Light distortion caused by bodies of mass bending light.
We see light that was sent from galaxies thousands of light years in the past.
Sometimes observing this light may appear distorted or even in a different spot in the sky than where it actually is.
This is due to light BENDING when traveling from its source, passing a massive body such as a galaxy cluster in which interferes and causes the light to bend.
By the time this light reaches us, it can completely throw off calculations, imagery and location accuracy.
All due to these darn objects getting in the middle of the light’s path from point A (the source) to point B (us).