https://zh.wikipedia.org/zh-tw/%E5%A4%AA%E9%99%BD%E7%B3%BB%E5%A4%96%E8%A1%8C%E6%98%9F
太陽系外行星或系外行星是位於太陽系之外，圍繞太陽以外的恆星公轉的行星。截至2024年4月1日，有4,161個已知的系外行星系統，合共有5,653顆已確認的系外行星，其中896個系統擁有不止一顆行星。
How were the exoplanets discovered? (ChatGPT, 2024-6-2)
Exoplanets, or planets outside our solar system, have been discovered using several methods:
1. **Transit Method**: When a planet passes in front of its host star as seen from Earth, it causes a slight dimming of the star's light. This periodic dimming can be detected by telescopes, indicating the presence of an exoplanet.
2. **Radial Velocity Method**: Planets exert a gravitational pull on their host stars, causing the star to wobble slightly. This wobble affects the star's light spectrum due to the Doppler effect, shifting its light towards red or blue. Measuring these shifts can reveal the presence of an exoplanet.
3. **Direct Imaging**: By using advanced telescopes and techniques to block out the star's light, astronomers can sometimes directly capture images of exoplanets.
4. **Gravitational Microlensing**: This method involves detecting the bending of light from a distant star when a planet passes between the star and Earth, acting as a lens and magnifying the star's light.
5. **Astrometry**: This technique measures the precise movements of stars on the sky. If a star shows a periodic shift in position, it might indicate the gravitational influence of an orbiting exoplanet.
These methods have led to the discovery of thousands of exoplanets, expanding our understanding of planetary systems beyond our own.
