Gravitational Lensing

This interactivity shows an example of the planetary microlensing effect.

First, choose the 'Unlensed' option. The image in the upper left corner of the illustration shows the view of a star as we would usually expect to see it.

Next, choose the second option 'Lensed by star'. This image shows what happens if another star crosses our line of sight to the background star (which we looked at in the 'unlensed' option). Light rays traveling from the background star towards us pass very close to the second 'lensing' star, and the gravity of the latter bends the light path just as a lens system would. The lensing effect can also temporarily magnify and brighten the image of the background star.

A similar effect happens when a massive planet, orbiting the lensing star, also crosses the line of sight to the background star. Choose the option 'Lensed by star and planet'. In this case, however, the duration of the planetary lensing effect is much shorter than the stellar lensing effect, because the planet changes its position in the sky more rapidly. We cannot see the planet directly, but we can detect its presence through observing the effect of a sudden and quick magnification of the light of background star. This combination is a very finely tuned technique which we use in the search for new planets.