In the mesosphere, temperature again drops as altitude increases until the coldest point in the Earth's atmosphere, the mesopause, is reached where temperatures fall to −225 °F (−143 °C).

The rows of the Periodic Table are called periods and contain elements that have the same number of electron shells ordered from lower to higher atomic number. 

In contrast to the solid terrestrial planets, the outer planets (Jupiter, Saturn, Uranus, and Neptune) consist of hydrogen and helium gas and water.

Clouds are categorized based on their shape, size, and altitude. Stratus clouds are low-altitude clouds characterized by horizontal layering with a broad flat base. When stratus clouds occur on the ground the result is fog.

The metric system is a number system that designates one base unit for each type of measurement.  For example, the base unit for length is the meter and the base unit for mass is the gram.