SKY-WATCHER'S DIARY: Why we cant see Stars in day time?

Night sky with full of shining stars is always spectacular site to view from the country side. If moon is not present in the night then the site becomes fascinating. We cant see this view during day time. After sun set also we cant see stars suddenly appear in sky. It takes sometime for coming them out entirely until the sky becomes dark after sunlight totally goes off. Question that why we cant see stars in day time wonders most us. Whats the reason behind it?

Straight answer we get for this is due to sun's strong light we simply cant see them. But, what exactly happens when sun comes in our sky and how it limits us from seeing stars. Our Earth's atmosphere plays key part in this phenomenon. When sun comes in our sky sun's light is scattered by the atmospheric gases and dust particles. Due to this scattering earth's sky illuminates. Due to this illumination day time sky outshine other stars.

Night time sky with full of stars

We have seen that on Full moon night we do not observe much stars due to moon light. Sky near the moon is much brighter than rest of sky so in this area we see very very few stars. Same during dawn and dusk also we can see very few stars. We can understand this phenomenon by recalling our experiences, what happens if we lit small bulb in front of much brighter street lamp? in this case we could hardly see light coming from small bulb. This can be observe during night driving, if a small bike is riding ahead truck we could hardly notice bike in front of trucks brighter light. For our eyes it is difficult to sense small intensity of light in front of big intensity light source.

Then how much brighter object we can see in our day time sky?

Many times astronomers looks distance space objects like galaxies which having magnitude more than 14. In such conditions astronomers looks for the very dark sky means having magnitude more than this object. As atmosphere scatters light due to dust and gas particle it behave as light or illuminated object. If sky appear more brighter then such faint object will disappear. Object visibility in the sky depend on how much object is bright and how much sky is bright or dark. Sky conditions varies during dawn or dusk, presence of sun or moon in sky and nowadays light pollution from greater cities affects sky views.

Brightness of celestial objects measures in magnitude. There are two types of magnitudes astronomers use, apparent and absolute. Here we will discuss only about apparent magnitude scale. If we look at the night sky, we can see stars with different brightness. Some stars are much brighter on the other hand some are so faint that we hardly notice them. Astronomers in ancient time made a comparative scale to measure intensities of stars. They took one star for a reference which they denoted as 1 magnitude star and with the caparison to this they measure fainter stars and brighter stars. If star appear 2.5 times fainter then it will be 2 magnitude star. If it is 2.5 x 2.5 times fainter then it will be 3rd magnitude star. so, 3rd magnitude star will be 6.25 fainter than 1 magnitude star. Human eyes could observe 6 magnitude star which is 100 times fainter than 1 magnitude star. same way for brighter object if object is 2.5 brighter than 1 magnitude then it will be 0 magnitude. Brightest star of night sky is Sirius which is having magnitude of -1.45 means it is much brighter than fainter stars visible to human eyes. this measurement scale is very ancient. This method is adapted and developed by various astronomers time to time in historical time course. If we take full moon it have magnitude of -12 and sun is having magnitude of -29 means it is trillion times brighter than any star.

Venus can be observe in day time if know its exact location in sky

Seeing objects in day time depends on many conditions like brightness of object, sky conditions and position of object from sun. Near sun, sky is much brighter so its very difficult to see anything near it although we know exact position of object. if moon is in big enough in size then its easy to spot it in day time. Venus is the second object which can be observe in day time when you know its exact position. Venus shows magnitude of -4.4 means magnitude of day time sky at that region must be below this magnitude. It also depends on position of object from the sun in sky. Sky at different distance have different brightness. It will be maximum near to the sun and as moving away from sun its brightness decrease. Many astronomers do these activity of finding stars or planet in day time sky. Its interesting and test many skills of astronomers. On various website one can get information about this. Human eyes are very poor in spotting celestial objects in day time. For spotting object you also need fine instrument like telescope and position data too. Try out how many celestial objects you can see in day time.