The Northern Lights
The solar wind constantly streams toward the Earth, but dont worry because a protective magnetic field surrounds our planet. The same magnetic field that makes your compass point north also steers the particles from the Sun to the north and south poles. The charged particles become trapped in magnetic belts around the Earth. When a large blast of solar wind crashes into the Earths magnetic field, the magnetic field first gets squeezed and then the magnetic field lines break and reconnect.4
Watching auroras is fun and exciting, but normally you cart only see them in places far north like Alaska and Canada. The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate, flicker, or even move like waves. During solar maximum,5 auroras are seen as far south as Florida, even Mexico!
We hope you are able to travel to far-north places like the Arctic Circle and see the Northern Lights at least once during your lifetime. We know you will never forget it!
1. The Suns gravity is too weak to keep its plasma from flowing to the Earth.
2. The Earth is quite safe with a magnetic field surrounding it to protect it from the attack by the solar wind.
3. Some scientists are worrying about the possible disappearance of the Earths protective magnetic field in the future.
4. The auroras are formed when the electrons falling into the Earths atmosphere at the poles and colliding with gas molecules in the atmosphere.
5. You cannot see the Northern Lights unless you are in Alaska or Canada.
6. Tens of thousands of tourists take special trips to Norway and Sweden every year to watch the Northern Lights.
7. An aurora is generally close to the ground and is very long and thick.
答案：BACABCB