What are four common methods used to discover exoplanets?

Because all planets only emit a faint glow, especially compared to their parent star, it can be difficult for astronomers to view exoplanets directly. Due to this, they must rely on other methods to best discover and accurately identify these planets. The following are four ways that this is done:
1. Radial Velocity-
When a star has a planet in its orbit, the planet will create a small orbit for the star itself due to the planet's gravitational pull. This means that the distance of the star from the Earth (or its radial Velocity) will vary slightly as the planet's gravity creates a variation in the star's orbit. When there is a variation in the star's Radial Velocity, we can deduce that there is an exoplanet in the star's orbit that is affecting this.
2. Polarimetry-
When a star gives off light, the direction of the light wave is not focused, meaning it is un-polarized. However, if there is a planet with an atmosphere in the star's orbit, the light will become polarized when it reaches that atmosphere. If an astronomer can analyze the polarization of the stars light, they can deduce that an exoplanet is within the star's orbit. The one downfall to this method is that it will not detect a planet with no atmosphere, as the star's light will not polarize.
3. Direct Imaging-
Though a planet is hard to see in relation to its star due to the star's light, if an astronomer uses infrared imaging and the planet is far enough away from the star, they may be able to capture the planet directly. There are several downfalls to this; if the planet is too close to the sun, the heat of the sun will eclipse the planet and astronomers will not be able to see it. It is also difficult to get a reading on the planet's actual mass or composition, as the image is based solely off of its heat index.
4. Relativistic Beaming-
When the gravity of a planet in orbit pulls on the star it is orbiting, there is a variation of the photons of the star. This concentration of photons creates a small, almost imperceivable variation in the brightness of the star. Astronomers can use that variation to locate and detect the planet's gravitational pull. The downside to this is that the change in light is very minimal- sometimes making it very difficult to detect.
These are only four of many ways that astronomers identify exoplanets. This is an always evolving science, and astronomers continue to discover new and more precise methods.

There are many ways that exoplanets are discovered. Pulsar timing is a process in which radio waves emitted by pulsars are timed. Shifts in the timing indicate the presence of an exoplanet. A more direct method of observing exoplanets is direct imaging, which uses thermal imaging to discover heat sources around a star. An anomalous heat source can indicate the presence of an exoplanet. The oldest and most common method of discovering exoplanets has traditionally been astrometry. This is the process of measuring a star’s position in the sky and tracking to see if it has an elliptical or circular orbit, suggesting an exoplanet in the area. One final method of discovering exoplanets is relativistic beaming. This process tracks changes in a star’s brightness that occur as a result of a planet influencing the star with its gravity well.