There are over 3000 confirmed planets in 2000 systems
Doppler spectroscopy
Doppler spectroscopy is used to detect the "wobble" of the parent star around the centre-of-mass of the system, due to a planet orbiting it.
Photometry
When a planet passes in front of its star, it would block out some of its light. This would cause the star's brightness to decrease, which could be detected by a telescope. This would make a shadow, which can be used to find the radius and the size of the planet as well.
Timing variation
A planet transits regularly with a strict period (without external influences). Any variations in timing would indicate another body with a significant mass in the vicinity, which could be other exoplanets. This allows for the detection of other exoplanets within a system.
Pulsars
Slight anomalies in the rotation of pulsars can be used to track the motion of the pulsar, and they are still subject to gravitational influence from other bodies. By tracing their motion, their orbital parameters can be determined, allowing for the detection of exoplanets.
However, pulsars are rare and planets orbiting them are even rarer, so the use of this technique is limited.
Direct imaging
Direct imaging involves capturing either light reflected off from the planet from the parent star, or from black body radiation due to the planet's temperature. However, the parent star usually outshines the planet, and planets detected from this could actually be brown dwarfs, which are warmer than planets.
Gravitational lensing
Gravitational lensing occurs due to general relativity when the light from a star is bent by the gravity of an object between the Earth and the source star. The object acts as a lens. The planet's gravity distorts the light, and such variations can be detected. However, this technique relies on the alignment between the source, lens, and observer, limiting its effectiveness.
Astrometry
Astronometrty involves measuring a star's position in the sky accurately and detecting how that position varies over time. Since a star with a planet orbits the centre-of-mass of the system, it is easier to detect massive planets further away from the star. However, the time taken to complete an orbit is long, as the exoplanet is far away.
Reflection
The lesson was interesting and were full of content. The lesson was engaging as well.
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