Birds and compasses know north from south because, like a giant bar magnet, the earth's magnetic field has two poles that line up closely with the planet's axis of rotation.
Birds and compasses know north from south because, like a giant bar magnet, the earth's magnetic field has two poles that line up closely with the planet's axis of rotation.
候鸟与指北针都知道何为北方、何为南方，因为地球就像一条巨型磁铁棒，它的磁场有两极，且这两个地磁的磁场线和地球的自转轴非常接近。