Deuterium is an isotope of hydrogen. It has mass number of two. which describes a deuterium atoms

not only is it colder, it also becomes darker, less salty, and more dense.

imagine a line passing through the center of earth that goes through both the north pole and the south pole. this imaginary line is called an axis. earth spins around its axis, just as a top spins around its spindle. this spinning movement is called earth's rotation. at the same time that the earth spins on its axis, it also orbits, or revolves around the sun. this movement is called revolution.