How can you tell the age of a tree?

by: Googles Images

       

        In species with annual rings, these rings can be counted to determine the age of the tree, and used to date cores or even wood taken from trees in the past, a practice known as the science of dendrochronology.

What comes first, lightning or thunder?

by: Google Images

               Lightning comes first before thunder does because light travels faster than sound.


http://www.vernonkids.com/cedarmountain/4thgradelinks/tests/Lightning/ThunderLightning.htm

Why is the sea salty?

by: Google Images

          As water flows in rivers, it picks up small amounts of mineral salts from the rocks and soil of the river beds. This very-slightly salty water flows into the oceans and seas. The water in the oceans only leaves by evaporating (and the freezing of polar ice), but the salt remains dissolved in the ocean - it does not evaporate. So the remaining water gets saltier and saltier as time passes. 

http://www.palomar.edu/oceanography/salty_ocean.htm

Why the sky is blue?

      

by: Google Images

        
       A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light.  When we look towards the sun at sunset, we see red and orange colors because the blue light has been scattered out and away from the line of sight.


http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html

Why do stars twinkle?

by: Google Images

     
       Stars do not actually twinkle when viewed from outer space. They appear to twinkle when we see them from the Earth's surface because we are viewing them through thick layers of moving air in the Earth's atmosphere. 

http://www.enchantedlearning.com/subjects/astronomy/stars/twinkle.shtml

Where does a rainbow come from?

by: Google Images

  

       A rainbow  is an arc-shaped spectrum of color seen in the sky opposite the Sun, especially after rain. It is caused by the refraction and reflection of sunlight by droplets of water suspended in the air. The colors of a rainbow are usually identified as red, orange, yellow, green, blue, indigo, and violet.

http://eo.ucar.edu/rainbows/