The light from a distant star is bent towards the Earth because of the presence of a star system passing between the Earth and the star.
Albert Einstein’s Theory of General Relativity taught us that gravity causes a distortion of space-time. Thus a large mass, such as a star, causes the fabric of space to bend around it, in the same way that a bowling ball on a mattress will deform it. Gravity can therefore bend and focus light, just like the lens of a magnifying glass.
The gravitational microlensing method allows planets to be found using light from a distant star. The path of the light from this star will be altered by the presence of a massive lens – in our case, a star and a planet. Thus, for a short period of time, the distant star will appear brighter.
In the video, the trajectory of the light emitted by the star in the background is changed as the lens – the star and planet system – passes in front of the distant star. The star becomes momentarily brighter for an observer on Earth.
Astronomers can’t predict where or when in the sky this type of event is going to happen. Therefore, it is necessary to observe a large number of stars for a long period of time to discover planets using the gravitational microlensing method.