“Science casts a long black shadow back over who we think we are, and where it falls the temperature falls with it. Its touch is chilly and unforgiving.” –Richard K. Morgan
Here on Earth, when we’re dealing with normal matter, it’s relatively easy to measure the temperature of something. Even if you don’t have a thermometer handy, if you can do something like measure the speed/kinetic motion of the particles in there, you can easily figure out what the temperature of a system is.
But things are a lot more complicated — and elusive — if you want to measure the temperature of something you can’t even directly detect, like dark matter. But if you’re clever in your methods, this task not only is possible, but there are multiple different ways to go about measuring it!