How do we know?
↻ One of the pages with a moving picture
A scientist weighed a cloud, with math.
- The Sun heats the ground, and the ground warms the air. Warm air is lighter, so it rises, carrying invisible water vapor.
- Up high, the vapor cools and sticks to specks of dust and pollen. It turns into tiny droplets.
- A cloud is less dense than the drier air below it, so it floats on that air.
- Rising air, called an updraft, holds the droplets up. Only big, heavy drops fall out.
A scientist did the math. A puffy cloud 1 kilometer on each side holds about 1.1 million pounds of water drops! It floats because the drier air below it is even heavier.
Some clouds float very high, up to 12 miles above sea level. And fog is a cloud that touches the ground.
Near Burketown, Australia, a tube-shaped cloud called the Morning Glory can roll across the sky from September to November. It can be hundreds of kilometers long!
Wow number
12 miles above sea level: that’s how high some clouds float. It’s more than twice as high as Mount Everest!
Myth or fact?
Clouds are made of steam. Myth. Clouds are tiny water droplets or ice crystals.
Fog is a kind of cloud. Fact. Fog is a cloud that touches the ground.
Think about it
Puffy clouds often pop up on warm, sunny afternoons. Why do you think that is?
Where in the world?
Burketown, Australia where, from September to November, a tube-shaped cloud called the Morning Glory can roll across the sky — 17.74° N, 139.54° E.
Where these facts come from
Every number on page 33, and who measured it
This page explains how rising air makes clouds, with help from dust and pollen.
Clouds and How They Form — UCAR, a group of U.S. universities that study the air and weather
scied.ucar.edu/learning-zone/clouds/how-clouds-form
We checked it on 31 October 2026
This page does the math on how much a cloud weighs, and why it still floats.
How Much Does a Cloud Weigh? — The U.S. Geological Survey, the government's Earth scientists
usgs.gov/special-topics/water-science-school/science/how-much-does-a-cloud-weigh
We checked it on 31 October 2026
This page tells us that rising air holds cloud droplets up.
Precipitation and the Water Cycle — The U.S. Geological Survey, the government's Earth scientists
usgs.gov/special-topics/water-science-school/science/precipitation-and-water-cycle
We checked it on 31 October 2026
This page tells us how high clouds can be, and that fog is a cloud on the ground.
What's the Difference Between Fog and Clouds? — NOAA's weather-satellite service
nesdis.noaa.gov/about/k-12-education/atmosphere/whats-the-difference-between-fog-and-clouds
We checked it on 31 October 2026
This page tells us about the Morning Glory cloud near Burketown.
What's the science behind these spectacular weather photos? - Social Media Blog — The Bureau of Meteorology, Australia's weather service
media.bom.gov.au/social/blog/2272/whats-the-science-behind-these-spectacular-weather-photos
We checked it on 31 October 2026
Has this changed?
Why clouds float is not going to change.
Clouds themselves change by the minute, which is why the sky never looks the same twice.
Words from this page
- dense
- Heavy for its size. Something less dense than what is around it will float.
- updraft
- Air that is rising.
- fog
- A cloud that touches the ground.
Try it!
Watch a liquid float on another, like a cloud on air.
1. Fill a clear glass halfway with water. 2. Slowly pour in a spoonful of cooking oil. 3. Wait a minute. Where does the oil end up?
What happens: the oil floats on top because it is less dense than water. A cloud floats on denser air in a similar way.
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