The two main methods of detection talked about in class were the following method, where we see a star periodically get slightly dimmer, caused by the planet blocking some of the star's light (but we never see the planet) method, where we see the star's spectrum periodically redshift and blueshift slightly, caused by the star wobbling as the planet orbits it (but we never see the planet)

Transit

Radial

Explanation:

Here the author is talking about the methods of finding an exoplanets. An exoplanet is a planet that orbits another star just like our planet revolves around the Sun. There are multiple ways of finding such exoplanets. Two which are mentioned here are:

1. Transit Method: Since the exoplanet is orbiting around its parent star. There will be a time when the planet will block the star if it is in the line of sight of Earth. There will be a dip in the brightness of the star when the planet will transit the star. By measuring this dimming in the star's brightness we can get a lot of information about the exoplanet.

2. Radial Method: Since the star is very massive it makes the planets go around it because of gravity. But the planets also have gravity and they also have impact on the stars due to which stars wobble. Because of this wobbling the star seems to move closer and away from the observer periodically. As per Doppler effect when it will move closer to observer the spectrum of star will be blue shifted and when it moves away from the observer, spectrum will be red-shifted. By measuring this wobbling and studying the spectrum we can discover and study exoplanets.

the minimum amperage that the current in this wire would have to have so that its weight is completely supported by the magnetic force due to earth's field, assuming that no other forces except gravity act on it