 6:00PM to 6:00AM)? Each defintion of night and day has its own meaning that can alter the answer to your question.
If there was no atmosphere, no gases, no dust then one would be able to see stars during the day (sunrise to sunset) as well in the pitch black sky as one would see during the night (sunset to sunrise). The only difference will be that during the day sun will illuminate the day more than it illuminates with atmosphere but the rooms & covered areas will be darker as the only light comming in such spaces will be due to reflection from the land mass or heavenly bodies - no reflected light from the atmosphere. Nights could will be more luminous due to unobstructed light from the heavenly bodies in absence on any artificial light.
There's also the question of the sky being dark at night. Obler's Paradox states that the sky is dark at night, but it should be full of bright stars. No matter where you look, you should see a star. Instead, the sky is dark with pricks of stars. You can read more about this here: http://www.amnh.org/education/resources/rfl/web/essaybooks/cosmic/cs_paradox.html
The sky would be dark light the night sky if there were no atmosphere to difract the light. So, the answer is yes.
The idea of Obler's Paradox here is interesting. As I understand it, we do not see the starlight from all the stars in the universe at night as a blanket of light because the stars are too far away and moving away from us faster than the speed of light - or they at one point moved away faster than the speed of light and are now out of "light reach". (I don't know if I've got that completely correct though.)
In response to post 4 & 5, I would say seeing is believing. If we look at the images taken by Voyager or other satellites, where there is no atmosphere, we see a dark sky (http://voyager.jpl.nasa.gov/image/saturn.html and http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/Brian_Herold/gallery.html).
What one sees is generally a dark sky with celestial bodies and that is how the sky will appear.
The Moon provides a good example -- with no atmosphere, the night side is well on its way towards absolute zero at -170F ( or -110C) and well above the boiling point of water at 265F (or 130C). The night side sky is pitch dark, as the lack of atmosphere denies any light scattering from the sunlit side. Only the light from the stars overhead are visible. On the sunlit side, the full brunt of the Sun may heat the lunar surface, but with the exception of the Sun, on the sunlit side the sky looks exactly like it does on the night side --- black with the points of light from the stars.
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