Skip Navigation
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

On the Dot

moving circles

Focus on the dot in the center,
and move your head forwards and backwards.
What happens?

Reveal Answer

The outer circles appear to turn in opposite directions

space
Other stuff you might like ...
Natural World
About the world around us, and space, too!
Go!
Back to Top