Habitable Zone
Habitable Zone
[Cueball stands in front of a huge telescope, looking through the eyepiece.] Cueball: I've discovered an Earth-sized planet in a star's habitable zone! It even has oceans! And visible weather! [Caption below the panel:] To mess with an astronomer, put a mirror in the path of their telescope.

While searching for extrasolar planets this gullible astronomer is very excited because he believes he has found a planet in a star's habitable zone , with oceans and visible weather. From these observations, he has determined that it is quite likely to have life on it, which would be a major groundbreaking discovery.
The caption explains, however, that someone has used a mirror as a prank to fool the astronomer, so he is in fact looking at a reflection of the Earth.
The title text goes on says that the astronomer would also be able to see the reflection of his telescope, which would convince him that there definitely is intelligent life on the other planet, looking straight back at him no less!
There are quite a number of issues (listed below) with the practical implementation of this prank, though of course they don't matter much in terms of the joke itself
[Cueball stands in front of a huge telescope, looking through the eyepiece.] Cueball: I've discovered an Earth-sized planet in a star's habitable zone! It even has oceans! And visible weather! [Caption below the panel:] To mess with an astronomer, put a mirror in the path of their telescope.
