National High Magnetic Field Laboratory
Magnet Academy: Magnetic Field of a Solenoid
You can create a stronger, more concentrated magnetic field by taking wire and forming it into a coil called a solenoid. (Java tutorial)
National High Magnetic Field Laboratory
Magnet Academy: Magnetometer 1832
The Earth, the moon, the stars and just about everything in between has a magnetic field, and scientists use magnetometers when they need to know the strength of those fields.