The Earths Magnetic Field
the earths Magnetosphere
The solar wind mentioned above is a stream of gases that blows outward from the Sun at about 400 km/second and that varies in intensity with the amount of surface activity on the Sun. The Earth's magnetic field shields it from much of the solar wind. When the solar wind encounters Earth's magnetic field it is deflected like water around the bow of a ship, as illustrated in the image.
parts of a compass
Not all compasses include each of these parts and some compasses include even more.
- Base-plate: A hard, flat surface on which the rest of the compass is mounted. It has rulers on its edges for measuring distances on maps. It's edge is straight and useful for laying lines on a map.
- Scales: Each edge of a compass may have different rulers for use with different map scales.
- Direction-of-Travel Arrow: Marked on the base plate. You point this the way you will be traveling.
- Magnifier: For seeing small map features better.
- Index Pointer: The end of the direction-of-travel arrow. It ends right at the edge of the dial and is where you take degree readings.
- Dial: Ring around the housing that has degree markings engraved. You hold the dial and rotate it to rotate the entire housing.
- Declination Marks: use to orient the compass in an area with known declination.
- Orienting Arrow: Marked on the floor of the housing. It rotates with the housing when the dial is turned. You use it to orient a compass to a map.
- Orienting Lines: Series of parallel lines marked on the floor of the housing and on the base plate.
- Needle: Magnetized piece of metal that has one end painted red to indicate North. It sits on a fine point that is nearly friction-less so it rotates freely when the compass is held fairly level and steady.
- Housing: Main part of the compass. It is a round plastic container filled with liquid and has the compass needle inside.
- Bubble: A bubble of air in the housing liquid is useful for making sure you are holding the compass fairly level.
- Mirror: Lets you see the compass face and distant objects at the same time. Useful for emergency signaling.
- Sight: Improves aiming your compass at distant objects.