Distance Learning Module: Investigating Clouds
Learn how clouds form—and see it in action!—with this at-home science lesson and video demonstration.
How much you know about clouds? What are they made of? How do they form?
CLOUDS are collections of condensed water vapor floating together in the atmosphere. They form when warm, moist air rises and cools. Here’s how this process works:
When a liquid warms up, it evaporates—or changes from a liquid to a gas.
On Earth, the Sun heats water on the ground, which evaporates and rises into the sky as vapor.
The air can only hold a certain amount of water vapor, depending on the temperature and weight of the air (atmospheric pressure) in a given area. The higher the temperature or atmospheric pressure, the more water vapor the air can hold. When a certain volume of air is holding all the water vapor it can hold, it is said to be saturated.
When a saturated volume of air cools, or the atmospheric pressure drops, the air is no longer able to hold all that water vapor. The excess water in the air condenses, or changes from a gas into a liquid.
On Earth, rising water vapor runs into cooler air, and the water condenses into liquid droplets.
iMAGE CREDIT: ESCHOOLTODAY.COM
Droplets often form around tiny particles floating in the air. These particles may be dust, salt crystals from sea spray, bacteria, or even ash from volcanoes. It takes more than 1,000,000,000,000,000,000 (one quintillion) individual water molecules to form a single droplet!
Image credit: NASA/JPL-Caltech/Alex Novati
A collection of droplets floating together is a cloud. Individual droplets are too small to see—but they become visible when many droplets are collected together in cloud form.
Demonstration: watch one of our educators manufacture a cloud in a plastic bottle
What’s happening?
For this demonstration, we used isopropyl alcohol in place of water. Alcohol evaporates more quickly than water and forms a denser cloud—which makes a more effective visual demonstration. Here’s a step-by-step guide to what’s happening:
Educator Faithe first adds liquid alcohol to a sealed plastic bottle. We can’t see it, but over time the liquid is evaporating and filling bottle with alcohol vapor. This is the same process as water evaporating and rising from the surface of the Earth as water vapor in the atmosphere.
Faithe then uses a pump to add more air to the inside of the bottle. Because the volume of the bottle remains constant, but the contents are increasing, this increases the air pressure inside the bottle. As the pressure inside the bottle rises, so does the temperature.
When she releases the nozzle and opens the top of the bottle, the internal air pressure and temperature drop immediately. Recall that a decrease in atmospheric pressure causes vapor in the air to condense into droplets.
As the gaseous alcohol inside the bottle condenses into droplets, a visible cloud forms!
Scientists study clouds to learn about Earth’s atmosphere and weather.
Space agencies all over the world use satellites orbiting the Earth, armed with special recording equipment, to collect data on cloud formation and behavior.
For example, NASA captured this image of clouds over the Indian Ocean in 2007 with the cameras on the Imaging SpectroRadiometer (MISR) instrument, which orbits Earth on the Terra satellite. Image credit: NASA/JPL-Caltech
Since 2006, NASA’s CloudSat mission and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) spacecraft have helped scientists to study the role that clouds and aerosols play in regulating Earth's weather, climate and air quality.
Other planets in our solar system also have clouds.
Remember that in our demonstration, we learned that substances other than water can evaporate and condense to form clouds.
The clouds in the atmospheres of other planets (and celestial bodies, such as moons) are often made of substances other than water. For example, scientists think that:
On Saturn’s largest moon, Titan (above, far left), the clouds are mostly made of methane (CH4)
On Jupiter (above, 2nd from left), high-altitude white clouds are made of frozen ammonia (NH3), while lower dusky clouds are made of ammonium hydrosulfide [(NH₄)HS]
On Neptune (above, 2nd from right), the clouds are made of methane (CH4)
And on Venus (above, far right)—which has some of the most severe weather in the solar system—the clouds are made mostly of sulfuric acid (H2SO4), which is caustic enough that it would burn through our skin!
