Why is iPhone so popular?

It’s been 4 years since Apple released the first generation of iPhone, and now the iPhone is still the best mobile at the market. There are other phones that can do some things better than the iPhone. But what keeps the iPhone selling more devices than any other cellular phone manufacturer?

Why are the poles colder than the equator?

It is easy to know that each part of the world has its own climate. In general, it is true to say that the poles are colder than the equator. This results from the earth‘s tilt, the warmer receive more direct sunlight.

Why is the ocean salty?

Ocean water is salty as minerals get dissolved into the rain water from the solid earth. The majority of these minerals come from rivers whereas some originated from the rock or the plan living in the sea. 

Why is the sky blue?

In the sunny day, you look the blue sky above. Have you ever asked yourself why the sky is blue?

Why does the lunar eclipse occur?

The moon rises and sets every day as it orbits around the earth, even on the night when there appears to no moon. Like the moon, the earth goes around the sun in circle in the period of twelve month. Sometimes the sun, the moon and the earth are aligned exactly or very close so, with the earth between, a lunar ellipse happens.