Aura (EOS CH-1), launched 2004, is a satellite in the Earth Observing System. Originally flying a heliosynchronous orbit, it has since been allowed to drift, to conserve fuel. It is part of a constellation of three satellites collectively known as the “A train”.

In 2024 it celebrated its 20th anniversary, and is expected to operate at least through 2028.

It carries four major instruments, all examining elements of the atmosphere, including water vapor, ozone, methane, CFCs, and other pollutants and trace elements.