Some people have noticed a strange triangular shape “object” entering the field-of-view of the HI2 telescope on STEREO Behind around December 26, 2011. You can see the feature in question in this video moving from right-to-left. What is this?
According to NASA:
The answer lies on the exact opposite side of the image. At the same time as this strange-looking feature starts being visible, the very bright planet Venus enters the HI2-B field-of-view from the lower left. Notice that Venus and the feature stay in step almost exactly opposite each other across the middle of the detector.
This is not a coincidence. The strange looking geometrical “object” is actually an internal reflection of the planet Venus within the telescope optics. This effect has been seen many times before. Here’s a particularly striking example of internal reflections caused by the planet Earth as seen early in the STEREO mission, taken from our image artifacts pages.