You may recognize the eerie green glow in this cold northern sky as the northern lights, or aurora borealis. But do you know what causes the northern lights? Earth’s magnetic field is a major factor.
Earth’s Magnetic Field
Like a bar magnet, planet Earth has north and south magnetic poles and a magnetic field over which it exerts magnetic force. Earth’s magnetic field is called the magnetosphere. You can see it in the Figure below.
Like an Umbrella
The sun gives off radiation in solar winds. You can see solar winds in the Figure above. Notice what happens to solar winds when they reach the magnetosphere. They are deflected almost completely by Earth’s magnetic field. Radiation in solar wind would wash over Earth and kill most living things were it not for the magnetosphere. It protects Earth’s organisms from radiation like an umbrella protects you from rain.
Q: Now can you explain the northern lights?
A: Energetic particles in solar wind collide with atoms in the atmosphere over the poles, and energy is released in the form of light. The swirling patterns of light follow lines of magnetic force in the magnetosphere.
Finding the Way
Another benefit of Earth’s magnetic field is its use for navigation. People use compasses to detect Earth’s magnetic north pole and tell direction. Many animals have natural “compasses” that work just as well. For example, the loggerhead turtle in the Figure below senses the direction and strength of Earth’s magnetic field and uses it to navigate along migration routes. Many migratory bird species can also sense the magnetic field and use it for navigation. Recent research suggests that they may have structures in their eyes that let them see Earth’s magnetic field as a visual pattern. You can learn more at this URL: http://www.smithsonianmag.com/science-nature/How-Do-Birds-Find-Their-Way-Home.html
Q: In the past, Earth’s magnetic poles have switched places and reversed Earth’s magnetic field. How might a magnetic reversal affect loggerhead turtle navigation?
A: You can find out at this URL: http://www.pbs.org/wgbh/nova/nature/magnetic-impact-on-animals.html
- Earth has north and south magnetic poles and a magnetic field called the magnetosphere.
- The magnetosphere protects Earth’s organisms from solar radiation.
- Some organisms—including humans with compasses—use Earth’s magnetic field for navigation.
At the following URL, explore the interaction between a compass and Earth’s magnetic field. Move the compass around the planet and observe what happens to the needle. Also observe what happens to the compass when you flip polarity (in other words, when a magnetic field reversal occurs). Describe your observations.
- Make a sketch of Earth’s magnetic field.
- Explain the northern lights in terms of Earth’s magnetic field.
- How is a loggerhead turtle like a compass?