Weather means the day-to-day conditions of a particular place. Meteorologists are scientists who study weather. Wind is air in motion, or the movement of air. It is produced by the uneven heating of the Earth’s surface by the Sun. A wind vane is an instrument that shows the direction of the wind. Precipitation is water that falls from the sky to the ground in a solid or liquid form. Rain, snow, hail, and sleet are different forms of precipitation. Rain gauge is an instrument for measuring amount of rainfall in a particular place over a certain period of time. The temperature of air tells us how hot or cold the air is. It is a measure of heat in the air. An instrument used to measure temperature (how hot or cold a thing is), usually in the Celsius or Fahrenheit scale, is called a thermometer.